I'm on annual leave during the month of August 2025. Apart from attending my eldest daughter's wedding, I'm just taking some time out to catch up on mostly personal stuff and little R & D so I'm not going anywhere.
There's one exception to my leave however, and that is to ensure that those customers who pre-ordered my PML-TX01 replacement transformer for the Marshall JMP-1, are looked after and that all pre-orders will be sent out as soon as they land.
It's been over a month since I should have received my latest batch of transformers and although not my fault or that of the manufacturer, I feel a sense of responsibility and can only apologise for this unprecedented situation. It's just not happened before and I'm trying my best to resolve it.
LATEST NEWS (31st July 2025)
The transformers are made in the same factory that made the original JMP-1 transformer. TRX Electronics is based in Malta. I've now confirmed that the transformers are being held in UK Customs. Yesterday I sent an email to ParcelForce Customs Processing requesting more information. Of course, I'll keep everyone updated.
Please check in here regularly.ย
UPDATE - 10th August 2025
No news yet, people. I'm getting annoyed but my hands are tied. I did have an auto response to my email of 31st July just to tell me that someone should get back to me in ten days. Great! Thanks! ๐ก
UPDATE - 20th August 2025
I've just received an email from ParcelForce confirming receipt of my shipment from TRX Electronics and that all information pertaining to the shipment has been recorded.
Unfortunately, when I look at the tracking information, nothing seems to have changed! ๐ก
UPDATE - 15th September 2025
I have received an email from ParcelForce informing me that the transformers will be delivered the day after tomorrow (Wednesday 17th September).
UPDATE - 17th September 2025
After waiting all day for ParcelForce to turn up, I decided at 9:00 in the evening, to check the tracking. Here's what it's showing...
I know damn well that I paid Customs charges but I checked anyway. Hmm... Yes, of course I did Mr. ParcelForce. The full amount requested, is showing as having been been deducted from my PayPal account on err... Monday! ๐ก
ParcelForce is one of the worst organisations on the planet.
If it's going to go wrong, guaranteed ParcelForce will be involved.ย
I'm so sorry people. Not sure where to go from here. I'll try to sort this out tomorrow.
UPDATE - 24th September 2025
Well, after holding on the phone for almost an hour, I did indeed manage to talk to someone at ParcelForce.
I was informed that there was no record of my shipment from 22nd August and it is assumed that it has been returned to the sender (the factory in Malta). The person I spoke with, confirmed that the duty did appear on the ParcelForce system as having been paid. I questioned this and didn't get a satisfactory answer. I was however, told that it would be refunded if the shipment had been returned. I was also told to "key an eye on email" and to expect a communication from ParcelForce.
The duty paid has not been refunded and neither have I received an email.
Sorting out ParcelForce is my problem but no transformers is my customers' problem. I have therefore, informed the factory to expect the return and we have agreed to use a proper courier. In fact, I'll be using my DHL Express account which usually only takes a few days to ship. I'll be arranging collection myself.
Once again, I can only apologise for this mess but I hope you'll all appreciate that it's not of my making.
It was my wife's birthday on 22nd May and a couple of weeks prior, I decided to buy her tickets for Duran Duran. I actually bought four tickets, two for our friends Belinda and Andy.
Today is 6th July. It's stupid O' Clock in the morning and we've all just got back to Hemel Hempstead from a fantastic day out.
Duran Duran were playing at Great Leighs in Essex, very close to where Julie used to live and where I also lived for a while.
The best of company, Nile Rogers supporting and of course, Duran Duran, a real blast from the past for me both professionally and personally made yesterday really special.
I even bumped into Adrian, one of my customers and our long time friends Sarah and Neil who used to live opposite us like a million years ago and who now live in Scotland.
Old neighbours Neil and Sarah. How lovely to see you guys again!
One thing about being in music production though, is that you sometimes need to switch off, forget the detail that you would listen to in the studio and just lose yourself in the vibe. When things got serious for me, the slightly high mix of Alex Van Halen's hi-hat for example, really started to get on my nerves. Seeing one of my favourite bands of all time live, required that I kind of had to train myself to let my emotions take over and to leave my studio ears in well, the studio!
Another example is George Lynch, who's sound and technique were a big influence on me but many years ago, I went through a phase when I found it hard not hear the badly mixed lead guitar overdubs.
The energy that Duran Duran projected into the crowd was amazing but I have to say that the overall sound wasn't at all great. Nile Rogers' mix was so much better. Duran Duran's sound was messy and inarticulate and I must admit to being deeply disappointed with Tom Brown's guitar sound and playing. He had way too much distortion (as opposed to overdrive) when he should have and some riffs like the unmistakable Rio, simply weren't played properly, with the signature 'slide' not being present. How come none of the other guys spotted that in rehearsals?
Of course, Belinda, Julie and Andy were quite oblivious to any of that and the girls in particular simply danced the night away. I eventually got sucked in and just enjoyed myself. ๐
Last year I developed several peripherals for the Simmons SDS7 and it would seem that they're now becoming quite popular. Here are four 2025 Simmons SDS7 upgrades that Iโve had in recently.
Here's the upgrades that have been installed into these units:
A โ Dark Matter switched-mode power supply installed. Pleiades lithium battery conversion and discrete MIDI platform installed. NC-7 noise-cancelling mod installed.
B โ Dark Matter switched-mode power supply installed.
C โ 120V โ 240V conversion. Pleiades lithium battery conversion and discrete MIDI platform with Tubbutec uniPulse installed. RESET-7 Power-on-Reset upgrade installed.
D - Dark Matter switched-mode power supply installed. Pleiades lithium battery conversion and MIDI platform with Tubbutec uniPulse installed. Repair of bass drum module.
E -ย All customers have also purchased AMEP Advanced Memory Expansion Pack.
I've used the adjective 'discrete' to describe the MIDI platform feature of Pleiades. That's because all of my upgrades are designed around three main objectives:
The outside of the equipment should remain untouched.
The inside of the equipment should require no permanent alteration.
Any upgrade can be easily removed and the equipment can be returned to factory.
Working to those three objectives can be quite challenging but hey, that's what I do! ๐
Okay so you all know that I really love my job but the four Simmons SDS7 upgrades I've done so far this year have been a particular delight to work on, great fun and most rewarding. It gives me a true sense of comfort and pleasure to know that these iconic instruments will be banging away for another forty years!
A lot of the early Simmons stuff, can be, well... rather interesting to work on but nothing is quite as quirky as the SDS7. With a personality which can only be described as unpredictable, you really need to know what you're doing and in particular, you kind of need a lot of patience. Yes, it's only classic early eighties electronics and yes, that should sound easy but nothing ever goes quite according to plan when working on a Simmons SDS7!
