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Old 27th May 2008, 05:56 PM   #11
rossl is offline rossl  United States
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Hi Russ / Brian.

Good work guys. -117 THD is nothing to be disappointed about

What is the frequency spectrum of the offending noise? MCLK/64?
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Old 27th May 2008, 06:03 PM   #12
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Quote:
Originally posted by rossl
Hi Russ / Brian.

Good work guys. -117 THD is nothing to be disappointed about

What is the frequency spectrum of the offending noise? MCLK/64?
Thanks.

That's what I don't really know yet.

But check this out.

With the IVY circuit as follows:

R1-4 357R

R5-8 187R

C1 C2 C7 C8 empty.

R9-16 2K.

220pf across R13-R16

Add 12nf accross the inputs at the terminal blocks(+IN to GND -IN to GND) you get a nice 120Khz(-3db) or so filter and pretty good looking square waves. And it sounds absolutely great. At MCK/64 it is -20db.

This is what I meant by using the output impedance (195R approx) of the Sabre in stereo mode to your advantage.

Cheers!
Russ
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Old 28th May 2008, 02:02 AM   #13
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Quote:
Originally posted by matejS
On IVY connect + and G (of balanced output pins) to RCA
OK, I checked the schematic of IVY and I understand now

I think there are two mechanisms at play here:

1) You have eliminated half of the opamps in the stage so even
though the bal to SE summing OPA is very low distortion, it still may
have some sonic effect.

2) Taking one phase of the THS chip will significantly increase 2nd
harmonic distortion. That's how these balanced OPA's work, they
cancel H2 (and other even H's) what you get left with is the residual
odd harmonics with H3 being dominant. The ratio of H2 to H3 can
be up to 20dB, so you are possibly hearing a healthy dose of H2
being added.

cheers

T
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Old 30th May 2008, 02:16 PM   #14
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I have been most happy so far with the IVY configured as follows:

R1-4 357R

R5-8 178R(as supplied with early kits) or 187R (which gets you precisely at 2VRMS output).

C1 C2 C7 C8 empty.

R9-16 2K.

220pf across R13-R16 (solder under board to pads is the easiest)

Add 10nf (12nf also ok) accross the inputs at the terminal blocks(+IN to GND -IN to GND) you get a nice 120Khz(-3db) or so filter and pretty good looking square waves. For the 10nf caps I used big C0Gs under the board on the terminal pads.

To me it sounds absolutely great. At MCK/64 it is -20db.

This is what I meant by using the output impedance (195R approx) of the Sabre in stereo mode to your advantage.

I will be ready to settle on this configuration as soon as someone else besides me has a chance to listen to it and verify that it sounds good to them as well as me.

Cheers!
Russ
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Old 30th May 2008, 02:44 PM   #15
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Quote:
I will be ready to settle on this configuration as soon as someone else besides me has a chance to listen to it and verify that it sounds good to them as well as me.

Yeah yeah. I know. I'm getting to it.
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Old 31st May 2008, 02:51 PM   #16
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I am dying to get my hands on a Buffalo. I have decided to go with the DAC and feed it an I2S signal from a computer and DSD from a Denon player. As you had suggested, I will tap a wire on the "SACD" light to switch from I2S using an OTTO. The DAC will be used as a voltage DAC fro a while as I still have my heart set on build a tube based I/V stage. I am building a balanced 24v Aikido(SE version first) and would love to know what you think about using tubes in place of the IVY? If I was to build a tube based current amp to amplify the current output of the DAC and then a simple passive resistor for I/V conversion. Would this work, or might it be better sounding than amplifying voltage? My understanding is that if I increase the amount of current the DAC generates by use of a tubed(or fet) current amplifier, then using a passive resistor for I/V conversion should result in enough voltage swing. Sound right?
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Old 31st May 2008, 03:55 PM   #17
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Quote:
Originally posted by khundude
I am dying to get my hands on a Buffalo. I have decided to go with the DAC and feed it an I2S signal from a computer and DSD from a Denon player. As you had suggested, I will tap a wire on the "SACD" light to switch from I2S using an OTTO. The DAC will be used as a voltage DAC fro a while as I still have my heart set on build a tube based I/V stage. I am building a balanced 24v Aikido(SE version first) and would love to know what you think about using tubes in place of the IVY? If I was to build a tube based current amp to amplify the current output of the DAC and then a simple passive resistor for I/V conversion. Would this work, or might it be better sounding than amplifying voltage? My understanding is that if I increase the amount of current the DAC generates by use of a tubed(or fet) current amplifier, then using a passive resistor for I/V conversion should result in enough voltage swing. Sound right?

Tapping the DVD-1920 SACD indicator is actually not as easy as I had hoped. It would help if I had a schematic for the player. I will probably end up using a switch.

Tubes aren't really something I know a lot about. So I can't offer much advice there, but the Sabre chip is very flexible. You should be able to cook something up without much trouble. You have all the info you will need here and in the Buffalo manual.

Cheers!
Russ
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Old 31st May 2008, 07:03 PM   #18
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Essentially what is the IVY doing? Do I understand correctly for the use of a balanced output? There are resistors that do the I/V conversion. Then that signal is amplified with the two balanced opamps, right? What type of gain are we talking here?

Does anyone see an advantage to using the current output of the DAC and before the I/V is done, use a current amplifer and then do a passive resistor I/V conversion? Would that not be a good way to maintain the integrity of the signal?
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Old 31st May 2008, 09:41 PM   #19
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OK,
Way too many pages here to read through everything
on a public library computer!
Is this Buffalo DAC suitable for 8 channels.
I wouldn't mind having some of the Sabre chips in stereo
mode to get top performance from each chip rather than
trying to do 8 channels on one chip.
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Old 31st May 2008, 10:46 PM   #20
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Quote:
Originally posted by khundude
Essentially what is the IVY doing?

The IVY can be configured to act in at least three ways.

First as a low input impedance fully symmetrical I/V stage. Those wanting limited filtering will really like this option. Or if you want just SE output you can do your filtering at the BAL/SE stage.

Second more as a medium input impedance (<200 ohm) fully symmetrical buffer/filter. this is a sort of a hybrid configuration between a standard I/V and a standard voltage buffer/filter. This is the way I am currently using the IVY with very good results to my ears. This scheme allows for filtering of the input signal before it ever hits the active components. The fully symmetrical amplifier is perfect for this task.

Third as a relatively high input impedance(1K or more) voltage buffer/filter. This actually works very well too, and this is how some people are using the IVY with voltage output DACs like the opus.

One important note, the less capacitance you can use in the symmetrical amplifier's feedback loop the better, in fact with the THS4131/OPA1632 etc no cap there is the best. That why I like the second configuration so much. No feedback cap is required at all because with filter is before the amp.

Cheers!
Russ
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