Yes, it is for the customers choice.

The whole sound amplitude will be splitted for two waves. That is it. I believe there is no any impact to the sound quality inside my transformers while splittering coils because of toroidal type of the core I use in my transformers like it happenes in non-symmetrical types of cores.
In case of ES90x8 it is prefered to use primary coils with as lower active (DC) resistance as possible because I believe the Voltage mode of ES90x8 is only for sound checking (works/not), but the only really high SQ mode is the current mode.
In terms of low DCR the primary coil in my transformer I can make is about 20H. In this case 1:1 will be quiter than 1:4.
1:1 is better than 1:4 in terms of transformers specs (FR, slewrate etc.) but the louder sound level you can grab from your DAC without FR losses the better will be SQ (as far from noise flor as possible). So 1:4 is a good compromise between DCR/winding length and resulting FR and amplitude level.

They arrived today,
I have been trying to understand the whole thing better since

this didnt fully answer my question and im quite curious:
So the 1:4 transformer is trading current for voltage,
the 8k I/V resistor is converting current to voltage (i.e amplitude).
Wouldnt a 1:1 transformer with 2k resistor result in the same voltage level
with better specs of 1:1 transformer?

Is is that you are aiming for the ''sweet spot'' with transformer roll-off around 20Khz instead of the widest FR, avoiding filtering after the transformer?

Also should I naturally use higher (32k) i/v resistor with 9038pro (4x output) and 1:4?
as you say it will require some tweaking but that would be logical starting place?

i think I am confusing the impact of the I/V resistor value, in that higher or lower resistance will not result in more or less voltage linearly...

The question remains that if 4 times the current with Pro version will result in 4 times the voltage why not use 1:1?

Yeah, they are hooked up now and the output level is much too high as I feared... anything past 25% on digital volume is too loud.
sounds great though.

Laserscrape, if the sensetive of the next stage (amplifier) is ~2V and the impedance is high (~50k for example) to achieve full power, then your impedance (resistor) value at the secondary should be 1.8kOhm in total. So, try to use 1k-2k shunt to be synchronised with your amp impedance.

The DC resistance of the 1:1 transformer used with AK4490 (for example) tens times more and sounds worse with ES.
There is more powerfull LPF in case of ES (or AK) DACs - its inner Digital LPF. My aim is not to add additional LPF if possible.
Yes, you can, but the output level will be respectively high.
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Because there is the limitation by your next stage' impedance. If you will load transformer to the really high impedance like oscilloscope, then you will see the wave level dependance from resistor value adequatelly.

But what if the next stage (amplifier) will be with 1kOhm of input impedance? In our days - it is not so rare case. I think it is not absolutely right to limit output capability of the powerful DAC when it can be more universal for different types of amplifiers including low input impedance models.

Oh, so i had the I/V resistors effect backwards! thats a relief.
With that in mind 2k was still high in volume, 500r is giving about the same output as the old op amp output stage, I use headphones so output level is probably very low.
thanks for helping me out.

Anyway the SQ is instantly appreciatable, very nice and natural sound :)


About 1:1 transformer, this is what confused me:
The 1:1 you mention here wont have low DCR suitable for Sabre DAC?

EDIT: sorry, you just explained that

What is the sensitivity (in Volts) of your amplifier to achieve the maximum output level?

it has a usable output up to 3vpp.