The 120V to 240V conversion of SDS7 'C' in the image above, should have been really quite straight-forward but for the first time ever, I had a duff transformer. I couldn't believe it but the 240V tap was open circuit. This fault must have existed since production.
Destined to be for the US market, there's no way the that the transformer's 240V tap would have been tested at the Simmons factory or during the SDS7's past forty year life in the US.ย Luckily, due to the Dark Matter upgrades I've done over the past few months, I've built up a small stock of spare transformers.
Between common and the 240V tap, this Simmons SDS7 mains transformer should read about 38ฮฉ. As you can see, this is definitely not the case.
WANT TO FIND OUT MORE? Here are links to posts featuring the products mentioned above:
All items are available for purchase in the Simmons SDS7 Heaven category in my online store. If you're unable to install stuff yourself, then as you can see, I'm always happy to take in your SDS7 and do the work for you. Just contact me for a chat.
Four Simmons SDS7 upgrades so far this year and it's only June. Wow!
Simmons SDS6 serial number 178 of one hundred and ninety units built.
Mike Walden's replacement CPU board for the Simmons SDS6 is an amazing rescue resource for one of the rarest eighties music machines ever! On my recommendation, one of my customers bought one of Mike's boards as soon as they were available. Here's the story...
The Simmons SDS6 was an analogue sequencer with eight trigger outputs and a hi-hat open / closed output, all intended to drive systems like the Simmons SDSV and SDS7. Of course the trigger outputs could be fed into many electronic drum systems of the time.
Simmons only made a hundred and ninety SDS6 sequencers. It was a beast at the time and by today's standards, is positively over the top.
Famous for its massive LED display, the first revisions (yes, there were several, even for a hundred and ninety units) only had tape sync and didn't include MIDI. Memory back-up was via the expansion port at the rear and users looking to copy / back up data had to do so via Simmons' proprietary Memory Expansion Pack. Incidentally, my 'Advanced Memory Expansion Pack' (AMEP) works just great with the SDS6.
Like many machines of that era however, the SDS6 used Ni-Cd batteries for memory back-up and if not charged regularly, these damn things leak and badly. If not caught quickly, the result is more often than not, a bricked Simmons SDS6.
For me, things started about this time last year when a customer turned up with a Simmons SDS7 and a SDS6, neither of which was powering up. As it turned out, the memory back-up batteries in both machines had long expired and had badly leaked.
It took several months to repair the SDS7 but the SDS6 was a lost cause. Having only made a hundred and ninety units, seeing one in this state is quite upsetting, to say the least.
After a few weeks of trying to repair the damage, I was forced to draw a line as it became obvious that my efforts were quite futile. I proposed to my customer, that I design a replacement CPU board.
Another view of the original SDS6 CPU board showing even more damage.
Well, round about the same time, a certain Mike Walden had recently purchased a SDS6 which by the sounds of it, had suffered the same fate. Mike had the same idea. After having spent most of 2024 designing a whole load of bits and pieces for the Simmons SDS7, I really didn't have the time to take on something like a whole CPU reverse engineering project. Mike sounded keen so I left him to it.
Reverse engineering something like this is a mammoth task but you also need to bear in mind that there are very little resources on this stuff, out there. On top of that, there are technically two types of SDS6; the standard trigger output version and the MIDI version. Both were substantially different. Mike's failed SDS6 was a MIDI version which was great for me or rather my customer, as his was a MIDI version, too. Hey but more about that later.
On 27th April 2025, Mike announced on Simmons Drums Users - Past and Present (private) Facebook group, that his project was finished and that his replacement CPU board for the Simmons SDS6 would be available on ebay.
As soon as Mike's replacement CPU board for the Simmons SDS6 was on ebay, I telephoned my customer giving him the ebay item number. Yes, it was the middle of the night but this was a big deal.
Usually, the minimum production quantity for PCB projects is five. Mike had four boards available on ebay so I'm guessing that one of them ended up in his own SDS6. As you can see in the image below, I'm also guessing that the one Peter bought is, well... No. 2!
It looks like Peter my customer, bought the second board, serial number 002.
Peter immediately bought one of Mike's boards and then contacted me again to arrange drop-off.
The next day, Peter drove down to Hemel Hempstead from Cambridge and I simply couldn't wait to see Mike's board. Packaged extremely well, there were a few anxious moments before all was revealed.
On first sight, the first thing that went through my head was complete and utter respect. I'm an electronics design engineer and all I could think of were the hours of work that must have gone into this. "Mike, this is awesome!"
Mike Walden's replacement CPU board for the Simmons SDS6 looks awesome!
If I'm brutally honest with myself, then I must confess to feeling slightly envious. I really wanted to take on this project but you simply can't do everything and there was no way I could commit to this. Again, Mike did well to make the time for such an ambitious endeavour.
Anyway, a few days later and I decided to pull out Peter's SDS6. Oh boy. Memories of trying to resurrect this came flooding back. ๐ Not good but I'm glad we decided to keep this.
Before attempting to fit Mike's replacement CPU board for the Simmons SDS6, I decided to check the PSU voltages. Everything was fine so let's go.
In his ebay listing, Mike warned that there may be slight differences in mounting between various SDS6s, something I'm used to and not just with Simmons gear. Mike's board wouldn't quite 'drop' into Peter's SDS6 and I would suggest that if Mike's going to make more of these, perhaps enlarging the mounting holes might be a consideration. As it turned out, I drilled out one of them from about 3.5mm, to 4.5mm. After that, the board fitted without requiring any nudging or force.
The power on reset (POR) circuit in the original SDS6 looks as if it was an afterthought. Electronically similar to that in the SDS7, the POR circuit in the SDS6 is on a separate and very small PCB that's secured to the centre screw on the CPU board. Four cores of ribbon cable connect power, 0V, unregulated +8V and RESET to the CPU board in anything but an elegant manner.
Mike tidily incorporated the POR on to his design, a pin being made available for the connection to the pre-regulated voltage from the PSU. I ended up removing this pin and wiring the connection directly to the board but from underneath.
Like the SDS7 and many other Simmons machines from the same era, the power-on-reset circuit is built around a CD4011. In the same way, a pre-regulator voltage is picked up from the power supply and injected via J6, which you can see on Mike's board located just in front of the battery pack.
By the looks of it, Mike chose to include some type of battery charge monitor on his board. Comprising very small SMDs, there's nothing I can identify but D7, Q1 and U25 PCB references are a bit of a giveaway for a diode, a transistor and an IC. A status LED is also present but strangely, it isn't a surface mount type. A key above the battery pack offers reference to what the LED would indicate.
