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 Forum index » DIY Hardware and Software » The Repair Shop
Rene Schmitz 4069 VCO
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crazeydazey



Joined: Feb 15, 2007
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PostPosted: Fri Jan 24, 2020 1:39 am    Post subject: Reply with quote  Mark this post and the followings unread

yeah I thought it might Smile no problem mate.

I am using BC550 and BC560 for T1, checked double checked and triple checked that all the trannys are in the right way.

I wonder if the PW is like the CV where the range didn't seem very good until I plugged something into it then it was pretty good.

My problem is this is my first complete Module and I don't have a PWM source to to try that with.

I am hoping to complete my ADSR this weekend, hope to god I have no problems with that Very Happy Very Happy

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JovianPyx



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PostPosted: Fri Jan 24, 2020 6:44 am    Post subject: Reply with quote  Mark this post and the followings unread

It's easy enough to try Smile
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crazeydazey



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PostPosted: Fri Jan 24, 2020 7:16 am    Post subject: Reply with quote  Mark this post and the followings unread

you mean easy to test the PWM ?? Do I just need something that spits out a pulse signal (like another VCO??) , as I don't have anything at the moment Sad I guess I could knock up a simple 555 timer circuit that puts a pulse??

Something like this ... http://www.theorycircuit.com/pulse-width-modulation-circuit/

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flagada



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PostPosted: Fri Jan 24, 2020 7:31 am    Post subject: Reply with quote  Mark this post and the followings unread

Why not use your midi2CV?
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crazeydazey



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PostPosted: Fri Jan 24, 2020 8:09 am    Post subject: Reply with quote  Mark this post and the followings unread

could I ?? how ?? (Sorry I really do have a lot to learn Very Happy )
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flagada



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PostPosted: Fri Jan 24, 2020 8:52 am    Post subject: Reply with quote  Mark this post and the followings unread

If you can modulate the pitch of your VCO with your mid2CV you can also modulate your PWM input the same way. Plug it in and play high and low notes and listen if the PWM changes. Also, watch it on your scope. The pitch will not change this way but that doesn't matter.
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crazeydazey



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PostPosted: Fri Jan 24, 2020 8:54 am    Post subject: Reply with quote  Mark this post and the followings unread

cool cheers mate I will give that a go
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PHOBoS



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PostPosted: Fri Jan 24, 2020 10:57 am    Post subject: Reply with quote  Mark this post and the followings unread

yep it just needs a voltage which can come from a midi2CV. However, like I mentioned it looks like adding a (positive) CV will make it
even worse at least if I understand that part of the schematic correctly. This is also why asked if the PW pot was turned to V+ or GND.
But I am curious about the results you'll get.

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Aleencabralia



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PostPosted: Mon Feb 10, 2020 8:35 am    Post subject: Reply with quote  Mark this post and the followings unread

Hi there! Built this one too and had the exact same issues... Try 2n3904/6 and the bc ones... Same thing. Then saw this post from a guy in the synth diy fb group, he made an adaptation for the freq pots (connecting them to + and -, and adding a fine pot). He says pwm works fine. Didn't had the time to test that, or sending cv to the pwm to see if it works... Did you worked it out?
Edit: the link to the post : https://docs.google.com/document/d/1URX2i15RqMDOawcnhF3xEqg0qdi2XjVNp54tWK-HXfk/edit?usp=drivesdk
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crazeydazey



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PostPosted: Mon Feb 10, 2020 8:44 am    Post subject: Reply with quote  Mark this post and the followings unread

awesome no I never worked it out, just accepted it and moved on to next mod, but would LOVE for it to work 100% Very Happy Very Happy Very Happy

I will try that as soon as I get chance (maybe tonight Wink ) and let you know

the other problem I am now finding is I can't tune it, BUT I never matched my trannies and they are supposed to be thermo coupled to the NTCs so I guess that is my fault and to be expected Very Happy Very Happy Very Happy

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crazeydazey



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PostPosted: Mon Feb 10, 2020 9:48 am    Post subject: Reply with quote  Mark this post and the followings unread

Sorry I'm a bit confused now.
I have just had a look at the link you added and it says in there he is not using the PWM ??

