XLR to RCA

[nightflier]

I have an amp that only takes XLR input. Can I safely use an adapter from a preamp that only has RCA outputs? Alternately, I could use an XLR to RCA cable, but what would I be loosing in doing this?

[Feanor]

I have an amp that only takes XLR input. Can I safely use an adapter from a preamp that only has RCA outputs? Alternately, I could use an XLR to RCA cable, but what would I be loosing in doing this?

This is generally perfectly save to do, but check your amp's manual for any caveats. Of course, use a cable with a male RCA connector on the source end and an XLR male on the other end; othewise a standard RCA cable with a target-end adaptor with female RCA and male XLR.

You will loose 6 dB of gain compared to a fully balanced connection. However you probably won't loose that much, if any, actual power output. Also you won't have the noise cancelling benefits of a fully balanced connection, however that probably isn't of any significance.

[nightflier]

Also you won't have the noise cancelling benefits of a fully balanced connection, however that probably isn't of any significance.

Actually that is the gist of my question. I'm planning on going 15-ish feet with the cables (to the sub and back). There's a lot of other cables back there and I'm wondering what kind of noise canceling we're taking about here.

[Feanor]

Actually that is the gist of my question. I'm planning on going 15-ish feet with the cables (to the sub and back). There's a lot of other cables back there and I'm wondering what kind of noise canceling we're taking about here.

For any noise cancellation to take place you have to have a balanced signal, that is, two active signals, + and an equal but opposite (opposite phase) - . In that scenario both signals get affected in the same way by the noise but because the signals are equal but opposite, the noise is cancelled out. A single ended signal has single active signal, (delivered by a 'live' wire and a 'neutral' wire), hence there is no noise cancellation.

[nightflier]

Maybe my question should be re-phrased: at what point does the signal stop being noise-canceled on an RCA to XLR cable?

[Feanor]

Maybe my question should be re-phrased: at what point does the signal stop being noise-canceled on an RCA to XLR cable?

Sad to say, it starts not cancelling (curious phrase) at the single-end source because there is only one 'live' (active) wire which acquires the external noise. (You need two active, opposite phase wires to get any cancellation.) In principle it makes no difference which end the adoptor is on.

But BTW, even with a balanced source, if your downstream component is single ended you won't get cancellation unless the latter has a circuit that combines the '+' and '-' signals. This would only ever be the case with if the single-ended downstream has XLR inputs, but even then if the downstream just routes the '-' signal to ground, there won't be any cancellation.

[nightflier]

So if I understand this correctly, it's only balanced if the following requirements are met:

(1) the components between the wire are both truly balanced
(2) the wire is XLR on both ends and doesn't combine the signals

Barring that, it's not balanced and thus does not benefit from any noise cancellation. One final question: combining signals using an adaptor (or cable) cannot damage truly balanced equipment, right?

[Glen B]

So if I understand this correctly, it's only balanced if the following requirements are met:

(1) the components between the wire are both truly balanced
(2) the wire is XLR on both ends and doesn't combine the signals

Barring that, it's not balanced and thus does not benefit from any noise cancellation. One final question: combining signals using an adaptor (or cable) cannot damage truly balanced equipment, right?

The issue of equipment being "truly balanced" is not relevent. Balanced is balanced, whether via circuit topology that is full differential from input to output or accomplished electronically.

Even where the circuit topology of a component is single-ended and employs balanced converters on the input and output, you will still gain the benefits of noise reduction on long cable runs (provided the other equipment in the chain is also balanced).

A single-ended to balanced transformer is one option for interconnecting balanced and single-ended equipment.

The adaptor does not combine signals, it only uses 1/2 . No damage will occur.

[Feanor]

....

Even where the circuit topology of a component is single-ended and employs balanced converters on the input and output, you will still gain the benefits of noise reduction on long cable runs (provided the other equipment in the chain is also balanced).

A single-ended to balanced transformer is one option for interconnecting balanced and single-ended equipment.

....

I agree, Glen, (in case 'Flier is in any doubt about that).

Many single-ended components have cicuitry that creates balanced out put or combines balanced input signals. (So a center tap transformer is one way to create balanced, +/- signals from live/neutral single-ended source.) McIntosh preamps, for example, have long had balanced inputs and outputs though internally they are single-ended.

[nightflier]

Well, I've been using RCA-XLR adapters, and I did some A/B testing and there's no discernable difference. That said, I would feel a lot more comfortable with a single cable, even if there's no difference in sound - I hate that cobbled-together look.

[Feanor]

Well, I've been using RCA-XLR adapters, and I did some A/B testing and there's no discernable difference. That said, I would feel a lot more comfortable with a single cable, even if there's no difference in sound - I hate that cobbled-together look.

Go for it!

[E-Stat]

The issue of equipment being "truly balanced" is not relevent. Balanced is balanced, whether via circuit topology that is full differential from input to output or accomplished electronically.
What is relevant in the context of this discussion is using RCA adapters immediately renders the connection unbalanced.

rw

[nightflier]

Ran into another caveat: with the extra gain on XLR, it's extremely hard to set the sub to an appropriate volume level. It's somewhere in the first millimeter of the dial, and a pain to set correctly. I decided to use an outboard volume attenuator, but I've got to be loosing something in the chain. Because both the front L&R speakers and the sub are on the same chain there's no way to do this at the pre/pro end because that reduces the volume of the fronts too.

On a side note, I'm giving serious thought to switching back to the MC1s for the fronts instead of the MG12s. Yes, I know I'll be giving up all that bass, but this is just too much of a headache. If I go that route, the I'll be using two subs, one for the deep bass and the other for the mid-bass. I sure hope this doesn't become directional.

[JoeE SP9]

Balanced connections reject hum for several reasons.
1. The signal is not referenced to ground.
2. Balanced connections feed differential inputs that amplify the difference between the plus and minus signal.
3. Radiated noise and hum that is picked up during signal transmission is usually common and equal on both the plus and minus signal and therefore does not get amplified. The specification for this is CMRR (Common Mode Rejection Ratio). It is a measurement of how much common noise and hum is not amplified.

If a single ended output feeds a balanced (differential) input there is no real benefit as far as noise rejection is concerned because one end is referenced to ground. Therefore one signal carrying wire will usually have more inherent and induced noise than the other. This results in a difference that will get amplified.