Converting XLR to RCA using transformers

January 16, 2023
 by Paul McGowan

17 comments on “Converting XLR to RCA using transformers”

  1. A schematic would really help. I’m not understanding how the transformer is wound to have 2 input wires (RCA, single ended) to 3 wires out (XLR Balanced). Do the secondary have a center tap? Are there 2 sets of secondary windings? How do we get from single phase to a pair 180 degrees out of sync where we can use the balanced circuity to cancel out noise and why would that even matter if the second signal is sort of “Synthesized” from the first, there wouldn’t be any noise to cancel.

    What are the draw backs of a high quality passive adaptor if using a short, high quality RCA cable (say about 3′ long)?

    If an amp has a (True) balanced input and a single ended, unbalanced RCA jack input that is introduced to the input circuitry after the XLR balanced circuitry and a switch to remove the balanced circuitry from the input stage all together, would the use of a transformer at the balanced input sound better than the RCA jack unbalanced input (Again, short, high quality RCA cable)?

    Thanks,

    Eric M.

    1. Hi,
      It seems not easy to put a picture in this forum.
      However, you can us the datasheet provided by Lundahl:
      – Datasheet of LL1588 is here: https://www.lundahltransformers.com/wp-content/uploads/datasheets/1588.pdf. LL1588 is a model widely used by Jeff Rowland.
      – You can found other transformer here: https://www.lundahltransformers.com/input-and-line-output-application/

      In my case, I think I get an improvement if I insert a LL1588 at the output of a Totaldac D1-single. Spatial positioning is better, bass and low mids seems more clear.

      1. Good input. Lundahl is famous for their audio transformers. Perhaps Triad and Jensen are also interesting. When using a transformer it is necessary to keep an eye to the output source impedance and the load on the secondary. This can have influence on the frequency response and distortion. Depending on the windings the output may be too high or too low and thus the receiving input should be able to handle it.

      2. Thanks,

        In the first schematic from Lundahl, what does wire #8 represent in the windings? Is it just attached to the metal core as a “ground”?
        Does that #8 wire play a role in the balanced output of the transformer? We have 2 wires at the input (Those could be your single ended, unbalanced wires from an RCA jack) and on the opposite side we have 2 output wires and the #8 wire. Would those make up the input for your 3 wire balanced input?

        Thanks,

        Eric M.

        1. Pin 8 is connected to the metal box and to an electrostatic shields inside the LL1588.
          Personnaly, I have used “Serial-serial connection”, with pin 8 connected to 9 and 10, like the right side of “Phase splitting” (in a cable XLR to XLR).
          In this configuration, we have 2 wires input (could come from RCA or XLR) and 3 wires balanced output.
          After 2~3 weeks of listening, no issue in the bass (which could be the theoretical weakness), and still improvement in medium/acute with a D1-single (probably because filtering + galvanic isolation).
          Because Lundahl is a little bit expensive, it is interesting only with revealing system. Otherwise, cheaper solution exist elsewhere.

          1. OK, I think I have it figured out now. (I had to print the schematic and draw out your set up!).
            In your set up, #2 and #5 go to the unbalanced RCA connection.
            On the other side of the transformer is the balanced (XLR) output with #7 being HOT, #6 being COLD and #8 being GROUND.
            #6 and #7 are 180 degrees out of phase, the balanced circuitry of the amp (or whatever you’re plugging into) compares the signal at #6 and #7 and rejects anything common (Buzz, hum, distortion, etc. that would be in phase / identical on both #6 and #7), leaving us with a clean signal.

            Is that correct?

        2. I forget… Transformer dislike DC current, so I have inserted a 2.2uF capacitor between 4 and 1 (instead a wire), and add some resistance+capacitor in order to be “non resonant” (flat bandwidth, good transient response).

