balanced, differential output vs simply a balanced output ( from a preamp )

[serlv]

I am a simple layperson with no real knowledge of electronic circuitry. There is a power amp I'm interested in that has a differential XLR input jack. That is it's only input.

In a discussion in a forum about these amps and preamps that are suitable for them, a company rep, in trying to clear things up a bit, stated,
"These amps require true differential inputs -- as long as we mean the same thing here. These amps require an XLR connection where (a) both the hot and cold signals are driven, (b) the hot and cold signals are inverted versions of each other, and (c) the ground connection is actually connected to the source's signal ground. In some cases (c) won't be required. Fortunately, this is how the majority of line-level equipment with XLR outputs is configured today.
Also, to clarify any possible confusion, both the DVA M225 and DVA M750 will produce output with sources that don't meet (a) and (b). However, they won't reap the benefits of the bridged configuration these amps use, and so they won't sound as good nor make the same power."

Am I worrying about it too much? I have a highly considered preamp, a Bryston BP-26, that has balanced inputs and outputs but I do not believe it is fully balanced inside. I would love to use it as it has such clean output.

Scott

 

[staticV3]

These amps require an XLR connection where (a) both the hot and cold signals are driven, (b) the hot and cold signals are inverted versions of each other, and (c) the ground connection is actually connected to the source's signal ground. In some cases (c) won't be required.

Not true.

Fully differential inputs work with both differential signals and Single-ended signals.

The full CMRR (noise immunity) can be preserved, even with a Single-ended signal source.

 

[serlv]

OK, but these amps only have the one input jack, an XLR...
I'm just trying to ascertain whether my Bryston will work fine with these amps, with no degradation in SQ. I'm mighty fond of it

 

[staticV3]

I'm just trying to ascertain whether my Bryston will work fine with these amps, with no degradation in SQ.

The Bryston has proper XLR out and the Amps have proper XLR in.

I don't see the issue..

 

[serlv]

The Bryston has proper XLR out and the Amps have proper XLR in.

I don't see the issue..

Well, that is all I need to know, then. I think it was all the talk about differential that threw me. Thank you.

 

[somebodyelse]

Not true.

Fully differential inputs work with both differential signals and Single-ended signals.

The full CMRR (noise immunity) can be preserved, even with a Single-ended signal source.

That's true, but possibly not applicable to the amp in question. We have seen a few power amps where the XLR input isn't actually differential. Instead it uses a pair of bridged amps with single ended inputs, using hot and ground as input for one, and cold and ground for the other. That fits the manufacturer's description of needing both hot and cold driven and ground referenced.

 

[Speedskater]

My answer to your same question on another forum:

Notes: for interconnect systems.
a] 'balanced' inputs or outputs are a sub-set of 'differential' inputs or outputs.
b] there are 3 types of 'balanced' or 'differential' outputs:
1] transformer outputs
2] passive or impedance outputs
3] active or powered outputs.
* * * * * * * * *
a 'differential' input or output is way easier than a 'balanced' one. No precision matching is required.

 

[sergeauckland]

My answer to your same question on another forum:

Notes: for interconnect systems.
a] 'balanced' inputs or outputs are a sub-set of 'differential' inputs or outputs.
b] there are 3 types of 'balanced' or 'differential' outputs:
1] transformer outputs
2] passive or impedance outputs
3] active or powered outputs.
* * * * * * * * *
a 'differential' input or output is way easier than a 'balanced' one. No precision matching is required.

And to 1) I would add that the transformer outputs can be fully floating, in which case either leg can be grounded for unbalancing, or centre-tapped , i.e. ground referenced, where one leg can't be grounded.

To 3) I would add that active outputs can also be fully floating or earth-referenced. By far the easiest is always to go fully balanced out to in.

Power amps are a bit of a nightmare since BTL amps became common, as these can often be two unbalanced amps connected differentially. They will work fine with a differential active preamp, but probably not with a passive or impedance balanced output.

I like transformers. You know where you are with those...usually!

S

 

[Lambda]

"These amps require true differential inputs

Some Amps do need

XLR connection where (a) both the hot and cold signals are driven,

Many Amps can give you full power even if only one side is driven.

 

[Speedskater]

Many of the current crop of active powered balanced outputs are at 4 Volts.
While many passive impedance balanced outputs are at 2 Volts.
With transformer outputs, well it depends.

Note that many older (pre op-amp) pro-audio & broadcast balanced outputs were way more than 4 Volts.

 

[Speedskater]

Power amps are a bit of a nightmare since BTL amps became common, as these can often be two unbalanced amps connected differentially. They will work fine with a differential active preamp, but probably not with a passive or impedance balanced output.

Do they actually make amps like that?

What a poor design. If they use 2 single-ended input stages connected to a balanced input. Won't work with a transformer either.

 

[Speedskater]

Am I worrying about it too much? I have a highly considered preamp, a Bryston BP-26, that has balanced inputs and outputs but I do not believe it is fully balanced inside. I would love to use it as it has such clean output.

A 'balanced interconnect system' is one thing and a great thing at that.
While a fully balanced internal circuit is another thing. It's a challenging & expensive circuit for the design engineer.

 

[sergeauckland]

What a poor design. If they use 2 single-ended input stages connected to a balanced input. Won't work with a transformer either.

They will with a centre-tapped transformer. They'll even work OKish with a floating transformer, as the input impedance of each side will be in series with the 'other' side, so will attenuate the output of the source, but not an ideal solution. I do this with a pair of Quad Ii valve amps driven from the balanced output of an electronic crossover to get twice the power of a single amp, but I agree it's a specific case, hardly universal.

Mixing single-ended, differential and balanced ins and outs is always problematic.

S

 

[Speedskater]

Thinking about it further. The amp doesn't use a balanced interconnect system. It's using an XLR for 2 single ended interconnects.

 

[nagster]

In a discussion in a forum about these amps and preamps that are suitable for them, a company rep, in trying to clear things up a bit, stated,
"These amps require true differential inputs -- as long as we mean the same thing here. These amps require an XLR connection where (a) both the hot and cold signals are driven, (b) the hot and cold signals are inverted versions of each other, and (c) the ground connection is actually connected to the source's signal ground. In some cases (c) won't be required. Fortunately, this is how the majority of line-level equipment with XLR outputs is configured today.
Also, to clarify any possible confusion, both the DVA M225 and DVA M750 will produce output with sources that don't meet (a) and (b). However, they won't reap the benefits of the bridged configuration these amps use, and so they won't sound as good nor make the same power."

Considering the manufacturer's insistence on an inverted signal input, it seems that the power amplifier does not have a differential input section. (It just replaces the two RCA input terminals of a stereo amplifier with one XLR terminal.)
In that case, be careful of the DC offset of the BP-26 XLR outputs. Usually Pin 2-3 should be fine, but not sure about Pin 1-2 or Pin 1-3.

 

[Chrispy]

Good grief so much consternation over a simple connection concept. No wonder "audiophiles" aren't taken seriously.

 

[babadono]

and (c) the ground connection is actually connected to the source's signal ground

Wrong,wrong, wrong...and oh BTW did I say wrong.