Gary 7 MIDI Kit Selector for the Simmons SDS7

Alex-PML7 April 202613 May 2026

One afternoon in late September 2025, a customer turned up to collect his Marshall JCM-800 combo that I’d serviced. My customers mean everything to me and it’s not unusual for those who turn up at my door, to stay a while. 😊 Anyway, Iain and I really hit it off and after mentioning his software work, I told him about my Gary 7 MIDI kit selector for the Simmons SDS7 idea.

Gary 7 was going to be another one of my software-based ideas which would probably never see light of day but then Iain offered to pop over one afternoon to help get me started with coding for the Raspberry Pi. First, he gave me a short list of various bits ‘n’ pieces I should buy in advance of his visit.

Well, Iain stuck to his promise and sometime in November 2025, he came round to explain how Raspberry Pi stuff worked. We had a fantastic afternoon and I learnt so much. THANKS Iain! 😎

Unfortunately, it was also roundabout this time that my doctor told me that a recent routine blood test had come back with a high PSA level. As it turned out, I was eventually diagnosed with prostate cancer. As you can imagine, the news was quite devastating. On the other hand, life goes on and the only way I could focus on the future was by being with my family and working on stuff that I love… like Gary7.

I also had another project that would help keep my mind off things. Nebula-X balanced outputs for the Roland JX-10 had been on my shelf for a couple of years. My third and last revision PCBs had been delivered and I was very keen to get this done too. Hence, my Nebula-X project took priority over Gary 7.

Iain introduced me to the whole Raspberry Pi thing and showed me stuff which, if I had to suss out on my own, would have taken me weeks if not months. More than that, his patience and general way was particularly inspiring. Iain’s a Java programmer specifically but showed me some Python code which kind of pointed towards what I wanted Gary 7 to do. Yes, I know that the firmware used for MIDI is either written in C or C++ but it wasn’t about the language or code. Iain had a way about him and well, gave me the confidence to make a start. It was a kind of Eureka moment, if you like.

While I toiled with how I was going to approach this whole software thing, I began designing a development board for Gary 7. This was by no means a prototype but simply a board which had a lot of open connections and which would allow me to easily change things if necessary. I believe 'versatility' is the word I'm looking for.

Indeed, although the objectives of this project were quite straight-forward, there was one major aspect of my Gary 7 MIDI kit selector for the Simmons SDS7 in which I had no real experience and that was of course, software.

My Gary 7 development board happened quite quickly. Of course, I didn’t use a full Raspberry Pi but chose the much smaller Raspberry Pi Pico. I was soon talking to Iain and other friends about the best way to proceed.

On a side note, with a chunky 7805 regulator, Gary 7 can be powered from an external 9V - 12V DC power supply. 😎 Indeed, I used a 12V PSU to drive my development board.

I’ve always been quite critical of AI but this project seemed to be an ideal opportunity to ‘have a go’. It was round about this time that another new friend and I decided to meet up. As soon as Mike Walden brought out his newly designed main-board for the Simmons SDS6, I contacted the customer of a unit that had been brought in and subsequently bought the first of Mike's boards. Since getting to know Mike, we'd hooked up several times on line but just before Christmas 2025 he kindly agreed to come over to my place to chat Simmons SDS6.

I mentioned Gary 7 to him and that I was considering using AI to develop the software. "Give it a go. See what happens" was his response. With a lot of initial help from Iain and a word of reassurance from Mike, I decided to start where everyone starts and that was with a prompt, a detailed and methodical description of my objectives and the means with which I intended to deliver them. That might sound simple but like most things in life, what you get out of AI is only as good as what you put in.

December 2025 was a weird time for me and my family. Nebula-X and Gary 7 were much needed distractions and with the latter, I also immersed myself into the whole AI thing. It only took me two prompts to get something working but boy, did I learn a lot.

After getting the MIDI to SDS7 kit selector lines to work, I decided to push things. With sixteen switches to allow manual kit selection of the SDS7, I introduced a way of setting Gary 7’s MIDI channel with those switches, for example. Of course, it would have been kind of frustrating if Gary 7 didn’t remember the MIDI channel. Hence, the set MIDI channel had to be written to the Pi Pico’s memory. Then I came up with the idea of getting Gary 7 to remember the last kit selection prior to power-down. I referred to this as 'the last command'.

