Thanks for this informative video I have a VAC PA 100 100 that l bought back in 1995 and still using today I always wondered why it was single ended only

Off topic: “Sunlight” is the update I always wanted… Thank you!!

Great Q&A. I built monos and indeed the input double triode (6n2p) is wired to use only half the tube. But there are 6 more tubes after that and doubling all of that would take a lot of real estate and be pricy to re-tube every couple of years. I laid out the system to require RCA cables that are about a foot.

Primaluna makes tube amps with balanced inputs. I’ve seen McIntosh tube amps with balanced inputs and these are just 2 among many.

Except that most tube amps with single ended inputs have another tube for a phase inverter, typically just before the output section (on each channel). So if you had a true differential input, you wouldn't need that tube and you could now use both sides of a (hopefully gain balanced) 12AX7 or similar for your balanced input. Actually saving the 2nd PI tube. Only problem there is that you wouldn't be able to handle the option of a single ended input. Which severely limits who could buy the amp. So it's better from a marketing standpoint to have a single ended input to accommodate the most users, and convert to differential (push/pull) after the initial gain stages. As you say, transistors being cheap and simple enough to apply, it's easier to design something that will handle either input.

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Howdy. A lightning of inspiration struck me. Using a balanced input would eliminate the need for a phase splitter. Phase splitters are the most difficult circuits to design to produce exact mirror signals for the end pentodes / beam tetrodes. My graphical equalizer delivers balanced outputs. Now I must update my projects agenda and attempt building a splitterless tube PA to investigate. Regards.

Hi Paul it's Shane from Australia I'm a big fan mate love your work and "l Do Subscribe" 😁👍🎧

Excellent!

Balanced Audio Technology VK-7SE is a fully balanced vacuum tube amp design and so does the Convergent Audio Technology JL and SL series of tube amps. Good for driving difficult-ish loudspeakers.

I found (and still find) that balanced XLR offers an exactness and clarity that unbalanced can not match. But, if you seek a mellower than real life sound? Something more homogenized in effect? Balanced may not be what you seek.

Love your videos Paul. Just a heads up, next to American beer, EVERYONE else makes really strong beer. :P

A 12AX7 is indeed a dual tube, as are most if not all of the 9 pin miniatures. I am dubious about the advantage of balanced circuitry unless you are running 50' cables. Since I have never heard, and am sure I never will, otherwise identical electronics in balanced and single ended mode, I cannot say for sure.

Excellent explanation. I have a question : Can FM transmission be of audiophile quality ?

For my computer desk I use 2 of those little 3.5w per channel el84 stereo tube amps from TubeDepot with the channels in push pull from the balanced out of a Schiit DAC.

Hi Paul! My McIntosh MC275 Gordon Gow Commemorative reissue (No. 1) from 1993 is a true balanced amp from input thru to the output transformer. The first tube , V1, under the shield, is the phase splitter when using the RCA unbalanced mode and the tube is simply bypassed when using the balanced XLR input. You’re right that the amp needs more tubes, though, as the MC275 uses 11 tubes for its 75 WPC whereas most KT88 stereo amps usually have only 7 tubes, like a Conrad Johnson Premiere 11A. Unfortunately, the MC275 is no longer balanced when the outputs are paralleled or strapped together, not bridged, for 150 watts mono.

Currently designing/building a DIY headphone amp - balanced differential cascode feeding drivers and totem push-pull OTL output for each channel. A total of 16 tubes. More tubes = higher cost. I also have a design in the works - direct digital using tubes only. The tube op-amps being fully differential results in a large number of RF tubes. More tubes often mean more issues todo with distortion due to non-balancing but at the same time allows you to deliver good bandwidth. Lastly more tubes = power requirements on the PSU which results in higher current and complexity thus more cost.

Paul in this video explain why it's difficult to have a tube amp with BALANCED TOPOLOGY Having a balanced input/output in a single ended topology is easy, just add balanced connector and some adapter/transformer. That's what most tube amp with balanced output/input do (they are still single ended tho :) ). But being true balance (having balanced topology) is difficult, just like he said, amount of tube will grow exponentially everytime you add components which are not fully differential.

Also the user of tube amps often enjoy the high 2nd Harmonic Distortion that tube amps often create. Balanced working would tend cancel the 2nd HD.

Audio Research has been making balanced tube amplifiers for decades.

