Yu Synth Moog VCF No Audio

mypetkiwi · Joined: Sep 08, 2018 Posts: 1 Location: New Zealand

I have begun the journey down the rabbit hole of DIY with the Moog VCF from Yusynth, I'm going a little mad. Here's a link: http://www.yusynth.net/Modular/EN/MOOGVCF/index.html

I've been trying to get this circuit to function for the last month and man, have I hit a brick wall. I've got no sound out of the filter at all, except for a bit of very low floor noise. I made it the first time on a piece of perf board that was a bit small, so it was very messy and hard to see signal flow from a glance, the first one did not make any sound. This one I soldered up hoping it would work, and if not, at least it'd be easy to troubleshoot. I've checked it with a multimeter many times, checked it visually many more, and I can't for the life of me figure out what I'm doing wrong, as like the first circuit, this one also makes no noise.

The current flows through half of the circuit, but never appears to reach the ladder, as there's never any sound coming from the output.

In terms of differing components from the original, I'm using regular log pots instead of rev log and I've shifted some things around in the circuit to make it fit, wiring is the same as the original schematic, all ICs and Transistors are as suggested.

There is 15v running through the circuit from my power supply, ground goes to AC ground.

Here's some voltage measuring I've done on the 3 ICs and 7 transistors:

If anyone could please lend their expertise I'd really appreciate it, I really don't want to have to shove this thing in a drawer and start something else, as it's my first piece of real audio equipment I've made.

Also, here's a list of voltage readings, just ask and I can do some more on different components.

U1 3046:
1. 0.186v
2. 0v
3. 0.165v
4. 0v
5. 0.175v
6. 0v
7. 0v
8. 0v
9. 0v
10. 0v
11. 0v
12. 0v
13. 0v
14. 0v

U2 3046:
1. 0.853
2. 0.926
3. 1.644
4. 0.825
5. 0.230
6. 0.139
7. 0.824
8. 0v
9. 0.270
10. 0.928
11. 0.852
12. 14.97v
13. 14.97v
14. 14.97v

U3 TL072:
1. 1.273
2. 1.259
3. 0
4. 14.97
5. 0
6. 1.068
7. 1.479
8. 0

Q1 BC557:
C:14.97
B:0
E:0

Q2 BC547:
C: 0.228
B: 0
E: 0.234

Q3 BC547:
C: 0.202
B: 0
E: 0.202

Q4 BC547:
C: 0.224
B: 0
E: 0.220

Q5 BC547:
C: 0.191
B: 0
E: 0.180

Q6 BC547:
C: 0
B: 0
E: 0.237

Q7 BC547:
C: 0
B: 0
E: 0.184

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Photo of top of circuit

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DSCF1526.JPG

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Photo of circuit wiring on the bottom

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Photo of both sides super imposed in Photoshop, to make it easier to see.

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icnagy · Joined: Jan 29, 2017 Posts: 6 Location: Glasgow, UK

U3 TL072 pin 4 and 8 looks wrong to me.

Pin 4 should be -VCC (-15V)
Pin 8 should be +VCC (+15V)

See http://www.ti.com/lit/ds/symlink/tl072.pdf (Page 5)[img][/img]

Screen Shot 2018-09-09 at 11.55.26.png

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Part of the schematic showing U3s power connections.

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