xlr/balanced Input

[STURMJ]

what you see above is Hammond transformers (1k 1:1) mounted on a small piece of aluminum plate. Terminal plates mounted to that as well. That is wired as a input. the stock kit is configured to have one output xlr. I instead used rcas on both outs.  The stock configuration has the caps hanging from terminal strips to the xlr pins. I hope this makes more sense.

[Paul Birkeland]

22K is a decent start for loading the Cinemags.

There's nothing wrong with feeding the BeePre from unbalanced sources, then using the balanced outputs.

-PB

[dcham]

Thanks guys!

The reason I want to go in balanced is that my D/A converter is balanced out +4dB. I could just do a balanced to unbalanced cable, but the proper way to do it would be to use sort of an unbalancing transformer that would step down the impedance and levels. Just wanted to do things right. Still thanks. Want to try the Manline then tackle the BeePre.

Dennis

[adamct]

Want to try the Manline then tackle the BeePre.

I have to correct my post from earlier this week. That might be one of the funniest Freudian slips ever...

[Doc B.]

The idea behind the balanced output on the BeePre was to get balanced without the use of transformers. This is because I have always found a transformer to soften the leading edges of the bass notes. At +4 you have tons of signal, and you will be able to kick it up even more through the gain of the BeePre. So if it is possible to take just half of the output swing from the DAC - for example if that output is a differential circuit rather than a floating transformer secondary - it might actually sound a tiny bit better to do that than putting the signal through the transformer and you won't experience much if any loss of the level. The BeePre won't add any of that kind of transformer sound itself, as the balanced output does not use a transformer. Of course this all depends upon what kind of coloration you are looking for. If you are trying to mellow the sound overall the transformer might be what you want. If you are trying to sweeten the top end and flesh out the lower mids a bit but want to preserve the bass punch, no transformer might work better.

[Paul Joppa]

@dcham - here is a link to the Jensen Transformers white paper on interconnection: http://www.jensen-transformers.com/an/an003.pdf - just in case you wanted a more thorough pro-studio perspective!

You can see from the "Typical Balanced Output" figure that it has two outputs of opposite phase, but both are derived from the same internal signal. In this case, as suggested by Doc B, you can use either phase (plus ground) as an unbalanced output at half the voltage, without loss of performance except for the increased possibility of ground loops. 

My further comments below are more than anyone has asked for, but I'm putting them here so as to be easier to find in the future by search engine.

A few - mostly old-school - balanced outputs are done by using an output transformer, which may or may not have a grounded center-tap. In this case you can use either phase with the grounded CT, or ground one phase (and un-ground the CT if used) and use the other as "hot" for a 6dB voltage increase. You can't to this with the "typical" circuit because it would be shorting one of the op-amps.

A few digital sources may have dual, independent split-phase DACs per channel. Using just one phase as above would then be using just one of the DACs per channel, losing at least theoretically some increase in performance in fully balanced mode. In that case, an input transformer for the downstream device is needed to obtain true balanced operation, at the prices (as Doc B says) of introducing some transformer sound.

Finally, it is possible to make a balanced to single ended tube circuit without transformers, adding two triodes per channel. Personally I doubt the transformerless advantage would outweigh the effect of added stages, but since we haven't done it that remains just a guess.

[dcham]

Thanks everyone for the input. Learning as I go. ;-)

[Paul Birkeland]

Finally, it is possible to make a balanced to single ended tube circuit without transformers, adding two triodes per channel. Personally I doubt the transformerless advantage would outweigh the effect of added stages, but since we haven't done it that remains just a guess.

I built just such a circuit this week, though we haven't evaluated it sonically.

-PB

[dcham]

Just re-reading the replies between my sessions here at work. I think I confused everyone, I understand the BeePre has a transformer-less balanced output. No arguments there and I agree that transformers may degrade the sound.

My question was regarding installing the balanced inputs with a transformer, which is what you recommend.

Apologies for all the confusion. Thanks for the patience and answers.

[Doc B.]

I understood what you were saying just fine, and attempted to explain that my own philosophy is to avoid the transformer anywhere possible. We offer the ability to install a transformer to receive a balanced signal. But personally I try to avoid the transformer where possible, and in this case I would suggest taking one half of the signal (i.e. a single ended signal) from your DAC and running that into the single ended input if the BeePre  - if that is possible. If you must use a transformer then balanced is a good way to go.

[dcham]

Thanks Doc! Got it now.