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JovianPyx



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PostPosted: Mon Feb 10, 2020 11:18 am    Post subject: Reply with quote  Mark this post and the followings unread

I was looking at the schematic again especially the PWM part and I see some things that might be helpful.

Most important is that the PWM generator is made up of 3 4069UB gates. What this means is that the voltage at the input of the leftmost gate must be no lower than zero volts.

The first gate is a linear amplifier and it works like a crappy op amp.

T3 in an emitter follower amplifier where the lower 100K resistor is its output.

The 68K resistor (has nothing to do with T3) and supplies a positive bias to the "op amp".

The PW adjust raises or lowers the waveform with it's output which is a DC bias.

The input to the op amp is a summing node.

The op amp output is then passed to 2 logic gates which switch at (Vdd-Vss)/2 which is what is converting the saw to a PW controlled pulse wave.

So I would think that if the 47K resistor is removed (this feeds the saw into the PWM circuit), some combination of CV and the PW pot should allow the CV to move the PW from near zero to at least 50%. This would mean the voltage at the output of the first gate in the PWM circuit should move from (I think) zero to perhaps as much as 1/2 Vdd or even all the way to Vdd measured against ground.

I don't see anything about how high the CV for PWM can be, but logically it can't be higher then V+. So in testing, I'd start with the PW adjust wiper to ground and move the CV from 0 to 10v. You can just use a pot to make this CV (0v and 10v on outside terminal, wiper is CV out) Then move the PW pot and try that again. It's good to know what is going on and maybe this will give clues about how to fix it.

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Aleencabralia



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PostPosted: Mon Feb 10, 2020 12:12 pm    Post subject: Reply with quote  Mark this post and the followings unread

Yes, Juanito Moore (the guy that did the deadbug build-he has a cool yt channel with same nice projects and a crazy modular) didn't build the pwm, but he said that he did once,and worked for him as it is...
I didn't try to tune it cause I need to gather the ntc (got them jumpered). Maybe I try these today also.
At the beginning actually mine sub-oscillated, then I replace those 10k ntc for 100k or 200k I think and got it sounding.
JovianPix: strange thing is that it worked for that guy. And also is a little strange also that Rene posted something that doesn't works, right? I mean, the guy seems to know what he's doing.
Maybe i'll try that one. It's a little hard for me mess some parts of the circuit case the only pcb I had was a little small, so it's pretty crowded in tjere :S
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JovianPyx



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PostPosted: Mon Feb 10, 2020 12:57 pm    Post subject: Reply with quote  Mark this post and the followings unread

Rene definitely knows what he's doing (Ph.D. I believe).

Unfortunately, I never did the PWM part on mine, mainly because it requires a CV and I don't have a modular. I built mine for a PAiA Fatman which is linear CV and it doesn't have a CV for PWM. So my version is sans PWM and linear instead of expo.

I have this feeling there may be some build error causing the problem and the test procedure I outlined should give more information about what the circuit is doing.

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crazeydazey



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PostPosted: Tue Feb 11, 2020 1:54 am    Post subject: Reply with quote  Mark this post and the followings unread

OK just for clarification (As I am a bit stupid sometimes Very Happy Very Happy )

Remove 47K get a pot (any value ??), create as shown in image below (+10v might be difficult to get, suppose 15v is not ideal ?? )

Then does the CV from this pot go to the PWM (not to one of the CV inputs ??)

