Balanced vs Unbalanced?

I would like to point out that it's not all lollipops and roses. One unmentioned difficulty is that for everything to work as designed you have to have a circuit capable of producing 2 signals that are exactly the same except for their polarity. I agree that using a differential circuit makes it easier but there are still a lot of things that can cause an imbalance. If there were not the CMRRs achieved would be much higher than they are.

The other problem I see with Atmasphere amps is the OTL output. Ralph has done an admirable job of overcoming the stability problems experienced by earlier designs but I don't think you can overcome the inherent problems caused by paralleling a bunch of tubes and using them in a push-pull circuit. I have no explanation but cathode follower amps have never sounded as good to me as common cathode.

I have 3 directly coupled triodes and an output transformer between my source and my speakers which I believe leads to much better sound than you can achieve with a more complex circuit. Of course, if anybody wants to send me an OTL amp to try I would be happy to entertain them.

While I do agree with Ralph's explanation of the technical side of things I disagree that this leads to circuits that sound better than an SET, but of course this is a debate that cannot be won on either side.

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Herman,
IMHO, SETs are distortion generators. They can make a Yamaha violin sounds
like a Stradivarius. Like guitar amps, they should be considered more like a
musical instrument than audio reproducing equipment. Can SETs sound
good? Sure, I like them too. I used to built them when I was much younger.
But they are not Hi-Fi amps.

I know many people will disagree. Since we are talking about Hi-Fi here, Hi-
Fi or High Fidelity means faithfully reproduce. If an amp can make a Yamaha
violin sounds like a Stradivarius, it is not Hi-Fi, no matter how good it may
sound to some people.

06-01-10: Sidssp
IMHO, SETs are distortion generators. They can make a Yamaha violin sounds like a Stradivarius.

So can poorly designed/executed push-pull circuits(tube & solid state). Well designed/executed SE circuits in properly associated systems can also make Stradivarius sound like Stradivarius. The same can be said for most other well designed/executed circuit topologies.

Sidssp, There are many forms of distortion. SETs are the most linear devices on the planet. How does that equate to distortion generator? I lived through the distortion wars of the 80's where we ended up with vanishingly low distortion on amplifiers that would make your ears bleed.

The problem with SET amps, low power. The solution, highly efficient speakers.

Good source + triodes + good horn speakers = bliss

Sitting with a smile on your face and your toes tapping or dancing around the room are the defining factors. Audiophile nerds who sit frozen in one spot, never moving, never physically reacting to the music, discussing how black the background is and how much air there is around the instruments have so completely missed the point that they are hopeless. I hope you aren't one of these nerds.

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Herman, just for the record, I like SETs a lot myself and have built a number of type 45 and 2A3 based amps.

But before we go into that,

One unmentioned difficulty is that for everything to work as designed you have to have a circuit capable of producing 2 signals that are exactly the same except for their polarity. I agree that using a differential circuit makes it easier but there are still a lot of things that can cause an imbalance. If there were not the CMRRs achieved would be much higher than they are.

The above comment is not exactly correct. It only applies to the use of balanced circuits **that are not differential**. IOW, if you have an imbalance in a differential circuit, it will be corrected in the next stage. In addition, a differential circuit will absolutely insure that the inverted and non-inverted phases of the signal will be absolutely 180 degrees out of phase but otherwise identical, even if their amplitudes are slightly different. So it does not have to be as exact as you describe in order for the CMRR to be retained.

I have found in the execution of differential circuits that the constant current source used in the circuit is a big deal. Most CCS circuits only have a single device (tube or transistor) and so are ineffective. They have to have at least 2 stages to work right. My point here is that doing balanced right is like anything else: a matter of execution. We get CMRRs well in excess of 100 db, even without perfectly matching signals.

Although its a different subject, you did mention the multiple tube issue in OTLs. That is no different from using multiple tubes or transistors in other amplifiers, and just like in other amps (including SETs) there are ways to make those tubes work quite well together! I agree that SETs have a lot of linearity, especially in that first watt where everything is so critical. It might interest you to know that the only other type of tube circuit that has the same behavior is an OTL- if designed right they have no crossover or notch issues, so like an SET the distortion vanishes as power goes down. Unlike an SET, they don't make nearly as much distortion at higher power, and so offer less coloration and smoother sound. It is easy to demonstrate. PM me.

Good source + triodes + good horn speakers = bliss

This is a formula that has worked well for me for a very long time :) I add to it: balanced operation- this ends the sonic role that interconnects traditionally play.