Duo-Phase not phasing

mybud

Member
Hello again folks: I finished this quite complex (for me) build, but no joy on the phasing aspect so far. Both LED's respond to trimmer adjustments and there are no issues with the audio. When I switch it in, the audio level increases and the guitar is clearly 'amplified.'

Shining a flashing torch on the LED's produces a nice phase effect but that's the only way to get the phasing to happen at this point. I don't think somehow I'll manage playing the guitar and holding the torch at the same time ;)

Other symptoms: the B side resonance pot produces a self-oscillating squeal during part of its travel.

Two caveats:

I subbed 300R for the required 330Rs (R45A and B) in each case.

The 1nF cap on the B side (C18B) had to be replaced and it's a bit of a kludge job. I did try tack soldering an extra one on the pot side of the board in case there was a faulty connection but this made no difference.

IC6A and 6B show different voltages. I don't know if this is significant enough to make a difference. Also D1A and D1B, as you can see.

Voltages:

9.4V (once connected I seem to get 4.5V?)

1 2 3 4 5 6 7 8
IC1A -0.01 -0.02 0 -2.65 0.001 -0.034 -0.035 4.176
IC2A -0.038 -0.032 0.001 -2.65 0.001 -0.027 -0.016 4.179
IC3A -0.026 -0.026 0 -2.65 0.001 -0.025 -0.031 4.178
IC4A -0.026 -0.030 0.001 -2.65 0.001 -0.032 -0.033 4.178
IC5A 3.113 0.123 0.144 -2.65 0.001 -0.031 -0.045 4.175
IC6A -1.21 0.001 -1.1 -2.61 0.001 -0.003 -1.03 3.48
IC7A 4.16 2.4 0.001 -1 -2.62 1.43 2.68 4.16
IC1B -0.04 -0.04 -0.001 -2.48 0.001 -0.04 -0.03 4.16
IC2B -0.06 0 0.001 -2.48 0.001 -0.05 -0.05 4.16
IC3B -0.03 -0.04 0 -2.48 0.001 -0.041 -0.038 4.17
IC4B -0.05 -0.05 0.001 -2.48 0.001 -0.04 -0.05 4.17
IC5B 3.2 0.14 0.17 -2.48 0.001 -0.05 -0.07 4.17
IC6B 2.7 0.001 0.47 -2.48 0.001 1.45 -1.09 3.46
IC7B 4.16 2.38 0.001 -0.96 -2.49 1.47 2.7 4.17
IC8B 1.03 -0.03 0.001 -2.48 0 -0.04 -1.01 3.46

E B C

Q1A 2.49 3.12 4.19

Q1B 2.92 3.56 4.19

Cathode side:

D100 4.2

D1A 3.5
D1B 0.123
D2A 3.47
D2B 0.204

Any suggestions welcomed as ever. Thanks in advance.

Duo-Phase_03.jpg Duo-Phase_04.jpg Duo-Phase_05.jpg
 

mybud

Member
Thanks for swift reply. I apologise for being apparently half-witted but I heard phasing with the lights off and of course I've been testing it in broad daylight. I hang my head in shame. But this is real progress. In this case, they seem to function best when almost off.

There does appear to be something weird going on with the A-side resonance pot. With both switches engaged down (towards you with pots northwards IOW), there's a point where the circuit self-oscillates which can't be right, since the other side behaves according to plan.

I'll check this all out afresh tomorrow. There are two other circuits apparently misbehaving which your solution will fix, I have no doubt. Thanks again, much appreciated.

I'm no longer 'in the dark.' :cool:

Best
 

jimilee

Well-known member
Thanks for swift reply. I apologise for being apparently half-witted but I heard phasing with the lights off and of course I've been testing it in broad daylight. I hang my head in shame. But this is real progress. In this case, they seem to function best when almost off.

There does appear to be something weird going on with the A-side resonance pot. With both switches engaged down (towards you with pots northwards IOW), there's a point where the circuit self-oscillates which can't be right, since the other side behaves according to plan.

I'll check this all out afresh tomorrow. There are two other circuits apparently misbehaving which your solution will fix, I have no doubt. Thanks again, much appreciated.

I'm no longer 'in the dark.' :cool:

Best
:cool: Nice
 
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