simmons tech Archives - Plasma Music Limited

My NC-7 noise cancelling mod for the Simmons SDS7 is for those SDS7s that didn't get this mod factory fitted.

"Surely that can't be" I hear you ask.

Pictured below, is part of the Simmons SDS7 showing the quad op-amp, part of which is used to buffer the stereo outputs. Due to the mish-mosh of analogue, digital and power tracks on the back plane, Simmons was forced to come up with an easy retrofit solution to reduce specifically, CPU noise picked up by the stereo buss. Able to take advantage of a spare op-amp stage in the TL084 and dropping an 'aerial' on the rear of the back plane, inverted noise was mixed on to the stereo buss, thereby cancelling out the 'in-phase' noise. Highlighted in red is the pre-set pot and the two 10kΩ resistors which were part of that mod.

There are however, a few SDS7s out there that didn't get the mod! Pictured below, is my test SDS7 which I used to develop Pleiades, Dark Matter and AMEP and as you can see, it didn't get the mod fitted back in the day.

You'll also notice the absence of a small green capacitor, highlighted in yellow on the second image. This 47pF capacitor which is connected between pins 10 and 12 of the TL084, is sometimes soldered on the back of the back plane PCB. More about this later.

Well, I was going to implement the mod as per the original service bulletin but as it turned out, the track layout of the back plane version in my test SDS7 was different to later revisions and I wasn't able to drill the three holes for the pre-set without busting a track.

Then I had a thought; "Why don't I knock up a little snap-in PCB to do the job?" That way, anyone with a SDS7 that didn't have the noise cancelling mod installed, could also benefit. 🙂

Snaping into the IC socket that the TL084 is in and taping the aerial on to the rear of the back plane, means that NC-7 can easily be installed in a few minutes.

Of course it's not quite that straight-forward. The noise cancelling circuit has to be 'tuned', hence the pre-set pot. Instructions on how to do that are in the installation manual and that process also takes only a few minutes.

The two through-hole resistors of the original mod, are replaced by SMD 0805 resistors that are situated underneath the IC on NC-7. That 47pF capacitor I mentioned earlier, is also superfluous as on the underside of the NC-7 PCB is a SMD 2010 47pF capacitor. Hence, if the original capacitor is indeed soldered to the rear of the TL084, it must be removed.

47pF capacitor on back of TL084 — Irrespective of where the 47pF is located, it should be removed as NC-7 has a 47pF on-board.

NC-7's aerial wire can't simply flip over the back plane PCB. That's because one of three guides guide in the SDS7 top-case secures the back plane PCB exactly where the aerial wire needs to be. The wire I chose for the NC-7 aerial wire is CAT5/6 cable strand so it's solid. If it catches into the guide of the top-case, it'll break. Hence, the aerial wire has to go to one side.

Rear view of SDS7 back plane showing NC-7 aerial glued in place — In a similar manner as the original mod, the aerial from NC-7 is hot-glued to the rear of the back plane in between the edge connectors for modules 9 and 10 and across the stereo outputs busses.

So while looking into the infamous SDS7 noise and testing my NC-7 noise cancelling mod for the Simmons SDS7, I thought it might be an idea to actually record this annoying phenomenon.

The video below shows the effect on overall noise level, as the NC-7 noise cancelling mod is gradually tuned in. Check out the VU meter on the right.

WARNING!!!! The signals have been amplified so TURN DOWN YOUR SPEAKERS

Below is a spectral capture of the noise and the effect of the NC-7 noise canceller. As can be seen, tuning in the NC-7 noise cancelling mod, reduces noise between 3kHz and about 11kHz but doesn't do anything for lower frequency noise.

There's one other thing... In fact, you may already have noticed, that instead of using a TL084, NC-7 is fitted with a newer NJM2060. This device is of a much higher specification than the humble TL084. Since two stages of this quad op-amp are used to buffer the stereo buss, having a quieter device will no doubt improve things a little. 🙂 Having said that, I'm not sure the difference will be too noticeable with all of that other stuff!

NC-7 is handmade in Hemel Hempstead, Hertfordshire, United Kingdom, only a few miles from St. Albans where Simmons used to based and where I used to work.

I do not keep NC-7 units in stock and each NC-7 is built to order.

SDSM MDI for the Simmons SDSV installed — Pictured is NOT a hacked original SDSV blanking plate but a newly developed aluminium plate which is the basis of SDSM. Hey, just in case you're wondering.

SDSM - MIDI for the Simmons SDSV does what it says on the packet. With the addition of a Tubbutec uniPulse MIDI to trigger converter, SDSM makes it really easy to add MIDI triggering to the Simmons SDSV WITHOUT drilling holes or making any other permanent modifications to your vintage synthesiser drum system.

When looking to buy my first Simmons SDSV several months ago, I immediately considered adding some type of MIDI triggering. The problem was that MIDI to trigger interfaces are quite thin on the ground, probably because it's such a limited market. Something like the Simmons MTM was a bit over the top for my needs so imagine my delight when I stumbled across uniPulse by Tubbutec.

Yes, of course I considered designing my own MIDI to trigger converter but after buying a uniPulse to basically try out, I knew I'd found what I was looking for so why would I reinvent the wheel, guys? From my trial tests, tubbutec has done an excellent job and they come across as really nice guys, too.

At the heart of the uniPulse kit is a small PCB but also supplied, are various accessories, allowing for easy integration into many different electronic drum systems and even vintage, pre-MIDI drum machines. When buying your uniPulse for your SDSM, just ask Tobias for a SDSM pack for the Simmons SDSV and he'll send you exactly what need.

