Tube Amps with Balanced Inputs

Why do so few tube amps come with balanced inputs, especially SET amps? I'm looking for a pair of SET amps (hopefully 300B), but can't seem to find any with balanced inputs, even the very expensive ones. Why is this?

- Stew
Check out Atma-Sphere amps. SE, OTL's, will probably give you the sound your looking for in spades, with good bass response as well. Fully Balanced. Just my opinion, hear them for yourself. Highly recommended. Happy Listening.
A true balanced amp processes the inverted and non-inverted components of each channel of each balanced input through seperate circuits (including discrete volume control sections). The amp responds to the difference in signal across the inverted and non-inverted components.

SET amps are just that - single ended. By definition they cannot process seperate inverted and non-inverted signal components since there is only one signal path. To properly (note the word "properly") handle a balanced input an SET would have to supply fron end circuitry to invert the inverted component and add it to the non-inverted component to yield a single ended signal for the remainder of the SET to process. This circuitry would be more complex than the SET itself and is most easily implemented by an op amp, though it could be done with tubes. Either way you've lost the minimalist philosophy that is one of the appeals of these amps.

If you must use balanced inputs then use an adapter. Typically these connect only the non-inverting signal component to the single ended input, thus destroying the key technical advantage of balanced connections: interference rejection.

Thanks for the tip. I'll take a look.


Ah, I hadn't thought of that. I'm running long interconnects to the amps, and it seems running balanced from the preamp to the amps is considerably less noisy than with a single-ended connection.
I don't think a true 'balanced' output is possible with a single-ended amp. George Wright's Mono 10 amps use a pair of 2A3's in Push/Pull and are one of the closest things to a SET sound I've heard from a P/P. Great little amps, but don't know what you are specifically looking for (price range, power, system matching, etc). The Mono-10's have both balanced and RCA connections and were wonderful amps in my system.


Thanks for the tip. I don't know anything about their amps, but the price is certainl right. Basically, I'm currently using AES (Cary) Sixpac Amps (with KT-66 tubes), and just switched to Zu Tone speakers, which are very sensitive (claimed 101db). I'm using a BAT VK-5i, which is a balanced preamp, and thought of switching amps to try to get that SET magic I keep reading about. I really want to stay fully balanced, which was the reason for my post to begin with.

You mentioned that these sound close to SET amps. What amps have you compared them to?

- Stew
As I said earlier, SET is an unbalanced technology - you can't stay fully balanced all the way to the speakers.
I got it, thanks.
You mentioned that these sound close to SET amps. What amps have you compared them to?

I've directly compared them to my Quicksilver 300B SET monos and Wright's own WPA3.5 SET amps that utilize the same 2A3 tubes but solo, in a SET topology. The Mono 10's have some qualities of both...they do a wonderful job of that airiness and holography that bring a breathy presence to the SET amps, but, at the expense of perhaps the last word in those qualities, the Mono 10's bring a bit more muscle and boogie-factor into the equation. They do a better job with more dynamic, layered music (orchestral, for example) than the two SET amps I've owned can. They're still relatively low powered at around 11 watts. The lows are a bit tighter and lower than either of the SET amps could muster. The SET's put all their eggs in the midrange basket, but boy do they do that right. The 300B's are a bit more versatile than the 2A3 SET amps in my experience with the two amps I've mentioned, but be aware that system synergy is a make-it or break-it proposition here. YMMV according to what you choose and what you try to match it up with. I would say the Mono-10's require similar care in choosing the right speaker (ie sensitive speaker) for your room/musical tastes, as would a SET, but they would probably be just a bit more versatile in that regard. I'm sure I've written about this before, so you can search the archives. Of course read what others have to say, listen to examples for yourself, and make your own call. It may not be your cup of tea, but if it is you will be very happy to have found that out because it's like nothing else out there. OTL is also quite a unique sounding alternative. I don't have enough experience there to give you any input, other than I think it's worth considering too, as someone has already suggested. In that realm read some of the posts by member TWL (Tom Lyons) for further input. I don't think he's posting here anymore (sadly) but the archive should have plenty of his input on OTL amps.

Hope that helps.

Thanks much Marco for all the info. Based on that and other research I've done, I just purchased a pair of Mono 10's from someone here on Audiogon. I'm using Zu Tone speakers with a claimed 101db sensitivity, so hope that there will be enough power (I sometimes do enjoy listening at fairly high levels). These amps do seem like a good choice, since they seem to have a combination of some of the SET qualities, and are balanced in design, so I can run my long balanced interconnects without adding noise.

Thanks again for the suggestion...

- Stew