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ESS Sabre Reference DAC (8-channel)
ESS Sabre Reference DAC (8-channel)
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Old 26th May 2008, 12:10 AM   #781
Spartacus is offline Spartacus  United Kingdom
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Thanks for that Ross. Have been spending much of the day reading up on PIC programming so i can play with stuff that the GUI doesn't permit. I have a background in Java and C++ so it shouldn't take too long.

Will be interesting to see if your thoughts concur with Russ'. Are you still using a Lundahl transformer connected directly to the outputs of the Sabre? How are you doing volume control?

Cheers.
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Old 26th May 2008, 12:37 AM   #782
rossl is offline rossl  United States
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Quote:
Originally posted by Spartacus
Thanks for that Ross. Have been spending much of the day reading up on PIC programming so i can play with stuff that the GUI doesn't permit. I have a background in Java and C++ so it shouldn't take too long.

Will be interesting to see if your thoughts concur with Russ'. Are you still using a Lundahl transformer connected directly to the outputs of the Sabre? How are you doing volume control?

Cheers.
So far, the sound is very detailed. I like the 9 bit mode. I don't perceive that there is more THD this way. It's very difficult to do an A/B test when I have to swap out processor chips.

The test rig has a Jensen 4:1 transformer directly on the outputs with no op-amps. It lowers the volume a lot so I have to turn up the gain on my preamp. My PCB that I am designing will use op-amp IV conversion and then a Jensen 1:1 line output transformer that is capable of very low distortion when driven with a low impedance source.

I have no plans on doing the volume control in the Sabre. I plan on using a preamp.
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Old 26th May 2008, 10:16 AM   #783
BRN is offline BRN  United States
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Ross,

Are using the I/V out on the dac? If so why when it has a voltage out.

Thanks,
Brad
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Old 26th May 2008, 12:53 PM   #784
rossl is offline rossl  United States
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Quote:
Originally posted by BRN
Ross,

Are using the I/V out on the dac? If so why when it has a voltage out.

Thanks,
Brad
Hi Brad,

Right now I have it connected as a passive transformer output. The 4:1 transformer is connected to the DAC outputs and a short cable to a high-impedance preamp input.

An op-amp IV circuit will likely have a little less distortion and will be able to drive longer cables, headphones and the like.

Still, The passive transformer on the Sabre8 sounds very good.

Transformer output stages give DC isolation between the power supplies of the DAC and the pre/power amps. Since I am using optical and coax-transformer SPDIF inputs, all inputs and outputs are isolated from the other equipment to prevent unwanted noise currents.

I live in a 50 year old house. The electric was upgraded in the 1980s but there is still a lot of noise on the power lines. I go to great lengths to get rid of pops, clicks and hum
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Old 26th May 2008, 05:42 PM   #785
Russ White is offline Russ White  United States
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Hey guys,

I have a couple DACs running now (and 4 different I/V stages so far), so I can A/B pretty easily.

I can't really tell much difference sound wise between 6-bit/true differential, and 9-bit pseudo differential. That is to say they both sound great, but that's not the end of the story. The HF noise coming out of the DAC in 6bit mode is noticeably more than it is in 9 bit mode. And this does not seem like a small amount either.

One other note. In 6 bit mode to get the best performance you should use the n/64 notch delay.

What I have noticed, is that in the 9bit(pseudo differential) mode that DAC output seems to require less filtering while still sounding very sweet. The amount of digital garbage(quantization noise I guess) that makes it out of the analog inputs seems to be much reduced.

Running the analog section with a less aggressive filter has some nice benefits (better slew rate etc) to the final audio.

If you plan a little you can use the output impedance of the Sabre to your advantage. You can create a low pass RC filter to the input of a fully differential output stage. I have had my best sounding results so far using this scheme. It results in a not exactly orthodox I/V scheme, but it is a very effective one and it keeps the components in the signal path to a minimum.

One thing is for sure, you must filter out the quantization noise. This DAC requires more attention at the I/V stage than a PCM1794A to be sure. This is especially true in the stereo mode!!! 4 times the noise per channel, and unfortunately its not all common mode.

Cheers!
Russ
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Old 27th May 2008, 02:51 AM   #786
risingtenpi is offline risingtenpi  Australia
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Russ,

Forgive the rudimentary understanding; are you suggesting to use the ~700 ohm output impedance (from memory) with a cap to make an RC low pass filter, used in conjunction with differential outputs? If so, to filter out a little quantization noise from the 192 khz output, what freq would we need to aim for? (around 96khz?)

BTW, received all my goods safe n sound. Wow, they are so much smaller than I imagined! Thanks!
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Old 27th May 2008, 05:32 AM   #787
Russ White is offline Russ White  United States
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Quote:
Originally posted by risingtenpi
Russ,

Forgive the rudimentary understanding; are you suggesting to use the ~700 ohm output impedance (from memory) with a cap to make an RC low pass filter, used in conjunction with differential outputs? If so, to filter out a little quantization noise from the 192 khz output, what freq would we need to aim for? (around 96khz?)

BTW, received all my goods safe n sound. Wow, they are so much smaller than I imagined! Thanks!

Hello, and your welcome.

Its a little more complex than just adding caps. You have to add a bit of series resistance right after the filter caps. Tis make the IVY stage not very close to zero impedance. This would normally be a bit strange. But with a fully differential output stage, it actually make a lot of sense. What more, it sounds excellent.

I will give more details later, I have not settled on exactly the best way to do it yet and I am still testing things.

Cheers!
Russ
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Old 27th May 2008, 02:26 PM   #788
4real is offline 4real  Netherlands
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I'm not sure if it had come up already, but I just saw that ESS has put some more info on their download page. Specially this document should be usefull to the DIY community: http://www.esstech.com/techsupp/Appl...PCB_Layout.pdf
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Old 29th May 2008, 05:25 AM   #789
francolargo is offline francolargo  United States
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Default Denon DVD-1930CI is similar to the 1920

Quote:
Originally posted by khundude
Does anyone know what difference is with the Denon DVD-1920, 1930, and 1940 are and if the boards are different?

Greetings,

The Denon dvd-1930CI matches the photos of the 1920 posted by Russ in almost every way. On this photo of the digital board, the region Russ modified is indicated by the arrow.
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Old 29th May 2008, 05:40 AM   #790
francolargo is offline francolargo  United States
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Default Denon DVD-1930CI is similar to the 1920

The one obvious difference is that the 1930 has an RS232 port while the 1920does not. It's connections originate in the region of the HDMI plug but I haven't investigated further. The manual describes no function for this port - it only mentions something lame about 'future compatability'. I bet they weren't planning for it to be hijacked by DIYers!

BTW, those vias with the DSD are both small diameter and closely spaced.

Frank in Mpls.
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