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-   -   Salas DCG3 preamp (line & headphone) (https://www.diyaudio.com/forums/analog-line-level/296406-salas-dcg3-preamp-line-headphone.html)

nashbap 1st March 2017 06:42 PM

Quote:

Originally Posted by Salas (https://www.diyaudio.com/forums/analog-line-level/296406-salas-dcg3-preamp-line-headphone-post5004951.html#post5004951)
I also use no SLB in my DCG3. The only one SLB of the whole system is located in the power amplifier. My DCG3 chassis has a bolted wire connected to mains earth. The signal ground is again bolted to chassis with a thick wire taken from one point only where the In-Select returns line and the channels input coax screens meet at the volume pot's return points bridged. Pot's metal parts are already at chassis potential because mechanically secured with an L bracket. DAC, preamp, power amp, are all using three wire IEC. No ground loops buzz in the background with ear on the HF horn's mouth.

Salas I thought that the purpose of a SLB/connection is only as a safety device that would permit current to be transmitted from the PCB or PSU to chassis if there was a catastrophic failure. This would be in addition to the mains earth to chassis connection. Maybe it is only needed in large current consumers like power amps?

nash

Salas 1st March 2017 07:04 PM

It's a safety device when you need the signal ground lifted from mains earth if a direct connection causes buzz in a system. In case of failure the SLB turns almost direct.

Salas 1st March 2017 07:15 PM

In other words SLB is an electrically safe ground lift scheme.

nashbap 1st March 2017 10:55 PM

Quote:

Originally Posted by Salas (https://www.diyaudio.com/forums/analog-line-level/296406-salas-dcg3-preamp-line-headphone-post5005008.html#post5005008)
It's a safety device when you need the signal ground lifted from mains earth if a direct connection causes buzz in a system. In case of failure the SLB turns almost direct.

OK but if a resistor or CL60 is inserted in parallel with a diode bridge connection as is typical we still have a direct connection so the signal is not lifted. Maybe I misunderstand. I measured around 0.15VDC and around 9.0VAC between the DCSTB G point and chassis.

nash

Salas 1st March 2017 11:04 PM

When referenced with a resistor then its a safety ground loop breaker. Not direct again.

drpro 2nd March 2017 12:40 AM

I have finally started my build. A quick question regarding R3 on the DCG3 board. The schematic shows a 150R resistor. Teabag supplied 221R in the kit. Has there been a change, 221R ok to use or simply a mistake packaging all of the small parts.
Thanks
David

Salas 2nd March 2017 12:50 AM

Its on purpose. He found 221R better matching his J3(Q5) batch for circa 5mA in circuit current where my batch was lower average IDSS.

drpro 2nd March 2017 01:12 AM

Got it, thanks Salas. Just wanted to be sure.

AIM65 2nd March 2017 05:37 AM

Quote:

Originally Posted by drpro (https://www.diyaudio.com/forums/analog-line-level/296406-salas-dcg3-preamp-line-headphone-post5005297.html#post5005297)
Got it, thanks Salas. Just wanted to be sure.

You could take a look to Teabag's blog, it contains useful information about the kit

http://www.diyaudio.com/forums/blogs...er-supply.html

AndrewT 2nd March 2017 10:31 AM

Quote:

Originally Posted by MagicBus (https://www.diyaudio.com/forums/analog-line-level/296406-salas-dcg3-preamp-line-headphone-post5004903.html#post5004903)
Perhaps the scheme is not as clear as I would like. Circuit GND is not connected to chassis nowhere except at one point through the SLB. The rest wiring from pcb to inputs/outputs is as your suggestions

your sch says otherwise.
Pin1 is shown connected to a symbol. The other pin 1 is also connected to the same symbol.
The signal returns on the two RCA/Phono are shown connected to the same symbol.
That tells me you have taken the signal returns to the same chassis as the two pin 1 are connected to.


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