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Question on matching transistors

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Synsound

Question on matching transistors

In building the modded MXR noise gate it was suggested to match the 2N3904's. To my understanding these are not jfets. In this case am I just looking to match the HFE values?

What is it that the matching actually accomplishes?

When the gate is on the verge of closing I get a slightly choppy break up. Could this be caused by mismatched transistors or is this just to be expected (I have never owned a noise gate)

I was curious if my matching could be a bit off due to using a cheap meter with an hfe function.
Thanks for any input.

Give a man a match and he'll be warm for a day.
Set a man on fire and he'll be warm for the rest of his life.

Silver Blues

Re: Question on matching transistors

I'm not sure what the electronic theory behind the matching is, but the choppy breakup is most likely caused by an hFE mismatch - I've heard this complaint from builders of the gate. Try to get them as close as you possibly can.

I would say as long as you use the same meter for both transistors you should be fine - if there'll be an error, it will be the same across both, i.e. the ratio of the two hFEs will be the same.

Also, how do you like the circuit? I have a buddy that's been looking to have me build him a noise gate and I've been scouring for the best possible option.

Through all the worry and pain we move on

Synsound

Re: Question on matching transistors

It seems to work well but getting it dialed in is a little touchy. I can't hear much change with the attack knob and the momentary switch doesn't seem to do anything. I don't have anything to compare it to.

I will meter my transistors again and pos try another pair to compair. Thanx

Give a man a match and he'll be warm for a day.
Set a man on fire and he'll be warm for the rest of his life.

Synsound

Re: Question on matching transistors

In reply to this post by Silver Blues

Silver,I see you checked into the single knob noise gate thread. Between the MXR and the one Boratto posted I would lean towards his. It is simple, a quick build and it works. Seems like it pretty damn close to unity. I don't know if it's advisable on his but I didn't even check the transistor values and it seemed fine with a clean shut on the gate. Either I got lucky on the values or it simply doesn't matter. That's my two cents.

Give a man a match and he'll be warm for a day.
Set a man on fire and he'll be warm for the rest of his life.

Silver Blues

Re: Question on matching transistors

Much appreciated man. I was thinking the same thing, it's so simple and if it works well it'll save me so much headache.

Through all the worry and pain we move on