Early tests revealed unreliable memory retention so this had to be addressed and so the memory architecture and management of the Pi Pico were examples of what I learnt from the AI that I was using.

All versions of Gary 7 up to 1.6 were developed with the aid of AI so that was six prompts. I specified that all variables should be listed at the top of the code so tweaking the next three versions of the software was easy and something I could do myself.

By version 1.9, Gary 7 MIDI kit selector for the SDS7 was rocking!

With my cancer prognosis constantly in the back of my mind, getting Gary 7 MIDI kit selector for the Simmons SDS7 working was just so exciting, I just had to record it all. The two videos below show my bench testing.

Before I continue, let's quickly consider the whole kit selector thing of the Simmons SDS7 and the hardware I chose to do this...

The mechanism behind the kit selector of the SDS7 is simple but ingenious. Four signals from the SDS7 are switched to four outputs in a rather clever combination so as to allow for sixteen options. Gary 7 uses optical relays, emulating the zones or ‘pads’ on the Simmons selector pad, thus switching the four signals in the combinations required, to the four outputs.

Now then, questions could be asked like…

“Why have the expense of the opto-isolated relays when I could have just got the Raspberry Pi Pico to generate four signals and switch them accordingly?”

Well, any SDS7 user will be aware that this ol’ girl can be a bit temperamental and I figured that yes, it’ll cost a bit more and yes, things will be slightly more complicated for me but I really wanted to keep SDS7 as isolated as possible. I also wanted to ensure that SDS7 sees exactly what it wants to see on the four returning lines.

Gary 7 main-board showing dual SSRs and switching transistors — Here you can see the four dual SSRs (middle of image) and the the eight transistors that switch them (just a little up from middle of image).

Electromechanical relays would have cost more, potentially drawn more current and perhaps more importantly, they would have been much slower than optical ‘solid state’ devices so the reason to go for SSRs was clear.

The next challenge was to find a suitable enclosure. There wasn’t much point to start designing PCBs if I didn’t know what they were going to go into. To be honest, I had a rough idea of the size of box required so I actually started looking for something back in November 2025, when I first had the idea of Gary.

The Takachi CF series of cases, specifically the CF16-11BB consistently came back as my favourite and one of my suppliers seemed to have this in stock so I bought one for prototype purposes. Yes, it was more expensive than I’d have liked but it was small, made from aluminium and readily available.

There was however, one very slight problem. The rear of the enclosure had a 10° slant from the vertical axis. To ensure that the rear sockets sat flush with the rear panel, I had to come up with a plan.

Takachi 16-11 for Gary 7 — Lining up PCBs and rear sockets was particularly challenging with the Takachi CC16-11 case. As you can see, the rear of the enclosure is sloped. I superimposed my ideas over the original datasheet drawing after adding some dimensions which were missing.

You'll notice in the image above, that my 'plan' was to use slightly higher PCB stand-offs at the rear and slightly lower stand-offs at the front.

Despite lots of experience and all my best efforts, my first attempt at the Gary 7 enclosure had a couple of errors. The cut-outs for the switches were 1mm too big. I had to scrap the black anodised Takachi panel and get Lenton Engineering to make a new one from just plain aluminium.

Gary 7 Prototype Top View — Gary 7 prototype top view. Not the top-panel that came with the enclosure as I originally made the tact-switch cut-outs 1mm larger than they had to be. Grr...

The other issue I had was down to the big multi-pin connectors on the rear panel. Basically, they were set too high. You can't see this too well in the image below but on the rear of the chassis mounting sockets, the securing nut butted into the top channel used for the side-screws of the enclosure. Lenton Engineering cut the channel but this wasn't the way to go, long term.

Gary 7 Prototype Rear View — Gary 7 prototype rear view.

I got the switch-board right first time but the main-board had to be redesigned. I had to cut away a section of the PCB, specifically to the left of the MIDI sockets, so as to allow access to secure the chassis mounting multi-pin connectors.

Here are the two Gary 7 PCBs: the switch-board and the main-board. Also shown is a 20-way IDC ribbon cable that connects the two.

Power ON / OFF, power input (+9V DC) and MIDI are all soldered to the main-board while the multi-pin connectors to the SDS7 and the selector pad (if you have one) are chassis mounted. You may notice that the DC input and MIDI sockets look slightly lifted as if they're tilted. This is to help alignment of these sockets with the sloped rear of the enclosure.

