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nickster
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Post by nickster » Mon Nov 27, 2017 3:42 am

Interesting issue I have got recently. After about 3 hours of my unit being switched on it suddenly starts going all over the place tuning wise. Jumping octaves and generally misbehaving on all 3 oscillators. Before I open her up can anyone kindly point me in the right direction as to probable causes. As this happened after a longish time switched on I'm wondering if this is a heat issue as the unit is held in a semi confined box?? :sadbanana:

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nickster
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Post by nickster » Mon Nov 27, 2017 6:01 am

Edit: problem not solved. Moved the MME into my large Eurorack so plenty of air space around it now. All good for the first hour. But after 2 hours the problem is back. Tuning is all over the place and changes if I move a switch or turn a knob. Any ideas anyone?

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Post by bemerritt » Mon Nov 27, 2017 10:11 am

How well did you match your transistors?

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jdelgoulet
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Post by jdelgoulet » Mon Nov 27, 2017 11:06 am

nickster wrote:Edit: problem not solved. Moved the MME into my large Eurorack so plenty of air space around it now. All good for the first hour. But after 2 hours the problem is back. Tuning is all over the place and changes if I move a switch or turn a knob. Any ideas anyone?
Sounds like a PSU issue or something like that. Is the MME the only module in your rack ? What PSU are you using ?

- Also if you think that it could come from the board to board connectors (pin header) there are holes on the PCBs to attached them together -

PS : could you describe a bit better the behaviour, for example : MME is out of tune but filter and envelopes behave correctly etc etc

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nickster
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Post by nickster » Mon Nov 27, 2017 4:08 pm

Thanks for getting back to me Julien, The mme was running initially from a doepfer psu when I first noticed the issue running inside its own case so I moved the mme into my main Eurorack case with a different psu again made by Doepfer. So I think we can rule out the psu as the behaviour was duplicated elsewhere. The behavior is as follows. After a 30 min warm up the MME plays as expected with no tuning issues. However after 2 hours or so the overall tuning becomes completely unstable. Which is triggered typically by flipping one of the switches Glide, OSC Mod especially or even changing any of the oscillator wave form values. Filter controls Noise and both envelopes seem to behave correctly EDIT This is confirmed. At first the master tuning is off and can be corrected via the master tune knob but engaging say the glide switch causes the tuning to drop an octave or to randomly alter as a new note is triggered via cv/gate control. Bit perplexing. What I think I am hearing is also possibly random oscillator modulation which is a bit similar to noise modulation but this just might be me reading something into this. Many thanks in advance.

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jdelgoulet
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Post by jdelgoulet » Tue Nov 28, 2017 7:05 am

Lets start by bypassing the glide circuit :
- use the MOD-CV input to drive the pitch (instead of the main CV)
- keep gate at gate input.
- try to reproduce the behaviour by playing with the glide switch.

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nickster
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Post by nickster » Tue Nov 28, 2017 9:01 am

I tried the Mod cv suggestion and then using the glide switch caused the same behaviour as in the pitch became random.

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analogdata
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Post by analogdata » Tue Nov 28, 2017 1:27 pm

Damn! Lost a solder pad.
Help!

Image

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jdelgoulet
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Post by jdelgoulet » Tue Nov 28, 2017 1:34 pm

analogdata wrote:Damn! Lost a solder pad.
Help!
No worries ... pin 10 is not used. You can go on :party:

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Post by analogdata » Tue Nov 28, 2017 2:17 pm

jdelgoulet wrote: No worries ... pin 10 is not used. You can go on :party:
phew!


Another thing, will a 2.2k trimm resistor do instead of a 2.5k at R328?

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jdelgoulet
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Post by jdelgoulet » Tue Nov 28, 2017 2:41 pm

analogdata wrote:
jdelgoulet wrote: No worries ... pin 10 is not used. You can go on :party:
phew!


Another thing, will a 2.2k trimm resistor do instead of a 2.5k at R328?
You should be fine. This is the noise level trimmer.