  2. A question on the topic of XLR cables not for stereo…..
    I’ve got a friend who has a 5 channel Home Theater amp and wants to use XLR on the front 3 channels, but does have enough XLR cables for the REAR two channels of his Home Theater receiver. He wants to use RCA cables rather than buy more XLR cables for the rear channels.
    So, the question is… can you combine RCA and XLR cables on a Home Theater Pre-AMP and will the preamp adjust the volume during the Calibration step of Audyssey software when doing room calibration ?
    I am gonna assume yes, but is combining the cables have a negative effect .
    Thanks

  3. Hi Eric, will try to answer some of your questions. Since I worked on several vintage and some newer professional mixer desks and mic preamps I came in contact with all kind of XLR and RCA configurations. So first, the transformer. If the input is single ended (RCA) it is just one winded coil for this. Since isolated it can be grounded at either end but there might be a preferred orientation regarding capacitance to other windings or the core. The secondary (XLR) can be also a single winded coil, either with or without a mid tab. If without the tab then XLR ground is often the transformers case or with mid connected to XLR ground.

    Passive adapter from XLR source to RCA input works fine as Paul explained. Internal connection depends on the XLR output whether it is true balanced (transformer) without ground needed or it is both + and – working with ground reference like on IC outputs.

    Third, XLR or RCA input better? This depends on the internal circuit of the amp input. There is no general clue on this depending on brand and model.

  4. Hi Paul.
    As an aside, sometimes a simple and perhaps-not-considered solution works the best.
    Why not just put a commercial self-closing mechanism on that door–the kind that closes softly but securely closes the door! Then it would take more effort to prop it open rather than let it close. You’d save paper, ink, tape and calm some nerves also.
    Problem solved.

  5. Excellent mobile high-end audio players with balanced outputs have been available for some time. These players also sometimes support DSD and have balanced TRRS headphone outputs. The headphones are then controlled symmetrically and this type of connection e.g. with Audeze headphones sounds very good. Very good results are also achieved using short cable adapters from TRRS to RCA or XLR. The only downside is that these players somehow don’t have the right punch/performance.
    Paul, now you’ve given me an idea. I will now get two excellent transformers that will connect the symmetrical TRRS signal from the mobile player via a transformer that can drive longer cable distances, in the hope that I can get the music about 3 meters from the couch to the system via the mobile player in very good quality (without cable losses) and can control with more pressure. I think it’s worth a try.

    Maybe someone here in the forum has experience with something like this?

    1. Hi, mentioned the TRRS on your portable the question is whether there is one jack for left and another jack for right channel? If it is only one jack for both channels then these are not balanced but single ended. If your sound system input is balanced XLR then transformers may be of value. On the other hand when the input is single ended RCA two transformers make for me no sense. Better would be a very low capacity screened cable for the three meters single ended output to RCA input. Since it is a portable then ground loop problems should not be a problem. I don’t know whether the right adapters exist on the market place. Perhaps somebody should solder this special cable.

    1. Opa-Alli, sorry, you are right. I did not know this special balanced output since I have no portables. With TRRS both channels can be balanced in one plug. But there is no ground connection. If your stereo gear input is RCA, then just use two balanced shielded cables (perhaps there is also a balanced stereo cable available). Then place the transformer in the near of the stereo input. The shielding should connect to the input ground(s). If the input is already balanced then there is no need for a transformer.

  6. Hey Paul,
    Nothing to do with transformers or XLR to RCA in today’s post, but:

    Why not put some self closing hinges, or a pneumatic/hydraulic door closing mechanism, on that door and make the crews happy(ier) so they can come up with even more creative solutions and better products? The door can always be propped open if temporary unencumbered access needed. Sometimes simple little things can make a big difference in quality of life and work environment.

  7. I use the better Cardas adapters, rewired for XLR to RCA from a VAC preamp to JL Audio subs. Haven’t noticed any SQ problem. In addition to the cost of two transformers, there would presumably be an extra set of ICs needed, which for a system already with top of the line cables would be a lot more than $150 each.

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