Tonepad MXR Noise Gate Issue

[TeeWX]

Hey everyone, just signed up!

I've built the MXR Noise Gate (callate 2) from Tonepad. I didn't do any of the mods, but I did fill the RA slot with a 150K. There was also an orange highlighted area calling for a 47pF cap that didn't seem to be in the schematic and I put that in there anyways. I'm wondering if that is the problem. Anyways, I have two issues and they may be related.

First Issue: The pot seems to work backwards of what I'd expect, it kills more signal the further to the left you turn it, which seems wrong.

Second Issue: It kills WAY too much of my signal. At the "lowest" setting it sounds like I have my guitar volume rolled almost all the way off, and I'm playing through a boosted 5150 with an EMG loaded guitar. With the pedal off it's modern metal distortion and with it on it sounds like I've switched to the clean channel!

Anyways, any help would be greatly appreciated, it's so close to working!

Thanks!

[MrStab]

hi TeeWX

weirdly, the Threshold pot IS the "right" way round. i think it's counter-intuitive, but it does kinda make sense from a theoretical standpoint. i used a 1M log pot instead of the recommended 1M rev-log pot, so it works the other way round.

i've scoured the net like a crazy person and managed to find the best combination of mods (ime, at least) to get 2 of these working. my post here more or less summarises it:

it's pretty much this: http://www.sabrotone.com/wp-content/uploads/2011/08/MXRNoiseGate.gif except R5 becomes 4.7K, C7 becomes 2.2uF and there's a 60pF (though this time i only had 100pF) between output & inverted input on the left half of the opamp.

(from http://www.diystompboxes.com/smfforum/index.php?topic=105136.40, other handy info on that thread too)

note that i've built the modded version with Attack, Release & Attenuation controls - if you search for the modded schematic (there're only, like, 2 on Google Images), maybe you could add the pots in or use the schematic to work out how to change resistors to taste.

hope that helps some

[TeeWX]

I'm a bit of an electronics noob and so I'm having a hard time comparing that layout to mine as I have the tonepad PCB. I actually have no clue how to read that layout that you've posted. I noticed however that you have (4) 10uF caps in your layout and I only have (3). I also noticed that you have only (3) .047uF caps in your layout and I have (4)! You also talk about a 1M pot in your post and both my plans and the one you've linked call for a 500K instead. I'm kind of confused on the transistors, what is matching hFE? I have two identical transistors for Q1 and Q2 and a different one for Q3. I used a 2N3904 in Q1 and Q2 and a 2N5485 in my Q3.

Thanks!

[MrStab]

damn! i totally didnt realise i'd linked to a vero layout. it's good that you're using the Tonepad schematic though, because that's more or less what i've based mine on.

i'm about to go to bed, but when i get up i'll list out the mods i used in a form you can relate to. sorry about that.

in the meantime, there's some debate as to whether or not the 2n5088 (or whatever NPN transistors you used) need to have their HFE matched - you can do that with a standard multimeter, have a search. i matched em for both my builds just to be safe.

[duck_arse]

please! don't further the myth of the matched transistors in this circuit. they don't need it, won't benefit from it, are used in two completely different configurations. the one at the front is just an emitter follower, to provide a high to low impedance, and the second one is used as a switch across the 150k//1uf feeding the fet.

another common method used to make these things work is to reduce the value of the 1M resistor, between the gate of the fet and the 150k//1uF//second transistor collector. some go as low as 1k8. you can but try.

[MrStab]

there's some debate

i didn't pick a side, i just covered my paranoid bases!

Duck's suggestions pretty much cover the problem areas

[TeeWX]

I guess I just don't understand. Why is it killing too much of the signal?

My part list and board is EXACTLY as this one.
http://www.tonepad.com/getFile.asp?id=77

[PRR]

Lift at-least two legs of Q3. That gives No-Effect. It should be unity gain. Is it?

DC Voltages all three legs of Q1, also chip pins 1 and 7.

