I personally do not like transformers in the signal path, especially for IV conversion which I believe must be active in any case in order to get the maximum performance of the DAC itself. For example the PCM1794 where TI recommends an active IV stage with as much gain as possible to get the most out of the PCM1794 itself.
Normally, everyone has their own choice as it suits them.
Normally, everyone has their own choice as it suits them.
Well, honestly, I have not yet found a tube amplifier with which I would be satisfied and I listen everything from classic and jazz to techno. But, that's why I made a hybrid amp without NFB that used a 6S4P as a voltage amplifier and laterals in the output, I was satisfied with it because I canceled out the shortcomings of the transformer in the output.
Soon I will start making something similar but this time with ECC88(PCC88) due to better availability and distribution so that anyone can assemble that amplifier.
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I think you are extrapolating and applying things the way you deem suitable to you and the point you are trying to make, but during that process, you did make an error; in particular, you failed to see vastly different use-case scenarios between tube amps and transformers, and low current out DACs and transformers.
Transformers in valve gear are used due to high voltages/stage coupling issues/ extracting AC signal from the DC & superimposed AC signal... therefore, they are simply required and the necessary evil (unless OTL).
AD811 has something that no other IC has... a very low input impedance while providing great speed. The way Jung used it allows DAC to see virtual 0 dynamic input impedance. It is vastly superior to AD844; however, AD811 needs to be implemented properly to prevent oscillations. Also, AD811 does not like capacitors with long leads, the resistors should be non-inductive as well....
But with a very low current-out level like PCM1704 for example, AD811 is unparalleled as an I/V converter.
Transformers will colour the sound and slow the DAC substantially. They are far from being a good choice for DAC I/V. Maybe for something with a lot of current-out (1794), they may provide okay-ish sound, but in this particular case (1794), the simple high-quality resistor (TX2575) will work much better.
Grunf,
I looked for these PNM resistors and the selection of available values is extremely small at Mouser and DK. I normally use Susumu RG, RS, RR in the signal path, but would be willing to try these. Where did you source them?
@Vunce ,I bought these from Mouser, but as you say the offer is quite bad, I hope it will be fixed in the future because these are excellent resistors, at least around AD811 
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I normally use Vishay MELF for everything and I don't think much about it, but here I deliberately went for a better resistor. AD811 is a demanding op amp so everything around it plays a role, that was the primary reason for the new PCB with much smaller traces that can only be obtained only in SMD.
btw; I didn't get any reply to my last pm.
.I normally use Vishay MELF for everything and I don't think much about it, but here I deliberately went for a better resistor. AD811 is a demanding op amp so everything around it plays a role, that was the primary reason for the new PCB with much smaller traces that can only be obtained only in SMD.
btw; I didn't get any reply to my last pm.
Today the DAC got a new regulator, it is again Walt Jung UnivReg_122714 but an improved version and the first complete SMD version. Op amp in reg is ADA4625-1 and output voltage is 5V/120mA to pin22(output interface) on PMD100 . It is interesting that in the DAC, the regulators themselves contain four ADA4625-1 and four ADA4897, the voltage range is from 3.3V to 14V(negative and positive).
But more importantly, DALE PNM non-magnetic are a perfect match for AD811 and I recommend them for this I/V stage. Unfortunately, the problem is poor availability, as @Vunce says, but the values 1K, 50K and 33R, all 1206 are available and just what I need for my setup. The problem arises with a different DAC current when the feedback needs to be adjusted. There is also a PTN version that is not non-magnetic and Mouser has a few more choices above 1K.
But more importantly, DALE PNM non-magnetic are a perfect match for AD811 and I recommend them for this I/V stage. Unfortunately, the problem is poor availability, as @Vunce says, but the values 1K, 50K and 33R, all 1206 are available and just what I need for my setup. The problem arises with a different DAC current when the feedback needs to be adjusted. There is also a PTN version that is not non-magnetic and Mouser has a few more choices above 1K.
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