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Digital Line Level DACs, Digital Crossovers, Equalizers, etc.

Audio GD DA-M1 R2R Dac Module
Audio GD DA-M1 R2R Dac Module
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Old 18th March 2017, 05:57 PM   #21
Ben Mah is offline Ben Mah  Canada
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Yes, I see the "recommendation". However in nige2000's picture he did not stack his boards and he also heard the low level noise. I can remove the standoffs and just leave the pins connecting the two boards. I doubt that it would make any difference but I supposed I won't know until I try it.

I may try it in a few days. I am happy listening to my TDA1541A right now so I have no desire to go back to the DA M1's low level noise.
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Old 19th March 2017, 04:08 PM   #22
rickmcinnis is offline rickmcinnis  United States
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I did not go back and look at what Nigel did. I do know he threw it together since he is involved in a gigantic amplifier project. I know he inserted a reclocker into the thing and found improvement but not nirvana.

Whenever the mood strikes ... I would not do it either.

Hoping the push/pull version doesn't so the same thing.

Could sharing the same power supply be part of the problem?

I won't be doing this for a couple of weeks.
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Old 20th March 2017, 01:29 AM   #23
Ben Mah is offline Ben Mah  Canada
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My stereo two-board dac is now a one channel push-pull dac. It still has the same power supply and r-c/c-r filter output.

The low level noise is gone, and the sound is pretty good, even though I am only listening to the left channel. Initial impression is that it is similar in sound to my TDA1541A dac, but maybe a bit more forward. The difference may be due to the tube gain stage that I use to raise the TDA1541A output voltage, or it may be TDA1541A technology vs Audio-gd discrete resistor ladders and FPGA, or other reasons.

Right now I don't have the urge to rip it out of my system and put the TDA1541A back in. Since I was quite happy with my TDA1541A dac and I only bought the DA M1 boards out of curiosity and not because I wanted to replace my TDA dac, this is a good thing. Now I need another channel.

The question now is did I mess up with the simple stereo dac setup to get the annoying low level noise, or was that inherent in the design and a push-pull setup is required for optimal performance? I suppose time will tell as other diyers try these boards.
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Old 20th March 2017, 03:15 AM   #24
rickmcinnis is offline rickmcinnis  United States
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I do think the designer intends this to be used in the push/pull configuration since his intention was to mimic the 1704.

I am big on separate supplies so I wonder if there could have been some strange interaction with both powered by the same supply? I am tempted to power analog and digital sections separately. When something is distilled down to as little as this DAC power supply becomes really important in my experience.

Now you have me excited.

i ordered some of their power supplies so that is why I am waiting to proceed. Great price for shunt regs and I get the feeling this fellow is very good at what he is doing so i thought I should give them a try.

THANKS for your report!

Take care,
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Old 20th March 2017, 03:53 AM   #25
abraxalito is offline abraxalito  United Kingdom
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Quote:
Originally Posted by Ben Mah View Post
The question now is did I mess up with the simple stereo dac setup to get the annoying low level noise, or was that inherent in the design and a push-pull setup is required for optimal performance? I suppose time will tell as other diyers try these boards.
Quite possible that the low level noise was due to grounding issues - with a DAC you have digital currents flowing in the 0V and they may well share common impedance with the analog 0V without fastidious attention to detail. Once you run balanced the grounding issues are taken care of by the CMRR of your next stage.
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Old 20th March 2017, 04:29 AM   #26
Ben Mah is offline Ben Mah  Canada
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I have it running in push-pull mode, not balanced.
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Old 20th March 2017, 04:57 AM   #27
abraxalito is offline abraxalito  United Kingdom
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Aren't they two different ways to talk about the same thing? How do you connect it in push-pull?
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Old 20th March 2017, 07:00 AM   #28
Ben Mah is offline Ben Mah  Canada
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According to Audio-gd:

"4 pcs modules built the NOS DAC with IIS input and working with Push / pull mode : Every channel had 2 pcs modules and the J1 must with jumpers , 1 pc module must push into a jumper to J2 for setting working for negative wave .Another module without jumper on J2 for working as positive wave . Every channel had connect J81 to J106 (The J104 and J105 can short by tins), PINA and PINB. The input signal and output signal just want to connect from one module."

I believe his intent is to mimic the PCM1704's sign magnitude architecture to eliminate zero crossing glitches.
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Old 20th March 2017, 07:15 AM   #29
abraxalito is offline abraxalito  United Kingdom
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Ah I see to some extent, my original assumption about balanced was incorrect, apologies. I can understand the sign-magnitude architecture (used originally in PCM63 as 'co-linear') but cannot yet see how its possible to convert a pure R2R type DAC to be push-pull. Without a schematic I can't make sense of the text you've quoted from Audio-gd.

I'm now completely unclear how this method of interconnecting two DACs solved your noise problem. But happy that it does nevertheless
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Old 20th March 2017, 07:27 AM   #30
Ben Mah is offline Ben Mah  Canada
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You're right, the two things may be totally unrelated and just coincidental. In post #23 I did question whether it was a screw-up with the first setup on my part or whether it had something to do with the design.
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