Output transformers for DACs

[bisesik]

Hi Terry,

Your transformers look great.

Thank you.

Do you have any distortion measurements for them?

Sure I have distortion measurements, some of them you can find in this thread earlier.

For example Jensen and Cinemag both have THD versus freq and level.
They also both have effect on distortion of varying drive impedance which is really important.

Yes, there are a lot of measurements in the net, but I do not see any benefits to make such general measurements without the relation to the DAC chips to which I do making my transformers for.

Theoretically I can make some remote comparison measurements like I did for this Sowter' transformer (compareble specs to mine): 9762 DAC Interface Transformer :

But there can be some unaccounted things during measurements at both sides 🙂 ...

If somewhere in the internet there will be a straight measurement of the branded transformer connected to the real DAC chip, then I agree it will be useful to make similar measurement. AFAIK Jensen/Cimemag/Lundahl/Sowter have not use so called "nanocrystallyne" core material. From practice I know that in terms of Sound Quality it is more important than THD measurements... So that is why I believe the real listening tests gives to me and to my clients much more benefits than the abstracted measurements.
But I am ready to discuss measurements if you will point to any you want to compare with.

Lastly Jensen also have required termination (RC snubber) to achieve proper Bessel LPF response, IOW
no ringing or overshoot with a square wave and linear group delay.

Can you point to this findings\discussion please?
I have discovered this direction previously and found some solutions, but again it is the task more for the specific case of specific DAC usage, than to transformer's specs.
Take a look to the measurements I have made for different DACs and different digital LPFs:
1) PCM63 in NOS (no digital LPF) mode loaded to my transformer (without extra circuits after or before):

2) ES9038Q2M (chineese Smpcb 1.07) with regular i/v stage on 5532 OpAmp (factory default) in different digital LPFs (it is impossible to use NOS mode as you know):

fast roll-off linear phase

slow roll-off linear

fast roll-off minimum phase

slow roll-off minimum phase

fast roll-off apodizing

fast roll-off hybrid

brickwall filter

Just for reference: as you see the ringing issue is not the transformer's issue. But if you really need to fight somehow with DeltaSigma artefacts as LPF' ringing, then I can recommend to use RC snubber in parallel to the secondary coil.

Here are some findings:
RAWvs-Snabber — imgbb.com

As you see, it is possible to fight with ringing, but the speed of the signal will fall a bit.
Later I will try to find the most-flat-top version for Ian's dual 9038.

Also
- do you make microphone pre amp input transformers?
- quad filar OP transformers?

Technically it is not the problem to make such transformer, but it is not economically profitable for me at the moment (have no time and enough financial motivation for R&D).

- What are the advantages of Toroidal core?
Thanks

I believe it the only way to use all the benefits of this core material. If you will split this material then the Efficiency will drop sharply (the situation differes even from amorphus material not to mention permalloy or iron).

 

[bisesik]

As mentioned above here I just have done the measurements of Ian's Dual ES9038Q2Mpi DAC with my transformers (3.9k Ohm load) for different source sample rates and square signals (filter is linear slow roll-off).

SR768kHz - 1kHz

SR768kHz - 20.2kHz

SR384kHz - 1kHz

SR384kHz - 24kHz

SR192kHz - 1kHz

SR192kHz -24kHz

SR96kHz - 1kHz

SR96kHz - 24kHz

And the final, most popular 48kHz (44.1kHz - will be similar):

SR48kHz - 1kHz

SR48kHz - 12kHz

So there is a question: around what measurement do we want "to dance" trying to fight with ringing?..

 

[bisesik]

As you can see the ringing frequency differs from one sample rate to another within the same signal frequency. I do not understand how it is possible to fight with all of them at once using the one snubber value?.. 🙂

 

[Simon1972]

Bisesik,
What's delivery time like currently? I'm interested in a pair and pcb for ians 2x9038qm board.

Simon

 

[bisesik]

Hi Simon. Delivery time is about 2 weeks to EU or USA, but is still needed ~month for manufacturing due to existing orders before.

 

[Deleted member 537459]

Thi output is the best i listen. I try opamp sparkos, burson v6 vivid 1612ecc lundahl. The best is this trafo output!!! Epic job! Thanks
Some guys buys from italy is my friends, they listen this output stage and were enthusiastic!!

 

[TioFrancotirador]

Thi output is the best i listen. I try opamp sparkos, burson v6 vivid 1612ecc lundahl. The best is this trafo output!!! Epic job! Thanks
Some guys buys from italy is my friends, they listen this output stage and were enthusiastic!!

I got similar experience. 100% agree!

 

[Deleted member 537459]

Wich and why you use on c1a c1b c3 and r3 optional??
For what?
Reguards

 

[bisesik]

Thank you guys for the feedback!
It is the first version of PCB, it was just for my experiments with LPF and i/v at the primary side of transformer (you can find similar components in Ian's LL I/V PCB (DocumentDownload/LL1544aTransformerIvSch.pdf at master * iancanada/DocumentDownload * GitHub). It is not needed normally and probably will be deleted from PCB if the next versions of PCB will occur.

 

[Deleted member 537459]

And for use rca need solder point right?

 

[bisesik]

Yes, for RCA it is needed to short J5/J6

 

[bisesik]

Here is the schematic of the i/v board:

 

[Deleted member 537459]

Thanks!!

 

[soundcheck]

I might also interested in the transformer HAT solution that attaches to IANs dual-mono HAT.

The question I have relates to the amp integration.
I'm currently running an Abletec amp directly connected to my current ES9038Q2M DAC from Audiophonics.
I'm also running 100% software volume control on that DAC .


Can the output level of the transformer be adjusted or customized to better integrate with the amp gain/speaker sensitivity for minimum losses in conjunction with 9038Q2M software volume control??
Usually 2V DAC out is much too high as output voltage for direct DAC->amp coupling. If you'd go balanced out things even get worse.

Thx.

 

[bisesik]

Hi soundcheck,
The answer was here in #146
The given values are the impedances for targeted level: resistors R1a, R1b, R2a, R2b in parallel with the input impedance of the next connected stage (your Abletec Amp for example). Just use the values you needed to be at the desired maximum volume level. Tell me the input impedance and sensitivity of your Amp and I can tell you values of the loaded resistors.

 

[soundcheck]

Great. Thx.

 

[soundcheck]

One more.

Could you supply the HAT without jacks being soldered?
I'd directly solder wires from HAT to the amp.

Any idea when you'll release REV2 of your HAT? You mentioned earlier that
you'll apply some changes.

THX.

 

[bisesik]

Sure, it is up to you, you can solder everything by yourself. I am not ready for REV2 right now, don't want to make rev3 very soon after it 🙂
Transformers can be detachable for easy migrating from one PCB to another if needed.

 

[paoloilpizzo]

Hi Bisesik, I’m interested to buy a kit (trafo + board + components) to put upper the IAN 9038q2m hat dac.
Do you sell it? Which is the cost and how to buy?

I am also interested on the difference I can obtain respect the usage of IAN I/V board with the LL1544A trafo. Which improvements I can obtain?

Now I’m using the opamp board with opa1612 with unbalanced output and it sounds good but I understood that the trafo approach is much better in terms of sound quality

 

[Deleted member 537459]

I try all output stage, opamp burson v6 with linear supply(better of lifepo4) ll1544a, and rhis trafo for me is the best, i buy another 4 pcs for my friends.

Bisesik, i buy 9038pro, can you said me the resisor i need change or is good this setup i have.
Thanks