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Buffalo II

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#341
Dear Russ,

very interesting! I will buy a Legato when it is finished.

But I will not use the SE output. Instead I take the SE output from one of the balanced outputs (one less amplfier in the signal path).

If you show the schematic, you might get more input.


Regards,


Russ White said:
This is just to show how things are progressing on the discrete output stage front. This circuit is called Legato. It is a derivative of Counterpoint but without the folded cascode and with an optional buffer and some other changes. Both the input and the output impedance are quite low when this buffer is employed. When I say low I mean less than 1 ohm low. 🙂 Without the buffer output impedance is around ~200ohms(back of the envelope calc) but the input impedance is still extremely low. Low input impedance is the key to getting the most out of the ES9018.

Now some of you will spot IC1. It is an optional Balanced to SE converter. I only added it because I had room. You don't have to use it at all.

It is is exactly the same form factor as IVY-III and will come ready to work with Buffalo II. Though it will also work quite well with our COD DAC too with some component value changes.

Anyway I am posting here to get some gauge of interest.

Oh and one more critical detail. There is no negative feedback employed in the core circuit. So if you use balanced outputs there is zero global NFB.

I have tested the circuit. It is sounding very sweet.

Cheers!
Russ
Click to expand...
 
#342
IngemarR> Since this is almost exactly what I was thinking of doing I'd be very interested in how it's working out for you?
Are you happy?
What are the pros/cons?
Have you done any measurements?
Regards
Markus

IngemarR said:
Dear Bob,

I today use the LL1674:s to do passive IV on the Buffalo II with a 4k nude Vishay TX2352 resistor on the secondaries (a 10k pot then follows).

What Lundahls will you use?

Regards,
Click to expand...
 
#345
IngemarR said:
Dear Bob,

I today use the LL1674:s to do passive IV on the Buffalo II with a 4k nude Vishay TX2352 resistor on the secondaries (a 10k pot then follows).

What Lundahls will you use?

Regards,
Click to expand...


LL1674 is 1:4 (N=4) transformer so 4K on secondary is transformed to primary (is seen on primary as) with equation: Rin=Rout/(2*N^2) so Sabre DAC will see 125ohm (DCR not taken into account) . not bad but I suggest to lower as much as output level still on acceptable level - the lowest possible impedance seen by DAC the lowest THD.
Install RMAA and make some measurments...
 
#346
IngemarR said:
From the B2 manual:

"Each analog output at 0DBFS is equivalent to a voltage of approximately 92.4% of AVCC in series with 195 Ohms. So given 3.3VDC AVCC it will be about 3.05Vpp across 195 Ohms. The output will be DC biased at AVCC/2. This works out to about 16ma peak to peak at each output. The amount of bias current will depend of the voltage of the virtual ground."

Thus, 16mA AC peek-to-peek riding on a DC current for each phase (L_HOT, L_COLD, R_HOT, R_COLD) when in stereo mode (ie 4 differential DACs in || per left and right channel) when AVCC = 3.3VDC. A bit more current when AVCC=3.5 VDC. That is, each DAC phase delivers 16/4 = 4 mA AC p-p riding on a DC current.


Regards,

​

​
Click to expand...

I think manual deal with voltage output mode because in current mode output voltage depends od load and it's not defined...
 
#347
Hi Russ

I'd certainly be in the queue for a Legato, though I would probably not use the BAL/SE stage either, but use "half" the SE output (though I've yet to try this with IVY III).

What I'd really like to try- though I suspect it's not on TP's horizon 🙁- is a discrete component I/V stage that takes the balanced current output of the 9018 and converts it directly to a SE voltage output, as an intrinsic part of its design- i.e. no with balanced output at all!

Paul
 
#350
The manual deals with current mode like in my previous quote,
but if you want to calculate the output voltage at the single ended and balanced outputs, you need to take into account the gain of the 2nd OPamp and the gain in the summing OPamp.


Regards,


Marek said:
I think manual deal with voltage output mode because in current mode output voltage depends od load and it's not defined...
Click to expand...
 
#351
You forgot to include the 10k pot that is in parallel with the 4k TX2352 resistors -> load seen by ESS9018 is 90 Ohms according to your formula. Not that bad.

The load seen by the ESS9018 chip could be lower of course, but it is a compromise between output voltage and impedance, and I do want around 1-2V AC on the output pins.

No measurement made, but it sounds fine.

Regards,


Marek said:
LL1674 is 1:4 (N=4) transformer so 4K on secondary is transformed to primary (is seen on primary as) with equation: Rin=Rout/(2*N^2) so Sabre DAC will see 125ohm (DCR not taken into account) . not bad but I suggest to lower as much as output level still on acceptable level - the lowest possible impedance seen by DAC the lowest THD.
Install RMAA and make some measurments...
Click to expand...
 
#352
Yes, I like the transformer IV+filter on the Buffalo 2.

No measurements made.

Pros: elegant solution with IV and filter in the same component, no semiconductors in the signal path, you get a bit of transformer sound, blacker background (less noise), you get bakanced and SE out, galvanic isolation

Cons: heavy, cost, lots of wire in the signal path, maybe more distorsion.

Why not give it a try and compare to the IVY3?


regards,


markusG said:
IngemarR> Since this is almost exactly what I was thinking of doing I'd be very interested in how it's working out for you?
Are you happy?
What are the pros/cons?
Have you done any measurements?
Regards
Markus
Click to expand...
 
#353
IngemarR said:
You forgot to include the 10k pot that is in parallel with the 4k TX2352 resistors -> load seen by ESS9018 is 90 Ohms according to your formula. Not that bad.

The load seen by the ESS9018 chip could be lower of course, but it is a compromise between output voltage and impedance, and I do want around 1-2V AC on the output pins.

No measurement made, but it sounds fine.

Regards,
Click to expand...

Ok, If you take into account DCR of windings (33ohm primary and 605ohm secondary) you will get 140ohm...
 
Last edited:
#360
Just like to report that my Buffalo II DAC using Sowter 9454E transformers is now alive and well.

I have the DAC output going directly into the Sowters. All seems well. I'll let things burn in for a short time on my home office system, before trying it on the larger system downstairs.

ianp

ianp said:

Initially, I am planning to send the DAC output through a pair of Sowter 9545E transformers. Anything special that I need to do, or be aware of, for using the Sowters ?​
Click to expand...
​
 
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