S&H/Noise module - S&H not so functional anymore

haricots · Joined: Aug 15, 2007 Posts: 33 Location: guelph

Sometime last year I completed the S&H/Noise module (Bridechamber kit). It's been working great up until now. The S&H output seems really 'low' - as in I'm not getting much modulation out of it. It's outputting but very weakly. Everything else works fine (like the noise outputs, random). Any ideas where I should start looking? I can build kits but can't troubleshoot worth a damn. Confused

yusynth · Joined: Nov 24, 2005 Posts: 1314 Location: France

Is it clocking normally ?
Try to replace U2, the TL074, one of its AOP may have died.

haricots · Joined: Aug 15, 2007 Posts: 33 Location: guelph

Upon further inspection, I think the cv out is ok 'strength'-wise, but the range is in the low end of the spectrum which makes the modulation pretty rumbly. Does this make sense?

yusynth · Joined: Nov 24, 2005 Posts: 1314 Location: France

I dont understand your explainations can you develop ?
Can you describe the patch your are using and the potentiometer settings ?

haricots · Joined: Aug 15, 2007 Posts: 33 Location: guelph

Sorry for my horrible explanation. What I have noticed is that if i invert the signal it is at least in the usable range. When the S&H output is used without inversion the range of the modulations is too low to be usable (like it is pitched very low). Even inverted it doesn't give that nice syncopated change that you would expect with a clocked S&H. Maybe the glide circuit is somehow messed up? It is so hard to tell let alone explain what is going on here.

Here is my patch > vco with standard cv in, outputted to a vca. s&h module with clock in from a pulse divider (/2). s&h output to the vco expo cv in. nothing but low register rumbles. If I invert the signal it is within a usable range but still sounds 'off' to my ears. Strange as it has worked flawlessly up until now.

yusynth · Joined: Nov 24, 2005 Posts: 1314 Location: France

haricots · Joined: Aug 15, 2007 Posts: 33 Location: guelph

Nothing in this case - it being hardwired to white noise. I've also tried manually patching in white and pink - same result.

Argitoth · Posted: Mon Sep 06, 2010 5:32 pm Post subject:

Alright, I now have Haricot's damaged yusynth module, now it's my turn to attempt to figure out the problem! hehe.

So, looks like there's a problem with the module... now I'm not even sure if I simply didn't notice it before or it suddenly stopped working. All I know is that the "output" is supposed to be a S&H out, but what comes out of it sounds as if it's AC-coupled. I get random-ampitude spikes instead up/down DC behavior that S&H is known for.

Should I replace TL074 or might you have a better idea with my new description of the problem? Thanks Yves!

Argitoth · Posted: Mon Sep 06, 2010 7:25 pm Post subject:

Looking at the PCB there are some cold solder joints. Also, I see flux all over the place as if the board was never washed. Isn't it supposed to be washed?

Audio demo of "output" going into a VCO FM and directly into audio path. http://www.elanhickler.com/misc/random-problem.flac

Is Flac OK?

yusynth · Joined: Nov 24, 2005 Posts: 1314 Location: France

Hi Argitoth

I am on leave now and stuck in an airport because of a strike.
I'll get back to to you tomorrow when I will be returned home.

Cheers

Argitoth · Posted: Tue Sep 07, 2010 8:58 am Post subject:

I fixed all the cold solder joints I could see, no improvement of behavior, but that's expected. Even a horrible soldering job is still good enough for a synth module to work.

yusynth · Joined: Nov 24, 2005 Posts: 1314 Location: France

Argitoth · Posted: Wed Sep 08, 2010 5:50 am Post subject:

I don't have a scope. I want to at least get a multimeter soon...

Everything works. The nosie level outputs are good, the internal clock is solid.

yusynth · Joined: Nov 24, 2005 Posts: 1314 Location: France

Without measurements it's difficult to figure out what's happening.
The simple things to try out are :

Argitoth · Posted: Thu Sep 09, 2010 12:43 pm Post subject:

I can't find anything documents that tell me where C5 and other parts are. I just see values.

drapdap · Posted: Thu Sep 09, 2010 2:32 pm Post subject:

Argitoth · Posted: Thu Sep 09, 2010 2:46 pm Post subject:

Drapdad, are you saying you fixed it?

Sorry, I have a very hard time reading a schematic. Could you tell me what part the C5 capacitor and D3 is near?

yusynth · Joined: Nov 24, 2005 Posts: 1314 Location: France

C5 is the 100n cap located midway from the SLEW POT connector and the S&H IN connector

NoiseSH-LAYOUT.jpg

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Argitoth · Posted: Fri Sep 10, 2010 7:49 am Post subject:

By the way, is the lin/log on the board for slew type or is it something else?

yusynth · Joined: Nov 24, 2005 Posts: 1314 Location: France

Argitoth · Posted: Fri Sep 10, 2010 8:18 am Post subject:

ah shoot, one question per post sorry...

Is it possible the access the slew limiter outside the S&H circuit by deriving some wires to sockets or something?

yusynth · Joined: Nov 24, 2005 Posts: 1314 Location: France

You would have to cut a track

Argitoth · Posted: Fri Sep 10, 2010 8:41 am Post subject:

Alright, so there's an input and an output. So either there's two traces I need to cut to derive input and output from or maybe one or the other is derived from a wire already.

Could you show me!? Smile

Argitoth · Posted: Fri Sep 10, 2010 10:44 am Post subject:

WHAT THE F...

Oh great, now my other Yusynth Random S&H half stopped working. The clock is dead. There's nothing coming out of "out."

So this is what happened. I plugged it in. I check outputs. "Oh good everythings working on my module that never had problems before." After a few minutes, the LED stops blinking "what the ****." I re-check outputs.

Now nothing. Noise still functions like it does on the other one.

yusynth · Joined: Nov 24, 2005 Posts: 1314 Location: France

Did you plug something special in it ?
If the clock stopped working you may have to replace the TL071 ?