Mike's replacement CPU board for the Simmons SDS6 includes a monitor circuit which via a LED, provides a visual indication of the condition of the NiMH batteries.
Initially, I found the inclusion of this circuit somewhat curious for two reasons:
Iโve never seen a SDS6 with issues resulting from component failure. Every faulty SDS6 Iโve ever seen has suffered a battery leak. It seems strange therefore, to continue using rechargeable batteries.
There is no way to observe the battery charge status LED without opening up the SDS6.
The first point can be immediately dismissed. Instead of the original Ni-Cd batteries, Mike's design uses nickel metal hydride (NiMH) types which shouldn't leak! Excellent decision, Mike.
So let's continue...
After the afore mentioned and partly expected minor adjustment, the board slipped in nicely, well almost. On this particular SDS6 (#178), there was very little gap between the power supply PCB and the new board. Perhaps Mike could have got away with shaving off a few millimetres.
Mike's board was a bit of a tight fit in Peter's SDS6. My contingency plan was to increase the hole sizes in the power supply PCB so as to offer some wiggle factor.
I'd already connected unregulated +8V from the PSU to the POR circuit directly. All other connections had been secured, checked and double checked, so let's switch on and see what happens...
Wow! The SDS6 powered straight up and seemed to boot. The battery status LED was on so I figured I'd have a cup of tea and leave the batteries to charge. Good so far.
Mike's board fully installed and looking very hi-tech in SDS6 #178.
While I had my tea, I thought it a good opportunity to familiarise myself with the operation of the SDS6. After all, it's been a few years since I've seen one of these. Hmm... I think I might need more than just the one cup of tea. Those batteries and that SDS6 user manual aren't going to happen quickly.
After my break, I came back to SDS6 #178. I switched off, closed the lid and powered up.
Cycling through several functions, everything seemed to work just fine. I then connected my test SDS7 and proceeded to enter a simple pattern. The once totally dead SDS6 played the SDS7 just fine. I didn't test the hi-hat open / closed function and neither did I test the tape sync but the fact that this SDS6 is triggering a SDS7 seemed quite a result to me.
WOW!!!! Everything works!
CONCLUSIONS
Yes, my admiration for what Mike Walden has done should hopefully be obvious by now but somehow it doesn't seem enough? Mike's board is amazing and loaded into SDS6 #178, it works. I've also previously mentioned that I fully appreciate the effort that can go into a project like this, especially when there are so little resources available. In fact, I now need to ask my readers whose native tongue is not British English, to forgive me as slip into a little colloquialism and refer to Mikeโs work as stonking (an adjective used to emphasizeย something impressive, exciting, or very large).
I was a bit concerned about the continued use of rechargeable batteries butย NiMH is a good compromise and I fully endorse Mike's decision to do so.
Mike had five boards made and I don't know if he'll be making anymore. At the time of writing, the four that he put up on ebay had all gone.
There are nine link options which in theory, will allow this board to work in non-MIDI SDS6s. Mike told me that the link options emulate the modifications that appear on the schematics advising on non-MIDI to MIDI conversion. A nice and very forward-looking touch, Mike. Unfortunately, Mike doesn't have the firmware for these early SDS6 versions and on top of that, it would be good if he could validate his board. In fact, I'm aware that Mike's put a call out to borrow a non-MIDI SDS6, just to confirm operation. In his ebay listing, he also advised that those interested in this board for use in a non-MIDI SDS6 should contact him prior to purchase. If Mike's request for a guinea pig non-MIDI SDS6 is successful, then I'm assuming that this isn't the end of the story.
Link options, five of which are on the underside of Mike's replacement board, allow for MIDI and non-MIDI configuration. As yet, the latter is untested.
With less than two hundred SDS6s made and more than forty years on, one wonders how many are still in existence. I do however, hope that Mike decides to release a few more boards.
Many will be aware that I'm ex-Simmons and once in a while, Dave and I actually manage to catch up with each other. Dave consistently expresses his delight at the work I and others are doing to keep what he started back when it was really exciting, alive and kicking decades later.
NOTE:
This replacement CPU board for the Simmons SDS6 is NOT my board. I had no hand in the design, manufacture or testing of the main item that's featured in this post.
I do NOT sell these boards. Neither do I offer any technical support for these boards.
Initially, Mike had five boards made. I have no idea if he'll be making any more.
Whilst the pricing of Mikeโs board was amazingly acceptable, I do not know if heโll maintain that, should he release more boards.
It would be most impractical for Mike to cater for all possible variations in SDS6 design. Hence, if Mike makes more of these boards, then I think it only fair to point out that purchasing and installing one is done entirely at your own risk.
I wonโt be publishing or distributing Mikeโs contact details so I guess that the only way to keep up to date on further developments, would be via the Simmons Facebook group quoted earlier.
RESET-7 power-on-reset upgrade for the Simmons SDS7.
My RESET-7 POR upgrade for the Simmons SDS7 was designed to extend effective battery life when the SDS7 has been converted to lithium battery backed up memory. This might not seem like a big deal but please allow me to explain...
The Simmons SDS7 uses a CD4011 to buffer, invert and interface a signal derived from the power supply on power-up and power-down and which providesย the chip enable (CE) signal for the SRAM and RST (reset) for the processor. It's an important part of the Power-On-Reset (POR) circuitry in the SDS7. Since the device is on all the time, it's powered by the memory back-up battery when the SDS7 is switched off. Yes, that's right! The 'memory back-up battery' doesn't just back up the memory! CE on the 6116s needs to be high, when SDS7 is switched off. To do that, the CD4011 needs to be on.
The SRAM in the SDS7 comprises ten 6116 chips. These have a minimum memory retention voltage of 2V so theoretically, the memory back-up voltage can run down to this value and memory will be retained.
Oh, if only life would be that simple...
The minimum operating voltage of the CD4011 however, is 3V. If the memory back-up battery voltage falls below 3V, memory integrity will be compromised and corruption may occur.
Bypassing the SDS7's original POR circuitry, my Dark Matter replacement power supply for the Simmons SDS7 gets around this problem with a completely new POR design. Apart from being based around a power management IC, Dark Matter's POR circuit uses a SN74HC14N hex inverter to buffer, invert and distribute the RESET pulse and to maintain CE as required, for the 6116s. The big deal is that the SN74HC14N has a minimum operating voltage of (you guessed it), 2V.
Apart from being a really cool (literally) replacement for the original SDS7 power supply, Dark Matter includes a more modern POR circuit which, making the original SDS7 POR quite redundant.
Having a lower current consumption than the CD40111 and Schmitt-trigger inputs, also constituted towards my decision to use the SN74HC14N. For a simple hex inverter, it's a the perfect device in this situation.
