DIY XLR -> RCA Transformer

Discussion in 'DIY' started by Luckbad, Oct 15, 2017.

  1. Luckbad

    Luckbad Traded in a unicorn for a Corolla

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    The standard recommendation for professional XLR/balanced to consumer level RCA/single-ended output is the Jensen PC-2XR, but the thing is pretty expensive. In the interest of saving a few bucks, I plan to build one.

    So far, the best plan I've seen is the CineMag CMLI-10-600:

    http://cinemag.biz/line_input/line_input.php
    http://cinemag.biz/line_input/PDF/CMLI-10-600 (1).pdf

    @willsw turned me onto this and I'm hoping he can provide additional thoughts and interior pictures of the one he built.

    Is anyone else aware of good options for XLR->RCA conversion between a DAC and amp?

    I'd like to connect the XLR output of my Sonic Frontiers SFD-1 MKII SE+ to the single-ended input of my Eddie Current Super 7. I'll likely build it in a project box first, but might end up putting it in there permanently given sufficient room and motivation to avoid an unnecessary pair of cables and connectors.
     

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  2. Armaegis

    Armaegis Friend

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  3. Thad E Ginathom

    Thad E Ginathom Friend

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    Ahh.... a practical, reasonably-priced answer.

    But it would have been more interesting to watch @Luckbad build something!
     
  4. Luckbad

    Luckbad Traded in a unicorn for a Corolla

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    Oh I will.
     
  5. joeexp

    joeexp Don't ship this man FD-X1 ever

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  6. randytsuch

    randytsuch Friend

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    If you join Jensen's website (was easy), you can look at their app notes.
    See AN-003 for examples of balanced to single ended, and vice versa if you care.
    Would take two jt-10kb-d's. Pretty good chance you'll find these inside their box, imho

    Randy
     
  7. bengo

    bengo Friend

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    Have you tried an XLR to RCA cable? Is there a reason to assume such a cable (or a simple RCA cable using the SE outputs) would sound inferior to the Jensen etc?

    Good trafos are expensive, and cheaper ones, maybe even the PC-2XR you mention, will just add colouration or roll off at both ends or lose some transparency. The balanced input option on @Donald North Stellaris is $2200!

    I would recommend buying some cables and try to borrow a PC-2XR to compare the three options and see what really sounds best to you.

    Is the DAC hardware balanced? Otherwise there really shouldn't be any advantage to the transformer. IIRC some folks preferred the XLR to RCA cable option of the 3 with Yggdrasil (which is hardware balanced, so effectively 50% of the DAC chip is unused, but... tradeoffs).

    I have a personal stake in this, btw, since I own a Pavane (hardware balanced) and M-22 (single ended). Would love to see a proper 3-way comparison.
     
  8. Hands

    Hands Overzealous Auto Flusher - Measurbator

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    The Pavane's SE outputs should be transformer coupled. They sound pretty good and arguably less colored than what I remember from the PC-2XR. I would just not even worry about it.
     
  9. Cspirou

    Cspirou They call me Sparky

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    @bengo

    Transformers are a good way to deal with ground loops. Pros use them all the time.
     
  10. Armaegis

    Armaegis Friend

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    Sometimes those adapter cables grounds the negative, which can cause problems (such as if the positive side relied on the negative for some reason, or if the output buffer can't supply the current to a ground short). Even leaving the negative floating can cause issues if the dac output halves inherently rely on each other.
     
  11. bengo

    bengo Friend

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    @Marvey may be able to share some experiences / advice based on the Aficionado development.
     
  12. Armaegis

    Armaegis Friend

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  13. Thad E Ginathom

    Thad E Ginathom Friend

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    These days I have no need of balanced/unbalanced conversion. Have had in the past, may have in the future... so keeping an eye on this one :)
     
  14. Luckbad

    Luckbad Traded in a unicorn for a Corolla

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    I'm beginning to wonder if it's even worth the attempt for the SFD-1 MKII. I'm not convinced the balanced output is going to be superior. Looking at the PCB and guessing at a couple of traces, the only difference between balanced and single-ended output might be a relay (and of course signal from the other channel for balanced-ed-ness).

    Will the signal degrade with a transformer? If so, probably not worth going balanced with the DAC only to convert it back to single-ended. If I can find a cost-effective (but very good) DIY solution, I'll still try it.

    IMG_20170929_221848.jpg
     
  15. purr1n

    purr1n Desire for betterer is endless.

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    LOL, the other channel for "balancedness", the differential signal, is what makes it balanced. Hard to say what would be better without trying. A transformer will always degrade the signal (distortion in higher levels, mainly in bass, phase shift, etc.). But a transformer also takes into the account the other half of the differential signal.

    For the Schiit DACs, I prefer a decent transformer to sum the differential signals in lieu of the extra FET stage inside the DACs. A decent balanced to SE transformer is not cheap. More clarity and more crisp.

    Also, get rid of those Solens. They are horrible.
     
  16. Luckbad

    Luckbad Traded in a unicorn for a Corolla

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    Those Solens are gone from my current DAC. That was a pic of the old one.
     
  17. Daveheart

    Daveheart Friend

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    @Luckbad that relatively cheap ART DTI that @Armaegis linked uses what look like Edcor transformers. I didn't pull everything all the way out of the case, but the general appearance/coloring made them look like Edcor to me. For a bit more, Rane has a converter called the balance buddy ($99 I think) that has what at least look to be more robust transformer. If you want to try those, I've got them sitting on my shelf not doing anything for now. PM me if you want to just try them out to see if you can tell a different between the SE and balanced outs from the SFD and if you can tell a difference between the two DI boxes.
     
  18. purr1n

    purr1n Desire for betterer is endless.

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    Cinemag CLMI 15 series or 600 series. 600 series is better, but at 600 ohms harder to drive. Both are better than the Jenson box 4:1 which warms and smoothes things out a bit - not necessarily a bad thing as synergy is most important.

    Jensen makes equivalents to the Cinemag CLMIs I believe. Those should be good too. The classic Cinemag / Jensen designs are similar if not the same.
     
    Last edited: Oct 18, 2017
  19. randytsuch

    randytsuch Friend

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    This guy
    https://www.parts-express.com/jensen-jt-11p-1-premium-line-input-transformer-1-1--246-0103
    has a 13k input impedance. It needs to be close to the device input, the single ended side for this application.
    They have other line output transformers with around 600 ohm input impedance.
    Seems like parts express has a good selection of Jensen transformers.

    I would expect the trade off for the high input impedance tranny is that it can't drive very hard, which is why it needs to be close to whatever it outputs to.

    If you can drive a 600ohm tranny, then you would get more drive out of it.
    Any idea what the output impedance is for the SFD-1?

    Randy
     
  20. willsw

    willsw Friend

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