Bear Hug Compressor...paging midwayfair! (SOLVED)

[pryde]

Problems: A little less than unity gain at full volume. Compression pot and H/L switch have no/very minimal effect. The effect sounds like it is compressing a little but it could be that it is just the volume issue.

Only sub is 100k at R10. Everything else is per build doc.

Q3 Source resistance to ground is ~15 Ohms with no change during playing with comp at max.

Reflowed all joints although none looked suspect.

Thanks in advance for the help!

[midwayfair]

Is Q2 socketted? If so, pull it out and see if the boost side works. If it doesn't, we'll have to debug that, first.

Q3 (drain) is the place you'll see a resistance to ground shift during playing -- but we need to make sure Q1 is working, first.

Post your voltages, and pics if you have them.

And just to be sure ... BS170 in Q1, right?

[pryde]

Thanks Jon.

I have to hit the road but will be back this evening and will start with your suggestions and report back

[pryde]

OK,

1: Q1 is a BS170

2: With Q2 removed, it makes no difference. The effect still works the same

3. Measurements:

Q1: D 7.1v, G .39v, S 2.0v

Q2: E .47v, B .65v, C 7.6v

Q3: D 0v, S 0v, G 0v

Obviously I am getting nothing at Q3. tried a few different 2n5457's with no luck.

Thoughts?

[Tremster]

Same problem here with mine, just volume but no compression.
Will follow this thread closely when I get home from work tonight.

[midwayfair]

Same problem here with mine, just volume but no compression.
Will follow this thread closely when I get home from work tonight.

This is the opposite problem. Pryde has no boost. Please start a new troubleshooting thread.

[midwayfair]

OK,

1: Q1 is a BS170

2: With Q2 removed, it makes no difference. The effect still works the same

3. Measurements:

Q1: D 7.1v, G .39v, S 2.0v

Q2: E .47v, B .65v, C 7.6v

Q3: D 0v, S 0v, G 0v

Obviously I am getting nothing at Q3. tried a few different 2n5457's with no luck.

Thoughts?

Your Q1 voltages are wrong. I don't have voltages for Q1 handy here at work, but I'm pretty sure you should have at closer to 5v on the gate. Try swapping out the MOSFET -- you can try any number of things, including a regular bipolar transistor, to see if there's something wrong elsewhere in the circuit. If it doesn't boost with something else in Q1, post pictures, and check the following parts carefully again:
R1, R2, R4-R7, C2, C4, C6, D2, and the volume pot. Fortunately Q1 is a very, very tiny portion of the circuit.

[Tremster]

This is the opposite problem. Pryde has no boost. Please start a new troubleshooting thread.

Oh. Derp. People who can read clearly have an advantage.

[midwayfair]

This is the opposite problem. Pryde has no boost. Please start a new troubleshooting thread.

Oh. Derp. People who can read clearly have an advantage.

[pryde]

Damn, wife has the camera. I cant get pics til later.

I swapped Q1 with other BS170 with no luck. re-checked ALL components and reflowed your suggested components and also changed D2 with another 9.1v zener. No changes, the circuit still behaves the same and getting same voltages.

consider myself stumped 

[midwayfair]

I swapped Q1 with other BS170 with no luck.

same deal with a regular transistor?

[pryde]

Sorry, forgot to mention that. Same deal with a 2n2222 and a 2n5088

[midwayfair]

Sorry, forgot to mention that. Same deal with a 2n2222 and a 2n5088

Do you have your audio probe handy? Check the signal on both sides of C2 and at the drain. I'm curious if you're somehow losing signal to ground at the input.

You can also pull Q3 (if you used a socket) and jumper the drain and source holes. It should become insanely loud.

[pryde]

OK.

Signal passes fine on both sides of C2 and Q1 Drain. Also jumped Q3 D and S, as you predicted the circuit became very loud.

Again, thanks for the ongoing help.

[midwayfair]

OK.

Signal passes fine on both sides of C2 and Q1 Drain. Also jumped Q3 D and S, as you predicted the circuit became very loud.

Again, thanks for the ongoing help.

What is your gate voltage now?

Something's weird with your Q3. Measure the resistance across the FET. It should be ~300R.

The thing that's really bothering me, though, is that even if Q3 were buggered, it would simply be taking the bypass cap out of the circuit, and so you should be at or above unity volume because of the 2.7K setting the minimum gain at ~2x.

Put Q2 back in. Keep Q3 out for the moment, since that appears to be part of the issue. You can audio probe up to D3/D4 at least -- it should continue to be extremely loud at that point, even louder than it is at the drain of Q1. Check the voltage on the anode of D3 and play a loud chord (turn the comp up). Does it change?