"Hold on a minute, Alex. The CD4011 is a quad 2-input NAND gate and the SN74HC14N is a hex inverter. How can you replace one with the other?" I hear you ask.
Okay, let's talk Simmons SDS7 RESET for a minute...
The POR signal in the SDS7 is derived from aย simple R/C network taken off the power supply, post rectifier / pre-regulator. The output of the R/C network is fed into a CD4011 quad 2-input NAND gate where it's conditioned, buffered, inverted and distributed to the CPU and memory boards. RESET (RST) to the CPU and chip enable (CE) to the SRAM chips, to be precise.
Only three of the four NAND gates of the CD4011 are used and only two of them are used for RST and CE. The two inputs of each NAND gate are joined together which means that only the 'N' of the NAND is used and not the 'AND', if you know what I mean. We can therefore substitute an inverter in-place of each NAND gate.
Of course my revised RESET circuit only uses three of the six inverters in the SN74HC14N but it's still a very perfect alternative. Hey, sometimes you have to look at what's actually going on, right?
Using just a power management chip might have given SDS7 a heart-attack. Putting a logic gate on the backend however, fools SDS7 into thinking that everything is as it was in 1983 (perhaps). ๐คฃ
The installation of Dark Matter is however, very involved and so it's not going to be for everyone. To allow for simple conversion of SDS7's memory back-up to lithium, I therefore designed Pleiades. Unfortunately, Pleiades doesn't address the problem described here and so I decided to come up with a solution.
Since the CD4011 is nearly always socketed (in fact, I've never seen a SDS7 in which the CD4011 isn't socketed), my idea was to make a simple adapter which would be easy to fit once the CD4011 had been removed from its socket. There was one major problem, though. The CD4011 (otherwise referenced as IC1) couldn't be in a more inaccessible place. I wanted this to be easy but being right at the back of the SDS7 chassis, kind of underneath the vertically mounted rear socket PCB and surrounded by other components, meant that it would be anything but!
The CD4011 in the SDS7 is annoyingly difficult to access.
There wasn't enough room to drop in a conventional, long pin vertical adapter so my first version of RESET-7 had right-angled pins on the back, the idea being that the adapter would be mounted vertically. Unfortunately, room was so tight that even this didn't fit.
So, my next option was to mount RESET-7 on the rear PCB and connect it to IC1 socket via a short IDC cable. Should I need to use this mounting option, I'd made a couple of 3.2mm holes on the RESET-7 PCB to accommodate a two self-adhesive PCB stand-offs.
Wow, that's more like it. Mounted to the rear PCB, RESET-7 is very secure and connects easily to the IC1 socket.
My RESET-7 POR upgrade for the Simmons SDS7 was designed with maintenance in mind so apart from having the same orientation as the original device, the SN74HC14N is also socketed, easy to access and the PCB has a couple of conveniently located test points, thus keeping an eye on voltage that's hitting the SN74HC14N when SDS7 is powered on or off, is simple.
You may be wondering about the relevance of the Schmitt trigger aspect of the SN74HC14N's inputs that I mentioned earlier. Well, unlike the old CD4011, the outputs of the SN74HC14N will only switch state when the respective inputs exceed a specific threshold. This means that no POR signal will be generated from spurious activity and so the possibility of a 'false' RESET will be greatly minimised.
With accessible terminals, the voltage to the SN74HC14 can be easily monitored.
So, if you're considering a lithium back-up battery conversion on your SDS7, I would firstly recommend Pleiades. If on the other hand, you're knowledgeable and confident to try something yourself, then do yourself a favour and please do consider RESET-7. Offering reduced current consumption from the battery when SDS7 is switched off and having a minimum operating voltage of 2V, your lithium battery (or batteries) will simply last longer.RESET-7 POR upgrade for the Simmons SDS7 is now offered as a highly recommended option when you buy Pleiades.
UPDATE - 18th June 2025
I've received an enquiry asking if RESET-7 would work in a SDS7 which has NOT been converted to lithium battery back-up. I haven't actually tested this but I honestly don't see why not.
The theory of operation remains the same but since a Ni-Cd needs to be regularly charged anyway, I'm not sure what advantage would be gained, other than having a very cool POR backend.
My bench power supplies all have built-in current limiters but sometimes it's necessary to limit the current delivered from the mains itself. I often receive items like old valve guitar amps that repeatedly blow fuses for example and a current limiter will help diagnose issues as well as keep me safe. You can't easily buy stuff like this anymore so I decide to make my own DIY test equipment current limiter.
There are some pieces of equipment which might have been readily available a few decades ago but today, they're simply not as common as they used to be. Indeed, this is something I've been meaning to build for a while, now.
In line with the look and feel of the guitar amps that my current limiter will be driving, I gave this bit of DIY test equipment, a slightly 'retro' touch.
Functionally, it's quite simple and works on an established principle of using an incandescent light bulb (or two) to limit the current into an attached load, like an amp. With no short-circuit in the load, the light bulb (or light bulbs) won't come on.
This current limiter has two 40W light bulbs allowing me to select two current ratings; about 165mA or about 330mA. Of course UK mains voltage is 240V. If larger currents are required, all I need to do is drop in higher power-rated light bulbs.
When testing 115V / 120V equipment, the current ratings would naturally be doubled.
The current limiter also has a bypass switch which allows me to conveniently bypass the limiter function without the necessity to unplug anything. A vintage style neon indicator reminds me when the unit is bypassed.
Using the limiter set to 'low', it would appear that the Randall shown below, clearly has a fault. As you can see, the amp is still on standby. Following a brief visual inspection which showed nothing obviously amiss with most of the amp, the power side did look as if it had sustained some fluid spillage in the past. There was corrosion and it just didn't look good.
My DIY mains current limiter in action and showing up a fault on this Randall amp.
My DIY test equipment current limiter isn't the only piece of gear that I've made for use in my lab. Amongst other things, one of my oldest items is a 2-channe,l heavy-duty 8ฮฉ dummy load. As we all know, valve amps need to be connected to a suitable load, when powered up. Not doing so, risks damage and possibly destruction of the output transformer so when working with valves, a dummy load is absolutely essential.
Built when all my heavy test gear was rack-mounted, one of my oldest pieces of DIY test equipment, is my 2 x 8 Ohm dummy load, now with switchable isolated outputs.
Built before a time when speaker simulators and 'power soaks' came to be, my 2 x 8ฮฉ load has lasted me well for several decades and continues to be used on a very regular basis.
It's a bit special. As you can see. it's rack-mounted. This was to save space at the time as all my heavy test equipment was in a 16U rack. As I'd often be out on the road, the rack solution was also very practical, if not bloody heavy!
