Zorch's build progress

I have been accumulating bits and parts for several months now in an attempt to begin my own modular setup and I thought I would share my journey here - as well as perhaps get some much needed help!

My interest began when my job at an escape room closed due to COVID. One piece of my severance package was this fully functioning little beauty:


I also as I mentioned in other threads I had a couple of PC PSU’s lying around that I didnt have a home for. I figured this was as good a jumping off point as any for me to take a stab at DIY synthesis.
This lead to the creation of this setup:

An ATX style connection has two +12 connections one -12 and a plethora of grounds - which I simply attached to the stripboard, splitting off the -12 onto two separate rails.


After a bit of research I found out that PC power supplies will not turn on unless you short pin 16. I wired a switch for this. Sadly my high hopes were dashed as the setup did not work - or so I believe. Exactly why it did not is still a question. I think the problem was not this setup, but instead what I was trying to plug into it. They powered on fine with my test rig here - but as soon as I hooked up my VCO (which we will get to shortly), both power supplies would behave in exactly the same way and turn off instantly. I just assumed it was because they were not happy about providing the necessary -12v since they seemed to be capable in all other respects. In the aftermath of this failure I took the older of the two PSU’s apart with the intention of using the plug socket and heatsinks. Its not a great loss as the fan was dead on it and it was the older of the two.

This brings me to my current problem(s). I have been trying to make the simple VCO and have been having some issues.

Being the type of person I am, I attempted the more complicated build with the square wave and PWM modules first. This was what was originally making the PSU’s turn off.

At first I attributed my failure at attempting something too ambitious, so I started over on the simple design without the extra bits.

I ended up with exactly the same problem. When I hook everything up, I get no buzz and the TL072 get SUPER hot.

This is the test rig I have set up:

(thanks to @Bitnik for this suggestion since I am currently waiting on my FC supply to arrive). It seems to provide +/-9.3v.

Now comes the part where I ask for help! I was really wishing I wouldn’t have to, but I have the feeling I am missing something fundamental and (hopefully) easy to overlook. I took the IC’s out and ran through all of the pins with my voltmeter if this helps at all:

Any help is appreciated because I have a few other related projects waiting in the wings. I have been pluging away at this for a while now and could really use a win XD


So this is measured from the copper side, with a ±9 V supply? If so, the voltages look ok, except for the negative supply to the 3340 which is wrong – it’s connected to the negative rail via a resistor and should be held near −7.2 by a zener in the 3340. See:

What resistor are you using between pin 3 and the negative rail? For 9 V, the ideal value would be 200-220 ohm, so if you’re using 620 ohm you might simply be starving the circuit. Try soldering in a 330 ohm in parallel with the 620 ohm, or simply replace it with a 220 ohm resistor. (And don’t forget to remove/replace it if you decide to use 12 V instead).


Yes, this is ultimately going to be used with a 12v supply - the pcb’s just arrived today and I already have all of the other parts. I’ll probably build one of them on stream next Wednesday.

And keep in mind, the voltages on the paper are with no chips in at all - I’m afraid of burning things up. Also, all of the resistors are the values from the board layout. The 5.6k is a 1% because it was all I had but everything else is 1/4w 2%


Will try the 330 next!

No luck after switching the 620 resistor for a 220.

Odd about the incorrect -12v tho.

Are your photo’s mirrored? check what your stripboard looks like compared to the layout.
correct me if im wrong (im still a modular noobie too) but with the IC’s the right way up the 10k trim pot should be in the top left.
when reading the schem’s, i see it as copper side down but ‘transparent’ so you know where to cut traces. =]

And for PSU i can only vouch for Sourcery Studios 'PSU v2.0 (+/-12,+5). its small enough and an easy build.
There’s also a PCB for a +/-12v only which is alot smaller, but its an older version and it suffered power ripple. would make a handy bench psu tho for testing =)
(I know your waiting on an FC PSU, but… the more the better)

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The photos are not mirrored (you can read the text on the ICs) and indeed the connections are incorrect, at least it looks that way: if red is +9V for instance it’s going to the 3340’s pin 1 instead of pin 18, et cetera.

See https://www.evilmadscientist.com/2010/basics-finding-pin-1/ for how to correctly identify pin numbers.

Here’s the stripboard layout

and the confusing thing about these diagrams is, even if the strips are shown, they’re on the bottom side of the board and the board is depicted as seen from the top side. That is, your board should look like the layout except that the strips are not visible because they’re on the bottom.

(Also, minor complaint about this layout: the text drawn on the ICs is 180 degrees off from the way the text on the ICs really is. That could cause more confusion.)


Hmm. This makes sense as painful as it sounds. I had problems with this early on and then committed. Might have committed incorrectly.

I don’t suppose soldering the socets on the other side would fix it.

You mean solder the socket to the copper side? I mean… yeah, i guess you can, the pins should be in the right place. but id only do it to test and not expect it to be permanent =P

its probable less hassle and better practice to just to start fresh, imo.


I mean… it would be one of a kind!

Huh, I only looked at the voltages which are indeed mirrored (hence the “measured from the copper side” assumption).

(looking again, it seems you’re missing a ground on the 3340, btw. See the annotations for where it’s supposed to be)


Another day another stab and still no sound at all.

At least this time the TL chip is not red hot.
Am I wiring my jacks wrong?

Or maybe the batteries are not giving enough voltage for any sound? Here are my readings - this time with the CEM chip in the socets. I had a .2 drop in overall voltage as I was doing the readings.

Thoughts? Or perhaps next steps? I have my power supply, but I’m hesitant to hook everything up to 12 volts if I’m not sure its working.

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Jack wiring looks fine.

Are you using the same chips as before? Incorrect connections may have fried them.

If you’re using new chips or have other reason to believe they’re okay, try measuring CV at points shown here:

And pin 3 voltage still looks wrong, try suggestions by @fredrik above.

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Swapping out that resistor was going to be my next move. Though at this point I am pretty stumped. I hope it works.

Also, these are all new chips as well.

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Good, so measure at the points on the annotated layout linked above.

Oh my gosh, it made sounds!

Its super low volume and low frequency no matter how much I twist the pots - but I imagine that is attributable to the 9v?

I’ve never been happier to hear a crappy buzzing sound.


Not sure if or how the 9V vs 12V supply affects that. 440 Hz isn’t that low (it’s A above middle C). Still, it’s progress and it might be a lot better with 12V.

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Weyyy! You got it buzzing. Gratz! A pre warning, dont worry about the Tri wave being lower volume… thats normal =)

Dont forget to flush trim your wires/leads on the copper side now its working. It only takes one of them bending to ruin the effort.

I notice your grounds are bridged, not sure it matters since its ground.
Ground loops, thats a thing… dont know if ‘that’ is how they work tho. If you get a ‘noisy’ signal thats a starting point I guess lol

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I think a ground loop is when your grounds are not in adequate electrical connection. If there’s a solder bridge between two ground pads on a board, that’s no bad thing.

While I’m here, it may be a good idea to check for continuity between adjacent strips. This may help you to spot unwanted solder bridges.


TY for the correction, I wasnt sure.
I was picturing the bridge as a schematic, 2 lines of ground connected. Oh no its a loop of grounds… lol

You should have all 6 ground pins connected to one another, at the connector or nearby. You want to distribute your current to ground over all 6 ribbon cable cores.