Debugging: "The Low Down" (chopped OC-2) by DC6FX

[elenore19]

Hey guys.
I'll try to make this quick as to not waste your time.
Build Doc:
https://drive.google.com/open?id=0B7QeV_7r70dTNE4xSHo4cHY3eEE
Board:
https://www.oshpark.com/shared_projects/RywmoHxm
Sound Clip: (I used a boost after the octave to get the signal up in this recording.)
https://drive.google.com/open?id=0Bye2ERj2uuOlZzNaQ05wRmZjNGJjX18tUGlJRC1ZeHExZnA0
Voltages:
TL074CN
1: 5.10    8: 5.10
2: 5.10    9: 5.10
3: 4.65  10: 4.77
4: 9.4    11: 0
5: 5.05  12: 4.77
6: 5.09  13: 5.10
7: 5.10  14: 5.10

CD4013BE
1: 0         8: 8.11
2: 9.40    9:  0
3: 5.04  10: 8.13
4: 0       11: 0
5: 9.40  12: 9.38
6: 0       13: 9.4
7: 0       14: 9.4

LM324N
1: 8.13    8: 5.03
2: 5.10    9: 5.10
3: 5.08  10: 5.07
4: 9.4    11: 0
5: 5.06  12: 5.08
6: 5.10  13: 5.08
7: 5.12  14: 8.14

Things that are different:
The chips I have have extra letters on them. Maybe this would cause the problem?
I'm using TL074CN, LM324N, CD4013BE.
For C5 I have 2.2nf parallel with another 2.2nf. Making it 4.4nf which is lower than the 4.7nf.
Maybe that would cause the problem?
Problem:
It's very quiet and has a little bit of background high pitched fuzz.  (you can hear it even with both pots zero'd)
Both pots seem to do what they're supposed to, yet when cranked the overall volume is still lower than bypass tone.


Thanks for any help you can offer. It's greatly appreciated!

-Elliot

[BrianS]

I'm going to ask a stupid question and plse don't take this as an intelligence insult but did you correct all the mistakes on the board as outlined (The jumper, resistor and trace cut)?  I myself have forgot to correct board errors outlined in the bdoc.

The meaning for the chip letters are on their data sheets.  The ones you used are what I would have used for the build.  Most of the time the letters indicate packaging info.  But when in doubt check the data sheet.

As far as the cap I don't think it would cause that huge of a drop but someone else who is smarter than me can answer that.

If you corrected all the board mistakes go back over and reflow all your solder points and look for bridges between pads.  Make sure your off board wiring is correct and there are no stray wires touching. Posting a picture (front/back) can also help when it comes to troubleshooting.  Some of the guys on here can spot problems quickly. 

[diablochris6]

I directly copied this schematic (from Sabrotone, I believe) to make my boards. The Chopped OC-2 design seems to have similar issues that are relieved by a buffer at the beginning. Maybe that can help?

I kind of want to redesign my board to resolve some of those issues and maybe add a decent mixer for the various mods. We will see.

[elenore19]

The board I have is corrected already so I didn't fix any of those problems myself, but I'm led to believe that they are all fine.

Here are some pictures.


I'll try and build a simple JFET buffer quick to put in front to see if that helps.
The volume thing doesn't need to be an issue for me, I plan on putting a boost at the tail end of the circuit. I'm worried about the octave up background fuzz stuff going on. Hopefully the buffer will fix that.

[elenore19]

Another picture

[elenore19]

Backside

[reddesert]

I don't have one of these, but the voltages on the ICs generally look reasonable.

I would measure voltages on the transistors also - if something is wrong with Q2 it could mess up your output; check continuity on critical components, esp. everything that comes after the last IC in the audio path (from Octave Vol pot to the output), and use an audio probe to test signal all along the audio path to find where it gets weak.

[gitaar0]

The high pitched fuzz was also a problem on Taylor's board. Look up the post on that on DIYSB. Taylor suggested some grounding on a certain part of the pcb but that did not help for me.My solution for that was to put a jfet buffer in front and it was gone.
I am still not sure why you have low output. Did you do any audio probing?
Did you already reflow all your soldering?