Output transformers for DACs

[bisesik]

Originally Posted by beardman

time to tell how the bisesik trafo play

my dac is JLsound AK4493,,with clock board and usb input

i have used 3 different output board

JLsound output board with Newclassd discrete opamp---absolute not bad

Mirand discrete output board---a little bit better

and now bisesik output trafo---by far the best

sound from the trafo..strong, dynamic,open,,nice for the ear,,lovely sound

i use the muting from JLsound output board,,so i have no click from the dac

well done bisesik
Best Bjarne

Thank you for your feedback!

Originally Posted by potstip

Hello Ivan;

4493 needs Low pass filter after dac chip. With output transformer are we eliminate this? Or still we need it before or after transformer?

Hello Erkan,

Transformers have their own FR limitation, but in case of 1:1 transformer the LPF is a bit out from the desired ~70-80kHz and it is laying in the range over 120kHz I suppose. It is a theoretical things anyway, practice is more important. In general the answer depends on the particular setup. I do not use any additional LPF within my setup, as I hear details loss if I apply any capacitor across the output no matter what is the type of the DAC (R2R, delta-sigma, SDM). Using transformers of course. The best ever way for me is to use Ext2 filter in HQPlayer without any other LPFs (DAC is in the NOS-mode) as I do not know any other (HW-transports included) way to get the maximum from any DAC but HQP.
If you want to discover the impact of the additional LPFs I do recommend to read the Rasmussen' thread here on diyaudio forum. According to his research (if to be short) - it is needed to be at -0.7dB at 10kHz and -1.5dB at 20kHz. He recommended to use Zobbel network across the output. I have tried in the past to shunt with 1kOhm+nF(0.5nF to 5nF) to be at the needed points, but as I said earlier, HQP with Ext2 makes it much better and I do not use any extra LPF circuits.

[pinnocchio]

Hi Ivan,

I have a little issue with the right channel output transformer for Ian's dual ES9038Q2M DAC. Seems like a high pitch ground loop on the right channel only (RCA). I swapped the cables left to right and the sound followed on the other channel. So I know it is the channel. I did solder the jumpers for RCA output and also removed the XLR jacks carefully due to space restrictions. What I don't know is if it is coming from the DAC board or the transformer board. I tried to separate the transformer output using ribbons but it didn't make any difference. Do you know what next I could check?

It is not loud and I have to be at 6-8 inches to hear it but I prefer silent to not lose micro details.

The transformer output sounds just amazing!

Do

[bisesik]

Hi Do,

Try to connect the right RCA's ground not at the j6 jumper, but on another point, under the grounding screw of the "Tr1 Left" transformer for example or even without grounding the right channel. I mean try to find another grounding point of the Right RCA please instead of j6. Thank you!

[pinnocchio]

ok, I'll try playing with that. I will have to ground both RCA though as my amplifiers are all build in dual mono or mono-bloc.

Do

[Flikoman]

Any info on AD1865 implemetation?

[bisesik]

Originally Posted by Flikoman

Any info on AD1865 implemetation?

I suspect that you know a little more about me, than what I have said here on this forum.

1865 is my lovely-favourite DAC right now :-)
I believe there is no any chances to achieve such a resulting SQ rather than to use high-turns-ratioed transformers right after its I_out. OpAmps are just far-far away in this terms...

[Flikoman]

Originally Posted by bisesik

I suspect that you know a little more about me, than what I have said here on this forum.

1865 is my lovely-favourite DAC right now :-)
I believe there is no any chances to achieve such a resulting SQ rather than to use high-turns-ratioed transformers right after its I_out. OpAmps are just far-far away in this terms...

Did you make a transformer like that and tested it? I have AD1865 with AD825 opamp, sound is excellent, but would like to try with trafo.

[bisesik]

Yes I did. AD1865 have a weak current output compared to other DACs, that is why the best SQ possible is at level of 0.3-0.4Vrms out (after transformer) for AD1865 in SE-mode (regular stereo mode for single chip). Differential connection is better in that terms as 0.775V (0dBu) is a kind of standard for many (tube) amplifiers. The minimum load (input impedance of the next stage) should be 10kOhm as the turns ratio is 22.

WhatsApp Image 2020-08-12 at 10.18.36.jpeg

[Flikoman]

Originally Posted by bisesik

Yes I did. AD1865 have a weak current output compared to other DACs, that is why the best SQ possible is at level of 0.3-0.4Vrms out (after transformer) for AD1865 in SE-mode (regular stereo mode for single chip). Differential connection is better in that terms as 0.775V (0dBu) is a kind of standard for many (tube) amplifiers. The minimum load (input impedance of the next stage) should be 10kOhm as the turns ratio is 22.

Attachment 878269

0.3Vrms? That is pretty low. I don't think I have a preamp with about 10, 11x gain. It can be made, but ....

I'm interested still, but it is a kind of a risk ... what is the price?

[bisesik]

Just use higher i/v loading resistor (impedance) to be at the desired output level (1.4Vrms is possible). Price is the same - $170 for pair (without PCB).