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

MagicBus 2nd March 2017 11:40 AM

1 Attachment(s)
Yes, I can see the confusion. Schematic updated!

AndrewT 2nd March 2017 11:58 AM

disconnect the two Pin1 from the audio.
Pin1 goes to chassis at the incomer.

The screen does not carry any signal, but it does carry interference.
You should not be connecting that interference to the audio side.

MagicBus 2nd March 2017 12:14 PM

Understood, but... how should the DCG3 be connected to input signal?

AndrewT 2nd March 2017 12:27 PM

pins 2 & 3 pass the signal.
The amp reads their difference and process that to become the output.

Do you remember that a signal needs two wires and those two wires should be close coupled along their whole route from source to receiver?

MagicBus 2nd March 2017 12:42 PM

But my DCG3 setup is pseudo-differential. It cannot amplify the difference at it's inputs!

AndrewT 2nd March 2017 05:56 PM

Quote:

It cannot amplify the difference at it's inputs!
it must, it cannot work any other way.
The signal arrives over two wires, the amplifier reads that voltage difference and processes it.

That is why it is important to keep the two wire connection close coupled all the way from the source to the receiver.

nashbap 2nd March 2017 05:59 PM

Connect both XLR pin1's to the chassis is what Andrew is suggesting. You have RCA signal reference connected to the DCG3 so that should work fine too.

nash

MagicBus 2nd March 2017 07:15 PM

Actually, this is what I do at the moment and works fine, but I'll test it like post #1511 as I believe signal pass through chassis/SLB. I can only tell when I check this! Eventually, I may do the R7 mod.

nashbap 2nd March 2017 07:19 PM

Balanced build
 
4 Attachment(s)
Please see pics of my completed balanced build.

R7's are lifted and linked together.

I have been experimenting with XLR pin 1's and in this build for balanced use only the lowest noise is with pin1's to chassis which is where I have them now.

My attempts at installing a SLB have not been successful. I have tried at the DCSTB G and at the DCG3 G points but they both introduce a buzz. With no SLB and XLRpin 1's to chassis the amp is very quiet.

I will be replacing the 11/2 in heatsinks with 21/2 ones very soon. At 130ma they are getting around 52C with lid open and 64C with the lid on at ambient 22C.

Just a note that with R7's linked adjusting the DC offset of one phase effects the other.

My initial impression of the sound is that the stage is a bit wider and the sound more revealing than my BA3B/SalasBIb. Depth about the same although I feel the sound has moved a bit forward but the separation is outstanding. All the positions of the performers seem correct. A bit of harshness in the violins but I bet after 100 hrs that will be gone.

Thank you Salas for sharing your designs with us and for your very generous support. Thanks Tea-Bag for another excellent PCB production and for all the effort taken in providing matched parts.

nash
__________________
F5TV3, AVC, BA3 bal pre

MagicBus 2nd March 2017 07:54 PM

Nice built Nash!
What are these resistors from XLRs to inputs? Also, is there any connection from GND to chassis?


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