Hello,
Just want to express my frustration about all this talk of balanced amplifiers from input to output. 90% of drive units have two terminals only. Do they mean bridged? 2 anti phase signals? (Closely matched they can cancel some THD etc). I am reading amplifier brochures like I am a novice.
Obviously this only has utility in 50 feet cable runs when your trying to reject common mode interference. 120db dynamic ranges (with any form of loudspeaker) you can forget about it. It _cannot happen_ or be audible.
Hopefully some from an amplifier background can enlighten me to advantages of amplifier bridging (Yup balanced I/O with XLR's/constant impedance etc has it's merits I know that).
Take Care
Kevin
Just want to express my frustration about all this talk of balanced amplifiers from input to output. 90% of drive units have two terminals only. Do they mean bridged? 2 anti phase signals? (Closely matched they can cancel some THD etc). I am reading amplifier brochures like I am a novice.
Obviously this only has utility in 50 feet cable runs when your trying to reject common mode interference. 120db dynamic ranges (with any form of loudspeaker) you can forget about it. It _cannot happen_ or be audible.
Hopefully some from an amplifier background can enlighten me to advantages of amplifier bridging (Yup balanced I/O with XLR's/constant impedance etc has it's merits I know that).
Take Care
Kevin
Example: In class D balanced circuits are advantageous because they prevent the amplifier from disturbing itself to some extent. I mean dealing with the signal in a balanced way inside the amplifier, not interconnects.
They say that there's beauty in symmetry😀
Class B and above are really commutating circuits (read power switching with all that is bad for analog signals) so some extra PSRR, CMRR and S/N can benifit.
Class B and above are really commutating circuits (read power switching with all that is bad for analog signals) so some extra PSRR, CMRR and S/N can benifit.
Tu put it simple: to save trees, to prevent global warming.
But I don't see any reason in symmetrical design that uses class A biased output stage.
But I don't see any reason in symmetrical design that uses class A biased output stage.
I would not get to hung-up on balanced (or symmetrical) designs vs non symmetrical designs. Both have their adhererants and ultimately a good designer can (and they do) build great audio systems using both approaches.
Look at Dist vs Pout curves on an amp (bathtub shape)
Assuming you did a great amp design/layout with limiting noise and PS hash simply adding balanced in and out can push down the whole curve down at the low power end (BTW where it's used mostly) by a min of 6 dB instantly. You've doubled your desired signal to a fixed distortion/noise level.
Assuming you did a great amp design/layout with limiting noise and PS hash simply adding balanced in and out can push down the whole curve down at the low power end (BTW where it's used mostly) by a min of 6 dB instantly. You've doubled your desired signal to a fixed distortion/noise level.
Balanced inputs with XLRs for example, does not necessarily mean that it is a balanced design throughout - ie., from input to output. The Krell FPB (Full Power Balance) series would be an example of an amp with fully balanced circuitry wherein each half of the signal is processed in one half of the amp and then combines only at the speaker terminals.
Otherwise, most so called balanced inputs mean just that, that the input can accept a balanced signal - hot, cold and ground. Many use either an opamp or sometimes a discrete input stage, to accept a balanced signal, prior to the input stage of the power amp proper. Rotel for instance uses opamps and Bryston uses a discrete circuit.
Then there are those like the Pass Labs Aleph series etc., which do not use a separate input stage.
XLR inputs will benefit from sources which have balanced outputs and from long Interconnects. This just helps reduce Common Mode problems. You could always short 'cold' and 'ground' and use the amp with an unbalanced signal for shorter interconnect runs and sometimes due to cable characteristics, can even benefit with better sonics.
When each phase of a balanced signal is fed to one complete amp and the 'live' outputs are terminated on a speaker/load, they are popularly known as bridged amplifiers. In reality, this is only a half bridge amplifier. A full bridged amplifier will actually have four amplifiers. Check the EV P3000 or P2400 schematics. Hope this helps.
Otherwise, most so called balanced inputs mean just that, that the input can accept a balanced signal - hot, cold and ground. Many use either an opamp or sometimes a discrete input stage, to accept a balanced signal, prior to the input stage of the power amp proper. Rotel for instance uses opamps and Bryston uses a discrete circuit.
Then there are those like the Pass Labs Aleph series etc., which do not use a separate input stage.
XLR inputs will benefit from sources which have balanced outputs and from long Interconnects. This just helps reduce Common Mode problems. You could always short 'cold' and 'ground' and use the amp with an unbalanced signal for shorter interconnect runs and sometimes due to cable characteristics, can even benefit with better sonics.