[MrStab]

i'll try to compare that schematic to what i used and see if anything jumps out at me. i don't know much a bout the FET issues, but i know there are some - my builds were fine with the 2n5952. try what Paul said, he knows way more than me

[MrStab]

as well as changing that 1M resistor to ~1.8k as Duck suggested earlier, i seem to recall changing the 680r resistor for 4.7k and the 1uF electro cap right after it for a 2.2uF (should go to ground).

[TeeWX]

I figured out which 1M resistor you were talking about. I replaced it with a 2.2K, I did not have a 1.8K handy. It seems like it works relatively close to how I want it but still a tad too high. However, in the FX loop it completely kills the signal like it did before...

[MrStab]

2.2k should be fine. you could always try lowering it later, once you've solved the other issue.

when you say you haven't done the mods, do you mean you have pots for Attack, Release etc., or not? because those are mods, but the Tonepad document seems to present them as stock. if  you do have these controls, for testing, you should set them all roughly in the middle, but put Attenuation on full (which iirc is clockwise, but i can't remember if i reversed that! don't think i did, though...)

i'm not too sure what you mean by the signal-killing, but you appear to be narrowing it down. could you describe your current problem in more detail? so it's fine when you run it into the front of the amp, but what exactly happens in the effects loop?

try to picture what's going on - the Threshold/Sensitivity pot is like a mega laser that'll suddenly chop off any signal, instead of gradually. i sometimes have to stop and picture stuff like that.

[TeeWX]

2.2k should be fine. you could always try lowering it later, once you've solved the other issue.

when you say you haven't done the mods, do you mean you have pots for Attack, Release etc., or not? because those are mods, but the Tonepad document seems to present them as stock. if  you do have these controls, for testing, you should set them all roughly in the middle, but put Attenuation on full (which iirc is clockwise, but i can't remember if i reversed that! don't think i did, though...)

i'm not too sure what you mean by the signal-killing, but you appear to be narrowing it down. could you describe your current problem in more detail? so it's fine when you run it into the front of the amp, but what exactly happens in the effects loop?

try to picture what's going on - the Threshold/Sensitivity pot is like a mega laser that'll suddenly chop off any signal, instead of gradually. i sometimes have to stop and picture stuff like that.

Thanks for your many posts already!

To clarify, I have no mods. There are jumpers where the jumpers are shown in the layout. I have the single 500K Threshold pot.

I play through a boosted 5150, and I also have an ISP Decimator handy for testing. I've noticed that on the lowest setting with the Tonepad MXR Gate, it seems like it is cutting the signal a little too much. If I play rather lightly, for example if I am tapping, then it kind of starts to "clean up" and doesn't sound very good. With normal picking as I play rather hard it doesn't seem to be that much different from the ISP Decimator. Now, put the ISP Decimator in the loop and it kills all of the hum but doesn't seem to effect my tone at all. However when I play the Tonepad MXR Gate in the loop it does what it was doing before. That is, pretend you're plugged into a very high gain amp, and turn your guitars volume as close to off as you can get it without it being off. It's really quiet and doesn't sound anywhere close to high gain.

[MrStab]

happy to help! it takes my mind off my depressing distortion project (damn tone controls...)

the ISP Decimator is, as i understand it, far-superior to the MXR Noise Gate, but the MXR should still be usable. just for fun: does your FX loop have a +4dB/-10dB switch? if so, does anything change when you hit that? also, do you have a guitar with passive pickups or a passive mode on your EMGs? if so, see what happens when you play passive. i doubt either of these suggestions will make a difference, but it could rule some things out.

i've just remembered you mentioned there being more parts in my link than yours - i'll have a wee look at that.

[TeeWX]

There is no level switch for the FX loop of my 5150. I find it weird that the ISP does not have any issues when run in the loop but this one does.

[MrStab]

if you run a (buffered) effect before the gate in the front of the amp, does it have the same problem as the gate on its own in the loop?
just asking because the biggest variable is that the fx loop send will probably be sending a buffered signal to the gate.