DIY XLR -> RCA Transformer

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

  1. StefanAC

    StefanAC Acquaintance

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    @Luckbad

    Why do you want to use a transformer with your SFD-1 MKII anyway? That only makes the signal path more complicated. The XLRs are just a convenience feature as that DAC is a single ended design unlike the SFD-2 / SFD-2 MKII where such an aproach might make sense.

    My former Audiomat Maestro 1 MKII was similar in a way. While it had two PCM1704 per channel, they weren't used in a differential layout but in parallel. What followed was the usual Audiomat output stage with only three transistors per channel for the single ended output - one for I/U conversion, one as a voltage reference and one as buffer. The balanced output used the output from that buffer and added four transistors to that - to generate a balanced signal and to buffer it. Guess what sounded better!

    The newer Audiomat DACs on the other hand use one PCM1794 per channel with a three transistor output stage for each positiv and negative signal. Here the balanced output makes sense in the same way as with the SFD-2 / SFD-2 MKII.
     
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  2. Druid

    Druid Hyperactive Tree

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    I'm going to be buying a non-hybrid tube amp soon, and was wondering if this would be necessary for my SFD-2 MKII? Does anyone know if the signal from the balanced outputs is going to be superior to the SE outputs? I could test with my Jot, but I'm afraid that I won't know if the difference in SQ is due to the DAC output or the Jot input...
     
  3. StefanAC

    StefanAC Acquaintance

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    @Druid

    It is up to you to decide which output sounds better in your chain. I don't have a SFD-2 MKII at my disposition, but judging from pictures it seems that the single ended output only uses one half of the UA20400A. There is no summing circuit, be it an op-amp (Schiit) or transformer (Metrum).

    My EAD DSP-9000 Series III is single ended only using one PCM63 per channel. The balanced version doubles the number of DAC boards and uses one board for the positive and one for the negative signal. If I had that version, I would buy a good transformer and make use of all the PCM63s I paid for.
     
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  4. Riotvan

    Riotvan Got lost for three weeks at Delft City Hall

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    So i wanted to hook up Yggdrasil(not Yggdrasil A2) to my Saga over a long cable run. Thus i did some reading got some advice from knowledgeable people and decided on a Lundahl LL1690 transformer. Put them in a metal box wired and them up as recommended.
    If you look at the data sheet here: http://www.lundahl.se/wp-content/uploads/datasheets/1690.pdf i basically did the serial to serial connection but in reverse, this was advised to be better. Center tap, pin 2 and 3 and shield from both cables are all connected to ground.

    But the problem is the volume is very low and there is no bass at all. I'll attach a pic of my handy work, i'm sure someone can figure it out:
    483C35E7-FD7F-41B8-8396-A72C5AA2D2E2.jpeg
    Edit: well the guy who told me how to wire it forgot to mention pin1 and 4 need to be connected. Will try that later :)
    Edit2: All works now, time for some music!
     
    Last edited: Jun 30, 2018
  5. Cspirou

    Cspirou They call me Sparky

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    Last edited: Jun 30, 2018
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  6. Riotvan

    Riotvan Got lost for three weeks at Delft City Hall

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    Yeah i know that is the neater solution but this won't be messed with so i guess my cable tie strain relief is fine :)
     
  7. Cspirou

    Cspirou They call me Sparky

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    I'm more wondering how to are attaching the transformers to the enclosure. Is it just loose in there?
     
  8. Riotvan

    Riotvan Got lost for three weeks at Delft City Hall

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    Oh no, i'm using double sided tape, the stuff that is like 2mm thick and really sticky. They are very secure.
     
  9. nachocheese70

    nachocheese70 Facebook Friend

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    I’m no expert on this so take this with a grain of salt. Based on your picture, it looks like you’re going for 1:1 serial-serial connection. In this case based on the Lundahl schematic on the input side you need to short pin 1 and 4 so the input windings are in series. Leaving it open means you have two separate parallel input winding. This could account for the screwed up FR (lack of bass).
     
  10. Riotvan

    Riotvan Got lost for three weeks at Delft City Hall

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    Yeah i fixed that later, you must have missed that i edited my post :)
     

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