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-   -   Output transformers for DACs (https://www.diyaudio.com/forums/vendor-s-bazaar/327794-output-transformers-dacs.html)

bisesik 9th April 2019 11:26 AM

ES9038PRo or 9018S have ~2VRMS (do not remember exactly now) at 2kOhm in the secondary. It is about 5.6Vpp. Well to be under 3Vpp it is needed to use 1k or less. Indeed your 500r (+/-) :)
Anyway kindly ask you to comment if it is good sound now after "right" resistor choised?

laserscrape 9th April 2019 11:16 PM

Quote:

Originally Posted by bisesik (https://www.diyaudio.com/forums/vendor-s-bazaar/327794-output-transformers-dacs-post5755284.html#post5755284)
ES9038PRo or 9018S have ~2VRMS (do not remember exactly now) at 2kOhm in the secondary. It is about 5.6Vpp. Well to be under 3Vpp it is needed to use 1k or less. Indeed your 500r (+/-) :)
Anyway kindly ask you to comment if it is good sound now after "right" resistor choised?

Yes, much better. At 2k it was also good and maybe having higher gain than before could sound better for DAC chip (or transformer could respond better?). With lower gain the lossless digital volume control has more resolution, that is the main benefit.

laserscrape 10th April 2019 05:57 AM

Im noticing there is a low ground loop noise, the DAC and amp ground are isolated and amp is silent with shorted inputs, so it must be from cable to transformer. There was no noise with old output stage and same cable so its confusing, the cable is around 1M twisted pair RCA.

bisesik 10th April 2019 06:55 AM

Did you connect the (-) wire of the secondary and shield to the ground of your DAC as shown in the first post of this thread? If we talking about 50/60 Hz from the mains, then of course you should avoid any loops of the ground.

laserscrape 10th April 2019 07:27 AM

no, I hadnt. thats fixed it and it sounds even better too.
I thought it was possible to seperate DAC and amp ground, but I guess that is only possible with balanced connection, which will give full galvanic isolation between devices.

bisesik 10th April 2019 08:10 AM

Quote:

Originally Posted by laserscrape (https://www.diyaudio.com/forums/vendor-s-bazaar/327794-output-transformers-dacs-post5756216.html#post5756216)
no, I hadnt. thats fixed it and it sounds even better too.
I thought it was possible to seperate DAC and amp ground, but I guess that is only possible with balanced connection, which will give full galvanic isolation between devices.

Personally in my practice full galvanic isolation doesn't "open the third eye", may be because all the people including musicians doomed to live grounded... I don't know...

:Popworm:

laserscrape 10th April 2019 08:19 AM

yes, it wouldnt be a big concern. maybe for PC and DAC isolation it could be a different story.

laserscrape 10th April 2019 08:36 AM

btw do you have any choice for I/V resistor type? metal film, wire wound etc.

bisesik 10th April 2019 09:22 AM

I believe that the sound is alreay "formed" inside transformer. But to be honest I don't have such recommendations because I do not hear any significant changes. Very subtle differences - sounds excellent with any type for my ears :)

laserscrape 11th April 2019 06:30 AM

So far I tried a couple small resistor tweaks.
500r 1/4W replaced with 500r 1W (2 x 1k 1/2w in parallel), this seemed to improve sound a bit.
But going even lower to 120R sounded much better!

The DAC volume still has a lot of headroom so I will try to go even lower if it means better SQ, these trafos have already met my expectations so anymore improvement is a bonus.
I read going too low can cause ringing , something I will watch out for.


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