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Post by Jesse8n » Tue Nov 28, 2017 3:43 pm

Finally getting around to looking at mine. It makes a noise when it gets a gate, not the kind of noise one would hope for, like a sad electronic wind. Filter and ADS alter it

I started going through calibration. TP1-7 are all good, close to their respective +/-10v and trimpot able to adjust them to where they need to be. TP8 is another story. That one is around -3.900 when it is supposed to be +10.00.

Have not found any bridges or anything. Anyone have any thoughts on what sort of blunder I have made?

Edit: did not really do anything but the noise is gone. Now I am pretty sure all I am getting out is the self oscillation of the filter. None of the 3 oscillators.
Last edited by Jesse8n on Tue Nov 28, 2017 4:13 pm, edited 1 time in total.

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Post by bemerritt » Tue Nov 28, 2017 4:02 pm

Jesse8n wrote:Finally getting around to looking at mine. It makes a noise when it gets a gate, not the kind of noise one would hope for, like a sad electronic wind. Filter and ADS alter it

I started going through calibration. JP1-7 are all good, close to their respective +/-10v and trimpot able to adjust them to where they need to be. TP8 is another story. That one is around -3.900 when it is supposed to be +10.00.

Have not found any bridges or anything. Anyone have any thoughts on what sort of blunder I have made?

Edit: did not really do anything but the noise is gone. Now I am pretty sure all I am getting out is the self oscillation of the filter. None of the 3 oscillators.
Have you put a scope on the molex connectors? The pin closest to the ground pin is the square wave.

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bemerritt
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Post by bemerritt » Tue Nov 28, 2017 4:02 pm

That doesnt help your TP8, but at least youll know if you are oscillating.

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Post by Jesse8n » Tue Nov 28, 2017 4:57 pm

Bemerritt - no access to a scope at the moment, will see if I can borrow one.

I have gone through all the analog board +10v test points. The following are giving me somewhere around a -4.000 ... Q31, R150, TP8, R145, R143 and R179. Have not gone though the other voltage test points, will chip away at that.

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Post by jdelgoulet » Wed Nov 29, 2017 1:56 am

Jesse8n wrote: TP8 is another story. That one is around -3.900 when it is supposed to be +10.00.

If you don't get +10V at TP8 :
#1: Check Voltage at pin 1 of IC23 : must be around 12V
#2: Check Voltage at pin 2 of IC23 : must be around 12V
#3 : reflow IC23 (don't unsolder it, just try to add more solder at the pins)
#4 : reflow R50, R51, R377 (trimmer)

(If you have a volt meter that has the 'bip' function, you can try and test that while your MME is switch of)
#1: pin 4 of IC23 is connected to TP8
#2: pin 4 of IC23 is connected to one side of R377
#3 : pin 5 of IC23 is connected to one side of R50 and one side of R51

Julien

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Post by Jesse8n » Wed Nov 29, 2017 12:54 pm

jdelgoulet wrote:
Jesse8n wrote: TP8 is another story. That one is around -3.900 when it is supposed to be +10.00.

If you don't get +10V at TP8 :
#1: Check Voltage at pin 1 of IC23 : must be around 12V
#2: Check Voltage at pin 2 of IC23 : must be around 12V
#3 : reflow IC23 (don't unsolder it, just try to add more solder at the pins)
#4 : reflow R50, R51, R377 (trimmer)

(If you have a volt meter that has the 'bip' function, you can try and test that while your MME is switch of)
#1: pin 4 of IC23 is connected to TP8
#2: pin 4 of IC23 is connected to one side of R377
#3 : pin 5 of IC23 is connected to one side of R50 and one side of R51

Julien
Thanks you Julien. I was not getting 12v at pin 2. Reflowed and now I am and I am now getting 10v at TP8. Still no output except filter self oscillation but it is still progress.

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Post by jdelgoulet » Wed Nov 29, 2017 12:58 pm

Great.

