No sound from Thor....very sad.....

[stm]

I used an LF411 in mine; sounds killer.

Any biasing changes needed if trying this ?

I mean heck...opamps are a buck and a half from Mouser.....try 'em all ! 

Dan

I have never had an LF411, but it sure has great specs.  You should try it by all means.  I also suggest testing an NE5534 (the single version of the NE5532).  With them both you should cover good JFET and bipolar opamps.  No need to change bias.

[stm]

This slew-rate limiting you are referring to could this be the cause of my Thor sounding gated? 
I've have used a TL071 op amp and been unsuccessful at attempting to remove a gated sound over the top of the distortion even though I can bias Q1 and Q2 to the specified voltages.
An audio probe seems to tell me that the gating is happening around the Mu-Amp section. 
It seems to sound correct at the gate of Q4 with the audio probe but then on the drain I get the gating sound either that or the problem is just amplified at this point in the circuit.

Could it be that perhaps I need to adjust source and or drain trimpots / resistors to allow for component / voltage tolerances?

If your voltages on the two first stages are properly set, and sound until Q4-gate is OK, you shouldn't touch them. "If it ain't broken, don't fix it!"

What you describes sounds like a problem with the mu-amp formed by Q3 & Q4.  Are you sure you are using a pair of same JFETs (i.e. two 2N5457's) instead of two different devices?
Mu-amps bias easily between 4 and 5V when fed from 9V.  Maybe there is some wiring problem, or one JFET is damaged.  I suggest reporting the source, gate and drain voltages of Q3 and Q4 with respect to GND as a start.

[MadMac]

If your voltages on the two first stages are properly set, and sound until Q4-gate is OK, you shouldn't touch them. "If it ain't broken, don't fix it!"

What you describes sounds like a problem with the mu-amp formed by Q3 & Q4.  Are you sure you are using a pair of same JFETs (i.e. two 2N5457's) instead of two different devices?
Mu-amps bias easily between 4 and 5V when fed from 9V.  Maybe there is some wiring problem, or one JFET is damaged.  I suggest reporting the source, gate and drain voltages of Q3 and Q4 with respect to GND as a start.

Thanks stm!  Here is my voltages - sorry for not putting these up first.  I just don't think that mine sounds as similar as I would expect compared to the sound clips.  The gating sound over the top of distortion sounds similar to other ROG pedals I have built that have not properly biased.

Supply Voltage 9.04V

Q1 2N5457

D=6.41
S=.31
G=0

Q2 J201

D=4.47
S=.24
G=0

Q3 2N5457

D=9.04
S=5.48
G=4.14

Q4 2N5457

D=4.86
S=.31
G=0

IC1 TL071ACP
1=.12
2=4.52
3=4.48
4=0
5=.12
6=4.53
7=9.04
8=0

Bright and Bottom switches off.

[grolschie]

The gating sound over the top of distortion sounds similar to other ROG pedals I have built that have not properly biased.

[EDIT]  I just saw this thread.  [/EDIT]

[stm]

Your readings suggest a problem in the last stage formed by Q3-Q4.  This is a mu-amp and should bias automatically.

WHat is strane is that the voltage drop across each 390 ohm resistor should be exactly the same, as they have tha same current.  However, your readings show 0.31V for the lower one and 5.48-4.86=0.62V for the upper one.  I suggest trying the following:

1) Interchanging Q3 and Q4 to see if voltages remain nearly the same.
2) As the 0.62V value is suspiciously close to a diode drop, is it possible that Q3 was placed inverted by mistake?  This is further suggested by the fact that Q3-gate is away from Vcc/2, or 4.5V, while you say you have 4.1V, which cannot be explained by "normal" resistor tolerances.
3) As a last resort, check if using two different 2N5457's in positions of Q3 and Q4 make a difference.

Good luck.