Mxr - Noise Gate / Line Driver

All about modern commercial stompbox circuits from Electro Harmonix over MXR, Boss and Ibanez into the nineties.
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daniel.madeireira
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andregarcia57
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Post by andregarcia57 »

The scheme has found with some changes of errors in other schematic
someone gives him? is right?
thanks
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kdude34567
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Post by kdude34567 »

I know this post was some time ago, but I have an original 1978-1980 grey MXR NoiseGate that hasnt worked for years. I finally got around to repairing it & had some issues. Then I found this thread.

Long story short, is I got it working & it is gating. But I'm having the exact same problem as you guys had that discussed on pages 3 & 4 of this thread. It's where when the gate is engaged it's filtering down or squishing the incoming guitar signal & it's at 1/2 volume & distorted. When the gate is off, the guitar input signal is full level & proper.

It should be noted that I changed a few components on my stock pedal to those discussed in this thread. It wasn't working right before I changed the components & it started gating after I did. Does that mean the original MXR design has some flaws in it? Because the pedal never did work 100% correctly since the day I bought it back in the late '70s as a teenage rock guitarist. Anyways, here the components I changed:

1M --> 1.8K (between JFet gate & 150K)
22K --> 680 (between 5.1V Zener diode & Vcc)
680 --> 4.7K (between -IN of U1 or U1a going to gnd)
1uf --> 2.2uf (same as the 4.7K)

What did you guys finally come up with that fixed the issue?
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ranko0537
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Post by ranko0537 »

kdude34567 wrote: 22K --> 680 (between 5.1V Zener diode & Vcc)
What did you guys finally come up with that fixed the issue?
I am figthing with this too, but I think that this resistor shouldn't be replaced. Try to leave it at 22k.

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