Tube overdrive pedal acting like a noise gate??

[ISuckAtPedals]

I used this schematic. Changed a few things The 220k resistor is a 270k, the electrolytic capacitor are two 470nf in parallel. The electrolytic on the potentiometer is a single 470nf metal film capacitor. I only changed these things because i don't have the "correct" ones. The pedal sounds great but only makes noise if i hit it hard. The tubes are 12au7 running at 12v.

[ISuckAtPedals]

Anyone care to help? My name is for real. I don't think the changes i made would affect the pedal like this?

[bluebunny]

Your subs look reasonable, although I'm not sure what you mean by "electrolytic on the potentiometer"?  There's only only cap connected to a pot and it's a 10nF (film) cap.  And are you sure your 270K really is 270K?  Can you show us pictures of your build?  Some voltages might be helpful too.

And "welcome", of course. 

[FiveseveN]

What are you powering it with? Can you measure the voltages on the valve pins?

[antonis]

The pedal sounds great but only makes noise if i hit it hard.

Due to my limited knowledge on tube behavior, I'd propose to place a grid stopper resistor of some tens of kilo-Ohms in case of that "noise" is some kind of blocking distortion..
(with secondary effort of a low-pass filter when combined with Grid-Cathode interelectrode capacitance..)

@Marc: There should be a 1μF electro on Tone pot - changed to a 470nF, according to OP..
(C4 & VR2 are interchanged in order on layout..)

[GibsonGM]

The pedal sounds great but only makes noise if i hit it hard.

Due to my limited knowledge on tube behavior, I'd propose to place a grid stopper resistor of some tens of kilo-Ohms in case of that "noise" is some kind of blocking distortion..
(with secondary effort of a low-pass filter when combined with Grid-Cathode interelectrode capacitance..)

@Marc: There should be a 1μF electro on Tone pot - changed to a 470nF, according to OP..
(C4 & VR2 are interchanged in order on layout..)

Yes.  Pins 2 and 7 of each tube should have SOME value of grid stopper in place.  10k would be ok...33k, really not that crucial what the value is as long as you don't go to high. 

If this is running on 9V...that is a bit low, honestly....but it SHOULD work.  Check that your VR1's are wired correctly, too.   I do not like gain done this way, would rather see a set cathode R and a bypass cap that may have a pot to vary its effect....gain best done with a pot between stages, IMHO, including grid stoppers after the pot.    Alter the bias enough, and you CAN get what you are complaining about (possibly, rectification).    So check the effect rotating the pot(s) has on the sound.   Maybe a 'mid-setting' on both will allow your signal thru normally (?) which would tell us your bias is off.    Unless there is some wiring error on the board not being noticed.....

[antonis]

I do not like gain done this way, would rather see a set cathode R and a bypass cap that may have a pot to vary its effect....gain best done with a pot between stages, IMHO, including grid stoppers after the pot.

I'm glad to see some of your nasty habbits remain imperishable, Sir... 

[amptramp]

Running the heaters from the 9 VDC supply reduces the emission from the tube and limits performance including a limitation on grid bias.  The grid-to-ground resistor is too small to develop much negative contact potential bias, so blocking distortion is probable.  Blocking comes from driving the grid positive, charging the coupling capacitor negatively towards the grid.  Since the R-C time constant of the coupling cap and grid-to-ground resistor is selected to pass the lowest frequencies, it can take a while for the capacitor to discharge.  During part of this time, the negative bias cuts the tube current off.

[GibsonGM]

I do not like gain done this way, would rather see a set cathode R and a bypass cap that may have a pot to vary its effect....gain best done with a pot between stages, IMHO, including grid stoppers after the pot.

I'm glad to see some of your nasty habbits remain imperishable, Sir... 

If not liking my bias to be moving around due to a changing cathode resistance - GUILTY of bad habits!!       

Yes, 9V is just too low to get good performance out of the tube.  Maybe grid stoppers can help a little, though - I don't know.

[PRR]

Gentlebeings (and bunny)-- he says he is running 12V supply.

The single Valve Caster is a known plan. I believe it often works, but can be VERY fussy about the tubes (not intended to run at 12V plate supply so VERY variable).

This DUAL Valve Caster looks to me like a world of pain. If it works at all (remember the single is fussy) then it has WAY too much gain to be innocently stuffed in a box. It is sure to oscillate unless obsessively and experimentally laid-out and shielded.

> only makes noise if i hit it hard.

That could be bad bias from using hi-volt tubes at 12V. Or it could be oscillating supersonically so bad it is always de-biased until you hit it with a hammer bigger than its own self-slamming.

"ISuckAtPedals" suggests you cut back to a SINGLE Valve Caster then post your voltages.

[amptramp]

You could use a 12U7 to replace the 12AU7 as it is designed to work from 12 VDC.  It has a maximum plate voltage of 30 VDC.