Tube screamer debug help

[m-theory]

I'm back.  This time, it's a GGG PCB tube screamer build that's giving me fits. http://generalguitargadgets.com/pdf/ggg_its8_lo.pdf

The light's on, but nobody's home.  No signal whatsoever when circuit is engaged, but the LED lights up. 

Mods are as follows:

R2 = 620k
R6 = 2.7k
R7 = 20k
C3 = .1uf
C5 = .1uf
C9 = .1uf
D1 = Ge
D2 = 1n4002
D3 = 3mm LED

Voltage readings are:

Battery = 9.57v
At circuit = 9.57v

Q1
E = 4.89v
B = 5.34v
C = 9.57v

Q2
E = 6.2v
B = 5.8v
C = 6.25v

IC
1 = 9.54v
2 = 9.47v
3 = 9.51v
4 = .3mv
5 = 9.54v
6 = 9.54v
7 = 9.54v
8 = 9.52v

D1
A = 9.53v
C = 9.51v

D2
A = 9.51v
C = 7.98v

D3
A = 9.54v
C = 7.98v

C7
9.53v +
.4mv -

C11
5.87v +
.8mv -

C12
9.53v +
.3mv -

Any thoughts?

[jlullo]

m-theory,
hey man!  i recently had the same problem with this circuit.  my op amp had similar voltage readings that yours does.  they shouldn't all be getting voltage like that.  what i did was retouch some solder pads to the resistors around the op amp.  i can't say if there is any reasoning behind that, i just figured if there were parts of the IC getting full voltage that shouldn't be, there must be some cold solders going to the surrounding resistors. 

regardless, i did that, made sure to hit any solder joint that looked "blobby", and it worked great afterwards...

jonathan

[Plinky]

While your transistors do appear a bit high, they look like they're working properly. Your IC voltages, however, are way off. You should have something around 4.5v on pins 1,2,3,5,6,7, no volts on pin 4 (IC ground), and battery voltage on pin 9 (IC power). Something is shorted to voltage I would guess (or possibly a loss of ground or poor solder joint???). Use a magnifying glass and double check the traces on the PCB. Make sure no solder is accidentally touching other traces. I'm currently debugging one of these myself, so I just took voltage readings off of a working one. Good luck. 

[m-theory]

Oh man, I should've replied long ago!  I found this almost immediately after posting this.  It was a very small solder bridge where one did not belong! 

Although, I must say that I only have 8 pins on my 8 pin chip, so maybe that's something to look at, too!   

battery voltage on pin 9 (IC power).

I got this running, and it sounds terrific.  I ended up going with two red LED's in one direction and a 1N4001 in the other for my main clipping diode option.  I've got 6 different configs put together on a daughter board and controlled by a 6p rotary switch, but I'm sort of hooked on that particular LED option.  Right now, I'm auditioning various IC's, although I must say that, at least currently, my favorite is the ol' standby. 

[Barcode80]

do some searching, i remember a thread a couple of months ago where someone (i think melanhead) tested nearly every conceivable opamp ever reported as used in a TS and listed sonic qualities of all. good read.

[Plinky]

IMO, I really couldn't tell any difference between any op-amps in terms of tone. I had 3 tube screamers I built all connected together and each had a different op-amp installed - a JRC4558D, an TI RC4558P, and a JRC4565. I guess I'm tonedeaf because they all sounded the same. Maybe they all look different on an oscilloscope. I just started putting the JRC4558s in them because the first question people ask is what opamp is in it.

[m-theory]

do some searching, i remember a thread a couple of months ago where someone (i think melanhead) tested nearly every conceivable opamp ever reported as used in a TS and listed sonic qualities of all. good read.

I read that, and I agree that it was a great read, although I found that not all potential contenders work with all diode combinations.  I got a horrible response from the TL2262 and CA3260E with LED's, though they sounded fantastic with silicon.  Right now, I'm narrowing down between JRC4558D, RC4558P, RC4559P, and NE5532.  I haven't had enough time to fully audition each one.  I just did a quick check to see that they're compatible with the LEDs, and at a quick glance, they all seemed worthy contenders.

I really couldn't tell any difference between any op-amps in terms of tone.

Based upon what I've heard thus far, other than the ones that just flat out don't seem to be compatible with LED's, I haven't noticed a massive difference.  It's very subtle.  At the quick glance that I made, I found the 4559 to be a bit "softer," yet gainier than the JRC4558.  The 5532 seemed a bit grainier to me, but that may be a good thing, when I get a chance to crank up a bit.  The RC4558 was very similar to the JRC4558 to my ears, but again, I did a very brief comparison.  By far, the most dramatic tone difference comes from the diodes.