Debug: Thor, too low on gain?

[Auke Haarsma]

thanks for your reply.

Vref at 56k (r13) = 4.7v
Vref at 100uF (C7) = 4.7v
Vcc (is this what I put into the circuit?) = 9.5v

Capacitors are correctly placed. 10k's are really 10k's (measured them).

[stm]

Now that you verified Vref, you need to know why it is being shunted at the other end of the 1M resistor (Q3-gate).
Measure again just at the other side of said resistor, and start lifting connections that go in that node, first, the FET, then the 100n capacitor and see who's responsible for dropping voltage at that point. If it happens to be the FET, then you either have a bad FET or your pins are not identified correctly, or you have more things at that point than you expected.

[Auke Haarsma]

If I measure right after said resiter (1M gate Q3) I already have 2.37 V, seems this resistor is too big. To get a voltage of around 4v I need to drop the 1M to somewhere around 150-250k. Though the voltages seem correct, the sound isn't.

[stm]

The 1M resistor value is just fine.  You only have one capacitor and the gate of a JFET after it.  Capacitors don't conduct DC current unless they are faulty or reversed in polarity, and the gate of a JFET has an input resistance that can be well as high as 100M.

Your problem is that either the FET pinout is wrong, the FET is faulty, the cap is faulty, or you have something else connected to this node by mistake.  As I said just above, start methodically disconecting the components that are tied to the other end of the 1M resistor (opposite to the Vref point) to find out who's pulling it down!

Also, please tell us what breadboarding method are you using (PCB?) and post a couple of pictures.

[Auke Haarsma]

I use an etched pcb (form pdf version 1.1)...but.... the problem has been located!!!

As suggested by stm I desoldered some components (after reading up on what a Voltage Divider is...learning all the time -> good site: http://hyperphysics.phy-astr.gsu.edu/hbase/electric/voldiv.html.

By checking them one by one I found that the voltage only dropped with the 100uF cap in place... replaced this one and voila! No voltage drop.

The circuit right now sounds better! Seems there are a lot of sounds available in the Thor. I love how it responds to the volume control on my guitar. I really really love the way it responds to my booster. I'm gonna fit the thor with a booster in one box.

Thanks for all the help, especially to all the ROG guys! While debugging this one, I build the EA Trem with ROG mods...love it!

Keep up the good work.

[stm]

Great! Glad to hear you are enjoying Thor!