Gary 7 PCB sockets — All the sockets and the power switch all lined up perfectly with the case.

What a pain in the butt but anyway... When the second drilled case components came back from Lenton Engineering, I couldn’t wait to see how things would fit together. Indeed this time, everything lined up perfectly and WOW... this is starting to look cool.

It's difficult to make a peripheral more than forty years after the original product was launched and keep a design connection with that product. I did try, though and having Simmons style switches was exactly the retro connection I was looking for.

SDS7 Switches on Gary 7 Switch-Board — Gary 7 has the same style of switches as Simmons used on the SDS7, over forty years ago.

With the PCB, multi-pin sockets and enclosure all fitting nicely, I sent a set of silk screen print files to my friend Ivor Mitchell. Ivor dropped round a couple of days later to pick up the case parts. It was only a few days later when Ivor returned with the job. I was delighted and rushed to get the electronics into the now very sexy looking case.

Gary 7 MIDI Kit Selector for the Simmons SDS7 — I've never been patient but the time it took to get Gary 7 to this stage seemed like a particularly long wait. Having said that, it all seemed worth it in the end.

I had to buy another enclosure and recut the rear panel, lowering the multi-pin connector sockets by only 2mm.

Rear of Gary 7 final with everything fitting and looking much better than my prototype.

Gary 7 MIDI kit selector for the Simmons SDS7 ended up being a BIG little project. My first project involving software, my first for which I made a bespoke development board and the first time I'd used AI for anything, it was seriously fun!

Gary 7offers three ways to select kits on the SDS7:

MIDI program change
Manually via the sixteen on-board buttons
An original Simmons kit selector pad

As well as being able to set the MIDI channel on Gary 7, the last MIDI program change or last button press on the front panel will be remembered and output to the connected SDS7 five seconds after the next power-up. The 'Last Command' feature will NOT remember the last pad hit on a connected Simmons kit selector pad. That's because the selector pad input and the connection to the SDS7 are simply paralleled. The pad input does not pass through the processor so any signals received from the selector pad, can't be written to memory.

THE DOWN-SIDE - GARY 7 IS EXPENSIVE! 😕

On the back of Gary 7 are a pair of female connectors, identical to the selector pad input that's on the back of the SDS7. One connects to the SDS7 and one is for connection of an original Simmons selector pad. There’s also a cable to connect Gary 7 to the SDS7. This cable has two male connectors, one at each end. At the time of writing, just those four connectors alone are over 72 GBP.

Hirose connectors as used for the kit selector pad connection on the Simmons SDS7 — Shown are the connectors as used for the kit selector pad connection on the Simmons SDS7.

In contrast, the heart of the system, the Raspberry Pi Pico (with headers) retails in the UK for just under 5GBP!

Raspberry Pi Pico on Gary 7 — At the heart of Gary 7 is a Raspberry Pi Pico costing less than 5 GBP.

Incidentally, in the image above that shows the connectors, take a closer look at the cable that connects Gary 7 to the SDS7. You'll notice that there's a ring around one of the connectors. This 'locking' ring is supplied by the manufacturer, with the connector. If you have a Simmons selector pad, you'll be aware that this ring is (blatantly) absent. That's because the socket on the SDS7 is recessed and unfortunately, Simmons didn't make the cut-out in the rear of the SDS7 big enough, thus making the locking ring almost impossible to comfortably access. 😕 This connector on Gary is mounted directly to the rear panel and therefore, NOT recessed. As such, I decided to include the locking ring to make things secure at the Gary 7 end of the connection. Trying to fit the connector with the locking ring to the SDS7, might be difficult!

Anyway, back to the expensive Gary 7... The Takachi CF16-11BB enclosure is pretty cool but at more than 30 GBP each, suddenly it's not so cool. Bear in mind that I have to get it drilled out and then silk-screened.

A WORD ON AI

The truth is that since this whole AI thing kicked off, I haven't exactly been keen. When I look back however, I was never a fan of having computers in the recording studio, LOL. Of course, it soon became obvious that computers in the studio was the way it was going back in the nineties and in contrast, AI is the way that everything's going now. NO! That's not quite true and there's a lot more to it than that.