My ol' faithful dummy load has recently been updated with a 600ฮฉ : 600ฮฉ audio transformer on the backend of each channel. Via the front-panel switches, I have the option to either have two conventional dummy loads or a pair of fully isolated loads which are perfect for the new generation of D-class amps with so-called 'balanced' speaker outputs which are isolated from mains earth. This keeps my oscilloscope very happy! ๐
The potentiometer simply provides a little control over the signal level going into my 'scope.ย As well as being perfectly suitable for attaching to 2-channel amps like the Marshall 9100 or 9200, it's easy to wire the two loads in series for 16ฮฉ or parallel for 4ฮฉ.
Just before Christmas, a customer brought me a loft-find Simmons SDS9. It was in pretty good cosmetic condition but didn't boot properly. With the start of the New Year, this Simmons SDS9 repair became my first of 2025.
Having been told that this was a 'loft-find', I figured that the battery should be the first thing I should check out. Yep, it was totally dead and the usual white stuff had started accumulating around it.
The customer got lucky though and there wasn't too much damage. Once I'd cleaned the area around the battery and replaced the original Ni-Cd device with a lithium CR2032, I reinitialised the unit as I powered up for the first time.
Okay, good news... it booted. We'll see how much of this SDS9 works but first a few words on that battery change...
I normally replace a Ni-Cd with a 3.6V lithium battery when doing the Ni-Cd / lithium conversion thing. On this occasion, I didn't. The reason I went for a more conventional solution on this Simmons SDS9 repair, is that since the main-board is secured to the top-case, components up, there's not enough room to squeeze in a CR123 or ยฝAA battery holder and battery. Neither did I want to mount the battery to the bottom case as it would have to be unplugged for maintenance, thus forcing the SDS9 to lose all of its pre-sets or kits as they used to known. Makes sense, I guess... drums, kits...
You can't just replace the original battery with a different type. Some modification to the circuit is required.
IMPORTANT - You CANNOTjust replace the Ni-Cd with a lithium battery. Remember that the Ni-Cd is charged when the unit is powered on. If you don't modify the circuit, the same will happen with the lithium battery and that's something you really don't want to do!
With battery surgery complete, I then discovered that all the switches had issues and were either sticking, double triggering or not triggering at all. To be able to access various functions, that was the second thing that needed sorting out.
After removing the switches from the board, they can be easily dismantled and the metal spring contact and terminal contacts can be cleaned. Yep, they were certainly grubby!
The SDS9 didn't use encoders for data entry. Instead, analogue voltages were derived via potentiometers so while I was at it, I cleaned them too.
I dismantled and cleaned the switches but as you can see, the integral buttons remains a little tarnished from age.
After reassembly, the switches worked perfectly and the integral buttons looked just a little newer. Other issues with this SDS9 soon became apparent, however:
The boot time was much longer than it should be (I actually noticed that before) and once in a while, it would freeze kind of mid-boot.
There was more than the usual amount of hum on the audio outputs.
The low-tom wasnโt triggering from the pad input but was working fine via button-tap and MIDI and the low-tom sound was playing in demo mode.
The rim and intermittently, the high, mid and low toms were self-triggering, like machine gun style. The frequency (tempo, if you like), of the self-triggering would reduce over several minutes and eventually it would die down to nothing.
Intermittently, triggering the snare / rim would also trigger the low-tom albeit with a low velocity. Triggering the low-tom didn't trigger either the snare or the rim, however. This thing was one-way and would also settle down after several minutes.
The customer told me that he reckoned this SDS9 had been in his loft for at least fifteen years, if not nearer twenty. With cold and damp winters and humid summers over here in the UK, I was surprised that the case hadn't at least, started to rust. I wasn't surprised that there were problems with the electronics, though.
So, I decided to replace all the electrolytic capacitors on the power supply. Actually, while I was at it and since there weren't too many electrolytics on the main-board, I changed them, too. If looked after and regularly used, the recap might not have been necessary but remember that this was a loft-find.
New capacitors on the power supply helped reduce hum on the audio outputs.
Now that the unit was booting as it should, I started to look at the other problems.
The self-triggering gave me the impression that capacitors were charging / discharging and so I checked out the schematics for some caps which I thought could be responsible.
Do consider this, however...
The term 'IC' stands for 'integrated circuit' and we can assume (as if we didn't know already), that most chips (ICs) comprise various components, including capacitors. So, while checking out the discrete capacitors, one shouldn't dismiss ICs.
Indeed, there are lots of (ceramic) 1nF capacitors all over the place and so I changed them, like all of them, not just those associated with the self-triggering channels.
On the pad trigger inputs, there's a simple RC pull-down network attached to the inverting input of the first op-amp. Virtually all SDS9s I've seen however, have the resistor and capacitor on the mid-tom pad trigger input, wired the opposite way around to those on all the other channels. Instead of being 'RC' it's 'CR' if you know what I mean. I can't remember why this was done but space is tight here, if you want to wire them 'correctly' so perhaps the reason was that simple... space. Anyway, when I get a SDS9 in, I always put this right.
After swapping out a couple of TL084s (yes, they can and do indeed go screwy as well) , I replaced IC19, the 4051 multiplexer that passes triggers from the 8031 processor to the channel trigger inputs.
By now it was time to reattach the main-PCB to the power supply and jack-board and fire up this thing.
The SDS9 was now booting as expected and consistently. The excessive hum on the outputs was gone. The self-triggering on the rim had gone too but the toms were still giving me a headache and I still had that weird snare / rim to low-tom crosstalk. ๐
I replaced all of the 1nF capacitors associated with the pad trigger inputs as well as several apparently duff TL084s with TL074s
There was one more component that often causes problems but which I was hopeful, I didn't have to change and that's the 4067 (IC50). Like the 4051, this infamous multiplexer is also a common source of issues in all kinds of gear from the same era as the Simmons SDS9. The reason I didn't want to change it was simply because unlike the 4051, it's quite difficult to procure now-a-days.
Scoping the trigger lines going into the 4067, I noticed that triggering either the snare or rim, also produced a pulse on Pin 4 (the low-tom channel) of the 4067. This confirmed a crosstalk issue between the snare / rim and the low-tom. Oh dear! There wasn't anything weird going on between the TL084 trigger outputs and the 4067 inputs. The connections were good so this suggested that there was indeed a problem with the multiplexer itself and I really didn't want that to be the case. ๐ก
After having checked for short-circuits, I tested all the other channel inputs into the 4067 and everything was clean.
As well as multiplexing the channel triggers, the 4067 also multiplexes the voltages off the potentiometers.ย If you have a SDS9 with potentiometers that are starting to act a bit weird, there's a good chance that the 4067 will be the root of the problem.