Now, I would suggest, checking the waveform at the molex headers. Even if you don't have an oscilloscope you can still, may be , plug some crap speakers ;-) (ground is at the bottom of each molex, any other pins will give you a waveform).

Julien

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Post by Kevin Mitchell » Wed Nov 29, 2017 3:33 pm

I haven't been able to pull the square wave of the 1st oscilator out yet. Not sure whats wrong.

Also the modulation is probably messed up. All mod switches give super quick modulation and are very muddy sounding. Like a synth from hell. The modulation controls aren't really useful with this issue I'm experiencing. :omg:

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Post by jdelgoulet » Wed Nov 29, 2017 3:52 pm

Kevin Mitchell wrote:I haven't been able to pull the square wave of the 1st oscilator out yet. Not sure whats wrong.
If I recall you had place one 741 opamp up side down on the control board. This 741 is responsible for PW/PWM for VCO-1 (since this was the one at the top) :
- did you replace it ?
- did you look around the 741 in case any other tranny get damaged ?
- when you look at square wave for VCO 1 do you get 'nothing' (0v) or a voltage ?

julien

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Post by Jesse8n » Wed Nov 29, 2017 3:55 pm

jdelgoulet wrote:Great.

Now, I would suggest, checking the waveform at the molex headers. Even if you don't have an oscilloscope you can still, may be , plug some crap speakers ;-) (ground is at the bottom of each molex, any other pins will give you a waveform).

Julien
Ok, tried the old speaker method, most I get is an initial pop sound when first touching to any of the waveforms on the molex

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Post by jdelgoulet » Wed Nov 29, 2017 4:21 pm

Jesse8n wrote:
jdelgoulet wrote:Great.

Now, I would suggest, checking the waveform at the molex headers. Even if you don't have an oscilloscope you can still, may be , plug some crap speakers ;-) (ground is at the bottom of each molex, any other pins will give you a waveform).

Julien
Ok, tried the old speaker method, most I get is an initial pop sound when first touching to any of the waveforms on the molex
So from now you have all the correct voltages as described in https://guinguin-instruments.github.io/ ... brate.html step 1.1 to 1.6 (that includes the -5v and -4v check) ?

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Post by Jesse8n » Wed Nov 29, 2017 4:28 pm

jdelgoulet wrote:
Jesse8n wrote:
jdelgoulet wrote:Great.

Now, I would suggest, checking the waveform at the molex headers. Even if you don't have an oscilloscope you can still, may be , plug some crap speakers ;-) (ground is at the bottom of each molex, any other pins will give you a waveform).

Julien
Ok, tried the old speaker method, most I get is an initial pop sound when first touching to any of the waveforms on the molex
So from now you have all the correct voltages as described in https://guinguin-instruments.github.io/ ... brate.html step 1.1 to 1.6 (that includes the -5v and -4v check) ?
Yes, have gone though and get correct voltages for all

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jdelgoulet
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Post by jdelgoulet » Wed Nov 29, 2017 4:32 pm

#1 : could you post a high res picture of your analog board so I/we can check resistors etc.
#2 : where did you get the 2N3954 ?
#3 : you said you can ear the filter self oscillating. Can you 'play' it when you plug a keyboard and engage the VCF 1/2 and 2/2 switches ?

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Post by Jesse8n » Wed Nov 29, 2017 6:03 pm

Julien - here is a shot of the analog board. Let me know if you need any more isolated shots.

Trying to find my receipt for the 2N3954s but not seeing it. They were one of the first few components I bought over a year ago, from somewhere I never bought anything from before so the name is not sticking out. Will keep looking.

As for the filter self oscillating... I only get a tone with emphasis and cutoff turned all the way clockwise. A gate in to Gate and cv into CV (and into CVF CV) from a sequencer tracks the pitch. Glide switch and knob react as expected. MOD-MIX knob and MOD-LEVEL knob will add and remove noise relative to how each is turned. Osc3 wave select knob kind of resets the vcf self oscillation and changes the tone slightly but not much. That is all I can tell does anything.

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