I have a lot of test equipment in my lab. I have a couple of oscilloscopes, signal generators, logic analysers. I have over 2500 GBP worth of state-of the-art soldering equipment. And I've never argued that I shouldn't have any of that. All that gear helps me fix music technology and design and build some really cool stuff.

Similarly, I use two computers in my recording studio. Both computers run the most amazing software. The music that comes out of my studio however, is still mine. The computers just help me get it out.

My decision to use AI as an aid to develop the software for Gary 7 was based on the firm commitment that AI would be strictly used as just another tool. Like any other piece of equipment in my lab and like the computers in my studio, my intention from the outset was to use AI to help me develop something specific and not to get it done for me.

GIVING A LITTLE BACK

I've mentioned how Gary 7 kept me occupied and my mind distracted while I dealt with my prostate cancer diagnosis. In the UK, one in eight men will develop the disease and while the treatment I received was quite simply amazing and the staff who looked after me were angels, I feel that more needs to be done. Wouldn't it be just perfect if I could help in some way?

I have therefore made the decision to DONATE ALL PROCEEDS from Gary 7 sales to prostate cancer research. Since I'm in the UK, the specific charity that I'm chosing to support is Prostate Cancer UK.

GARY 7 CREDITS

I'm by no means a genius and am always and forever grateful to the friends I have around me and some who are a little further away. 😊

CONCEPT:                             Alexander Bhinder
INSPIRATION: Iain Melville, Mike Walden
HARDWARE DESIGN: Alexander Bhinder
PROMPTS: Alexander Bhinder
SOFTWARE:                          Microsoft Copilot
TESTING:                               Alexander Bhinder
ENCLOSURE DESIGN: Alexander Bhinder
ENCLOSURE CUTTING:   Paul at Lenton Engineering
SILK SCREENING:                Ivor Mitchell at S & S Quality Print
CHEERING ME ON:   Ed Rose, Micha Buchner, Patrice Jacquot (my Simmons Vintage Technical Network buddies).

Gary 7 joins my other peripherals and upgrades for the Simmons SDS7 in the Simmons SDS7 Heaven category in my on-line store. Can't wait? You can buy Gary 7 here:

Simmons SDS9 Repair

Alex-PML1 March 202515 July 2025

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 ½AA 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...

Simmons SDS9 Ni-Cd to lithium battery mod — You can't just replace the original battery with a different type. Some modification to the circuit is required.

IMPORTANT - You CANNOT just 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.

Simmons SDS9 switches now cleaned and working properly — 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 wasn’t 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.

Simmons SDS9 power supply with new capacitors — 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. 😒

Many TL084s on this SDS9 were replaced — 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. 😡

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. 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.

A common source of issues in many systems from the eighties, the 4067 'traffic cop' multiplexer — 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.

Luckily the CEM3394s were socketed on this Simmons SDS9 — 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.

Downgrading the firmware on this SDS9 fixed the weird tom issues — 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! 😎

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.

Def Leppard Tour 1987 — 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! 😢

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. 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

Two Simmons SDS9s repaired and serviced 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! 😕

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.

AMEP Advanced Memory Expansion Pack for the Simmons SDS7

Alex-PML10 October 20247 June 2025

Over forty years and a couple of clones later, I'm delighted to announce the all new AMEP Advanced Memory Expansion Pack for the Simmons SDS7.

It can take days, weeks or even months to program a bunch of patches into your Simmons SDS7. After all your hard work, there's only ever been one way to back it all up and that's with a memory cassette via the expansion port. Well, not anymore! 🙂

The original Simmons memory cassette is exceedingly rare, more so than the SDS7 itself and finding one that hasn't been eaten by the batteries is virtually impossible. Unfortunately, the same can be said for the clones that have appeared over the years.

Also using 6116 SRAM chips, the original MEP was very large and just like the memory-board in the SDS7, it had built-in NiCad batteries that required the memory cassette to be regularly plugged into a powered up SDS7, so that the batteries could be recharged.

Original Simmons MEP — The original Simmons memory cassette was large, used a NiCad battery that required regular charging and was annoyingly unreliable.

Being a large device, connecting it to the SDS7 via the rear DIN 41612 socket that wasn't really designed to take that kind of thing, caused its own problems. A lot of people kept a box of matches with their memory cassette. Perhaps you can work out why.

