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Buffalo DAC (ESS Sabre 9008)

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Hi, all Buffalo/IVY users :)

I've been testing Buffalo for the last days and I've noticed one interesting thing.
Has anyone compared balanced/SE output vs. SE output is connected to + and GND of balanced output pins (of course, sound level will be halved in this configuration)?
I did and difference is huge, especially in soundstage and consequently in detail. And this is in favor in the second configuration! :D

Matej
 
matejS said:
Hi, all Buffalo/IVY users :)

I've been testing Buffalo for the last days and I've noticed one interesting thing.
Has anyone compared balanced/SE output vs. SE output is connected to + and GND of balanced output pins (of course, sound level will be halved in this configuration)?
I did and difference is huge, especially in soundstage and consequently in detail. And this is in favor in the second configuration! :D

Matej

Can you explain this more clearly please?

T
 
Has anyone compared balanced/SE output vs. SE output is connected to + and GND of balanced output pins (of course, sound level will be halved in this configuration)?

I think I know the reason for this difference. We have determined that with the shipped parts, the LM4562 is prone to oscillation, and are finalizing the value of some compensation caps for it. The current plan is to put some 220pF caps across the chips feedback resistors (R13-R16).

I plan on sending out a revised component pack this week to those of you from the first run. We just want to be solid on the values.
 
BrianDonegan said:


I think I know the reason for this difference. We have determined that with the shipped parts, the LM4562 is prone to oscillation, and are finalizing the value of some compensation caps for it. The current plan is to put some 220pF caps across the chips feedback resistors (R13-R16).

I plan on sending out a revised component pack this week to those of you from the first run. We just want to be solid on the values.

Wow, what a great support from you :)))

Can you also check balanced output vs. my suggestion? I've tried balanced and it does not play harmony to me (but I do have cheap balanced cables).

Cheers,
Matej
 
I think I know the reason for this difference. We have determined that with the shipped parts, the LM4562 is prone to oscillation, and are finalizing the value of some compensation caps for it. The current plan is to put some 220pF caps across the chips feedback resistors (R13-R16).

So I misspoke a but here (long weekend, coffee still kicking in). The LM4563 is not actually oscillating. There is just some HF noise from the Sabre that needs filtering, which is the job of the additional caps. This is true on the balanced outputs as well.

Can you also check balanced output vs. my suggestion? I've tried balanced and it does not play harmony to me (but I do have cheap balanced cables).

Using the THS outputs single-ended like this actually adds a lot of noise and distortion, due to uneven loading of the THS outputs/feedback. My guess is the distortion is even-order harmonics which sound okay. I think you will like the balanced outputs more once the proper filter caps are in place.

The current plan for the updated components is this (may still change slightly in the next day or so):

-> R1-R4: 178R (as originally shipped)
-> R5-R8: 357R (as originally shipped)
-> R9-R12: 2K (replaces 1K shipped, to fix SE gain)
-> C1, 2, 7, 8: Omit
-> Add 220pF MKP across input terminal block pins (+ to GND and - to GND, both channels)
-> Add 22-220pF MKP across R13-R16
Possibly replacement PIC with change to 9-bit quantizer

I will post pics of the cap additions as well.
 
Some notes about how the Buffalo/IVY measurements so far.

Dustin has graciously measured the Buffalow/IVY in a pretty basic configurations prior to my latest round of design changes (based on his feedback).

IVY on its own was measuring a very solid 133db DNR and -117db THD+N. This is actually a bit better than I had expected. :)

The Buffalo/Ivy combo was doing 122db DNR in the configuration Dustin was using (the limiting factor here being HF noise from the DAC) and -117db THD+N. Still excellent, but I know it can do even better.

This is the reason for the slight circuit change(input LPF). The combo has not been tested yet in the new configuration. But I ave good reason to believe we will get better DNR.

By way of example, my PCM1794 board has much less HF energy coming out of that DAC. This is very apparent in A/B tests. using similarly configured IVYs. Bottom line is the ESS chip just needs more attention to clean up the analog signal.

Dustin only has so much time, so he has not tested the latest changes I have tried. Maybe at some point.

If he can't do it I will see if some of my other friends can.

In the end I don't want to end up getting tied up just chasing numbers. It sounds excellent with the current setup, and the that's the main point. I think the numbers will be improved also. We know based on the limited measurements I have so far that the combo measures well, and I expect its even better now.

The main thing we learned on the IVY is that the THS4131 does not like a pure capacitive load, so you cannot use a feedback cap of >240pf or so without adding some series resistance. With the filtering on the front end you actually should not need any cap there at all.

Hopefully this sheds some light on the design process and will help others designing output stages for the Sabre chip. :)

Cheers!
Russ
 
rossl said:
Hi Russ / Brian.

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

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
 
matejS said:
On IVY connect + and G (of balanced output pins) to RCA :D

OK, I checked the schematic of IVY and I understand now :nod:

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
 
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
 
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?
 
khundude said:
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
 
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?
 
khundude said:
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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