SDE Mod: Confused by RES CMP switch wiring

UPDATE: I think I solved it, or at least found a solution that works. Scroll down or click here:

Original post:

I’m confused by the RES CMP switch wiring:

It says:

“c) Solder a flying lead to IC7 pin 14 (we’ve previously used this as LP4 for the filter shapes mod)”

but then in the diagram shown, there’s no connection going to IC7 pin 14. I tried wiring it as instructed, and there’s no effect when in “BITE” mode, and I’m not sure if “CMP” mode is actually working correctly.

I got all the other mods done no problem, but the RES CMP is super confusing because the text says one thing, but the diagram photo uses completely different terminology… so it’s hard to figure out where exactly some of the 4 “flying leads” go to… for example, the diagram shows MIX connected to one of the middle pins of the switch, but this signal (the middle pin of LP4 on the board), doesn’t connect electrically to any of the pins where I was told to solder flying leads.

Can anyone clarify in simpler language?

Also can’t get the FEED circuit to work properly. It does the opposite of what’s described: “acts as FEED when no cable is plugged into the input socket” – I don’t get any effect when the IN jack isn’t connected. I only get the described “circuit bent” sounds if I plug a dummy cable plug into the IN jack, because this lifts T from TN which is grounded.

What am I not understanding here?

Ok I think part of the problem is the “MIX” terminology. Earlier in the guide, MIX is described as “centre pin of the 2/4-pole connector” but I think in this RES CMP section he actually means MIXOUT, which is one of the sides of C15 where it’s instructed to put a flying lead. Making that change results in the RES CMP switch actually sound different in all 3 positions.

But now in the OFF position, adjusting the Resonance via the menu has no effect. I think something still isn’t right…

One other weird thing is that the circuit pic shows part of the switch connected to the side of R18 that is OPPOSITE from R19 / IC 3 PIN 4, but this side of R18 simply connects to GND. So I connected it to the other side of R18 which connects to R19 etc. Not sure if I should try connecting this part of the switch to the R18 GND anyway? Seems like it wouldn’t do anything.

Another weird instruction: “Solder a flying lead to IC7 pin 14 (we’ve previously used this as LP4 for the filter shapes mod)” ---- ok, but then in the circuit graphic that shows how to wire the switch, the IC7 pin 14 / LP4 doesn’t connect to anything at all!

The more I try to figure this out, the more confused I get.

The instructions say to “remove the existing R18 1k and R19 10k resistors” but then in the circuit diagram graphic, it shows both of them still there. It appears that all I’m supposed to do at R18 is lift the GND side of it and connect this to the switch instead. But R19 is shown exactly how it already exists on the regular PCB, with one side connected to R18 / IC3 Pin 4 and the other side connected to LP4. So why are we told to remove it?

My god I think I finally got it, 5 hours later…

First, the switch pins will connect 2-3,5-6 OR 2-3,5-4 OR 2-1,5-4

Check this continuity on your switch to make sure you have the proper type ON-ON-ON for those positions. I had to wire my switch backwards (left-right) from what’s in the SDE Mod Wiki. If you view the bottom of the switch, the terminals are numbered like this.

6 3
5 2
4 1

So I think the wiring goes like this.

  1. Remove C15.

  2. Lift the side of R18 (1k) that goes to GND.

  3. Remove R19 and replace with a straight piece of wire to bridge it.

PIN 6: Connect this pin to diodes then run a wire from the other side of the diodes to IC7 PIN1 (use the top pin of where C32 was if you did the Filter Shape mod)

PIN 5: Bridge a 1k resistor and a 1uf cap across pins 4 and 5. Now run a wire from PIN 5 to a GND source – you can use any nearby ground, for example if you already ran a GND wire to another mod pot / switch.

PIN 4: Now that you have already bridged the 1k resistor and 1uf cap from here to PIN 5, run a wire from PIN 4 to the side of R18 that you lifted (the other side of R18 stays in its original hole which connects to IC3 pin 4).

PIN 3: Connect a wire from here to the “bottom” hole of where C15 used to be (the hole farthest from IC3, and which connects electrically to R16).

PIN 2: Run a wire from here to the “top” hole of where C15 used to be (the hole which connects electrically to IC2 pin 1). Apparently this is where “MIX” in the original diagram goes and it actually corresponds to “MIXOUT” from the Filter Shapes mod. I figured out that this goes to the C15 hole by process of elimination.

PIN 1: Not connected to anything.

I don’t know if this is correct, but it sounds good and gives some hella crazy options when you tweak the resonance. If used in conjunction with the other mods, the 3 switch positions will vary from subtle differences to bigger differences depending on what filter mode you’re in and what filter “flavor” you use.

I hope this helps somebody. The original explanation and accompanying schematic were confusing and contradictory. I will monitor this thread for replies in the future so if anyone needs further explanation I will draw a diagram, just ask.

Here’s a pic of the finished synth. Love it! Sounds sooooooo great.

Everything works except the Feedback Input only functions when there’s a cable plugged into the input jack, while the description in the mod wiki says it’s supposed to function when there is NO input. Still haven’t been able to figure it out. When I want it, I just plug a bare cable plug into the jack to lift the ground.

I did the case design myself, based on the original Shruthi one. Re-did the labels above the buttons to a more pleasing font that’s a bit easier to read. It’s hard to tell in the pic, but the acrylic is a “smoky gray” which actually has a bit of a purple tint to it. The LEDs under the button labels are “warm white” (like old school christmas lights) with fairly strong resistors to keep it from being super bright (they’re not as yellow color as in the pic below). Note that the label for the RES switch is wrong, it should be OFF, CMP, BITE.

Considering that I barely knew how to solder a year ago and didn’t have any clue about laser cutting acrylic until a month ago, I think it turned out really nice.

Hi armandhammer,

I’m so pleased that you managed to sort out the Res Cmp circuitry, and congratulations on a fine-looking case design! :sunglasses:

Sorry it took me SO long to reply to this thread, but I’ve had horrendous telephone/Internet problems since mid-July, and even now I’m still limping on with a connection of 0.5Mbps until I get fibre finally connected in a couple of week’s time. Secondly, I hadn’t looked at these circuit mods for seven years.

I suspect the confusion lies in the fact that I chose to label the centre connection of the LP2/LP4 jumper as ‘MIX’, because this is where my Filter Shapes were formed by MIXing together various combinations of the LP1/LP2/LP3/LP4 circuit points.

Unfortunately , Olivier had also labeled those two other points connected together on his original circuit where the resonance control is placed as ‘MIX’. Where this got confusing is where I later developed the Res Cmp mod, and for this, I do refer to Olivier’s MIX point ( in other words, the Res Cmp mod refers to Olivier’s MIX connection).

All should hopefully become clear if I renamed my Filter Shape ‘MIX’ as ‘VCA’ in both the test and circuit diagram, so it refers to the input of the VCA section. I’d have to ask Olivier’s permission to log in and edit that archive though.

As for the confusion about my Feedback mod, if you look closely you’ll see that while Olivier’s original input jack has TN connected to ground, for my mod it’s connected instead to one end of that new 1uF capacitor. In my wooden case design I used new jack sockets wired like this, but if you’re still using the original ones on Olivier’s circuit board you’ll need to break the TN connection to earth on that input socket.

Hope this helps, and again, well done with that case design!


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