Over the years, clones have been developed but strangely, they're all copies of the original Simmons memory cassette. Hence the term 'clone', I guess. Despite huge changes in technology since 1983 however, this means that all the issues associated with the original Simmons memory cassette, have also been copied.

This year, while developing a couple of peripherals for the Simmons SDS7 which were intended to enhance performance and reliability and hopefully extend life span, I realised a need for a 'better' external data storage solution, especially since two of the peripherals I've developed, involve disconnecting the SDS7's memory back-up battery. Of course doing so, will mean losing all the data.

A good starting point for something like this was to define objectives so here's a sneak peak at the design brief I gave myself:

Small and compact design
More memory than the original MEP
Retain the 'Data' Protect' function
Remove dependency associated with rechargeable batteries
Battery should last for ten years minimum
Include a mechanism so that when the battery is changed, data is retained for a minimum of ten minutes
The new device must be affordable.

So all that was great but how was I going to achieve it?

The first thing was to get a concept together and then take a look at the Simmons SDS7 to see if something radical could actually work.

Well, I couldn't do all that by myself, not in any realistic timeframe, anyway. Fortunately, I've got a friend. In fact, I think I can safely say, that Guy Wilkinson is my best friend! 🙂

Guy and I got to know each other back in 2020, through the work he's done on the Roland Super-JX and my first product Aurora, a modular switched-mode power supply for the Roland MKS-80.

In June 2024, Guy and I took a day out and went to the 'Synthesised' exhibition at the National Computer Centre in Cambridge. We arrived early so went for a coffee and it was then that I mentioned my idea of AMEP Advanced Memory Expansion pack for the Simmons SDS7. Guy was surprisingly excited and quite keen to help.

Alex and Guy at Synthesised 2024 — Me and Guy at a coffee shop somewhere in Cambridge, UK.

As has already been pointed out, the original Simmons memory cassette was very large, exerting undue torque on the SDS7's DIN 41612 expansion port. Hence, the box of matches which people would put underneath the cassette! So, not wanting to copy (clone) the original device and using newer, more compact technology instead, my idea was to make AMEP such that the body would sit perpendicularly to deck and parallel to the back panel of the SDS7. Instead of sticking out from the SDS7, it would run up the back of the SDS7. To keep costs down, Guy and I also explored the potential for a 'caseless' design.

To achieve this, AMEP began as a sandwiched, 2-board idea which both Guy and I were really happy with and which allowed us some versatility with regards layout.

Oh and there's one more thing...

When hooked up to the SDS7, the original memory cassette obstructed access to the SDS7's sequencer input 1 jack socket. SERIOUSLY?!?!? It should be straight-forward enough to design AMEP so it doesn't do the same!

When engaged, the original Simmons memory cassette blocked access to the SDS7 sequencer input 1 — When engaged, the original Simmons memory cassette compromised access to sequencer port 1. AMEP does not!

Within a very short period, Guy had knocked up the concept and contacted me to come over and rip apart my test SDS7. I was developing my Dark Matter modular switched-mode power supply for the SDS7 at the time, as well as Pleiades, my lithium battery converter and Tubbutec uniPulse adapter, so I was a bit apprehensive. On the other hand, this had to be done and I really wanted all three products to go out at roughly the same time.

I had some other plans for the new storage device and so we checked out a lot stuff on the SDS7 than we actually needed to. Unfortunately, the 'keep these free for future expansion' lines as referenced on the original SDS7 schematics, didn't go anywhere and my idea of including MIDI for example, went straight out of the window. 🙁

8th September 2024 and we had our first prototype. Guy came over and plugged it in. I performed a bank dump. I removed AMEP, switched off my test SDS7, pulled the battery and then we tried to reload from the AMEP. Well, we were delighted. AMEP seemed to work. We tried this several times, checking the memory protect function and writing / reading from all four banks on the AMEP.

First prototype AMEP was a bit of mess but we had to make sure that the SDS7 would see it as a friend — The first AMEP prototype worked straight-away. Well, after I'd remembered how to save to an external device! You also get a glimpse of my Dark Matter prototype in this picture and if you know what you're looking for, you can even catch a bit of Pleiades.

Yes, AMEP prototype 01 looked a bit 'Heath Robinson' but Guy and I didn't know for sure if SDS7 would even talk with our new gadget so knocking up something to see if SDS7 would recognise a friend, was a necessary first step. Anyway, the test results were very encouraging. In fact, we were positively thrilled and so we continued.

