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Dual Differential / Balanced?

Hey all I’ve got that itch to upgrade power amps, and was wondering how valid the dual differential aka "balanced" monoblock or dual mono design is in terms of increasing fidelity compared to a conventional SE amp. note my preamp is also fully balanced

how much noise is avoided by using a fully balanced system?

right now I use 2 haflers horizontally biamping NHT 3.3. using mogami gold XLR
p4000 200wpc mids/highs p7000 350wpc lows

from what I’ve read it only matters if both the preamp and power amp are both truly balanced

I have a nice Integra Research RDC 7.1 fully balanced pre/pro, it was a collab with BAT, I would go for the matching RDA "BAT" amp but its pretty much unobtanium

So far I’ve looked at classe ca200/201, older threshholds, older ksa krell, as fully balanced monoblocks/ dual mono stereo

I was also told to look at ATI amps, they look very impressive but expensive

I’m looking to spend 1500-2500 preferably used products, I dont have an issue with SE amps I just want to exploit the fact my pre is fully balanced, and perhaps get better sound. If anyone has recommendations for awesome dual differential power amps. the NHT 3.3 are power hungry so at least 150wpc, class A/AB

I’ve also come across the emotiva XPA-1 monoblock, I can get a good deal on one of them I wonder if its worth picking this up and praying for a lone one to come on classifieds on ebay- note this is the older model in the silver chassis 500wpc 8ohm / 1000 4ohm

for context prior to the realization that I should use a fully balanced system I was looking at brystons and mccormack amps.. thanks
nyhifihead
kijanki's avatar
kijanki
4,428 posts
 
Cleeds, yes, balanced operation is used in professional audio in form of balanced cables, balanced inputs etc. I’m all for it. I just don’t see how fully balanced amp can have better noise rejection than plain amp with balanced input. Instrumentation amps, like one used in my Rowland amp have 90dB noise rejection at 60Hz. That would imply gain matching of two independent amps to 0.003% to achive the same result. I also don’t see how removal of even harmonics only can help. Since outputs have no ground reference (current doesn’t flow thru ground) feedback might cause instability. That requires additional third feedback for common mode.

Again, I don’t see how this scheme can help with noise. In addition even connection with XLR cable is not always the best. If you don’t have a lot of noise you might be better of with plain single ended RCA since additional circuitry to make balanced output affects sound.
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cleeds
5,960 posts
 
kijanki04-22-2016 11:15am " ... yes, balanced operation is used in professional audio in form of balanced cables, balanced inputs etc. I’m all for it. I just don’t see how fully balanced amp can have better noise rejection than plain amp with balanced input. "

A single-ended amplifier with a balanced input and/or output is still a single-ended amplifier and does not offer all the advantages of a differential amplifier, which provides common mode rejection.

" ... Since outputs have no ground reference (current doesn’t flow thru ground) feedback might cause instability. "

That's a red herring. I've never seen instability problems with differential amplifiers.
kijanki's avatar
kijanki
4,428 posts
 
A single-ended amplifier with a balanced input and/or output is still a single-ended amplifier and does not offer all the advantages of a differential amplifier, which provides common mode rejection. 
This is not true, IMHO.  Single ended amplifier with balanced inputs can provide huge common mode rejection, better in my opinion than fully balanced amp.  Fully balanced amp cancels (at the speakers) common mode input noise, only if gains of both half-amps are identical.  Gains can be matched with discrete components only up to certain point.  Fully balanced amps have some advantages like no output ground current, cancellation of even harmonic, doubled slew rate etc.  but have also many disadvantages.  One of them is the fact that signal goes true many more stages (bad for clarity), output impedance is doubled while the cost (and complexity) is much higher.
atmasphere's avatar
atmasphere
11,841 posts
 
Kijanki, I have to straighten you out on a few things!

1st- the use of balanced line is lower noise from the cables no matter the length, assuming that the input of the amp is properly designed.

2nd- the even ordered cancellation thing the way you are presenting it is incorrect! How that works is an amplifier that is fully differential and balanced will have even ordered cancellation **from input to output**, not just at the output. What this means is that less distortion will be compounded from stage to stage. If in the case of a tube amplifier, this means the primary distortion product will be the 3rd, which is still considered musical to the human ear. However it will be generated at a much lower level than the 2nd would have been!

At any rate you are not removing even ordered harmonics from the signal- all you are doing is preventing even ordered harmonic generation, which means the circuit will be more neutral.

3rd, the idea that the signal goes through many more stages is a myth. In our amps, the signal goes through exactly one stage of gain, which is less than most entirely single-ended amps. The complexity of the circuit is not the same as the signal path! Our preamps have only 3 stages of gain from the LOMC phono input to the line stage output. Thats a fairly simple signal path compared to almost any preamp. Additionally the output impedance has no bearing on the fact that the amplifier is fully balanced/differential.
Since outputs have no ground reference (current doesn’t flow thru ground) feedback might cause instability. That requires additional third feedback for common mode.

Again, I don’t see how this scheme can help with noise. In addition even connection with XLR cable is not always the best. If you don’t have a lot of noise you might be better of with plain single ended RCA since additional circuitry to make balanced output affects sound.
Essentially the statements in the above quote are false.
@nyhifihead,
if you are looking at solid state amps, the McCormick and Pass amplifiers are quite good and accept a balanced input correctly (many high end audio amps do not, likely because the designers don't know that there is a standard for balanced line operation, defined by AES file 48).
kijanki's avatar
kijanki
4,428 posts
 
@1 - I've never said that it doesn't.  But it will remove cable noise by means of either balanced input in single ended amp or fully balanced amp.
 @2 - again, I did not say it removes even harmonics from the signal. It removes even harmonics produced by the amp at any stage by means of cancellation AT THE OUTPUT.  These even harmonics often make amplifier sounding warm and euphonic.  Yes, the third one is not bad, but higher odd harmonics are quite nasty.  Removing only even harmonics while leaving odd harmonic intact will lower total THD but also will make sound colder, brighter.
@3 - Output impedance will double since there will be two output stages - similar situation to bridged amplifier.  Complexity is much higher no mater how simple the circuit is. If signal goes thru one gain stage only in single ended design, it will go thru two stages in the balanced one  (not to mention two output stages).  You might not see a problem with that, I do.
I won't even comment on the issue of instability because you can find it in any FAQ/primer on fully balanced design, but it appears that you question my notion that connection with XLR cables is not always the best.  Experience of many people on this forum was that RCA connection sounded better than XLR.  I'm sure that Al (our technical guru) would agree with me - that balanced output, because of additional circuitry might not always be the best.  I will leave it at that.
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