The same (new?) balanced input/output questions

[danox574]

Hello, I ordered my BeePre kit yesterday when Bottlehead was running their special to include a free BeeQuiet.  I have about a month until it gets here or so, but I've tried to read everything I can about the balanced inputs/outputs.

Does the kit come with four RCA pairs and one XLR pair, as shown?

For outputs, I plan to (eventually) use this with paramount monoblocks.  My current integrated amp has an auxiliary RCA output, running to a high quality relay-based switch box so I can disconnect that extra output or route to a tape deck for recording or a headphone amp for listening (A Zektor HDS 4.1).  To keep doing that, I would probably use RCAs for both outputs on my amp (one to power amp, one to aux functions).  From what I read here, is it correct that I would just wire them in parallel?  Does the manual explain this, or only how to configure the 1RCA/1XLR configuration?

For inputs, I have three devices - a Oppo DVD serving as CD/SACD player, my turntable on a seduction, and a Slim Devices transporter for playback and also used as an external DAC for other devices.  That transporter does have balanced outputs, but I have never used them.  It also has standard RCAs that I use now.  I was not under the impression that just because you have them, you should use them - do you recommend configuring one input with the Cinemag CMLI-15/15B just because I can?  I do hope to upgrade the SACD player eventually and could end up with something with a balanced output, but I would never be in a situation where I was *required* to have a balanced input.  If I'm running modern devices with both types of outputs, should I bother?

And I assume if I did do a balanced input, I'd want to order Neutriks of the opposite gender for inputs than the included XLRs, correct?

Your opinions as I plan out this build are appreciated!

[Grainger49]

The BeePree comes with 3 pair of RCA inputs, an RCA output and a balanced XLR output.  If you want a balanced input you will need to add a pair of transformers and XLR jacks.  Or, if you don't need the balanced output you can wire them as inputs and just add the transformers.

However, those balanced inputs will need to replace one of the RCA inputs.  IIRC, from two weeks ago, the selector switch is filled. 

I can't help you with genders.  I expect they are male but not sure.

[Paul Joppa]

I would not recommend an input transformer unless you need it, to break an intractable ground loop for instance.

The XLR output can be replaced with an RCA jack if you don't need balanced outputs.

[Paul Birkeland]

The XLR output on the BeePre will also work with XLR to RCA adapters, in case you change your mind down the road.

[Grainger49]

I would not recommend an input transformer unless you need it, to break an intractable ground loop for instance.  .  .  .   

I'm guessing you have posted how to make a balanced input without a transformer elsewhere, right?

[Paul Birkeland]

I'm guessing you have posted how to make a balanced input without a transformer elsewhere, right?

Yes, install the XLR jack, wire the cold pin to ground.

[Paul Joppa]

Yeah, you can't make a true balanced input without a transformer or a new design with at least one added tube. PB's adapter works in most cases. Balanced outputs are more easily created, as done in the BeePre.

I just think that a transformer damages the sonics - only slightly if you can get a really good transformer, but still audibly. If you can avoid it without penalty then it will sound better. The main penalty is hum and buzz from ground currents (including but not limited to ground loops). In complex systems with long lines and different power circuits (such as recording studios), ground current is enough of an issue that balanced lines are commonly used. Few home systems have intractable problems with ground currents, however. If it were common, balanced lines would be universally used for phono cartridges - but almost nobody does that.

Back when I was a research engineer doing aerospace acoustics, we never used balanced lines. For long cables we used 50-ohm coax with matched driving and load impedances. On the rare occasions where a hum problem occurred, we had high-quality 50 ohm to 50 ohm transformers - but it was pretty rare to find an occasion when they were really needed.

[Grainger49]

Paul & Paul,

That was what I was getting at, it isn't a balanced input without a transformer or additional circuitry.  An adapter for balanced to unbalanced is the only way to go as the circuitry is.

I do agree that the transformer is adding something that will surely color the sound in some way.  If he suffers from common mode noise then it is a viable answer.

[danox574]

Solid.  I'll skip the balanced input then and just use the RCAs that sound and work fine in my current setup.  I don't like the idea of adding a device that could modify the audio, the RCA is what the input is designed for so not re-routing through an additional device when I don't have to sounds like the best idea.

And, if it's easy to adapt out of the balanced outputs, I'll install those as well and then at least just have the XLRs there in case I want them someday.  Does a XLR to RCA output cable basically just connect to the HOT and GROUND and leave the cold floating?  I assume the inverted output is just ignored.

Am I to undrestand that the balanced outputs on the BeePre created just by inverting the signal and sending it to the cold pin, while feeding the main signal to HOT and ground to GROUND?  Is it that simple?

Thank you guys!

[Doc B.]

Balanced cables for home audio are in lots of cases used because of a good marketing job. You need them for long runs in noisy environments, like a studio might need to run from mics in a tracking room to preamps in a control room.

So the marketing logic is "hey they are used in studios, so it must be an ultra groovy thing to sell to audiophoo- I mean audiophiles."  How many manufacturers tell you they have balanced outputs? Lots. How many tell you they may not actually sound as good because there is more stuff in there to make the connection balanced? Not many. An example would be our Tube Repro. The balanced output has the advantage of 12dB more gain, a lower output impedance, and it uses very chi-chi Peerless transformers. I think it sounds great but I will use the single ended output when I can because there is less circuitry in the signal path and for me it has the tiniest bit better resolution.