The next couple of weeks were busy. Guy poured a considerable number of hours into finalising a pre-production prototype while I focused on further testing, graphics, enclosure and packaging.

You'll notice the very small LR44 type battery on Prototype 01 in the image above. Well, one criteria missing off the original list was that AMEP should use a standard and readily available battery and so the design had to be changed to accommodate a much larger CR2032. An appropriate battery holder has to make battery changing easy but should also be as discrete as possible.

I continued to test AMEP on my studio SDS7, my test SDS7 and a customer unit (thanks, Peter). Initially, AMEP didn't work on the customer's machine and I quickly discovered a problem with the 40-way IDC ribbon cable between the PSU board and the back plane. You need to remember that these cables are forty years old! One new IDC cable later and everything was fine. Hey, I'm not even sure if Simmons tested the SDS7 expansion port during the production process.

Replacement IDC cables for the Simmons SDS7 — After forty years, every SDS7 could benefit from new IDC cables.

One problem that Guy and I have is that we use different electronic design software. This makes exchanging files very difficult and with something as involved as a new data storage device for a forty year old synthesiser, we had to come up with workarounds, which was a headache in itself.

By 24th September 2024, we were ready to submit an order for the first batch of PCBs.

AMEP Advanced Memory Expansion pack for the Simmons SDS7 pre-production prototype PCBs arrived — 1st October 2024 and AMEP first production PCBs turned up.

Friday 4th October 2024, Guy came over and we made three AMEPs. It was an exciting and fun-packed afternoon. We even had Duran Duran playing in the background. Hey, all three AMEPs worked perfectly! 😮

Alex and Guy making the first batch of AMEP Advanced Memory Expansion pack for the Simmons SDS7 — 4th October 2024 and Guy and I are making the first AMEPs. By the way... THANK YOU Ed Rose for the awesome SDSV T-shirt! I can't believe you made this, Dude!!!

WRITE VERIFICATION

There's no mention in the Simmons SDS7 manual about any routine to verify that data has correctly been written to an external data storage device. Guy and I discovered however, that if AMEP's memory protection switch is ON and one attempts to write data to an AMEP memory location that already has that data, then the SDS7 display will flash up 'AC' meaning that everything's fine. We couldn't see any reason why SDS7 would respond differently, with an original Simmons memory cassette as this feature doesn't have anything to do with AMEP. We're definitely not claiming any credit for that one but it's a cool hidden feature.

Simmons SDS7 AMEP Write Fail Write Pass — The left image shows what is displayed on SDS7 when a write command fails. The right image shows what SDS7 displays when a write command is either successful OR with the AMEP memory protect switch ON and attempting to write data to an AMEP location that already has that data (verification).

I couldn't wait to tell my Simmons Vintage Technical Network colleagues the good news. With confidence high, Michael Buckner asked a question which was going to come sooner or later; "Would AMEP Advanced Memory Expansion pack for the Simmons SDS7 also work on the SDS6?"

Well, I couldn't see why it wouldn't but having confirmation would be a big deal so I decided to send Michael Buchner and Ed Rose, AMEP samples and await their response.

At last! Decades after its release, there's now a cost-effective and reliable way to save your valuable SDS7 and indeed, your SDS6 data to an external device.

AMEP is handmade in Hemel Hempstead, Hertfordshire, United Kingdom, only a few miles from St. Albans where Simmons used to be based and where I used to work.

And finally...

I really wanted to do AMEP justice so AMEP is supplied in it's own bespoke tin which has a transparent lid section.

I designed an insert, originally to be made from ESD foam but the quotes I received for this small item were insanely prohibitive. In fact, I figured that I could buy a 3D printer and make something better, myself.

Well, my graphics guy Tony and I have been meaning to get into 3D printing for a long time and we thought this would be a good excuse to make a start. Hence, the insert is 3D printed by me.

Plagued by whole load of things that gave the Simmons SDS7 the unfortunate reputation of being quite unreliable, albeit that virtually all the issues can now be resolved, I wanted SDS7 lovers to have something that they could depend on for a change. That's one reason why the AMEP packaging took a bit longer to sort out than I'd have liked. While AMEP is pretty robust and not particularly vulnerable to electrostatic discharge (ESD) damage, the same can't be said for your SDS7.