Decades later and a common source of issues in many systems from the eighties; the 4067 'traffic cop' multiplexer.
So back to the Simmons SDS9 repair...
Wow! That's more like it! Swapping out the 4067 resolved the self-triggering issues and the snare / rim to low-tom trigger crosstalk.
Now that I had a 'silent' SDS9, I looked at the duff pad trigger input on the low-tom. That was down to a broken trace between one of those 1nF capacitors and the associated TL084.
With a normal boot period, no self-triggering, all pad inputs working and no channel crosstalk, all seemed good but this Simmons SDS9 repair wasn't quite over just yet...
There was a really weird thing going on with this Simmons SDS9 repair. The high and mid toms didn't sound right. It seemed like there was noise missing from the high-tom and the pitch of the mid-tom was higher than I thought it should be.
I went into program mode and levelled the toms so that they all sounded identical. This wasn't a simple case of pushing over the pots to one extreme, though. Indeed the tone pitch of the mid-tom had to be tweaked so as to be the same as the high and low toms. The filter pitch of the high-tom also had to be tweaked so as to be similar to the mid and low toms. In fact, the lack of 'noise' on the high-tom was actually down to the high-tom filter not opening all the way. To be honest, I did have a hunch about that.
Each of the SDS9 tom signals passes through a CEM 3394 and it was common practice to socket these ICs. This was good because I was able to swap them around and quickly eliminate them as the cause of the high and mid tom issues. I was now able to focus my efforts further upstream.
The fact that the CEM3394s were socketed, made it easy to eliminate them from the cause of the problems with the tom channels.
Each CEM3394s is fed from a pair of LM13600 dual operational transconductance amplifiers (OTA). This makes conventional fault diagnostics a bit challenging as you can't monitor currents on an oscilloscope. The required technique involves a lengthy process of elimination, until such point that you're nearer 100% sure that the respective OTA is faulty. So, that's exactly what I did but... I wasn't convinced.
I sent a WhatsApp message to my friend and Simmons Vintage Technical Network colleague, Michael Buchner, telling him about my Simmons SDS9 repair and how it's almost 100% working now, except for these two annoying issues. He got straight back to me asking if by chance, the firmware was version 6.0. "Yes, it was." I confirmed. He immediately recommended that I downgrade to version 3.0. Seriously? I didn't understand how a firmware bug could manifest itself by producing such an obvious couple of symptoms.
Surprisingly, downgrading the firmware fixed the last two issues I was having with the toms. THANK YOU, Michael Buckner for the heads-up!
Well, believe it or not, downgrading the firmware fixed the weird tom issues. The bad filter response on the high-tom and tuning error on the mid-tom were suddenly gone! Perhaps there was a calibration error in version 6.0 firmware. Who know, who cares! Michael's recommendation worked!!
I was at Simmons during the SDS9 period but I must confess to not having any recollection of this issue.
WOW!! Thanks, Michael.
So let's see what got fixed with this Simmons SDS9 repair:
Battery leakage cleaned up and SDS9 converted to lithium battery back-up.
Bad switches and potentiometers cleaned.
Slow boot up fixed.
Excessive hum fixed.
Rim and toms self-triggering fixed.
Low-tom pad trigger input not working fixed.
Snare / rim to low tom crosstalk fixed.
Bad calibration of filter pitch on high-tom fixed
Bad calibration of tone pitch on mid-tom fixed.
Sad customer is now a happy customer! ๐
To be honest, I really quite enjoyed working on this one.
Despite having been used extensively by many named artists, the Simmons SDS9 never acquired the same legendary status as other Simmons systems like the SDSV and SDS7. It's a shame because it's actually very good.
I guess Simmons decided to continue with the SDS7 idea of mixing digital samples with analogue synthesis but being a bit choosy how they did that, thus making the SDS9 more affordable.
The kick is generated in software. At the other extreme of technology of the time, the toms are classic (Simmons) analogue generated. Well, that's not quite true. They're digitally generated but pass through analogue filters which changes the sound and feel considerably. The snare and rims are sample-based making the SDS9's sound sources, as diverse as they could possibly be in 1985.
The end result was really very good and as I said, the SDS9 is quite an underrated e-kit. The sounds are classically 'Simmons' with punch, analogue 'fatness' and yet retaining clarity and definition.
Simmons SDS9 repair - almost like new now.
SDS9 die-hards will notice that this example has blue knob caps on the volume controls as well as on the parameter controls. To the best of my knowledge, everything is original so how those knobs ended up not being grey like the pad input sensitivity controls (and like other SDS9s), I don't know.
A LITTLE SIMMONS SDS9 STORY
Back in the summer of 1987, I took a week's break with a whole bunch of friends, to the Isle of Wight. Halfway through our week, we all drove up to Hammersmith as having been involved with Def Leppard, I didn't just have tickets but I also had backstage passes. As soon as the show ended, we made our way backstage. Rick Allen clocked me, pulled me aside and asked if it sounded okay out front.
"Hang on a second. Rick Allen, the drummer from Def Leppard is asking me if it sounded okay?" WTF?!?!?!?
How do you answer a question like that from Rick Allen? The man who had been through so much but who was determined to carry on and carry on he did!
Anyway, Rick was using a SDS9 and WOW! What a show. I'll never forget it.
I've been trying to get permission to use this image but as yet, no one's got back to me. Could I kindly ask for someone from deflepparduk.com contact me?
ON A VERY PERSONAL NOTE...
For me, Def Leppard was not just another rock band. My connection with the band went way back, prior to my time at Simmons. In fact, I was a Phil Collen fan when he was in Girl and for a brief period in like 1981 (or '82), I had Pete Willis' famous white Hamer guitar as, while a student, a mate of mine lived in a flat above the Def Leppard crew.
The guitar went up for sale for only 350 GBP. I say "only 350 GBP" but as a student in the early eighties, I just didn't have that kind of money. The other guitarist in the band however, did and Neil bought that amazing guitar.
Neil had multiple sclerosis and sadly passed away many, many years ago. As for Pete Willis' Hamer, who knows what happened to that! ๐ข
As the eighties progressed, I have to admit that Def Leppard was very influential in the development of my own musical and production styles, my guitar sound and playing technique and even my song writing.
Today I look at the pictures, watch the videos and play those records and a sense of that ol' wide-eyed magic washes over me, as it did back in the day, forcing a nostalgic tear to run down my cheek.
Today, a simple Simmons SDS9 repair can seriously take me back and if I ever get around to writing an autobiography, Def Leppard would have to feature in it.
