MXR Noise Gate Tonepad Revisited Need Help

[Zipporello]

Hi all,

i've recently builted the MXR Noise Gate by Tonepad without mods: http://www.tonepad.com/getFile.asp?id=35

i've also change the 1M resistor -> 1K8 between Q3 and 150K resitor and the 680R resitor -> 4K7 resitor.

It works. But it filter too much.

What components i have to change to reduce the filter? This pedal reduce the noise too much even with the pot turned all left.

Really thanks for your patience.

Stefano

[Kipper4]

which one did you build version 1 or 2?
In version 1 the 10uf electrolytic going to the fet should have the + side going to the fet.
not as drawn in the layout.

[duck_arse]

you can reduce the gain of ic1a by reducing the 1M from pin 1 to pin 2.

I'm going to have to breadboard this to see how it works someday.

[Zipporello]

@kipper4

i've built the versione 1.
how could it possible it still work?
so, if i invert the capacitor i'll have less noise reduction?

[Zipporello]

@duck_arse

really thanks! so, i reduce the feedback resistor of first opamp.

i'll try.

any other suggestion? 

[Zipporello]

problem resolved!

really thanks to all! 

[Kipper4]

for future referance should anybody else have thye same problem it would really help if you could
please tell us what was wrong and how you put it right Zap?

[duck_arse]

@kipper, I know you were having probs with this circuit, and I wasn't helping, but I've thrown it on the breadboard and found a few whys and hows.

the original circuit as drawn didn't work, using a j210 and a pair of bc548b's. I looked at the signal on the gat of the fet, and it was only moving about 400mV, gate open to closed. this might be enuff for a j201, but we aren't using one here, are we?

so I looked up the mods. the first thing is to add a 68pF across the 1M on pin 1+2 IC1, this will reduce some of the switching mess from the op-amp.
I changed the 680R//1uF on pin2 to 4k7//2u2. this will shift the low-freq cutoff way down.
I changed the 1uF NP in series with the base of Q2 to 10nF, if only because the value is much nicer.
the 10uF cap connected to the fet should be plus towards the fet.

and the most important part, the change that made it gate, I changed the 1M from the transistor collector to the fet gate to 2k2. gate now swings, open and closed, between ~4V5 and 1V. the resistor only needs to be small enough to get the voltage swing the fets gate wants, as per its spec sheet. I tried 150k, 47k, 2k2, all worked.

so, now it's working, I might even build one. I hope this is of some help to someone; any questions, let me know while it's still on the breadboard.

[Kipper4]

Thanks mate thats really helpful I'll try  those.
Thanks for taking the time and sharing the knowledge.
I'm sure we will all benefit from it.

[Ajay]

@kipper, I know you were having probs with this circuit, and I wasn't helping, but I've thrown it on the breadboard and found a few whys and hows.

Interesting, will check these... Well, once the dinner table is free again 

[Zipporello]

to reduce the filter i've increased the feedback resistor (IC1a) from 1M to 10M.

[duck_arse]

@zippo, when you say "filter too much", do you mean it lets too much noise through, or cuts out with too much signal? I think 10M is too big, and you'll need the 68pF across it anyway.

[Zipporello]

@zippo, when you say "filter too much", do you mean it lets too much noise through, or cuts out with too much signal? I think 10M is too big, and you'll need the 68pF across it anyway.

cuts out with too much signal.
where i'll need to put the 68pF?

[duck_arse]

so I looked up the mods. the first thing is to add a 68pF across the 1M on pin 1+2 IC1, this will reduce some of the switching mess from the op-amp.

across the new 10M. it will cut the gain at high frequencies, and there is a lot of switching crap comes out of that opamp. I would have thought more gain there would make the problem worse.

I'll think about this tomorrow.

[Zipporello]

like this? http://img440.imageshack.us/img440/5020/42oh.png

[Kipper4]

pm sent
emailed

[Zipporello]

pm sent
emailed

i don't understand. 

[Kipper4]

I implimented all the suggested mods except the 68pf which im confused about.
Does the 68p go from pin 1 to 2 of IC or im parallel with the 1M?
i used the 150k between the transistor collector and  fet gate.
Its gating too much now.
im still using a 2n5458 fet and 2x 2n3904

should i now be using a j201 and some bc transistors as you said you are using?

[Kipper4]

right latest update
I'm using a j201 and 2x  2n3904
its doing a good job of gating now however
the gate shuts too quickly (cutting the ends off long notes that are fading and gating shut when i pick lightly.
I trialed it with a distortin (tone freak severe volume above guitars unity signal )
and it still shuts off really fast.
can i swap out the 2k2 between the transistor collector and the fet gate to try to make the transisition smoother ie gate close a little later?

[Kipper4]

right after a few more mods i have it working
smoothed out the decay by replacing the 1u in the place of the 2u2
replaced that 2k2 from transistor collector to fet with a 1k8
now it gates ok but ifeel it needs modding a bit more yet becuase most of the sensativity pot is useless.
i doubt i even go half way up the pot before it stops gateing.
Laters
Rich