Lowrider fizz on clean signal

[nimm]

1) Project:  Madbean Lowrider

2)  Issue:  Everything seems to be working how it should except there is some fizz/fuzz on the clean signal when you have the "clean" volume pot turned up at any level.  It seems to be "layered" with the clean sound and decays before the note is done sustaining. 

3) Steps taken:  Cleaned board, touched up solder joints, tested IC values and audio probed.

4) Substitutions:  C2 used 27n rather than 33n, deleted C12 and used 1n for C10, used 2sk30 for Q2 and Q3 (technically not substitution).

I am still new at building boards and especially troubleshooting and tried my best at following the input path during audio probing.  Everything sounds very clean until I reach resistor R5 at which point the fizz comes in.  Capacitor C4 is also very quiet to no signal but I assume it should since it's going to ground.  I thought of replacing IC1 but the R5 signal comes before it enters IC1 correct?

Here are the voltage values I think are relevant (I do have the other IC voltages as well if needed):
Input Voltage:  9.02

IC1   Reference   Measured
1      4.9              4.93
2      5                 4.93
3      4.3              2.41
4      0                 0
5      4.5              2.93
6      5                 4.95
7      4.9              4.95
8      9                 9.02

IC6   Reference   Measured
1   5             4.91
2   4.9             4.91
3   4.9             4.89
4   9             9.03
5   4.9             4.89
6   4.9             4.92
7   4.9             4.93
8   4.9             4.91
9   5             4.91
10   5             4.89
11   0             0
12   5             4.89
13   4.9             4.92
14   4.7             5.1

Q1   Reference   Measued
G     4.3             2.46
S     5.3             5.03
D     9.1             9.03
      
Q2      
G     4.2             3
S     4.9             4.89
D     4.9             4.89
      
      
Q3      
G     0                0
S     4.9             4.89
D     4.9             4.67


Any ideas on a solution would be greatly appreciated.  Other than that one issue this pedal sounds great and has already been an inspirational one!
Thanks

[madbean]

So, you have relatively clean signal at R4, but not at pin1 of IC1, correct?

Your VR voltage seem to drop off some after the two 1M biasing resistors, R2 and R4. Both are 1M. So, couple things come to mind: 1) your DMM is acting as a voltage divider when you measure those spots making the voltage appear lower, 2) you did not use 1M for those two resistors, 3) something is wrong with the resistors, 4) the pinout of your 2SK170 is not DSG.

[nimm]

Thank you for the quick responses.  Unfortunately, I'll have to wait until I get home to double check the audio probing. 

To answer a couple questions:  resistors R2 and R4 are 1M (4 band with colors Brown, Black, Green, Gold) and for Q1 I used a J201 from Tayda.  The spec sheet has the pins numbered 1,2,3 from left to right when facing the flat side of J201.  1=Drain, 2=Source, 3=Gate http://www.taydaelectronics.com/datasheets/A-121.pdf.  I think this matches up with the board?

[nimm]

I was able to double check the signal with the audio probe.  At resistors R2 and R4 the sounds completely clear and as soon as I go up to R5 the fizz starts.  The signal at pin 1 of IC1 is definitely fuzzed but maybe sounds more so because of the louder volume output here.

I measured the resistance of leftover 1M resistors, which were from the same strip as I used in the board, and they were well within tolerance.   

At this point maybe I'll still replace R2 and R4 with the measured good ones and maybe get a new J201?

Also, I wanted to be sure from the info I provided in last post that Q1 is orientated correctly, as in it has the pin out that matches up with the PCB?

Thanks again for the help.

[nimm]

Solved

I wanted to do a follow up in case anyone else comes up with the same issue.

The TL072 chip in IC1 must have been bad as I replaced it with a new one and the pedal is perfect now, I love it.