UPDATE - 5th March 2025
When the customer came to collect, we got talking and I mentioned how Simmons made available a ZIF socket set for the SDS9, the idea being that swapping out EPROMs would be quick and simple. It comprised three ZIF sockets and a plastic EPROM compartment cover which replaced the original steel factory cover.ย The replacement cover was raised so as to fit comfortably over the EPROMs.
Well, Simon thought it was an awesome idea. Only problem was that the kits are now considerably more rare than a nice condition SDS9.
Simmons SDS9 with ZIF sockets making EPROM swap-out quick and simple.
Anyway, I thought I'd help him out as best as I could and fitted some rather smart ZIF sockets.
UPDATE - 30th March 2025
These two Simmons SDS9s are now fully functional and in really nice cosmetic condition.
Late last night I put the finishing touches on the second SDS9 I had in this year and which I briefly mentioned earlier in this post.
The customer asked for a full service including the following:
Replace all electrolytic capacitors.
Supply ROM A EPROM with factory 'RIM A'.
Bass drum trigger input not working.
Not exactly an extensive list and after a thorough examination, I advised the customer that the electrolytic capacitors didn't actually need replacing and that I couldn't find anything wrong with the bass drum trigger input.
Adrian had also given me a SDS1000 which he said (also) had a non-functioning bass drum trigger input. I wonder if things got a bit confused. What I did discover on the SDS9 however, was that the rim trigger input wasn't working and that the entire rim channel wasn't producing any sound.
I quickly sussed out that the non-functional rim trigger input was down to a wrong value capacitor. It took me a little longer to sort out the rim sound.
A little known fact about the SDS9 is that the rim technically has two voicings which can be output simultaneously and from different physical outputs.
the 'processed' rim is mixed with the snare and is output via the tip pole on the SDS9 snare audio output.
the unprocessed rim is available on the ring pole of the snare audio output.
So what do I mean by processed and unprocessed?
Well, the processed rim passes through the CEM3372 with the snare but the unprocessed rim is basically the raw sample, directly off the EPROMs.
Anyway, there was raw rim being output so the problem was either with the CEM3372, the TL084 that supplies the CV or both. Yep, you guessed it, both! ๐
I managed to convince Simon, the customer of the first SDS9, that I should correct the colour layout of his unit's knob caps. The knob caps on the second SDS9 were seriously faded, like the grey caps were brown and the blue caps were almost green. Hence, both units got a mild cosmetic make-over.
Working on vintage synthesisers means that a lot of the time, I have to create a 'test' patch and with so many instruments that come into the lab, it often gets quite challenging. So a few days I ago, I made the decision to buy something that would simplify my life; the Kiwitechnics Patch Editor.
This little box is as rare as well, something that's really rare and I was very lucky to find a pristine example on ebay UK. It was expensive but of course it was... because it's a rare (I just said that), it's mega cool and this one was like new (I just said that too). So I snapped it up.
At the moment, I have a Roland MKS-70 in, as well as a Roland MKS-80 and two Cheetah MS6s. To date, I've used PC editors to create test patches but what's available for the MS6 isn't great and the one that is, isn't compatible with Windows 11. ๐ On top of that, I don't always want to switch on my PC, just to program a synthesiser module. Well now I don't have to. I can just plug in my new Kiwitechnics Patch Editor. Oh this is so cool.
Just some of the synth modules I get in on a regular basis. The Kiwitechnics Patch Editor is going to make programming these so much easier.
Made from steel with illuminated controls and a large display (for old gits like me), the design, attention to detail and shear build quality of the Patch Editor, is incredibly professional. It feels like it's going to last a lifetime.
Controls that are active for the selected profile, illuminate with a menu option to turn down brightness. The rear panel has the usual complement of MIDI and power sockets, the latter taking 500mA at 9V - 12V DC, with centre pin negative on a 5.5mm x 2.5mm low-voltage barrel connector.
You'll also notice the 'EXT IN' jack socket which is a nice touch, allowing a foot controller for example, to be connected.
Murray at Kiwitechnics told me that Unfortunately, the Patch Editor was eventually discontinued because it just wasn't economically viable.ย It's something I can relate to as I'm constantly struggling to keep the prices of the stuff I make, as low as possible.
Having said that, the Patch Editor is still very much supported. In fact, a CPU upgrade is available for older units providing the same power and profile storage capacity as those with newer serial numbers. Since mine is S/N 1045 (an early version), I've decided to buy the new Patch Editor Plus.
The Patch Editor originally retailed for 450 USD, exc. shipping. I bought mine for 525 GBP. Today's exchange rate makes that about 655 USD. It was second-hand but it's an amazing little box and in my humble opinion, worth every penny. Hey, don't forget... you're getting half-a-dozen programmers in one! I just wish there was a way to get Kiwitechnics to continue production of the Patch Editor and keep this ultra cool product out there. The vintage synthesiser world needs the Kiwitechnics Patch Editor!!!
Last year, a customer brought me an ARP 2600 that had just been serviced with the exception of the power supply. The customer said that the synth would sometimes freeze and be unresponsive so I gave him a choice; I could either service the original power supply or design something a little more up-to-date. We both decided to take advantage of the situation and my Sirius replacement power supply for the classic ARP 2600 was the result.
To be honest, I took on way too many design projects in 2024 . So much so, that my repair work seriously slipped and I found myself constantly apologising to my good customers and thanking them for their patience. I figured I'd done enough design work for a while and vowed that 2025 would be different. Time to take things easy.
Well, almost...
Sirius is one of two projects from last year that kind of overspilt into the New Year, the other being Nebula-X, my balanced outputs jack-board for the Roland JX-10.
Anyway, life is great so enough moaning...
The original ARP 2600 power supply, including the transformer but excluding the fuse (no idea why they did it like that but , hey), is attached to a metal plate which is screwed to the inside of the wooden 2600 case. This keeps things very tidy, focused and easy to work on. That being said, the power supply is at the rear of the instrument and can be a bit awkward to get to. The construction of the 2600 is such that you have to kind of reach over the synthesiser front-panel, to get to the back of the instrument.
The power supply in the classic ARP 2600 is very neatly mounted although it seems strange that the fuse is separate.
With only +/-15V lines, on the face of it, the original power supply couldn't be more simple. I measured the static current consumption to beย about 170mA per rail so that wasn't at all a big deal, especially when I had 25W converters in mind for this project.
Static current consumption of the ARP 2600 seems quite modest.
In the previous paragraph I used the phrase "on the face of it". That's because things are potentially a little more involved. The original PSU has a pair of potentiometers which allow for adjustment of the supply lines. The electronics will run fine with a reasonable margin of error but annoyingly, many synthesisers of this era, including the 2600,ย took reference directly from the power lines. The 'reference' voltage is used for things like the VCOs and hence, scaling of the keyboard. Wanting to use a modern, modular switched-mode design like my other power supplies, it wouldn't be easy to emulate this feature.
