Sunking II gain problems

[Tdub]

Hi there,

I've having a problem with my build.
The overdrive only kicks in at the last 1/4 of the gain pot, through the middle it seems to drop a bit of volume and comes back up. Otherwise seems to work nicely?

I haven't been able to see a list of good voltages but I think most of mine are way off.

IC 1
1: 4.08v
2: 4.08v
3: 0.01v
4: 0.00v
5: 0.22v
6: 0.04v
7: 4.08v
8: 8.32v

IC 2
1: 4.17v
2: 0.04v
3: 0.19v
4: -6.41v
5: 0.19v
6: 0.05v
7: 4.12v
8: 11.86v

IC 3
1: 8.32v
2: 3.99v
3: 0.00v
4: -3.47v
5:-6.41v
6: 1.05v
7: 2.49v
8: 8.32v

I subsitituted a BS250 for the BC250 but that's the only thing I've changed. I did try to pull some schenangians on the 392k and 422k resistors because I didn't have any available so I put resistors together to get those values.

Any ideas?

[madbean]

Voltages are way off. You need to pull the two TL072s first and re-measure. If the voltages are still off you need to check through the entire power supply section to find out why you are not getting +18, -9v.

[Tdub]

R32 is meant to be a 10R 1/2W, and is only a 1/4w...would that screw things up?

[Tdub]

Voltages are way off. You need to pull the two TL072s first and re-measure. If the voltages are still off you need to check through the entire power supply section to find out why you are not getting +18, -9v.

By pull do you mean replace them with other IC's or to take them out and measure the holes?

[Tdub]

Without IC's I get:

IC 1
1: 0.05v
2: 0.05v
3: 0.00v
4: 0.00v
5: 0.02v
6: 0.04v
7: 0.03v
8: 8.45v

IC 2
1: 0.00v
2: 0.03v
3: 0.08v
4: -6.81v
5: 0.08v
6: 0.00v
7: 0.00v
8: 12.31v

[Tdub]

So I've reflowed the solder for every part, scanned the board for potential part screw ups in the power supply, checked for solder bridges, and I can't find anything!

I've swapped out the MAX1044 chip I had there for a 7660 with no change.

Here are some pics of the board;

[Tdub]

Ok, so I replaced the whole power section with no change BUT happily found the issue.

I'd tried to jimmy up some 422k and 392k resistors through putting some resistors in parallel and series jiggery pokery, and as soon as I removed then and just replaced them with 430k and 390k resistors it all magically worked.

Hooray!

[TGP39]

Hi Tdub. Welcome to the forum. I'm glad you got it working. It's a good feeling when it powers up.... Hopefully you can put a build report together after you box it up. Good job.

Steve

[madbean]

Interesting. Well, glad it all worked out.

[playpunk]

I have the correct resistors if you want some


Sent from my iPhone using Tapatalk

[Tdub]

Thanks all, I feel very welcome here

Interesting. Well, glad it all worked out.

Me also. Cheers for these projects; my ears are ringing like crazy after boxing this guy up!