Sjöström Audio DIY forum

Projects => Preamps, buffers => Topic started by: yiancar on November 02, 2015, 10:32:38 AM

Title: UBC01 for QSXM3
Post by: yiancar on November 02, 2015, 10:32:38 AM
heaveno
I get a real good hum out of the balanced output of the ubc01 when connected with a qsxm3

here is how my wires are connected.
Title: Re: UBC01 for QSXM3
Post by: peranders on November 02, 2015, 07:06:06 PM
Is your ground connected in your balanced wiring?
Title: Re: UBC01 for QSXM3
Post by: yiancar on November 02, 2015, 09:13:36 PM
Pin 1 of the xlr is connected to the shield of the wire which connects to theground of the ubc01
Title: Re: UBC01 for QSXM3
Post by: peranders on November 03, 2015, 06:58:10 AM
If you disconnect one channel (the balanced output) does the hum disappear? I suspect that you have a massive ground loop.
Title: Re: UBC01 for QSXM3
Post by: yiancar on November 03, 2015, 02:12:51 PM
if i disconnect one of the xlrs completely, yes it does
any suggestions of how to rewire my ground?
Title: Re: UBC01 for QSXM3
Post by: peranders on November 03, 2015, 06:59:54 PM
Try to identify how a ground loop is created.
Title: Re: UBC01 for QSXM3
Post by: yiancar on November 04, 2015, 12:28:43 AM
By disconnecting one by one the grounds?
Title: Re: UBC01 for QSXM3
Post by: peranders on November 04, 2015, 06:19:21 AM
Yes. This should be quite visible.
Title: Re: UBC01 for QSXM3
Post by: yiancar on November 07, 2015, 07:18:03 PM
I have tried all possible round combinations, and virtually no change.

However i released that if i remove the inputs from the qsxm3 and i put jumpers j1 and j3 it is dead silent.

what does this man? is it my turntable?
Title: Re: UBC01 for QSXM3
Post by: peranders on November 07, 2015, 07:53:57 PM
Your tone arm must be grounded via a separate wire to the QSXM3. Is that the case?
Title: Re: UBC01 for QSXM3
Post by: yiancar on November 07, 2015, 08:18:24 PM
Yes its done. By the way the right channel has a louder hum than the left
Title: Re: UBC01 for QSXM3
Post by: peranders on November 07, 2015, 10:20:24 PM
So...

Cartridge connected to the QSXM3 and then via unbalanced to the amp = no hum
Cartridge connected to the QSXM3 and then via balanced to the amp = hum
Shorted inputs of the QSXM3 and then via balanced to the amp = hum

Shorted signal into the UBC01 = no hum?

Is that the case?
Title: Re: UBC01 for QSXM3
Post by: yiancar on November 08, 2015, 09:50:33 PM
ok tried everything again, i turned my transformer and puff hum disappeared, there is only a slight sinusoidal sound (much higher frequency than 50hz) but its down to the cartridge noise floor. I guess I can consider this normal?
unbalanced or balanced makes no difference, except that in balanced its more notable as all the volumes are louder anyway

with the outputs shorted now i get perfect silence
Title: Re: UBC01 for QSXM3
Post by: peranders on November 12, 2015, 07:17:17 PM
You mean inputs shorted?