Unlike machines that came later, the data lines on the expansion port on the back of the SDS7, are completely exposed and unprotected. THIS IS A BIG DEAL. Whether you have AMEP or not, please do take appropriate precautions when handling your SDS7.

Anyway, I digress slightly. AMEP packaging is made with a conductive PLA, thus reducing the risk of ESD damage, not to AMEP but to your SDS7. 🙂

AMEP Insert in design stage — Bambu Studio is a nice bit of software.

Tony observed that everything about AMEP except the tin, is made by Plasma Music Limited! How cool is that?

If you're keen to keep all your Simmons SDS7 data safe, you can buy AMEP here:

And finally, AMEP advanced memory expansion pack for the Simmons SDS7 would have taken much longer to develop and perhaps might not have happened at all, if it wasn't for the help, support and encouragement I received from my Simmons Vintage Technical Network friends and colleagues. THANK YOU Ed Rose, aka The Simmons Guy, Michael Buchner and Patrice Jacquot.

In particular, special thanks go to my dear friend Guy Wilkinson of Super Synth Projects who poured in hours and hours of work into this one. Guy, THANK YOU for doing so much to get AMEP finished and working. What you did is just brilliant! 🙂

UPDATE - 16th October 2024

Wow! I've already received the big question pertaining to the weird SDS7 Bank Anomaly. Whilst this hasn't got anything to do with AMEP, it's an important question and so I thought I would add my answer to this post.

According to the original owner’s manual, the SDS7 has two banks: HI and LO. The HI bank includes patches 40 to 79 and the LO bank includes patches 01 to 39.

Well, it doesn’t take a rocket scientist to notice that the HI bank has forty patches and the LO bank has thirty-nine patches! 🤔

THE SDS7 BANKS ARE NOT THE SAME SIZE 😡

So how the hell does this work? A good question and I don’t have a working original Simmons memory cassette to test that.

In theory, backing up the HI bank and then writing it to the LO bank will mean that you’ll lose a patch. Going the other way, backing up the LO bank and writing it to the HI bank will mean that you’ll have one patch unaffected (patch 40).

So here’s how it works:

Backing up the HI bank (patches 40 – 79) and writing to LO will result in patch 40 being lost. Patch 41 is written to patch 01 instead and patch 79 is written to patch 39.

Backing up the LO bank (patches 01 – 39) and writing to HI will result in patch 40 not being written to. Patch 01 is written to patch 41 instead and patch 39 is written to patch 79.

Yeah, I know. WTH?!?!?!?

Whilst AMEP is an incredibly cool piece of kit, it’s not ‘intelligent’. AMEP doesn’t have an on-board processor to negotiate the SDS7 bank anomaly. If it did, AMEP would have been prohibitively expensive and physically, much larger. ☹

BUT…. There’s a workaround:

!!! DON’T USE PATCH 40 !!!

Of course, if you save the LO bank and write it to the LO bank and if you save the HI bank and write it to the HI bank, everything will be fine. If however, you want to swap banks, then you'll have to use the workaround. I'd imagine it's the same if you have an original Simmons memory cassette.

UPDATE - 1st November 2024 - AMEP IS NOW ARM'D

Manufacturing tolerances have changed considerably over the past forty years and while AMEP will click in nicely into a brand new female DIN 41612 connector, that's not always the case with the same connector on the back of the SDS7. After four decades, things can feel a little loose.

To cater for a loose fit, AMEP now has an Anti Rock Mechanism (ARM) which securely keeps it in place. Not rocket science, just some PCB spacers added to AMEP's connector end but which work just great.

AMEP now has Anti Rock Mechanism — AMEP now features an Anti Rock Mechanism.

Unlike the original Simmons memory cassette, AMEP is small and light but the new ARM makes things feel even more solid and will hopefully reduce wear of the SDS7 expansion slot, over coming decades.

AMEP's anti rock mechanism keeps it securely in place — AMEP's ARM keeps it securely in place and prevents rocking when engaged with the DIN 41612 connector in the back of the SDS7.

The new anti rock mechanism allows AMEP to 'snap' into place. Yes, a simple idea but very worth implementing.

