2.2M resistor in silicone tonebender

[cnspedalbuilder]

Hello, quick question(s). I built the NPN Silicon Tonebender on Vero using this layout:
http://tagboardeffects.blogspot.com/2013/07/npn-si-tonebender-mkii.html

Initially sounded great (though a little bassy, not like samples I've heard), but every time I boxed it, no sound from circuit. I figured this might be because I ran 3 resistors in series to replace the 2.2M resistor, which I didn't have. I replaced it with a 1M resistor (biggest I have) and it now works, but the sound is weak, fizzy, with big volume drop. Could that be due to the resistor sub?

Also, I used the 5.6K resistor, but some use a trim pot to dial in bias on Q3. Is it possible that the fixed bias is screwing everything up?

Thanks in advance.

[anotherjim]

May point to a problem with that 4.7uF input capacitor. Check it's the right way around -  the negative plate to the top of that layout which is the signal input side. If you have it the right way around, try replacing it.

[cnspedalbuilder]

May point to a problem with that 4.7uF input capacitor. Check it's the right way around -  the negative plate to the top of that layout which is the signal input side. If you have it the right way around, try replacing it.

Ok, looks like orientation is right. I'll try testing it and replacing if needed. I am not sure that will do the trick, because I did have huge gain from the circuit before I pulled out the three-resistor 2.2M hack. But I also replaced the 2.7K and maybe the heat damaged the input capacitor.

By the way, is the 2.2M there just to eliminate the "pop" when you switch it on? If so, then I guess the resistor shouldn't matter too much, right?

[anotherjim]

Yes, it should work without the 2.2M - you can put it back later and I don't think it should harm too much if it were only 1M.
When in the box, check your wiring to all the jacks and that nothing is shorting to the case, especially the jack contact springs.

[cnspedalbuilder]

Resolved. For the archives, here is what (I think) happened. Intermittent shutoffs were probably due to two spots where I ran 2-3 resistors in series to sub for one I did not have. Pressure when I closed box probably screwed things up due to a short or stress on solder join. Lesson learned: probably better to sub a different resistor value than to hack it with multiple resistors.

Problem two: fizz when I replaced 2.2M with a 1M resistor. I think the 1M was sending too much input signal to ground thereby weakening signal. Now I realize that resistor is just mean to remove a small amount of signal which can reduce perception of footswitch click. I removed the 1M as suggested by @anotherjim and now works fine. Lesson learned: only install high value resistors right after input for pop reduction, and really no need to use them unless there is an annoying pop.

In retrospect, for the Silicone ToneBender MkII, I would replace the 5.6K resistor with an external pot to adjust bias to Q3. The fuzz is a little gated for my taste, and maybe that would do the trick.

[lukeferg]

That 2.2M resistor at the input also has another use other than stopping switch popping. It raises the input impedance of the pedal to ensure you don't lose high end. It forms a voltage divider with your pickups and causes very little signal loss. It's not in the schematic I looked at so probably safe without it. From what I remember, historically, fuzzes have lower input impedances.
Also, I would use a 10k trim pot for the 5.6k resistor. No need for it to be external. You'll likely just find the point it sounds best and leave it there.

[anotherjim]

I'm afraid the 2.2M is purely for anti-pop of the input capacitor. It will not raise the input impedance - no resistor to ground can do that. The reason it is as large as 2.2M is so it lowers the input impedance by a negligible amount. Some published schemes have 1M. Anything at least x10 the input impedance of the first transistor bias network will be fine. I happily use 10M anti-pop, because I got a pack of 100 to use up.

Many vintage fx have a lower input impedance (50k to 100k) than "theoretically" desirable (500k to 1M), and will load some treble off the guitars output. However, this turns out to be helpful with fuzzes - it automatically provides some pre-distortion eq for a smoother fuzz, but it only holds true when a passive guitar is feeding it. Indeed, some variants have a capacitor across the input to ground, which enforces a "tone knob rolled off" smooth fuzz tone.

In this case, that input pull-down should not have damaged the performance. Messing with it indicated something else was wrong. Probably an accidental short to another part of the circuit, which is very easy to have on stripboard builds.

And if it still sounds too bassy - well these vintage fx also (accidentally) relied on the poor bass response of a typical open-back guitar speaker of the day, so sometimes it helps to change the input cap (4.7uF) for something a bit smaller. Some go as small as 0.1uF.