Balanced inputs for a Crack or Crackatwoa or even a Mainline?

[jaschinski]

Possible? How much additional cost?
I have a DAC that has an unused output but it is a balanced output. The single ended output is going to my amp and it only has RCA inputs. I would love to drive my old HD600s with something like this.
Thanks for your help!

[Paul Birkeland]

Yes.  This is easier to do with a Mainline since you can swap out a pair of the RCA jacks for XLR jacks.  Depending on your DAC, you may not need to use -ve from the XLR cable at all, and at worse you would just need a pair of input transformers.  There's room back there on the chassis to add them.

The Crack is tougher because there aren't holes for XLR jacks and there's less space for input transformers.  The power transformer also isn't as magnetically quiet as the Mainline transformer.

[grufti]

You have endless options: plugs, simple circuits on eb, fancy buffers. I'll try to post some links with this message. You can also reconfigure the two Bottlehead amps.

https://www.markertek.com/product/na2fpmm/neutrik-na2fpmm-3-pole-xlr-female-to-rca-male-audio-adapter

https://www.ebay.com/itm/Stereo-Audio-Balanced-to-Single-end-RCA-Unbalanced-Preamplifier-Signal-Converter-/323236270664

https://neurochrome.com/products/universal-buffer

Whatever you do, it's likely to work just fine.

[ALL212]

If this were to be done on the mainline what input transformers would you recommend?

[jaschinski]

All, thank you for your exceedingly quick responses.
I know just enough about electronics to get into a moderate level of trouble so forgive me if I falter here.
The balanced outputs I am trying to use are from an Auralic Vega DAC. According to the manual:

Analog Outputs: The balanced and single-ended analog outputs of VEGA are individually buffered so as to be used simultaneously, however, it is still strongly recommended to disconnect unused ports to avoid any potential electromagnetic interference induced by cables. The amplitude of analog outputs is adjustable with maximum level at about 4Vrms on both  XLR  and  RCA  outputs.  The  output  impedance  of  XLR  output  is  very  low  at  4.7ohm  so  it  can  be  used  to  drive  almost  all  kinds  of  power  amplifiers.  Please  pay double caution NOT to short any pin of any analog output to ground.

It's that last sentence that gives me pause.
The way I read it is: Both outputs (RCA and Balanced) are "live" and producing a signal at all times. If I use the unused balanced outputs for the input on the headphone amp it would need all the proper transformers, etc at the balanced input and I should be cautious of adapters? Grufti, thanks for the links.

Again, a tip of the hat for your help.

Olaf

[Paul Birkeland]

I would use the Sowter 1475 with the threaded grommet mounting and the secondaries in parallel to make it a 1:1. 

The manual of your DAC says not to short any of the outputs of the balanced out, so I'd recommend using a transformer over an adapter.

The input transformers could be mounted inside the chassis.  I would put them on the outside of the chassis between the output transformer and wood case on the right side of the Mainline (the side without the power entry module).

[ALL212]

Thanks Paul!
Pricey little treasures!  For now this has to wait.  Covid19 is pulling on the purse strings.  We’re healthy but until this is over no spends for this.

[jaschinski]

Thank you for info on transformers. It sounds like this is the way to go for a balanced input.
One more question. I would like to have a remote on the volume. Can I replace the stepped attenuators with an Alps remote volume pot. Seems like it would be straight forward but I should ask before I go this route. I don't mind drilling a hole in the box face to mount it.
Olaf

[Paul Birkeland]

That's a lot less straightforward. You'll end up losing the functionality of the overlay on top of the chassis and you'll probably end up needing a ~10K pot.  You will also have to add a power transformer or wall wart to power the motor on the pot.

It's very unusual to put a remote volume control in a headphone amp...

[jaschinski]

Because this...

[jaschinski]

I relax far from my gear and while the DAC has a digital volume I would still like to change volume remotely on the headphone amp.