Part of the reason we offer the single ended cable kit we do is that I spent some time trying to figure out what we could do to make single ended cabling setups as resistant as possible to noise pickup, thus coming as close as possible to eliminating any percieved superiority of balanced cabling. As PJ described, a really good coax cable is very resistant to noise pickup.

The other benefit of balanced cables doesn't really have to do with their balanced connection - they use XLR connectors. It's a mechanically superior connector to the RCA, no doubt. That may be the most justifiable reason for using balanced cables in a home system. Of course they can be used on single ended cabling too. The problem there is simply that there are a few different ways to do the connections at the jacks in the equipment and you need to be sure that the gear at both ends of the cable is compatible in terms of the way they are wired to the jack. That's where transformers come in, it's a good way to allow the connection to handle any unconventional cable wiring.

[Paul Joppa]

...  Does a XLR to RCA output cable basically just connect to the HOT and GROUND and leave the cold floating?  I assume the inverted output is just ignored.

Am I to undrestand that the balanced outputs on the BeePre created just by inverting the signal and sending it to the cold pin, while feeding the main signal to HOT and ground to GROUND?  Is it that simple?

Thank you guys!

A balanced line connector does not have a ground. It has a shield, which is connected to the chassis (a continuation of the shielding function) but that is not a signal ground. Even if the signal ground is ultimately connected to the chassis, it is not done in a way that gives proper attention to hum and noise pickup. Consequently, an adapter connects + to the inside and - to the shield of the coax, no connection is made to the XLR shield pin.

Balanced means the impedance to ground is the same on both outputs, + and -. It says nothing about signal. In the BeePre, the - on the XLR goes to a network that has the same impedance to ground as the output impedance of the (single-ended) 300B output.

Combining these things, you can see that the source impedance of the balanced output through an adapter is twice the source impedance of the RCA output.

[danox574]

Thanks for the info everyone.  I'm quite tempted to just buy another set of Neutriks and make those a parallel set of RCA outs.  If I decide to wire the balanced outputs, I'll use an adapter cable and expect that the additional circuitry may introduce minor impurities into the output.

I did run across this page, which is interesting:

http://kc.flex-radio.com/KnowledgebaseArticle50265.aspx

It shows two different methods of cabling an balanced to unbalanced output cable.  Looks like whit Paul Joppa said there is "option 4" on this page - positive to positive, negative to shield, single conductor cable.  That means that this output is 'Not a transformer or cross-coupled output stage'.

I found it interesting that these two applications exist, but any commercial cable that does XLR Female to RCA male for audio that I've found absolutely does not specify how it is wired.  I'm guessing they are typically wired as 'Option 4' from that page, because you'd be in a really unique or specific situation to need #6.

[Paul Birkeland]

Thanks for the info everyone.  I'm quite tempted to just buy another set of Neutriks and make those a parallel set of RCA outs.  If I decide to wire the balanced outputs, I'll use an adapter cable and expect that the additional circuitry may introduce minor impurities into the output.

If you use an adapter, it will literally short out the extra components for the balanced outputs.  If you make your own adapters, you could ignore it entirely.

It shows two different methods of cabling an balanced to unbalanced output cable.  Looks like whit Paul Joppa said there is "option 4" on this page - positive to positive, negative to shield, single conductor cable.  That means that this output is 'Not a transformer or cross-coupled output stage'.

I found it interesting that these two applications exist, but any commercial cable that does XLR Female to RCA male for audio that I've found absolutely does not specify how it is wired.  I'm guessing they are typically wired as 'Option 4' from that page, because you'd be in a really unique or specific situation to need #6.

I believe most of these will connect 1 and 3, but you're correct, there isn't really a lot of information about how they are wired.  If you had a floating transformer secondary, for example, driving the balanced end of situation 4, ignoring pin 3 and leaving it floating would disconnect one end of the transformer, which isn't very desirable. 

[Paul Joppa]

Thanks for the info everyone.  I'm quite tempted to just buy another set of Neutriks and make those a parallel set of RCA outs.  If I decide to wire the balanced outputs, I'll use an adapter cable and expect that the additional circuitry may introduce minor impurities into the output.

I did run across this page, which is interesting:

http://kc.flex-radio.com/KnowledgebaseArticle50265.aspx

It shows two different methods of cabling an balanced to unbalanced output cable.  Looks like whit Paul Joppa said there is "option 4" on this page - positive to positive, negative to shield, single conductor cable.  That means that this output is 'Not a transformer or cross-coupled output stage'.

I found it interesting that these two applications exist, but any commercial cable that does XLR Female to RCA male for audio that I've found absolutely does not specify how it is wired.  I'm guessing they are typically wired as 'Option 4' from that page, because you'd be in a really unique or specific situation to need #6.

None of the diagrams matches what I tried to say, but the best approach is #6 - this retains the shield function without trying to make it a signal ground as well. To do this the whole cable is STP, not coax. My adapter is equivalent to a very very short cable #6, with a female RCA jack instead of a male plug.

The article is not clear about the meaning of "cross-coupled output stage" but that gets to the difference between push-pull and balanced. They are usually confounded and P-P is often sold as "balanced" but they are different concepts entirely. I think the confusion persists because it's too complexe to explain in a tweet or a post.