Tube Screamer SRV saturation issues?

Started by beeson, March 19, 2009, 08:13:34 PM

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beeson

Hey folks,
Ok, I built the beginner project and it worked the first time I fired it up...so I got a bit %^&*y and went straight to the Tubescreamer SRV Special on vero (link below).  I didn't do so well with that :-\ ...so I shelved it and built something else. Now I'm back at it with a bit more knowledge but I'm still having difficulty understanding some things. 

I plugged the pedal in, but no sound.  I probed around and it seems that the input signal won't get past the base of the first transistor.  Here are the voltages I've recorded across both transistors.

            C          B          E

Q1        8.65      7.14      6.64

Q2        8.65      7.66      7.03

It seems the base voltage is high to me.  From what I understand, the transistor(s) are saturated and can't produce a signal at the emitter.  I'm just not sure how I would go about lowering the voltage at the base.  I've double checked my resistor values are correct, and all grounds are correct.  In fact, this is the SECOND board I built with the exact same problem...I don't know what I'm doing wrong! Please let a fellow newb know where to start looking. :) Many thanks in advance.


http://www.aronnelson.com/gallery/main.php/v/ulysses/ulysses_layouts/ulysses_ts_srv_special/ulysses_ts_srv_special_vero_1_01.gif.html?g2_imageViewsIndex=1

ulysses

#1
here are the voltages on mine.. sorry for the late reply ;)

q1
c 9.0
b 2.695
e 2.047

q2
c 9.0
b 3.395
e 2.745

double check all cap orientations
double check all jumpers
double check all cuts on the underside
double check pot wiring - its pretty messy on that vero ;)

ACS

+1...

and TRIPLE check the pinouts on the transistors - google the datasheet...

Eb7+9

my re-design of the TS808 from the mid 90's ...

I took out "redundant" signal caps to get more transparency - in particular there's no cap between the input NPN buffer and the first op-amp ... this can cause a latch-up state with some op-amps upon power up ... try a different op-amp or install a signal cap between the two stages and a bias feed resistor to the op-amp non-inv terminal as in the original ...

doitle

Wow that's a big vero... The vero board I have doesn't have that many rows I'm pretty sure... I wonder if my dad might like this pedal though... He plays SRV all the time. Has a strat... wishes he could afford texas special pickups.

Now to search for sound clips...