General DAC Questions/Tech Thread

[Azazel]

My bet is do not do it the usual way (shorting pins 1 and 3), instead:

-wire pin 2 (XLR) to hot/center (RCA)

-best: use a signal transformer from XLR to RCA. There are cheap and good Pros, and Neutrik or Lundahl makes best ones.

[HeadphoneAddict]

If I need to use my XLR out with an SE amp I prefer to use my Jensen Transformers ISOMAX transformer box to convert XLR to RCA. Then I don't have to worry about shorts or no shorts, etc (but I still wear pants).

[NekoAudio]

+1 for a direct box to convert balanced to unbalanced or vice versa.

As Dreadhead stated, it can damage your DAC if you short negative and ground.

[some1x]

Isn't it just a matter of checking once that your XLR->RCA cable/adapter is wired correctly? Why add a transformer into the signal path?

[Azazel]

Why add a transformer into the signal path?

Because if your DAC is a true balanced design and you take just the "hot", you are listening to half its circuit. With a transformer you have the full thing working converted to single end.

[some1x]

Because if your DAC is a true balanced design and you take just the "hot", you are listening to half its circuit. With a transformer you have the full thing working converted to single end.

But what is the benefit of this, if all you need is single ended output? Just higher output?

[Dreadhead]

But what is the benefit of this, if all you need is single ended output? Just higher output?

Technically noise rejection as well. Though I'm not a huge fan of transformers in the signal path.

[n_maher]

Technically noise rejection as well. Though I'm not a huge fan of transformers in the signal path.

I'd rather take my chances with noise than introduce a trafo into the mix. Talk about an expensive (to do it right) solution to a problem that probably doesn't exist!

[Filburt]

Technically noise rejection as well. Though I'm not a huge fan of transformers in the signal path.

QFT

[darkless]

Just get a pair of standard XLR-to-RCA adapters, unscrew the XLR end and cut the thin wire shorting pin 3 (negative) and pin 1 (chassis ground).

My XLR-to-RCA adapters were wired this way. When I used them on the balanced outputs of my Weiss DAC1-MK2 they added a lot of distortion to the output. Thankfully no damage was caused since both outputs are short circuit-proof. I became fully aware of this issue when I approached the creator of my DAC:

If the XLR-to-RCA adapter shorts pin 3 (or pin 2) to ground then one of the DAC1-MK2's output amplifiers is shorted, which can cause distortion also in the unshorted output because of the high currents flowing.

[HeadphoneAddict]

The Eddie Current HD2 uses input transformers to accept a balanced signal, then the gain and volume stage are SE, then it uses output transformers to go balanced again. I haven't heard anyone complain yet that the input transformers muck up the sound.

[n_maher]

Would you pay that much for a switchbox?

[Azazel]

Technically noise rejection as well. Though I'm not a huge fan of transformers in the signal path.

Mmm... Something for my 'to do' list (oh how I miss my Palm btw!) id this AB test:

-'A' is the balanced out of my Pass D1 (it does use 2 chips per channel, one PCM63K 'hot' and another 'cold'), transformed (via Jensen trafo) to unbalanced.

-'B' is the single-ended out of the Pass D1 (just one PCM63K, the 'hot' of the balanced signal).

My bet is 'A' should sound better.

If I do the same experiment with my Benchmark (the XLR outs are sourced from unbalanced signals with the help of some opamps) my bet, then, is 'B' should sound better.

qed

[luvdunhill]

I think the problem with input transformers is people don't tend to know how to use them, by not respecting the input and output impedance. I think they can sound fantastic. For example, what configurations have you heard them in Dreadhead?

[grawk]

Quite a few people who don't like transformers in the signal path liked my old m3 which had cinemag cmlis as ipts.

[luvdunhill]

Quite a few people who don't like transformers in the signal path liked my old m3 which had cinemag cmlis as ipts.

exactly. I think it's more either a theoretical dislike, or people who don't like output transformers and think somehow that carries over to input transformers.

[Filburt]

For me, it's more than a theoretical dislike. From a practical standpoint, you can end up with undesireable component interaction and distortion as a result. I find them acceptable when it's the best option for a given task, but if I can avoid it by redesign, so long as I don't end up with worse performance, I'll probably go that route.

[n_maher]

For me it's the cost of creating a trafo coupled switchbox that holds no appeal. I don't think at face value that trafos are anything more evil than tons of other stuff you're likely to find in the signal path.

[swt61]

I don't think at face value that trafos are anything more evil than tons of other stuff you're likely to find in the signal path.

I was walking down the signal path once, and I saw this wolf. He wanted to help me find my Grandma's house. But something made me feel uneasy. So I took my gun out from my picnic basket and pumped lead into his ass.

Oh, I didn't see any transformers.

[Dreadhead]

Same here, theoretical dislike really. It's a trasformer, it has both phase and frequency response, usually introduces some noise, and is definitely not entirely passive. Hence not a big fan. Haven't really heard any transformer balanced stuff in detail (heard Dans M3 and liked it, but that was not in detail).

[luvdunhill]

Same here, theoretical dislike really. It's a trasformer, it has both phase and frequency response, usually introduces some noise, and is definitely not entirely passive..

not entirely unlike a discrete single ended to balanced converter, huh? We've sorta come full circle.

[Dreadhead]

not entirely unlike a discrete single ended to balanced converter, huh? We've sorta come full circle.

Considering the measured noise/frequency/phase performance on the discrete (or even active) SE -> balanced designs out there I'll take my chances with silicon.

Last time I looked at audio transformers the THD/frequency response didn't look to promising and it still doesn't:

http://www.rane.com/pdf/bb44xdat.pdf

I don't know if that's a "good quality" transformer but the Rane transformer stuff is very common in the studio as I understand it.

[luvdunhill]

Considering the measured noise/frequency/phase performance on the discrete (or even active) SE -> balanced designs out there I'll take my chances with silicon.

From the discrete designs (nevermind the monolithic designs) I've built and tested it might be higher than you think, at least that's what I've measured.

The transformer design I'm using on my preamp has a measure < 1 degree phase shift at 20Hz. THD+N is < .0005% at 1kHz. Response is varies by a maximum of 0.02dB at 20Hz. Again, all this is very dependent on the load, but since I control this parameter (a fixed input impedance, stepped attenuator follows the transformer), that's rather easy.

I'd be glad to compare this to some discrete designs of your choosing, but these numbers are pretty much down in the noise. They may be even better than this, I just cannot measure it.

[NekoAudio]

For the datasheet curious, here's the JT-11-EMCF transformer I use.

I tried a few different transformers, and yes some of them didn't do what they were supposed to in my opinion. Both to my ears and on the oscilloscope.

[Dreadhead]

From the discrete designs (nevermind the monolithic designs) .... snip

I haven't tested either myself (I don't own any AP stuff) but the numbers you quote sound excellent and I agree are well in the noise. The measurements I refer too are the measurements of for many of the DACs (eg Bel Canto DAC3) that convert SE to balanced using silicon.

That said I can't see how that Jensen transformer is anything but transparent. As I said I was not sure that was a good transformer and apparently it was not