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

Salas 2nd March 2017 07:58 PM

Your build looks excellent. Congratulations.

What are those (Shinkoh?) resistors in series with the inputs for?

nashbap 2nd March 2017 08:29 PM

Quote:

Originally Posted by Salas (https://www.diyaudio.com/forums/analog-line-level/296406-salas-dcg3-preamp-line-headphone-post5006228.html#post5006228)
Your build looks excellent. Congratulations.

What are those (Shinkoh?) resistors in series with the inputs for?

Thank you Salas and Kostas.

Yes they are matched 13K Shinkoh's. Direct from the XLR pins 2 and 3 to their respective inputs with a shunt attenuator between the PCB inputs. No unnecessary wiring needed. Maintains a very high CMRR this way. I made the shunt with Takman Rey metal films. After much experimenting on my BA3B I found this combo gives me the best balance of clarity and sonic density that I need for classical music. Better than TX2575 which I also tried. In my opinion the attenuator choice makes a very huge difference in overall sound.
You may also notice that I have used a couple of PTF's and RN60E's(25ppm, 0.1%) in key positions.
I do not have any connection from DCG3 G to chassis.

nash

MagicBus 2nd March 2017 08:47 PM

Is there any chance to test it with SE signal at one phase input and the other grounded to see if you get proper balanced output?

nashbap 2nd March 2017 09:39 PM

Quote:

Originally Posted by MagicBus (https://www.diyaudio.com/forums/analog-line-level/296406-salas-dcg3-preamp-line-headphone-post5006289.html#post5006289)
Is there any chance to test it with SE signal at one phase input and the other grounded to see if you get proper balanced output?


This is what I tested. Note R7's are linked. I connected the SE output of my CD player using a 1khz test signal on a CD. +of signal to input on DCG3 and signal reference to the G on the DCG3. I adjusted the out put of the CD player to get around 0.25VAC. I measured around 0.5VAC between Line and G on the phase to which the signal was connected and 0.25VAC between the Line and G on the other phase. Measuring across the two Line outs resulted in 0.75VAC which is 3x, the gain I have set for.
Next I shorted the R7's link to G on the PCB simulating what would be if the R7's were grounded as per the schematic and measured again. This time I again got 0.5VAC on the phase that was receiving the signal and 0VAC between Line and G on the other phase. However, to my surprise I still got the full 0.75VAC between the two Line outs.


nash

drpro 2nd March 2017 09:51 PM

Ready to purchase a stepped attenuator. From my reading either a 20k or 10k. Open to thoughts and suggestions.

Thanks

Salas 2nd March 2017 10:10 PM

20K

drpro 2nd March 2017 10:39 PM

Super, thank you Salas.

MagicBus 3rd March 2017 05:56 AM

Quote:

Originally Posted by nashbap (https://www.diyaudio.com/forums/analog-line-level/296406-salas-dcg3-preamp-line-headphone-post5006348.html#post5006348)
...However, to my surprise I still got the full 0.75VAC between the two Line outs.
nash

This and the ground to chassis problem may be because of the shunt volume control?

nashbap 3rd March 2017 02:13 PM

Quote:

Originally Posted by MagicBus (https://www.diyaudio.com/forums/analog-line-level/296406-salas-dcg3-preamp-line-headphone-post5006629.html#post5006629)
This and the ground to chassis problem may be because of the shunt volume control?

I did the test before any of that was connected. I also have the same setup on the BA3B. Today I will try SE input again and let you know. My interest in the first test was primarily to verify that the boards were working, so I want to make sure I am not giving you incorrect info.

nash

Salas 3rd March 2017 02:25 PM

How many K is the pot?


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