BeePre 2: floating signal ground?

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Deke609

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on: February 17, 2021, 06:02:00 AM
Unlike in the BP1, in the BP2 signal ground looks to be "floating" - i.e., has no 0V/chassis reference (other than by way of 0.1 uF ceramic cap that I assume is to shunt high frequency noise to ground). Is this in fact the case, and if so, is the purpose of the floating scheme to prevent ground loops?

I have an at best fuzzy sense of the possible benefit of eliminating the middle signal house ground reference in, say, a DAC -> BP2  -> Kaiju chain. I'm guessing you go from 3 possible loops to just 1 -- with the 1 formed by the rca ground connection at the DAC at one end, and the rca ground connection at the Kaiju at the other, connected in between by the floating signal ground scheme of the BP2.  In the unlikely circumstance that I'm right about the structure of this 1 loop, is there any "potential" (pardon the pun) for the notional signal "0V" of the DAC and the notional signal "0V" of the Kaiju to have different and varying voltage potentials relative to house ground, with the result that a small noise current runs through the signal ground of the BP2? I strongly assume not, and that any such differences are resolved by low impedance paths from signal ground to house ground in the DAC and Kaiju, but I thought I'd ask just to rule it out in light of a couple recent reports of hum. And apologies if I'm out to left field with this - please ignore if that's the case.

Independently of the considerations above, in cases of hum, I wonder whether it would be worth testing the effect of temporarily creating a chassis/house ground connection for each channel in the BP2 - e.g., by using clip leads to connect 4U (signal ground) to 3U (chassis connection) and 14U (signal ground) to 13U (chassis connection)?  Just a shot in the dark. Same caveat/proviso as before: please ignore if this makes no sense.

cheers and thanks, Derek
« Last Edit: February 17, 2021, 06:08:32 AM by Deke609 »



Offline Paul Birkeland

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Reply #1 on: February 17, 2021, 07:08:14 AM
Unlike in the BP1, in the BP2 signal ground looks to be "floating" - i.e., has no 0V/chassis reference (other than by way of 0.1 uF ceramic cap that I assume is to shunt high frequency noise to ground). Is this in fact the case, and if so, is the purpose of the floating scheme to prevent ground loops?
This is not the case.

What is done here is similar to what has been discussed in the Crack thread about eliminating noise from computers plugged into a Crack.

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Deke609

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Reply #2 on: February 17, 2021, 07:42:12 AM
Ah, apologies, I missed the (obvious) tie-in of the signal ground with the B+ ground.  I only saw the Z5Us at the rca inputs. Is there any chance that the 22R/reverse-parallel-diodes/0.1 uF-cap adds just enough impedance to chassis/earth ground that a tiny bit of 120 Hz B+ ripple can end up on the signal ground? Just a thought. Having suffered for months from a self-inflicted hum problem in my BP1 (from excessive "tweaking"), I know how maddening hum can be. Although, in light of my inability to solve that problem (I had to rebuild the amp), I'll put a cork in my speculations and leave the problem-solving to people with competency. 

cheers, Derek



Offline Paul Birkeland

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Reply #3 on: February 18, 2021, 06:18:06 AM
Is there any chance that the 22R/reverse-parallel-diodes/0.1 uF-cap adds just enough impedance to chassis/earth ground that a tiny bit of 120 Hz B+ ripple can end up on the signal ground?
I have not experienced this. 

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man