Hum in Balanced Mode in Balanzed Bride Of Zen

[Erlend Sæterdal]

Hi all diyers ! I have built 2 different examples of the Balanced Bride Of Zen. One for myself and one for Copenhagen Hifi Club.

Both of them uses the Twisted Pear " Darwin inputselector". On this inputselector there is 100 kohm from phase to ground by the relays at the input and as well at the output.
Both of them have massive hum when connected in Balanced mode to a balanced power amplifier.
When RCA is used there is no problem. I do not use the pots at the output.

Can anybody help ?

Greatings from E. Sæterdal Copenhagen.

[Nelson Pass]

Could be a lot of different things, but ground loops and
oscillation are where you start.

Is there a power transformer in the preamp?

Is it near the circuit?

Are you sure the circuits really have the same ground?

Are there Gate stopper resistors on the Gates of the devices?

Is there some output resistors in series with the outputs?

[Erlend Sæterdal]

Originally Posted by Nelson Pass

Could be a lot of different things, but ground loops and
oscillation are where you start.

Is there a power transformer in the preamp?

Is it near the circuit?

Are you sure the circuits really have the same ground?

Are there Gate stopper resistors on the Gates of the devices?

Is there some output resistors in series with the outputs?

I have not tried to measure it with Scoop. Maybe my input impedance is to high. I have done really many preamps in my life so I do not think there is any loops. Maybe there is a problem with the extra ground on the selector.

There is a transformer but I am sure its not a problem. No hum in single ended mode.

I use Gate stoppers. I use 500 ohm at the output.

[Nelson Pass]

Originally Posted by Erlend Sæterdal

There is a transformer but I am sure its not a problem. No hum in single ended mode.

Are you using XLR connector or twin RCA for inputs?

And you did not answer my last question.

Take the transformer out of the box and run it from a couple
of feet away and see what happens.

[Erlend Sæterdal]

The very first try was with the transformer in a seperate box.
I use XLR for inputs and RCA and I use a Darwin Relay selector. There is 100 kohm resistors on the selector both at the input and the output to ground.

The input impedance is 22 kohm and 50 kohm in the 2 Preamps. At the ouput there is 100 kohm on the board to ground and 100 kohm on the selector print.

R 15 is 500 ohm and 160 ohm.

[Nelson Pass]

OK, but what resistors are there in series with the inputs and outputs?

[Erlend Sæterdal]

In series with the output there is 500 ohm Vishay Bulk Foil SMD. And 100 kohm Vishay 1 W Bulk Foil to ground.
In series with the input 1,5 kohm Vishay Bulk Foil 100 kohm 1 Bulk Foil to ground. Gate stopper is 330 okm Carbon.

I am a little afraid about those Vishay resistors because I have bad experience with Ruepoint resistors. They made some circuits unstable. Now I am sitting changing the resistors from input to ground to Takman 22 kohm metal film. Also I change the R 15 to 200 ohm Takman from 500 kohm Vishay.

[Erlend Sæterdal]

Sorry Sorry Sorry for taken your time. I think I just found my problem. R 15 did not have contact with one of the sources on IRF 610 in each channel. No connection between the 2 sources.

[Gyuri]

All's well that ends well.
Is it true, Papa?

I committed a similar mistake already.
And I was surprised meanwhile.

[Erlend Sæterdal]

Originally Posted by Gyuri

All's well that ends well.
Is it true, Papa?

I committed a similar mistake already.
And I was surprised meanwhile.

Have a nice day !