Yusynth Wavefolder troubleshooting

YashN · Joined: Jun 27, 2011 Posts: 104 Location: Canada

Built and populated a Yusynth Wavefolder and I am quite happy about it. Merci Yves. Very Happy

I do seem to have a couple of issues. I tested it with my Fonik / Thomas Henry VCO-555 and using on board single turn VRs as that's what I had at hand. Now, the default TH VC0-555 has quite a low Sine output and I still have to mod that. Some settings I tried: VCO Tri into Wavefolder In, VCO Ramp into Wavefolder Control (really cool on some Pot settings!).

Issues:

1. The Shape Pot does sound like it is merely attenuating. I can also see the corresponding effect on my DSO scope.

2. An odd thing happens when I put my DVM +ve on the TL074 P6: my output buzzes (it is as if it now gets the Wavefolder effect out). I also find that when my hand is around the Shape wires or its pot, or just moving it around, that seems to also increase buzz on the output.

3. Both the Range and Control Pots sometimes go: 'No Sound/Low' to 'Big effect' and 'Back to No Sound/Low' depending on settings instead of an expected (IMO) smooth sweep from Nothing/Low to Large Effect.

I cleaned the board again today which seemed to help a bit. I also tested for continuity around the TL074 and R11, R14 and R15 and everything seems fine here.

I have 2 3904 transistors, so if I didn't mess this up, I used them 180 degrees rotated.

YashN · Joined: Jun 27, 2011 Posts: 104 Location: Canada

Re-tested and re-calibrated. This time I removed my circuit linked to the 1V/Oct to see whether that was making any interference.

VR A1 doesn't seem to do much for me.

Shape still sounds like an attenuator.

I used Sine into Control over a Triangle at Input. It does look like it's wavefolding a little. First, Control to minimum:

Posted Image, might have been reduced in size. Click Image to view fullscreen.

And the rest, as I increase the Control Amount:

YashN · Joined: Jun 27, 2011 Posts: 104 Location: Canada

Hopefully all components are the right ones. There are 2 or 3 resistors values that I had to do some series combinations as I didn't have the exact values at hand.

How would I really check whether the VCA is working properly or what else should I check?

I left out the CV3 pads untouched.

Grumble · Posted: Thu Apr 19, 2018 4:20 am Post subject:

If you didn't used a 10x probe and these are output voltages, they are very low compared to http://www.yusynth.net/Modular/FR/WAVEFOLDER/wavefolderscope.html.

Also I see some differences according to the populated pcb:
Posted Image, might have been reduced in size. Click Image to view fullscreen.

marfoski · Joined: Jan 26, 2011 Posts: 36 Location: Italy

IMHO, 1N4007 diodes are not a direct replacement for 1N4148, being rectifiers and much slower.

Just my two cents, tho

YashN · Joined: Jun 27, 2011 Posts: 104 Location: Canada

YashN · Joined: Jun 27, 2011 Posts: 104 Location: Canada

YashN · Joined: Jun 27, 2011 Posts: 104 Location: Canada

wackelpeter · Posted: Fri Apr 20, 2018 10:15 am Post subject:

Apart from the diodes that are in the Feedback path of the OPamp and Point in the opposite direction but that wouldn't matter as they're in parallel, i only spotted the trannie on the upper left... when this is not an BC547 and an 2n3904 instead, shouldn't it be rotated by a 180 degree?

YashN · Joined: Jun 27, 2011 Posts: 104 Location: Canada

Hubaswift · Joined: Jul 06, 2016 Posts: 91 Location: Canada

I don't see any problems with the part values. A picture of the bottom of the pcb would also be helpful.

Grumble · Posted: Sun Apr 22, 2018 9:54 pm Post subject:

bottom left resistor, should be 680ohm, you have 332ohm.

YashN · Joined: Jun 27, 2011 Posts: 104 Location: Canada

YashN · Joined: Jun 27, 2011 Posts: 104 Location: Canada

YashN · Joined: Jun 27, 2011 Posts: 104 Location: Canada

YashN · Joined: Jun 27, 2011 Posts: 104 Location: Canada

Any ideas?

How would I test only the VCA part to diagnose it and perhaps troubleshoot it if it's the culprit?

gabbagabi · Posted: Mon Jul 23, 2018 6:59 am Post subject:

refering to this schematic http://yusynth.net/Modular/Commun/WAVEFOLDER/wavefolder-schema.gif

u would connect ur probe to pin1 of U2a (before R1) and measure there if a signal goes thru as desired

good luck

edit: do u feed in a 10Vpp signal? or not?

YashN · Joined: Jun 27, 2011 Posts: 104 Location: Canada

gabbagabi · Posted: Mon Jul 23, 2018 1:30 pm Post subject:

well,
its better to measure than belive

YashN · Joined: Jun 27, 2011 Posts: 104 Location: Canada

Already measured. It was a while ago though.

gabbagabi · Posted: Tue Jul 24, 2018 12:24 am Post subject:

ok, it was just that the amplitudes looking so low on the scope-shoots

YashN · Joined: Jun 27, 2011 Posts: 104 Location: Canada

True, true. I will have to both measure again and re-calibrate: I made quite a lot of modifications on the VCO-555 itself to bring some of the low levels up (like Sine and Triangle, etc...)

I think I might either use a generated signal from Audacity or use my Kurzweil for the 10Vpp instead - will take less time to set up.

romaindegode · Joined: Feb 28, 2019 Posts: 26 Location: France.

Hi,
No news about your wavefolder ?

YashN · Joined: Jun 27, 2011 Posts: 104 Location: Canada

romaindegode · Joined: Feb 28, 2019 Posts: 26 Location: France.

Hanging around Yusynth website, I manage to find PCBs of Jurgen Haible 's TAU The Pipe Phaser and built it 15 months ago.

That module never worked properly and I probably spent whole days to debug it.

Last week, totally desperate, after too many beers, I had the idea to tap on all the components.
It actually gave me a way to spot few of bad connections , fixed the yelds and... Tadaaaaaa that little man is alive

https://youtu.be/qS8yvIZ00yY

Debugging can be sometimes a little bit funky 😁