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Old 27th February 2014, 10:38 AM   #1
lamir35 is offline lamir35  Israel
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Default Trying to build this preamp

It's documented in the phantom version or normal. It only works in the mic input, and it has a lot of white noise. Any ideas what could be wrong?

I calculated the current in the collector to be 0.7mA
(I fixed the disconnected joint pointed by the arrow)
EDIT: Apparently it was miswiring


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Last edited by lamir35; 27th February 2014 at 10:32 PM.
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Old 1st March 2014, 04:29 AM   #2
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Hello Lamir,

you have posted pictures of what seem to be two different amplifiers. We don't know which one is which by your pictures and even if we did, your pictures do not show your wiring well enough that we can see what is connected where.

My guess could be "with wiring/soldering like in the second picture, it sin't surprising that you have problems with noise". What I mean to say, more politely, is you can't expect to have a circuit without noise when all the leads are close to each other, nearly touching themselves.

Secondly, did you make a wiring mistake?
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Old 1st March 2014, 04:30 AM   #3
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Furthermore there is no emitter in a Junction FET. It is Drain, Source and Gate.
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Old 7th March 2014, 10:28 PM   #4
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You could try reducing the 3Meg resistor. That high a value, specially a .25 W carbon will introduce quite a bit of noise. Use a 1Meg metal film instead.
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