Dirtbag deluxe not working anymore

[gitaar0]

Dirtbag deluxe MN3005s on 15 volt

I had my dirtbag working and sounding really good but suddenly it was distorting.
I have know idea what caused it.
I can not get back to what I had.

IC 1
Pin1 6.06
Pin2  6.09
Pin3 5.94
Pin4 0
Pin5 5.52
Pin6 6.09
Pin7 6.08
Pin8 14.94

IC 2
Pin1 1.19
Pin2  1.81
Pin3 1.81
Pin4 0
Pin5 1.82
Pin6 1.80
Pin7 7.52
Pin8 1.82
Pin9 1.82
Pin10 7.39
Pin11 5.88
Pin12 1.83
Pin13 14.94
Pin14 1.81
Pin15 1.81
Pin16 0.64

IC 3
Pin1 6.06
Pin2  6.09
Pin3 5.95
Pin4 0
Pin5 5.88
Pin6 6.06
Pin7 6.07
Pin8 14.94

IC 4
Pin1 14.90
Pin2  7.48
Pin3 3.60
Pin4 3.60
Pin5 0
Pin6 7.48
Pin7 6.39
Pin8 0

IC 5
Pin1 14.90
Pin2  7.48
Pin3 3.93
Pin4 3.93
Pin5 0
Pin6 7.48
Pin7 7.43
Pin8 0

IC 6
Pin1 7.43
Pin2  7.39
Pin3 7.18
Pin4 0
Pin5 4.96
Pin6 5.12
Pin7 4.18
Pin8 14.94

IC 7
Pin1 ~
Pin2  7.84
Pin3 7.24-8.26
Pin4 0
Pin5 7.80
Pin6 7.43
Pin7 7.6-8.23
Pin8 14.94

IC 8
Pin1 6.06
Pin2  6.07
Pin3 5.88
Pin4 0
Pin5 6.72
Pin6 7.39
Pin7 7.39
Pin8 14.94

IC 9
Pin1 6.85
Pin2  8.02
Pin3 8.05
Pin4 14.95
Pin5 14.95
Pin6 14.95
Pin7 0
Pin8 0
Pin9 0
Pin10 7.48
Pin11 7.48
Pin12 0
Pin13 6.91
Pin14 14.95

I can not bias ic 4 with a clean signal. I know it is possible because it was like that before.
I am using 47k for r11 and r12 as that gives me a cleaner signal and less compressed and that way I have half powersupply on pin 7 and 10 of the Ne571.

Readings on IC 6 are a bit strange maybe?
I have changed all opamps and no change. i have changed the NE571 with another that I know is working well, also no change.

I have reflowed and reflowed my build. No change.

Any suggestions.

Thanks, marc

[Scruffie]

Audio probe, find out where it starts distorting.

[gitaar0]

Hi scruffie,

I had audioprobed it already and found the distortion to be most at pin 3 Ic 4. I realized that as I could not bias that Ic to get a clean signal. It might be either to loud a signal at the input of Ic 4 or there could be something wrong with the clock.
I replaced th 4047 and now i can bias it a lot better.

When I use 47k in r11 & r12 i have a better and cleaner signal at the input of Ic4 but it gets overdriven easily and it sounds as if the input is clipping. Voltage on pin 10 of the ne570 is half powersupply. With 68k i get a more compressed signal at the input of ic4 and less clear and i can bias ic4 better. No input clipping. But the result is a less clearer echo signal in the end.

You explained me before that voltage at pin 10 and pin 7 of the ne570 should be half powersupply. I seem to be only able to get that with r11/r12 47k. Is there a good way to  bring the level a bit down at the input of ic 4 when using this 47k?

I tried changing r21 to 2k5 or 1k5. That helped, but i think i am changing a filter there.

What would be best?

Why is the r11/r12 set on 68k in the design as that does not give me half powersupply on the ne 570?

[Scruffie]

The 570 in the dirtbag is also biasing the following low pass filter section, 68k was chosen for a reason (more headroom isn't always desirable) as you experienced, the clipping is reduced.

Yes you are altering a filter cut off playing with R21... you can make R21 10k & C14 3n3 to add more series resistance and keep the cut off the same... I don't exactly suggest it but if it works for you.

Basically anything you do is going to change the overall sound, so personally i'd stick with the 68ks for the 570 but, you could try reducing the gain of the input filter by making R16 27k, or lower.

[gitaar0]

Ok, i will try some of that.

Thanks for now.