Cupcake problems

[pinknoise]

Hey all,

I'm working on a cupcake project i've had open for about a year now, and cant seem to figure it out. I'm suspecting a bad ic but I'm not sure. It seems to work but the output is 1/2 the volume it should be. I tested it with an audio probe. I've attached the results. Red=no audio. Yellow=audio. If anyone could help with this would be awesome. I'm itching to start another project, but want to finish this one first.

THANKS,
pinknoise

[midwayfair]

When you adjust the bias trimmer, does the volume change? Also what do you mean by "it should be" -- do you mean there's a volume drop when the pedal is engaged regardless of the volume knob setting, or that you think it should be louder?

Voltages would also be helpful if adjusting the bias trimmer does Ze Goggles.

[pinknoise]

When you adjust the bias trimmer, does the volume change? Also what do you mean by "it should be" -- do you mean there's a volume drop when the pedal is engaged regardless of the volume knob setting, or that you think it should be louder?

Voltages would also be helpful if adjusting the bias trimmer does Ze Goggles.

both pots function the way they should. With the volume all the way up the volume is 1/2 what the bypassed volume is. I'll try to get the voltages tonight.

[midwayfair]

Okay. There's a couple other things: Did you sub any parts (i.e., are you using a different FET than 2N5457?); double check that your Ge diode is not dead (it would short the signal into the attentuation circuitry -- basically compressing all the time). You also need to check continuity to Pin 3 of the IC. You should be getting audio there, basically the same as your input.

For reference with your audio probing, your audio signal path (which is very simple) is: C1, R2, C2, IC1 pin 3, IC1 pin1, C6, Level lugs 3 and 2. (R9/R8/C5 are the feedback loop of the IC, and R6/R7 are the biasing resistors.)

The envelope and attentuation (the compression part) is handled by everything in the schematic between R10, C3, and Q1. If you get really stuck, you can pull R10 or Q1 and it will remove the compression effect from the circuit, allowing you to isolate whether the problem is in the audio or compression path.

[pinknoise]

Okay. There's a couple other things: Did you sub any parts (i.e., are you using a different FET than 2N5457?); double check that your Ge diode is not dead (it would short the signal into the attentuation circuitry -- basically compressing all the time). You also need to check continuity to Pin 3 of the IC. You should be getting audio there, basically the same as your input.

For reference with your audio probing, your audio signal path (which is very simple) is: C1, R2, C2, IC1 pin 3, IC1 pin1, C6, Level lugs 3 and 2. (R9/R8/C5 are the feedback loop of the IC, and R6/R7 are the biasing resistors.)

The envelope and attentuation (the compression part) is handled by everything in the schematic between R10, C3, and Q1. If you get really stuck, you can pull R10 or Q1 and it will remove the compression effect from the circuit, allowing you to isolate whether the problem is in the audio or compression path.

No subs. The 1n34a should be good. It's already the 2nd one and I tested it before I put it in. Definitely no audio on ic pin 3. Solder joint is great. Lifted r10 and q1 and it works great other than there's no compression like you mentioned. It it obviously the compression path.

9v in. 9.71
Ground. 0
Ic pin1. 5.33
Ic pin2. 5.33
Ic pin3. 5.25
Ic pin4. 0
Ic pin5. 0
Ic pin6. 9.16
Ic pin7. 9.16
Ic pin8. 9.71

Q1
P1. 0
P2. .414
P3. .414

Q2
P1. .414
P2. 1.455
P3. 9.71

[midwayfair]

Are those Q1 voltages with the FET in the socket? :/

[pinknoise]

Are those Q1 voltages with the FET in the socket? :/

yup

[midwayfair]

Are those Q1 voltages with the FET in the socket? :/

yup

Does the trim change the voltage on the center pin (or any pin for that matter)?

[pinknoise]

Are those Q1 voltages with the FET in the socket? :/

yup

Does the trim change the voltage on the center pin (or any pin for that matter)?

Q1
Pin1. 0
Pin2. .418 - 0 via trimmer
Pin3. .418 - 0 via trimmer

[pinknoise]

Are those Q1 voltages with the FET in the socket? :/

yup

Does the trim change the voltage on the center pin (or any pin for that matter)?

Q1
Pin1. 0
Pin2. .418 - 0 via trimmer
Pin3. .418 - 0 via trimmer

The level pot doesn't affect the voltage on q1

[midwayfair]

The level pot doesn't affect the voltage on q1

It won't. The bias trimpot is what changes the bias on Q1. The level is just the output level.

[pinknoise]

The level pot doesn't affect the voltage on q1

It won't. The bias trimpot is what changes the bias on Q1. The level is just the output level.

Any more ideas on how to troubleshoot this thing? Is my q1 voltage normal? I get a lot of output if I lift q1 and r10, but as soon as add the compression circuit the output drops like crazy.

[midwayfair]

The level pot doesn't affect the voltage on q1

It won't. The bias trimpot is what changes the bias on Q1. The level is just the output level.

Any more ideas on how to troubleshoot this thing? Is my q1 voltage normal? I get a lot of output if I lift q1 and r10, but as soon as add the compression circuit the output drops like crazy.

Did you ever measure whether the bias trimpot changes the voltage on the drain pin? With and without Q1 in the circuit?