Total Recall overdriven echos - Solved (@#$^& you R12!)

[Martan]

Hello all,

I've built two total recalls. Both function well, but one has very overdriven repeats. It seems like it is coming from the NE570 chip. The signal is clean going in, but overdriven coming out of pin 7. This is with the feedback all the way down.

All of the voltages are within 0.2 V of the build doc except pin 7, which reads 5.6 (1 V higher than the doc).

Does this sound like a bad NE570? They are expensive or I would just pick up a new one, and I already gave away the other build

btw, I can't bias it out of even the first MN3008.

Any thoughts?

Thanks,

Marty

[Scruffie]

I'd check all your values.

Are you sure it's actually a NE570 too? The SA571 for example biases up differently.

[Martan]

Thanks Scruffie. I've tried two NE570s from Small Bear. Here are the voltages on the second one (still really grainy repeats):
1 -13.89            9 -13.19
2 -13.18           10 -7.21
3 -13.18           11 -8.93
4 -15.01           12 -13.19
5 -13.19           13 0.00
6 -13.17           14 -13.18
7 -4.69             15 -13.18
8 -13.18           16 -13.92

Interesting that the first NE570 had a 1V higher pin 7, but this second one has a higher pin 10. Both say NE570 on the chip. Still have the grain on pins 3 and 4 of IC 6 and I can't bias it out. I've ordered 2 more chips (tested from DIYguitarpedals).

Thanks again,

Marty

[Martan]

And some other ICs around the NE570:

IC1
-7.62
-7.60
-7.57
-15.00
-7.55
-7.62
-7.63
0.0

IC3
-6.39
-3.19
-3.18
-15.01
-7.59
-7.61
-7.61
0

IC5
-7.61
-7.61
-7.59
-15.01
-7.14
-7.21
-7.21
0

REG
-15.2
-23.01
0

[lincolnic]

Just to chime in, I got my 570s from Small Bear as well and haven't had any trouble. You may have gotten unlucky but in general I trust them.

[Scruffie]

Did you check your values? For example the 68k between pins 5 & 6 of the compander increases the companders gain, or the opamp before with 200k/200k would increase gain in to the compander if one of them was wrong etc, etc.

[Martan]

I typically measure every resistor on the way in, but with a build like this might have missed one. Will double check.

[Martan]

All values checked out. The 200ks for IC1 are 200k. I socketed R 9 and 10 and went up and down in value but no luck. Tried a third NE570 as well. Still nasty distortion out of pin 7.

Any ideas?

Thanks,

Marty

[Martan]

Fixed a bad joint at R12 (damn you R12!). No distortion now.

Only mild complaint is clock whine at longer delays, though from my EHX experiences that is a normal thing.

Marty