DS-1 Troubleshooting

[pgorey]

I am troubleshooting a friends' DS-1,  pre-1994 I believe as it has the BA728N Op-Amp.  Upon first opening, I found the exploded D1 1N4004 power supply diode and noticed burn marks on both terminals of it on the solder side of the business.  So, I took to troubleshooting with a probe and voltmeter and am hoping someone can help me make sense of the readings and confirm my thoughts on what to replace.  I know these pedals aren't worth much but I'm looking at this as a learning opportunity to troubleshoot and hopefully fix a pedal that I didn't build.

* I only had a 1N4001 diode to replace the 1N4004 but it seems like from other DS-1 threads that this is not an issue.


The pedal's LED comes on and clean sound is passed in bypass.  No sound at all when the effect is engaged.


Battery voltage outside of pedal is 9.43v
Voltage at battery snap when plugged in 9.41v (9.37 by the time I finished testing voltages)

IC1 (BA728N in-line)
P1 0
P2 0
P3 .04
P4 0
P5 0
P6 0
P7 0
P8  9.40


Q1
C = 9.39
B = .01
E =1.75

Q2
C= 1.20
B= .03
E= .01

Q3
C= 9.38
B= .01w
E= .92

Q4
C= .05
B= 0
E= 0

Q5
C= .02
B= 0
E= 0

Q6
C= 0
B= .27
E= .27

Q7
C= 0
B= .28
E= .28

Q8
C= 0
B= .27
E= .27


D1
A (anode, the non-band end) = 0
K (cathode, the banded end) = 9.37

D2
A = 4.36
K = 9.36

D3 (can't find it - maybe the LED indicator?)
A =
K =

D4
A = 1.08
K = .95

D5
A = 1.08
K = .95

D6
A = 0
K = 0

D7
A = 0
K = 0

D8
A = 0
K = .04

Since I dont know the exact variation of the schematic to follow, here are the places I HAVE signal with the audio probe:

Q1 E+B
Q2 E,C,B
Q7 C faintly
Q8 E
IC Pin 1, 2 and 5 faintly, 3.

R1
R2
R3
R9
R10

One side of R4 and R5

J1
J2

Q8 all pins but collector less

Anode side of D6 and D7

Picture of the board below:

[pgorey]

Just as a quick idea to try, I clipped the old op-amp, built an in-line socket/harness setup to be able to adapt to the wider IC footprint and also swap ICs.  I started with an NE5532 and now it works!!!  It sounds like how I remember a DS-1.  Raspy top end and kind of a loose fuzz-like low end.  It will be interesting to hear other ICs I have. 

[iainpunk]

i doubt the IC in the DS1 makes much change, but if it does, i recommend the LM358!
the slew rate makes the most diference on the final sound, and that chip has only 0.3v/us, which is the same as the RAT's lm308, which means it would be a tiny bit smoother.

cheers, Iain

edit: the NE5532 has 9v/us

[pgorey]

Interesting!  Thank you for the recommendation.  I don't have those in my bin - closest is an LM 833 which I imagine is a much different IC.  I'll keep an eye out for some LM358s.  Thanks again!

[anotherjim]

The LM833 is faster still at 7v/us. I've had a few in stock for ages now. They're too good for anything I'm likely to make but I suppose I'll use them when my stash of NE5532 runs out (and I don't often have cause to choose those). I've also got some LM4562 and they are just crazy fast doing 20v in a microsecond!