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bisesik 23rd September 2018 08:07 PM

Output transformers for DACs
5 Attachment(s)
Hello everyone who looking for Sound!

After years of expirience the output transformers for current and voltage output DACs have been developed. Transformers tested with following DACs: ES90x8S/K2M/PRO/Q2M, AK4x9x, PCM63/58, PCM1702/04, AD1862/65, PCM1792, TDA1541/43, DSC dac. Speaking in general, transformers can be suited for any current or voltage DAC both in SE or PP modes.

These transformers are made on high permeable cores, have the low DC resistance at desirable inductive impedance to achieve the best frequency response of the DAC. Transformers provides significant sound quality improvement compared to other output versions. Your music will begin to live a new life, it will sparkle with a naturalness without plastic nervousness :-)

Here are some impressions from iancanada IanCanada's Latest RPi GB Goodies Impressions... and your tweaks, mods and hints...

Dimensions: OD=47mm, H=24mm, thickness=0.3мм

Frequency Responce of transformer with ES9038q2m at 1.4VRMS (~8kOhm in secondary loaded on 100pF cable): 20Hz=-0.3dB, 20kHz=-0.2dB (rel.1kHz):
Attachment 705302

Same, but with 470pF in parallel with secondary:
Attachment 705303

The possible output level depends on the output current of the DAC (and I/V resistance). In practice it sounds without problems on LF and HF with +/-2mA DAC types such as PCM63\TDA1541 at 2Vp level (1.4VRMS). Less powerfull DACs like PCM58 with +/-1mA have good enough LF even with 1.3Vp witout next buffers.

Here is an example of connection:
Attachment 705329

The prices for matched pair (13 pin max-mill version) are:
2 coils = 170 USD
3 coils = 190 USD
4 coils = 220 USD
6 coils = 250 USD

Worldwide shipping is included (small package service). Usually takes 2-3 weeks for delivery.
*it is possible to send with insurance (~30$) and by EMS (~40$).

Lead time depends on existing orders. Thanks.

BR, Ivan.

The relevant current documentation for my transformers available here: Output transformers for DACs

bisesik 2nd October 2018 08:14 PM

4 Attachment(s)
Have done some THD measurements of ES9038Q2M with transformers.

schultzsch 4th October 2018 10:43 AM

Very nice work you have done here!

bisesik 4th October 2018 03:13 PM

1 Attachment(s)
Thank you!

Here is the FR for a popular SMPCB ES9038Q2M board (ver.1.06, LPF=slow roll-off linear) with transformer:

Attachment 707340

bisesik 4th October 2018 08:47 PM

2 Attachment(s)
Thanks to and with permission of schultzsch here shown some approximative ("remote") comparison with LL1684 transformer (that was connected to Buffalo es3 9018 based DAC).

Attachment 707471

Attachment 707472

androa76 5th October 2018 07:17 PM

I have tested a lot with this Transformers. You did nice work. They are really optimized for current output dacs. I have not used any cap at output because at test is used 1.5 long cable with capacity of around 100pf or even more. Adding cap reduced 20khz response in my configuration. After a lot of testing we also added B1 and Tube buffer. I had a feeling that in some configurations dac couldn*t handeled load. Similar is seen in Audio note dacs.
For me this transformers are better than opamp stage. Highly recommendet.
At es9038q2m you can save a lot of time with testing opamp stages if you use this transformers.
It is pitty that this design is not intend for voltage out dacs, as far i know both constructors can*t do it because of large input impedance. Ak449x can handle till 1kohm...can*t be done something?
Congratulation this is not easy job what both of you did.

bisesik 5th October 2018 08:07 PM

Thanks for the feedback! Our transformers are still in the enhancement process. That is why this new version should be even better in terms of Load Capability compared to what you have right now.

Regarding transformers for voltage types of DACs - in process.

bisesik 19th November 2018 06:26 PM

2 Attachment(s)
Transformers for voltage DACs are done.
Turns ratio is 1:1. L=80H, DCR=450 Ohm. The output level in case of AK4490EQ is 1.9VRMS for 10K load. Some measurements was done as well:
Attachment 716522

Transformer output (green curve) vs stock NE5532 output (white curve)
Attachment 716523

bisesik 4th December 2018 12:25 PM

2 Attachment(s)
BTW, another design of transformer available for now.
Attachment 719855
Attachment 719854

schultzsch 4th December 2018 01:03 PM

Very nice work you did there. Congratulations!

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