When each phase of a balanced signal is fed to one complete amp and the 'live' outputs are terminated on a speaker/load, they are popularly known as bridged amplifiers. In reality, this is only a half bridge amplifier. A full bridged amplifier will actually have four amplifiers. Check the EV P3000 or P2400 schematics. Hope this helps.
Wavebourn said:
Not guessing I've seen the design before.😉
Maybe you should read the white paper and see if you still don't agree about class A output stages.
I see a good reason, and I think you already know it, Anatoliy: the completely constant supply current draw plus constant power per package for IC amps duals (there are power op-amp duals, too, like the LM4780 -- two 3886 dies on a common substrate with close thermal coupling). IMHO a nice way to make these chipamps sound pretty good...Wavebourn said:
And not to forget the elimination of the (sometimes) dreaded "ground".
- Klaus
I've come across that too. Though I've not seen their schematics, I believe they are basically bridged.
If I am not mistaken, the newer McIntosh Amps are described as balanced amps. Hence, their high power output.
Regards
Mike
infinia said:
What do you mean?
My class A output stages are asymmetrical, and asymmetrical only (well, except tube outputs with push-pull transformer, but it was only once, and no more).
KSTR said:
I still don't get it Klaus. My opinion is, let me repeat, symmetry is desirable for more effective power usage. Period. Other reasons are actually means turned by mistake into aims.
Fanuc,
There`s nothing to be frustrated about.
Wavebourn,
right?
Not necessarily. In balanced topologies, two devices operating in opposite phase, the signal is balanced and symmetric with respect to ground, for example in push-pull mode. Unlike in the single-ended unbalanced circuit, where the signal is referred to ground and is asymmetric with reference to ground.
There`s nothing to be frustrated about.
Wavebourn,
right?
Originally posted by Wavebourn
What do you mean?
see schematic page 14 http://www.firstwatt.com/downloads/f4_om.pdf
1) symetric class A no global feedback - compare the shape of distortion Vs Pout as Po is decreased so is the distortion reduced
Fanuc said:
Yes, if it's a power amp then they mean bridged.
When they have a balanced input and a bridged output they use the term 'balanced' for the whole amp for marketing reasons, when they should be claiming a 'bridged' output. Why? Because the word 'balanced' has positive psychological meaning in every-day conversation and they want to hi-jack that positiveness for the marketing of their amps. In other words they are happy to be technically inaccurate in their product description as long as it makes a couple of quid (bucks, euros, yen). That's marketing morons for you. The worst offenders are the headphone amp boys such as HeadRoom and RudiStor.
I run a mobile disco and have 5 metre cables from CD player to mixer and I dont get a problem with noise.
This is becasue the signal from the CD player is low impedance.
The only time i have found a problem is having an amp switched on with nothing connected to the inputs and I hear hum. This is easily fixed by using switched jack sockets and using the switched contacts to short out the input when nothing is connected. This works well even with high input impedance valve pre amp stages.
Some people seem to be looking for perfection in amplifiers and being conned by some of the propoganda put out by specialist amp makers. If it sounds good but is cheap then that is fine by me. Why use 50 transistors when 10 will do almost as well ?
It certainly makes repairing the amp easier.
I have lost count of the threads on here where people cant find faults in complicated amps.
This is becasue the signal from the CD player is low impedance.
The only time i have found a problem is having an amp switched on with nothing connected to the inputs and I hear hum. This is easily fixed by using switched jack sockets and using the switched contacts to short out the input when nothing is connected. This works well even with high input impedance valve pre amp stages.
Some people seem to be looking for perfection in amplifiers and being conned by some of the propoganda put out by specialist amp makers. If it sounds good but is cheap then that is fine by me. Why use 50 transistors when 10 will do almost as well ?
It certainly makes repairing the amp easier.
I have lost count of the threads on here where people cant find faults in complicated amps.
KSTR said:
Thanks to all the replies on this post, it has clarified my understanding.
Some quick questions.
If you have an power amp (could be just VAS & O/P stage) with poor PSRR on one supply rail (say the negative) but good on the other rail (positive) would balanced signals help here (anti phase) if you used another identical amp with the same problem ? (bridged)
I think I read in Electronics World an article from a well known contributor (Ian Hickman I think) that if you fed two amps with out of phase signals and both amps have predominately 2nd harmonic outputs (identical preferably) they would cancel. A lot of class A single ended amps do have that.
Anyway I would love to read some of the advantages to the approach overall. Do people have some good references (there must be some articles by Nelson or op amp app notes and so on). PS. I am not neccasarily against it or anything, just the nomenclature was doing my head in. (or sales speak)
Regards
Kevin
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