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Output transformers for DACs
Output transformers for DACs
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Old 14th August 2019, 06:27 AM   #161
bisesik is offline bisesik  Kazakhstan
Output transformers for DACs
diyAudio Member
Join Date: Sep 2008
Location: Kazakhstan, Almaty
Output transformers for DACs
Hi Terry,
Originally Posted by Terry Demol View Post
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.

- 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?
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).
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Old 14th August 2019, 05:08 PM   #162
bisesik is offline bisesik  Kazakhstan
Output transformers for DACs
diyAudio Member
Join Date: Sep 2008
Location: Kazakhstan, Almaty
Output transformers for DACs
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?..

Last edited by bisesik; 14th August 2019 at 05:12 PM.
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Old 14th August 2019, 05:34 PM   #163
bisesik is offline bisesik  Kazakhstan
Output transformers for DACs
diyAudio Member
Join Date: Sep 2008
Location: Kazakhstan, Almaty
Output transformers for DACs
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?..

Last edited by bisesik; 14th August 2019 at 05:56 PM.
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