1222 Tuner VCO Module

[antoine.pasde2]

Your search - sawadidoo - did not match any documents.

Care to explain?

[Farabide]

Sorry. It’s a Contraction of “it’s what I do”
Opamps smoke.

[Ben]

Okay so once again I’m at the end of my rope. I’ve built the second VCO with only the components mentioned by Sam without the tuner and the octave switcher.
I’ve put in a new CEM3340 (that’s the one I got so I have one more left untouched: https://www.thonk.co.uk/shop/curtis-cem3340-ic-vco-chip/) and it doesn’t get warm at all while running or after.
I have 4V at the test point
Voltage changes when I turn the trimpots as mentioned before
But I have no sound coming out of it, tried it in all waveform outputs and this time I’ve put the output directly into my Audio Interface, even turned it up enough that I could hear it when I touched the Panel / Knobs.

What am I doing wrong?

[analogoutput]

Pretty sure the 4V test point is irrelevant because it’s used for the octave switch, which you don’t have, and the fine tune pot, which shouldn’t make a big difference.

CHECK POWER ON THE 3340. Make sure you have +12 volts on pin 16 of the 3340, and make sure pin 12 connects to ground.

CHECK SUMMED CV. Make sure you have +12 volts between the first terminal of RV6 and ground, make sure the third terminal connects to ground, and adjust RV6 to get +6 volts or so from the RV6 wiper (center terminal) to ground.

If you don’t connect anything to the CV inputs you should have the following voltages at the resistors that connect to pin 15 on the 3340 (measured from the other end of the resistor to ground).

R19 0V because you have no octave switch
R24 <1V
R22 0V because you have no 1V/oct input
R25 0V because the link is unused
R20 0V because you have no CV input
R26 probably something small, turn down the RV8 trimmer if needed
R23 ~6V, same as the RV6 wiper.

These should add up to maybe 6 to 9 volts. Much higher or much lower and it may not be an audible frequency.

If you still get nothing on the outputs, my suggestion is to make an audio probe like this

Misc > Audio Probe : DIY Fever – Building my own guitars, amps and pedals

and use it to listen for signals at pins 4, 8, and 10 of the 3340. Vary RV6 while you listen. If you hear anything, trace the signal from there to the output and see where it disappears.

If you have ~6V on the resistors connecting to pin 15 and no signal on the output pins, the 3340 is probably bad. As long as it’s got power and a decent summed CV, it should be making oscillations.

[Ben]

Thanks mate!
I’ve checked all the voltages and it checks out so I’ll be building the audio probe next

[lookmumnocomputer]

do you have a pic of the back of it? I mean both seem to have the same problems? so maybe its just a little mistake

[Ben]

Sure! Here is the first build from the back:

Second build back:

and front, just to be sure

[Ben]

Also I just plugged in one of my Pocket Operators and the second VCO build in my mixer module. I could hear the PO fine but nothing at all from the VCO, even when I turned the mixer knobs up all the way (yes, also made sure it wasn’t on bypass )

[Claquoss]

I am not 100% sure, but on your first build : isn’t your tl072 backwards ? Seems to me that the dot is an indicator for the back of the IC and not for thé front but i might be wrong as i am a newbie

EDIT : i was wrong but i learned smthing !

image|281x500

[Ben]

Thanks, haven’t noticed that one. This TL072 didn’t have a notch in it but just to be sure I just switched it out with another one and that didn’t work either unfortunately

[Ben]

Can anyone tell me from the pictures if I made a stupid mistake?

[evAp0r8]

I’ve just finished building my third one of these so I’ve got the board to hand and will take a look!

[Ben]

Thank you very much. I hope it’s just a stupid mistake that can be easily fixed

[devicex]

and a hint here from a few of us that have had issues [ not being careful ] cover or put a blank socket in the link connection socket . your builds look really clean . keep digging the problem will show its self . a magnifying glass and look for solder bridges is a good start .

[Ben]

Yeah got the hint and to be perfectly safe I used a hdmi connector protection cap to “seal” the link port

[evAp0r8]

I can’t spot anything obvious - it’s hard to know if something critical is missing since I’m comparing a fully made with a partially made!

Did you get anywhere with the audio probe?

[Ben]

So, I took the ICs out to be safe and reflowed everything on my stripped down build. I built the audio probe but couldn’t get anywhere.

Though I found out something that might help (or not )
When I leave the IC out and measure voltage at one side of the resistor R23 I get around 9V (same as the RV6, if I turn it down to 8V I get the same 8V on R23) but I get around 4V on the socket where Pin 15 of the 3340 would be.
If I have the chip in and try to measure the same I get nothing at Pin 15. This might be normal, as I said I’m a total beginner at electronics, especially measuring / finding errors.

So far I’ve been thinking that the 3340 should be fine as it’s not the same as in my first build. But as I bought 3 together, maybe I got a bad batch and they’re just all fried?

[ChristianBloch]

@Ben

3360

You mean the 3340, right? Otherwise you’ve found your issue.

[Ben]

damn, what a Typo!
Yes, of course the 3340
That’s the one I bought: https://www.thonk.co.uk/shop/curtis-cem3340-ic-vco-chip/

[analogoutput]

@Ben

This might be normal

Yeah, it is. It’s going into an inverting amplifier which forces its inputs to 0V (but there’s still current going into that input). So control voltages need to be measured on the other sides of the resistors connecting to pin 15.