My 312 clone is very noisy, but quiet with condenser mic and 48v ?? Anyone?

My 312 clone is very noisy all the time, and only gets quiet with a condenser mic plugged in and the phantom power on.
Does anyone here know what this problem could be?

what about with dynamic mic

describe the noise

pictures of build and wiring might help

Does you phantom switch cut the ground etc?

Its noisy with dynamic mics and even with nothing plugged in. It's only quiet with a condenser and 48v enganged.
The noise is is like a hum, probably 50hz from the 230v. ?
I will post some pictures soon.

Does you phantom switch cut the ground etc? To be honest i don't know what you mean with that Kooma?

Every preamp is noisy with nothing plugged into it, same as if you plugged something with very high impedance into it.  To hear the noise of the preamp itself, place a 150 Ohm resistor across pins 2+3 of the input XLR, to mimic a microphone's impedance without the sound of the mic capsule there.

How is pin1 of your input XLR connected? 

picture1

pic 2

pic 3

kooma said:

Does you phantom switch cut the ground etc?

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how do i figure that out kooma ? All i know is that i need to turn the 48v on for it to be quiete.
The only mics that i use are tube mics and dynamic mics , which at moment makes my preamp useless as the noise without 48v is way to loud.

mitsos said:

mitsos said:

How is pin1 of your input XLR connected?

Click to expand...

Click to expand...

Pin 1 is connected to ground on the pcb.

I just saw that the black and red wires are wired opposite on the line output on channel 1 from channel 2. But that would only cause the phase to be inverted right?

madsimilius said:

mitsos said:

mitsos said:

How is pin1 of your input XLR connected?

Click to expand...

Click to expand...

Pin 1 is connected to ground on the pcb.

Click to expand...

I thought so. Couldn't tell where the white wire was going.
Pin 1 is not a ground  (except as used as ground reference for phantom voltage) 
Pin 1 is a shield, just like the preamp chassis.  Each Pin1 gets connected to the chassis by its own short wire.

get basic grounding right and your problems should go away.

Ground pin from IEC  gets connected to chassis by a short thick wire. 
0V from your PSU also goes to same chassis conection as IEC.  (use one of the ground connections for the toroid)
0V from preamp channels go to 0V on PSU pcb.

After you get it working, you might also want to use shielded cable for your DI, the way it's crossing over the whole PCB and near the opamp might cause problems.

good luck,

I didn't build it actually, but yes i need to learn how to wire ground right anyway, if i had known i wouldn't have had this problem .
I'm on my first diy now, a pqd2.  I'm about to put the pcbs into the chassie and wire the toroidal and ground.
I've been reading alot today , but not enought to dare wiring the last wires and starting it up
The closest thing to a diy build i've done is recaping my manley vari mu and uppgrading transistors and transformers on my chameleon labs pres.

And thank you !!