Tubbutec uniPulse PCB mounted to SDSM — Measuring a mere 43mm x 40mm, uniPulse is beautifully compact.

SDSM comprises two fundamental parts; the faceplate and an internal bracket to hold the small 40mm x 43mm uniPulse PCB.

SDSM mounting bracket for Tubbutec uniPulse — uniPulse conveniently mounts to the bracket that's on the back of the SDSM faceplate.

The faceplates were modelled on the original blank SDSV faceplates so they look quite at home on the SDSV. Having said that, it took a couple of tries to get everything to line up (metric, imperial, metric, imperial, GRRRR). When designing printed circuit boards, I always print on to paper first, when I can. It's quite different in this case however, to have a piece of aluminium in your hands and on your SDSV.

As you can see I even changed things slightly, between my second and third prototypes.

Original SDSV blank faceplate and SDSM prototypes — It took three attempts to get things right, two of which are shown above, together with a SDSV blanking plate. The first? Well, I couldn't have got the dimensions more wrong! Above, you can just make out the mill finish under the paint on the final prototype. It looks a lot more authentic in real life.

You may have worked out by now, that the installation of SDSM requires one prerequisite; that your SDSV has a spare module slot. 🙁 Yeah, sorry about that.

There are two types SDSM; SDSM and SDSM HH. The former is for any SDSV but the latter is specifically for those users who have an original Simmons SDSV hi-hat pedal. SDSM HH has an additional toggle switch to allow the hi-hat open / closed control function, to be taken from either an original Simmons hi-hat pedal, or MIDI.

If you have a SDSV with a hi-hat module but you don't have an original Simmons hi-hat pedal or have no desire to use the hi-hat open / closed function via a pedal input, then you should choose the standard SDSM module as the chances of picking up an original Simmons hi-hat pedal are going to be pretty remote.

SDSM HH MIDI for the Simmons SDSV — Available as SDSM and SDSM HH, the latter is specifically for those who are lucky enough to have an original Simmons hi-hat pedal and who would like to continue using it. The additional switch allows you to select between hi-hat open / closed control via MIDI or pedal.

As stated in the opening paragraph of this post and in keeping with all my upgrades and modifications, SDSM - MIDI for the Simmons SDSV, can be easily removed, thereby returning your SDSV to factory. You don't have to drill any holes or do any type of permanent modification to your SDSV, to get SDSM to work.

Rear of SDSV with SDSM MIDI to trigger installed — MIDI into the SDSV is via the unused pad trigger input so no holes need to be drilled into your SDSV.

MIDI IN is via the unused module pad trigger input and SDSM includes a male XLR to female 5-pin DIN so all you need to do is hook up a standard MIDI connection from your studio and you're off! 🙂 Coolamundo, dude!

SDSM includes a XLR to 5-pin DIN cable for easy MIDI hook up. — No hole to be drilled for a MIDI socket. Just use the redundant module pad trigger input.

SDSM mounts the uniPulse MIDI activity LED on the front panel which makes things very accessible. In fact, you have a choice of red LED, in keeping with the rest of the SDSV front panel, or a green LED, which is the same colour as the MIDI activity indicator on a lot of other gear in my studio, specifically Roland.

SDSM with green LED — SDSM is available with a choice of red LED to match your SDSV or green LED which is more standard amongst MIDI activity indicators.

I'm saying this a lot but... as with all my upgrades and modifications, SDSM is accompanied by a highly illustrated and detailed installation manual.

Below is my own Simmons SDSV. SDSM looks like it's always been there. Love it! 🙂

A WORD OF THANKS

In recent years, I've observed how people are tending to try to do stuff completely by themselves. Hey there's a video on YouTube, right?!?!? 🙁 In fact, the increasing lack of collaboration I see, deeply saddens me. The development of SDSM however, is a great example of just how things could and perhaps should work.

I'm a bit old school and since the SDSM faceplates were modelled on the original SDSV blanking plates, I felt obliged to give a call to my friend, Dave Simmons to ask his permission to use his logo.

I also contacted Tubbutec as it was my intention to have the Tubbutec logo on my new SDSM faceplates, too.

Well, Dave got back to me pretty quickly and he was delighted with all the work I'm doing, to keep vintage gear alive and hopefully going for a few more decades.

As it turned out, Tobias from Tubbutec and I really hit it off. In fact, following a couple of e-mail exchanges, he even modified the uniPulse firmware. What a star!!!! 🙂

During the development of SDSM, there's another gentleman who lent me a very big helping hand. Ed Rose, aka The Simmons Guy, has installed considerably more uniPulses than I have and Ed has extensive knowledge pertaining to the 'quirks' of the SDSV when adding MIDI triggering. Ed was also in on the suggestions for the 'Simmons' firmware upgrade for uniPulse.

So to conclude my acknowledgments, I have to say that I feel quite privileged to be in a position to thank Dave Simmons, Tobias of Tubbutec and Ed Rose but it all means just a little bit more because they helped me with one of my little upgrade projects.

You can buy SDSM here but please note that for the time being, you'll have to purchase a Tubbutec uniPulse yourself, directly from tubbutec.de

SDSM is made locally here in the United Kingdom. In fact, it's made a few miles away from where I used to work a million years ago, at the old Simmons factory in St. Albans, Hertfordshire. All materials, machining, mill finishing, painting and silk screening are supplied by local companies. It's something I'm quite passionate about and positively insist on. 🙂

Tag: simmons tech

NC-7 Noise Cancelling Mod for the Simmons SDS7

SDSM – MIDI for the Simmons SDSV