UPDATE - 26th January 2025

Compiling installation manuals and in the case of AMEP, a user guide can often take longer than the technical development of the respective product. Wanting my stuff to be available to the wider vintage music gear community, ideally, I'd like all of my manuals translated into several languages. Realistically that's not going to happen but when someone volunteers to translate at least one manual into one language, I simply have to jump at the chance.

That's exactly what happened while I was having a casual on-line conversation with my Simmons Vintage Technical Network buddy, Michael Buchner, who just asked "Would you like a German version of the user guide?".

Thanks to Michael Buchner for translating the AMEP user guide into German — My special thanks to Michael Buchner for translating the AMEP user guide into German

One of the guys who kept me motivated during my recent flurry of Simmons related projects, Michael did a great job and delivered a Bedienungsanleitung, within only a few days of our conversation.

Michael, THANK YOU so much for this! 😎

The AMEP user guide is made available after purchase but there's also a QR code on the packaging which will take you to a combined English / German file.

My Test Simmons SDS7 Is Back In One Piece

Alex-PML1 October 20247 June 2025

Today is a BIG day. Today, my test Simmons SDS7 is back in one piece! SDS7 serial number 70320 was finally put back together after several months of doing exactly what I bought it for… to host the development of a small range of peripherals for one of my favourite electronic drum systems. 😊

Back in December last year, I found a really nice SDS7 up for sale and having wanted one of these ever since I sold mine back in 1987 to help fund the purchase of my first SDX, I just wanted to get another one.

My early Christmas present to myself got me all smitten again and I had ideas to design stuff that would help keep this legendary instrument going for another forty something years. The only problem was that I didn't really want to develop stuff on the SDS7 I'd just bought, as it was immaculate.

Then in May 2024, a friend pointed me in the direction of a SDS7 that was up for sale relatively locally (London). It had some faults but having a few ideas of what might be causing the problems, I grabbed it for a really good price.

Subsequently, SDS7 #70320 became the platform on which I developed Pleiades lithium battery conversion and uniPulse MIDI to trigger platform, Dark Matter modular switched-mode power supply, AMEP advanced memory expansion pack and NC-7 noise cancelling snap-in, all of which will be launching very soon. Indeed, I’m delighted to announce that SDS7 #70320 is actually running Pleiades, Dark Matter and NC-7. AMEP will be here very shortly. In fact, the pre-production PCBs should arrive today.

Using paper cut-outs to make sure that Dark Matter would fit — After my initial designs, I used paper cut-outs, to make sure that Dark Matter would fit snuggly into the transformer cavity of SDS7.

You may have noticed that the top-case of my test SDS7 looks very 'black' and seems to have an acute absence of age-related scratches, dents and rust. Well, that's because I got it sand blasted and then re-powder-coated. I actually had a customer's SDS7 in at the same time so I got both top-cases done together.

Simmons SDS7 Top Case Refinished — I was absolutely delighted with the results of sand blasting and powder coating this old Simmons SDS7 top case. The guys even managed to reproduce that original eighties leatherette texture.

It's been a heavy few months and there were a couple of points during that period when I thought I’d been a bit too ambitious. Ed Rose (aka The Simmons Guy), Michael Buchner, Patrice Jacquot and my close friend Guy Wilkinson (of Super Synth Projects) were however, so incredibly supportive. Without their help and encouragement, things would have taken so much longer and perhaps, might not even have happened.

Finally and at long last however, my test Simmons SDS7 is back in one piece and #70320 looks and sounds amazing. I’m just so pleased that it all worked out. Pleiades, Dark Matter and AMEP will be launched at the same time and very soon, like within the next couple of weeks, hopefully so stay tuned. 🙂

UPDATE - 16:00, 1st October 2024

This is my very first post update that has the same date as the post itself! Yes, something happened a few hours after I published this post. My prototype AMEP PCBs arrived. 😮

AMEP pre production prototype PCBs — Oh! Look what just turned up! AMEP pre-production prototype PCBs. Oh WOW!!

Looks like I'm going to be busy for a few days.

UPDATE - 7th December 2024

All the peripherals that I've designed this year for the Simmons SDS7 are now available in my online store. In fact, I've made a category just for them.

Pleiades lithium battery conversion and uniPulse MIDI adapter kit.
Dark Matter 75W modular switched-mode power supply.
AMEP advanced memory expansion pack.
NC-7 noise-cancelling snap-in module.

I think I'm going to take a break now!