Then what is it you are wanting to see, do you want me to get some meter reading or put the scope on it.. sorry for all the questions, I'm still a bit new to all this (even though I started building my synth about 15 years ago Very Happy Very Happy ) I still don't fully get it .. I'm sure I'll get somewhere near in the next 15 years Very Happy


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JovianPyx



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PostPosted: Tue Feb 11, 2020 6:38 am    Post subject: Reply with quote  Mark this post and the followings unread

The point on the schematic labeled "pwm" is the CV input for PWM. So this VCO has two CV inputs, one for pitch, the other for controlling PWM.

Yes, that pot schematic is correct.

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crazeydazey



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PostPosted: Tue Feb 11, 2020 2:28 pm    Post subject: Reply with quote  Mark this post and the followings unread

Fixed it jackson dancing

I tried what you said, took out the 47k resistor and made the little CV thing using a pot and I used a 9v battery thinking that was pretty close to 10 Wink

And I was totally lost, it just didn't seem to do anything really so I gave in and went back to basics.. I got the schematic out and followed everything with the meter on continuity checking everything that should connect did and that nothing that shouldn't connect didn't.

And I noticed a very silly mistake I had made ..

I had put the wiper of the pw adjust to the what should have been the tip of the jack in the PWM input and vice versa (if that makes sense)

Easy mistake Very Happy

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JovianPyx



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PostPosted: Tue Feb 11, 2020 2:40 pm    Post subject: Reply with quote  Mark this post and the followings unread

So it was doing *something* just not the right thing. That can be a head scratcher. Good to find it though. Back to basics is always a good approach.

Did you put it back together and test it with the VCO connected (47K)?

If so, does it work better now?

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crazeydazey



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PostPosted: Tue Feb 11, 2020 3:00 pm    Post subject: Reply with quote  Mark this post and the followings unread

Yeah mate all back together and working really well..

Thanks to everyone who helped me here, I would have given up ages ago if it wasn't for you guys telling me to try stuff Wink

The only issue I have left now with it is something that is my fault and something I know I've not done right but I'm not too bothered to be honest and that is the tuning. I never matched my trannys, I wouldn't even know how to tbh, and I never thermo coupled them together but it's cool, I can still make cool little sequences with it so I'm very happy.

Also mate that schematic of yours for the ADSR on one of my other posts.. I am going to attempt that soon I think so might be bugging you again shortly Very Happy just want to build a simple LFO first.

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JovianPyx



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PostPosted: Tue Feb 11, 2020 3:20 pm    Post subject: Reply with quote  Mark this post and the followings unread

You can make two LFOs with one 4069UB Smile

http://scott.joviansynth.com/electronics/4069_lfo.gif

The drawing there is for just 3 of the 6 gates. Those unused gates can be hooked up the same way to give a second LFO.

If the longest time is too short, make the capacitor larger.

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crazeydazey



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PostPosted: Tue Feb 11, 2020 3:37 pm    Post subject: Reply with quote  Mark this post and the followings unread

Excellent, I am making that this weekend.. Thank you yet again kind sir.
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Aleencabralia



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PostPosted: Wed Feb 12, 2020 10:14 am    Post subject: Reply with quote  Mark this post and the followings unread

Congrats!!! So you left the pmw pot to +v and gnd, right? I've just checked if I did the same mistake. I didn't... Changed the tune pot and it's connection but didn'ttested it yet. Will feeding some cv and taking the 47k and came back with results when I have some time!
Regarding the tuning, didn't try to cause I don't have the ntc, but, Rene posted tjat the 680R could be replaced for a 1k trimpot to have high freq tuner, if it's a problem maybe it' s worth a try!
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PHOBoS



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PostPosted: Fri Feb 14, 2020 8:51 am    Post subject: Reply with quote  Mark this post and the followings unread

great to hear you got that fixed Very Happy
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Aleencabralia



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PostPosted: Tue Mar 10, 2020 3:00 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hi guys, just to update in case anyone reads this thread: Got mine working also, it was a bad solder from 47k resistor to pin 1!! Took me some time cause I was working on so many other things... (Lots have issues :/ ). Thanks to all for your help!
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