I was able to include independent voltage references on both my Aurora PSU for the Roland MKS-80 and my Supernova PSU for the Roland Juno-106 for example, as the original power supplies for these instruments didn't take references directly from the supply lines.
The 10V reference on Aurora emanates from a 5V reference source (Q1) with a tolerance of 0.1%. Amplified by a factor of 2, the output is also fully adjustable.
It's quite possible to use sufficiently accurate devices so as not to need adjustment and so I looked at how I could do that. The Vigortronix AC/DC converters I intended to use and which I'm very familiar with, have a specified accuracy of 2%. That's pretty good. I measured the voltages of several 15V AC/DC converters that I had in stock. Coupled with my experience of my other power supplies, all of which are sent out with a test certificate, I could see that the tolerance was no worse than 1.6% with the vast majority of devices falling within a tolerance of 0.75%. This was really quite encouraging.
Okay, let me provide a little perspective...
There's no denying that accuracy and tolerances of electronic components and systems has jumped leaps and bounds since the ARP 2600 appeared on the scene in the early seventies. In fact, we should question the accuracy of the equipment that was used to calibrate the supplies at the factory in the first place. With this in mind, I decided to continue with my Sirius replacement power supply for the classic ARP 2600 prototype but I also decided toย hand-pick the converters, choosing those which had an accuracy of no less than 1.0%. That would give a worst case scenario of 14.85V or 15.15V. It would be interesting to see what would happen.
After a couple of weeks of testing, it was a great relief to note that things seemed to work just fine. My ears, my oscilloscope and my precision tuner, didn't reveal anything strange. With a view to offer Sirius to the wider ARP 2600 community however, I thought I could do better and so the executive decision was made to use converters with an accuracy of 0.7%. Yes, I know... it won't make any difference in the real world but I'll be able to sleep better! ๐ด
Sirius has precision filters, voltage supply active indicators and convenient test points.
Weighing just 215g my Sirius replacement power supply for the classic ARP 2600 is less than a third of the weight of the factory power supply (727g). This meant that Sirius could easily be secured using the original mounting plate. Indeed, although the Sirius PCB is attached to the plate using M3.5 fixing hardware, I didn't see a problem using the original screws to secure the plate to the inside of the 2600 case. Not having to supply a custom mounting solution would help keep the cost down.
"M3.5 fixing hardware?" I hear you ask! Glad you spotted that. So I've just explained that I wanted to use the original mounting plate, right? Well, the plate had been drilled to accept countersunk screws of some old UNC or UNF standard and so I had no option other than to choose my fixing hardware to be as close to the original as possible. Adequate to support Sirius, M3 screws and hex spacers would have been too small and I wouldn't have been able to use the original mounting plate.
Removing the original power supply was straight-forward and simple. Securing Sirius to the the original mounting plate and then fixing that into the position of the old power supply was also straight-forward and simple. I was however, concerned about soldering the connections from the mains input, synthesiser and the keyboard port, to Sirius. It would mean leaning over the synthesiser and I wanted to reduce the risk of an accident for others who might be looking to install Sirius themselves. I therefore chose to use screw terminals for all connections.
Screw terminals means that hooking up Sirius to your ARP 2600 requires minimal soldering.
With over-voltage, over-current and even reverse polarity protection built-in, advanced noise filtering on the back-end and nearer 95% efficiency as opposed to perhaps 15% efficiency of the original PSU, Sirius will also allow your ARP 2600 to be powered from virtually any domestic power supply, like 100V to 240V. That means that there's no need to change transformer taps, should you suddenly find yourself on the other side of the planet, alone with your favourite synthesiser! ๐
The two power supplies couldn't look more different!
In contrast to the image above, below is a picture of Sirius fully installed and I can't help feeling that it looks like its always been there! ๐
By the way, those aren't the original power input cables. I took the opportunity to change them to something a little more 'standard'.
Sirius installed and working just fine.
You may also notice the addition of an extra earth wire which is strapped to the voltage lines going back in the direction of the synthesiser. This is important. Unlike a linear power supply, 0V on the output of a SMPS, is not always connected to earth through the power supply itself. For the filters on Sirius to work properly, the return path for the each supply has to be direct. Earthing 0V through the PSU will break this path and the filters will be ineffective. Instead, 0V is earthed through the 'load' (the synthesiser) and the additional earth wire shown, is connected to the metal chassis (front-panel) of the 2600. Of course, this maintains safety as well as providing the required return path integrity. Earthing in this way also ensures that the effect of any parasitic capacitances on the outputs of the AC/DC converters are completely removed.
I made sure that after several hours of operation, the ARP 2600 still worked fine. As for Sirius, it didn't even get warm!
Of course, once I'd established that Sirius was working, a complete recalibration was required. Don't forget, voltage references are taken straight off the PSU.
I'd only just got back from spending New Year's Eve in the Bavarian Alps two days ago and officially, I'm not back to work 'till Monday but I simply couldn't wait to tell my customer the good news. In fact, he asked if he could come over the next day. Of course, that wasn't a problem as Ryan had been very patient and appreciated all the precautions I took with his beloved ARP 2600.
So the next day, Ryan turned up. We went into the lab and he couldn't wait to switch on his baby. The first thing he noticed was that there was no hum! Oh yeah, I kinda forgot to mention that. ๐คฃ
It took Ryan a few minutes to remember how it all worked but then after dialling in an initial sound, Ryan commented that he wouldn't have been able to do that before, as the instrument would become unresponsive and kind of freeze soon after power-on. The only option was to restart.
I was so excited to hand over Ryan's ARP 2600, now working just fine oh and with no hum!
APOLOGIES BUT I NEED TO MAKE IT QUITE CLEAR...
It should be no surprise that in recent years, various clones have been made of the iconic ARP 2600. Please be warned however, that my Sirius replacement power supply for the classic ARP 2600 was designed for the original, now vintage, ARP 2600 from the 1970s. I don't imagine the Korg ARP 2600 FS or the Korg ARP 2600M to bear any resemblance to the original instrument. As for the Behringer 2600 type of thing, forget it. So... DON'T evenย think about fitting Sirius to any of these machines!
Yes, the original power supply can be fixed and in fact, it's not at all difficult to service but Sirius changes things big time offering reliability, stability, longevity and... NO HUM.
Sirius is available to purchase here:
All I need to do now, is compile the installation manual. ๐
In the meantime, here's some interesting reading regarding the legendary ARP 2600:
