Debugging tone pad tube screamer

[lizardking]

This is my second tone pad tube screamer.  The first one worked but was too shrill.  I tried increasing the cap on this one.  I found and fixed some solder joints but I'm still getting unity gain or a little less.  I've tried three different ICs and I replaced the transistors just in case.  I found the data sheet for the transistors and they seem to be oriented correctly.  The only mod I made was adding a symmetry switch for the third diode and I substituted some diodes.


1.What does it do, not do, and sound like?
IT HAS UNITY GAIN WITH NO OVERDRIVE AT ALL.

2.Name of the circuit = Tonepad Tubescreamer

3.Source of the circuit (URL of schematic or project) =tone pad.com

4.Any modifications to the circuit? Y or N
Symmetry switch


5.Any parts substitutions? If yes, list them.
I am using a 4001 diode, a 914 and a 34A.  I changed the .047 cap in the between Vb and the first stage of the IC To .1uF.  The IC is a generic 4558

6.Positive ground to negative ground conversion? Y or N
N

7.Turn your meter on, set it to the 10V or 20V scale. Remove the battery from the battery clip. Probe the battery terminals with the meter leads before putting it in the clip. What is the out of circuit battery voltage? =>
No battery.  9.04 v from power supply

Now insert the battery into the clip. If your effect is wired so that a plug must be in the input or output jack to turn the battery power on, insert one end of a cord into that jack. Connect the negative/black meter lead to signal ground by clipping the negative/black lead to the outer sleeve of the input or output jack, whichever does not have a plug in it. With the negative lead on signal ground, measure the following:
Voltage at the circuit board end of the red battery lead = V is 9v. Vb is 4.5v
Voltage at the circuit board end of the black battery lead =

Now, using the original schematic as a reference for which part is which (that is, which transistor is Q1, Q2, etc. and which IC is IC1, IC2, C1, and so on) measure and list the voltage on each pin of every transistor and IC. Just keep the black lead on ground, and touch the pointed end of the red probe to each one in turn. Report the voltages as follows:

Q1
C =9
B =3.5
E =4.63

Q2
C=9
B=3.7
E=3.26

IC1 (or U1)
P1=4.46
P2=4.46
P3=4.46
P4=0
P5=4.46
P6=4.46
P7=4.46
P8=9
.
.

D1
A (anode, the non-band end) =5.73
K (cathode, the banded end) =4.45

D2
A =4.47
K =5.73

D3
A =4.47
K =5.73

 

[R.G.]

Q1
C =9
B =3.5
E =4.63

If there's not a measurement error, there is something badly wrong here. The emitter has to be something like 0.45-0.6V lower than the base for this to work correctly.

Q2
C=9
B=3.7
E=3.26

... like this one.

D1
A (anode, the non-band end) =5.73
K (cathode, the banded end) =4.45

This is in conflict with the voltages you posted for IC1, pin 2. The anode should be connected to pin 2 by a wire, so they should not have different DC voltages. Is the measurement in error, or are they not really connected?

D2
A =4.47
K =5.73

D3
A =4.47
K =5.73

Likewise, the anode of D3 should be connected to the cathode of D2, so they should not be able to be at different voltages. Bad measurement, or not really connected. The voltages on the diode are also suspiciously consistent for voltages which should not be consistent.