An odd problem for a simple circuit

Hi everyone,

I’m getting into analog audio and have some electronics and soldering experience.
I’ve made the Regulated Bipolar PSU from which gives +/-12 to within .2v using the trimpots.
And bread boarded the simple cem3340 oscillator from sam’s 'Synth Voltage Controlled Oscillator ’ video.

The issue I’ve run into is that there is no noise/waveforms when powered,
But I’ve found that there is a solid (albeit, brief) tone when unplugging the psu and the oscillator is just using the charge left in the capacitors from the chunky power supply.

Has anyone else run into a similar situation? My google-fu appears to be weak in this situation.

Troubleshooting I’ve conducted;
Added resisters in series so that the values are as close to the schematic as possible.
Tried lower + and - voltage supply. (reverted as less savory tone upon power-down)
From the voltages and resistances I’ve measured cross-referencing some other posts here, everything seems in order.
Any insight into this peculiar situation would be greatly appreciated.

Almost sounds like you’ve AC coupled the PSU to the module. Do you have any picture of your layout?


It’s DC going to the module as far as I’m aware.
It’s not pretty but hears some pics. Apologies they are vertical, my dslr is tied up atm.

Can you also show your psu and how you’ve connected them?

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No 5v reg yet, just 12+, G and 12-

cannot make out anything glaringly obviously wrong from these pictures, other than that power connector pinout. I HIGHLY recommend you stick to the eurorack standard pinout, and get a 16-pin connector for adding the 5V line.

I’d say back to the drawing board and redo that breadboard layout. It’s quite easy to miss things on there, as I believe all of us have experienced

Or don’t add the 5 V rail. I mean, sure, add it and use the 16 pin connector if you’re planning on (or want the option of) building any Eurorack modules that require +5 V (or the CV or gate lines). But there are very few such modules out there — I’ve never built one. Nearly all Eurorack modules, and all standard Kosmo modules, require only ±12 V and a 10 pin connector.

But if you do add 5 V I concur you should not put it on a 10 pin power header where GND would normally be. And do connect GND to all six middle pins.

Also, this PSU is not going to be able to drive more than a few modules since there’s no heat sinks for the regulators. Include space for them on your next PSU.

What are you using to send AC voltage to the power supply? Should be a wall wart with 12 VAC output. That’s not mentioned on the page.


I mean, not that there aren’t worse possible connectors:

xkcd: Dual USB-C



Will do, Thanks.

This is a solid nugget of info, thanks.

I’m aware of this, and they’re on the list for the next trip to the electronics store.
I’m using a Quest AC/AC wall wart, that only gives 1amp though.

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