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Twisted Pear Buffalo Sabre DAC - Page 9

post #121 of 1283
5/2/08 at 2:36pm
Quote:
Originally Posted by fierce_freak View Post
Let me know if you remember the name of the new TI part. Just curious.
Its the OPA2827. Still in preview, but sounds great!

http://focus.ti.com/lit/ds/symlink/opa827.pdf
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post #122 of 1283
5/2/08 at 2:39pm
This part also looks excellent, but I have not got it in the IVY to test yet.

http://focus.ti.com/lit/ds/symlink/opa2211.pdf
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post #123 of 1283
5/2/08 at 3:29pm
My IVY and two other boards came in yesterday, can't wait to put it together when I have time!
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post #124 of 1283
5/3/08 at 10:14pm
To go back a few pages, how do you control the amount of digital attenuation? Is there a pot on the board somewhere?
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post #125 of 1283
5/3/08 at 10:19pm
Quote:
Originally Posted by Gautama View Post
To go back a few pages, how do you control the amount of digital attenuation? Is there a pot on the board somewhere?
Exactly, a 2K-5K pot which has its wiper connected to an ADC channel on the microcontroller. The ADC gives me an 8 bit value which I send to the DAC when the value changes from the previous state.

Its very simple, but effective, and cheap.

Cheers!
Russ
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post #126 of 1283
5/3/08 at 10:24pm
Here is a link to some source code for the inquisitive.

diyAudio Forums - ESS Sabre Reference DAC (8-channel)
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post #127 of 1283
5/4/08 at 10:25pm
Another question about I/V stage. Did you test THS4032?
Also I don’t have balanced gear yet so which parts should I use or could omit on IVY?
Did you hear any difference in sound with different chips and voltages? Which ones you tests successfully and which doesn’t work good enough in IVY.
Also could you provide a little insight in digital volume control? How good attenuation it could provide and what is workable range of attenuation: 1 –100%, or 50-100% (like SB)? Do we need to get extra parts or every thing is provided in dac kit?
Of cause it will be yours subjective opinion.
You answers will be appreciated.
Vlad
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post #128 of 1283
5/4/08 at 10:58pm
Quote:
Originally Posted by Vladco View Post
Another question about I/V stage. Did you test THS4032?
Also I don’t have balanced gear yet so which parts should I use or could omit on IVY?
Did you hear any difference in sound with different chips and voltages? Which ones you tests successfully and which doesn’t work good enough in IVY.
Also could you provide a little insight in digital volume control? How good attenuation it could provide and what is workable range of attenuation: 1 –100%, or 50-100% (like SB)? Do we need to get extra parts or every thing is provided in dac kit?
Of cause it will be yours subjective opinion.
You answers will be appreciated.
Vlad
Hello,

You would want to use all the parts on IVY.

The THS4032 is a solid choice. I have used it, it is quite good.

I don't really have a list of opamps not to try. Almost any decent dual opamp will work fine. I would actually tend to prefer good bipolar input types to FET input types. That may just be a personal bias. That said I do like the newer JFET devices from TI, and I would never say the AD8620 is bad.

I setup my volume control so that the minimum volume was at 50% attenuation (63.5db). This so that I had more pot travel to play with. I have no interest in listening to music at - 70db

Still the very best performance I personally have heard so far out of the IVY has been out of the LME49720/LM4562. It simply is very well suited to the task. yet there is no denying there exists a wide range of op amps which would work, and you may prefer a part I have not even tried yet.

Cheers!
Russ
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post #129 of 1283
5/4/08 at 11:13pm
As a side note, I was so happy with the THS4031/4032 that I cloned it as a discrete headphone amp at one point. You can read about it here:

diyAudio Forums - Diamante -a discrete medium power opamp

I still use that amp at work all the time, very nice.

Cheers!
Russ
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post #130 of 1283
5/5/08 at 7:25am
Russ,
Would the Buffalo be directly swappable with the original RAKK DAC which uses a transformer as the I2V converter?
RAKK have upgraded their DAC but yours sounds a more interesting proposition in terms of VFM.
Any news on replacement stocks? Seems like you need to make a few hundred to satisfy demand.
Steve
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post #131 of 1283
5/5/08 at 10:49pm
Quote:
Originally Posted by Evetsfrance View Post
Russ,
Would the Buffalo be directly swappable with the original RAKK DAC which uses a transformer as the I2V converter?
RAKK have upgraded their DAC but yours sounds a more interesting proposition in terms of VFM.
Any news on replacement stocks? Seems like you need to make a few hundred to satisfy demand.
Steve
Hi Steve,

I am not really familiar with the RAKK DAC or the transformer they are using for I/V conversion, so I can't say if it will work or not. I suspect it will, but I just don't know.


Cheers!
Russ
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post #132 of 1283
5/7/08 at 9:04am
Sorry, Russ - I should have given you the info but assumed you'd know the beast.
The transfo is a Lundahl LL9206 1+1 in to 10+10 out with 4K3 across the secondaries which are in series.
The primaries are balanced centre tap to ground.
Does that make sense?

Thanks
Steve
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post #133 of 1283
5/7/08 at 9:10am
Hi Steve, I think it would work, but I don't have one to test. You may need to adjust the R to get to 2VRMs. As it is the signal looks like it will be a bit hot.

I may not be the best person to answer as I generally don't prefer transformer I/V. So if anyone knows better than me please chime in.

Cheers!
Russ
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post #134 of 1283
5/8/08 at 5:57am
Thanks Russ,
As I understand it your kit can be configured to give a voltage o/p so perhaps I can dispense with the transformer.
How well does the DAC cope with the dreaded end-of-track pop?
Any news on when you might be able to get some more boards on the go?

All the best,
Steve
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post #135 of 1283
5/8/08 at 3:38pm
Hi Steve,

yes you can use the DAc voltage output no problem, the next stage should have an impedance of > 2K or so to be effective. There will be a DC offset of 1.65V at each output, so you will need to account for that.

I have never seen any end of track pop at all from Buffalo.

Well the boards will be here soon (next day or two). But it takes some time to get the modules built and tested.

Cheers!
Russ
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