Tonepad MXR noisegate 2 debug help

[MikeH]

I can't seem to get this one working!  I searched and found a thread that said I should try using a BF245(which I don't have) instead of a 2n5458, but that's about it.  I know the pinouts are correct, because I verified them against the datasheets from the manufacturer.  All solders look good, and I didn't find any bridges with the continuity tester.  So here goes:

Here is the checklist to fill out:
1.What does it do, not do, and sound like? Volume drop.  Crappy fuzz sound.  No noise suppression at all.
2.Name of the circuit =mxr noisegate 2
3.Source of the circuit (URL of schematic or project) =http://www.tonepad.com/getFileInfo.asp?id=77
4.Any modifications to the circuit? I haven't done any of the mods yet.  I have the jumpers in place for now.
5.Any parts substitutions? I used a 500k linear instead of rev log
6.Positive ground to negative ground conversion? 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? =>9.62
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 =9.62
Voltage at the circuit board end of the black battery lead =0.00

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 = 9.62
B =3.31
E =2.81

Q2
C=3.69
B=0.24
E=0.00

Q3
D=4.14
S=4.14
G=3.60

(or U1)
P1=4.10
P2=4.12
P3=3.91
P4=0.00
P5=4.10
P6=4.14
P7=4.13
P8=9.62


D1
A (anode, the non-band end) =0.00
K (cathode, the banded end) =4.13

[MikeH]

Hmmm... nothin' eh?  Can anyone tell me if my voltages for Q3 are any good?  They seem screwy to me.

[oldrocker]

Well if you did a search then you know you're not the only one who had problems getting it to work.  I assume you bought or etched a PCB.  For me this was the hardest pedal to get working.  I finally did get it going by changing out the dual op amp with two 741's instead but I perfboarded it so it wasn't too hard to do.  Keep plugging away at it and you'll get it.  Sorry I can't help more.

[kvb]

mine started working when I subbed one of Aron's J201s for the JFET.

Look to see that there is a voltage change at the gate of the fet as you play a note.
If there is a voltage change, then everything is working, but you need to find the fet with the right on off threshhold.
correct me if I'm wrong, but I think that's right.

[MikeH]

Well if you did a search then you know you're not the only one who had problems getting it to work.  I assume you bought or etched a PCB.  For me this was the hardest pedal to get working.  I finally did get it going by changing out the dual op amp with two 741's instead but I perfboarded it so it wasn't too hard to do.  Keep plugging away at it and you'll get it.  Sorry I can't help more.

Yeah, I saw this post, and actually I made my own pcb, but still, swapping out for 2 single opamps isn't really feasable.

mine started working when I subbed one of Aron's J201s for the JFET.

Look to see that there is a voltage change at the gate of the fet as you play a note.
If there is a voltage change, then everything is working, but you need to find the fet with the right on off threshhold.
correct me if I'm wrong, but I think that's right.

Awesome.  Thanks for the info, I'll try that.  And I'll start swapping in every FET I have to see if any of them work.

[PerroGrande]

There are a few things you can do to isolate where the problem is...

First, if you have an audio probe, verify that you have clean audio from the emitter of Q1. 

Secondly, remove two capacitors from the circuit -- without part numbers, this will be kinda hard to describe...

Remove the 10uF and the 0.047uF capacitors that are in the side-chain circuit.  The 10uF capacitor connects to the drain of Q3 (On the tonepad layout, there are two 10uF electrolytic caps in the lower left of the board. The cap of which I speak is the right hand one of those two).  The 0.047uF connects to pin6 of the dual op-amp.  (On the tonepad layout, this cap is just to the left of the 1uF NP cap.)

With these two caps removed, you should be able to get clean audio through the circuit.  This will reduce it to nothing except two buffers back-to-back (the side-chain is still there, but cannot impact the signal.  If you get clean audio, then we can concentrate our debugging efforts on the side-chain.  If this is noisy, then we have other issues to deal with prior to debugging the actual gate.

[rogeryu_ph]

Guys,
Check if the Zener voltage out , the correct  as they say is 5.1V dc. The FET center to me is DRAIN. The outside pin is the source connected to 10uf cap which according schematiic should be reverse so the drawing layout is wrong. Check these first. Mine I done it but louder level noise its hopeless but to use my BOSS NS2.

Roger