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Old 27th December 2002, 06:15 PM   #11
rljones is offline rljones  United States
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bmwrob,

I bought the ax10 in the US from a dealer. I did not have access to a service manual; I studied the pcb and drew out a schematic and then proceeded with mods. I have not tried it as a stand alone DAC.

Are service manuals easy to get; I'd like to buy one.

Jam,

I did not wish to use another op amp; I like well made transformers.
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Old 27th December 2002, 07:13 PM   #12
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Default No buffer!

The AX10 is perfect for mods since the DSD info is now PCMed so that there is no DSD noise shaping to deal with.....so, why use any buffer after the I-V converter? I have been using I-V converters (both op amp and discrete) with no output filtering with pure PCM DACs for over 10 years. Sounds fantastic. If you must, then use a large value of cap across the feedback resistor for one pole of filtering(set it to start rolling off around 16K). You should use at least 10 picofarads across the feedback resistor for stablization of the op amp. Simply run a 75 ohm resistor from the output of the op amp to the output jacks. You MUST float the output jacks from the chassis and run a ground wire for each channels ground from the ground point of the op amp (probably pin 3, ---you might try other ground points near the DAC also). No need for a transformer, unless you like the sound it adds.

If you are more adventuresome, you could put a resistor to ground and add a tube output stage.......but I would not. A very good I-V stage straight out is pretty killer.

Ric Schultz
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Old 27th December 2002, 07:23 PM   #13
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Default Forgot to add

Oops, Did not see that it had two DACs on the output. What I am suggesting is throwing away the use of one of the DACs on the output......Anotherwords you are using one of the two DACs per channel. Now, if you want pure balanced, then you can use both phases (DACS and I-V converters) and mount an XLR on the output. A super transformer might be better than running single ended out, but I kind of doubt it, as I just tried it with a silver transformer and I like the single ended (direct from the I-V stage) out better.

Another option is to have two sets of RCA jacks on the back of the chassis (one set would be non-inverted and the other inverted). This way you can invert phase in the analog domain without any loss of fidelity. Most Sony SACDs and many other discs are inverted phase. If you have a preamp with two inputs, you could just go between the two inputs for the different phase. Me, I have to unplug and plug each time, as I run my source directly into the power amp (built-in attenuator).

Have fun!

Ric Schultz
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Old 28th December 2002, 04:58 AM   #14
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Robert, I have attached the L/R output stage schematic. I'm at the moment scanning in my manual (very time consuming). If you have an ftp server I can send it to you. Otherwise I can send you a CD-R.

Ric, the AX10 already has XLR outputs (see link). What I was thinking of was if I could simplify the balanced outputs from IC341/IC391 onwards. There is a lot of stuff in the signal path before the actual XLR connectors. As I always run my machine in balanced mode, I don't need a switch to turn off the balance outputs. Any suggestions for improvement?

Robert as seen on the pictures this is the Japanese version of the AX10. It has digital inputs which I believe the U.S version doesn't have.


schematic

AX10 Rear view
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Old 28th December 2002, 06:48 PM   #15
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Default AX10 mods

Rob,
Just do as I suggested. Take a 75 ohm resistor directly from the I-V ICs (IC 310, 331 for one channel) and connect them directly to the output XLR jacks. Throw all the other circuitry away. You might want to hook up the output directly at the XLR to the output relay to get rid of any turn-on or turn-off surges. Try it! You can adjust the gain via the feedback resistor across the op amp.

Ric Schultz
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Old 28th December 2002, 08:02 PM   #16
rljones is offline rljones  United States
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Ric,

As I recall, I tried the resistor straight out and could not get a signal out. I'm not working from memory, which is a dangerous thing, but I seem to remember that these BB DACs need an I/V stage, unlike AD DACs. The transformer that I use, going direct to the XLR, bypassing the output XLR switch (as you mention, bmwrob), keeping everything fully balanced.

bmwrob,

I'd really like to get the manual from you. I'd be happy to send you a check for your efforts; just email me separately at mail@visionsurgery.net

regards, and happpy new year to all,

robert
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Old 28th December 2002, 10:16 PM   #17
jam is offline jam  United States
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Ric,

I suggested a buffer because it would help drive the transformer better and isolate the i/v stage from the transformer. A good buffer is pretty transparent.

Jam
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Old 28th December 2002, 11:51 PM   #18
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Robert,
Please reread what I wrote. I did not say to run a resistor directly from the DAC, but from the output of the I-V converter ICs. It will definitely work, and work tremendously. Try it.

Again, what I am suggesting is to leave the first op amp in place (the I-V converter) and then run a resistor from its output pin directly to the output jack. And if you want balanced then do it with the other phase as well. One 75 ohm resistor to pin 2 and one 75 ohm resistor to pin 3.

With this output stage you only have one resistor and one op amp in series with the signal with each phase. It is seriously transparent. Of course, you could always use a discrete I-V converter for even better results (if done properly).

Ric Schultz
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Old 29th December 2002, 03:24 AM   #19
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Default I/V opamp

Hi To All & Merry Christmas & Happy New Year.
Ric, You post an interesting suggestion.
Can you suggest a good opamp for I/V used &
the proper way to implement it for maximum
performance in this application.
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Old 29th December 2002, 04:09 AM   #20
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Ric, just to clarify, do you mean on pin 1 on IC311 (IC331, IC361, IC381) or pin 7? Any drawbacks by completely bypassing IC341 and the other corresponding OP-amps?
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