Paul kicks #ASS

For a single-ended input stereo amp. you'd have 1 tube for the 1st preamp stages, another for the 2nd preamp stages, and one for the phase-inverters. For a balanced-input stereo amp, You'd have 2 extra tubes for the 1st and 2nd preamp stages, but you'd *eliminate* the phase inverters! That would be a net increase of only one tube!

If you’re looking for a superb tube preamp with true balanced in- and outputs look at Einstein „The Tube“ or the successor „The Preamp“ and be done for life …talking HighEnd here. But this ain’t no mellow, slouchy sounding preamp but an extremely dynamic and resolving one. Really great 👍🏼

I've owned several BAT tube amps that only had balanced inputs.

listening this through balanced Loxjie P20

Paul, there is another way - a transformer! Most legacy pro tube audio gear used input and output transformers feeding single circuitry inside the box. Even some solid state pro gear still uses transformers to provide balanced I/O. Now as you no doubt know, good audio transformers are expensive. Like over $100. That exceeds the cost of any tube. For solid state gear, today's OPAMP solutions provide excellent transformer less balanced I/O at an even lower cost. Interface chips like the AD SSM2141 and SSM2142 as well at the Burr Brown equivalents are very good. But in the good old days, we used transformers. But that art is mostly gone except for the few left like Jensen. Hence the high cost of good audio transformers.

Mine Nat Audio gm70 mono's have xlr, don't know if it's true balanced though

You might want to think about 12au7 as a lower noise alternative to the 12ax7. 12ax7 is way better for guitar amp applications but might be a little "fizzy" for a tube based stereo.

Another issue I have seen is tube power amps almost never use a tube bridge rectifier , only full-wave . Solid state bridge rectification is so much cheaper and cooler running .

We learned what balanced inputs, outputs, and circuits mean. But, what is impedance-balanced output? I saw that on a lot of USB interfaces and DACs.

Maybe a vid on xlr vs single ended?

Most valve amps with XLR inputs are not actually balanced. On the inside you will find that only one of the + pins is connected. They add a resistor to reduce the higher balanced signal voltage to match the RCA. In practice this means that you get the convenience of being able to use a balanced cable however you don't get any of the advantages balanced offers.

I have a single ended stereo phonostage that uses 2 12ax7's. If the 12ax7 has 2 channels, why would Pro Ject use 2 of them on this Tube Box S2? Better isolation, perhaps?

Hybrid tube amps have balanced inputs! i.e, tubes on the preamp stage and solid state on the output stage! My Audreal XA6950 hybrid amp has balanced input which I do utilize !!

There are plenty of old tube mic preamps that are balanced all the way to the output.

You could use Transformer inputs an outputs but good transformers are very expensive.

I am not sure why if you have a balanced input do you need to have an amplifier that is balanced all the way. The advantages of balanced is to have noise cancelled out in the interconnects. Once you are inside an amplifier this can be mitigated very well with a single ended circuit. You could even have a balanced input transformer based attenuator and have the secondary coil unbalanced out.

Paul just some tube trivia, 12ax7= 12.6 volt heater, ax has to do with internal construction, 7 useful elements.

My Audio Research 250SE mono-blocks have balanced inputs

Can't stop looking at that crooked outlet on the right

The Decware Super Zen Triode can be upgraded to balance inputs for extra cost. With that being said, if you have a short run XLR cables are unnecessary and good RCA cables will perform just as well. XLR just increases the price of the product and makes you think you are getting something better but in reality probably won't benefit you.

It defeats the purpose of many tube amplifiers to have different tubes for the positive and negative part of the signal. The aim is purity. And purity means just one amplification element to handle the whole of the signal. Purity comes with its drawbacks. Fortunately, SET tubes match very well with some excellent high-efficiency loudspeakers, in a way that each part enable the other to perform their best.

Balanced is pro level, and transformers were used almost exclusively. Trouble is, they are broadcast quality, and expensive (check out a Peerless / Altec 4722).

My plexi definitely does not have a balanced input AND it’s mono (; it’s my favorite tube amp ever! Even though it’s definitely NOT hifi and not supposed to be. I am an absolute nut about tube guitar amps, understanding them much more than any other audio electronics.

I think my 275 mcintosh has rca and balanced if that's what this is about...

lets not forget that if you listen to music for 6-8 hours a day like me you'll have to replace the tubes very often,like every few years which makes it much more expensive.

Mold exhibits exponential growth - not tubes in a power amplifier!

Prima Luna has balanced inputs!

My Sonic Frontiers amps have balanced inputs...and many others.

Try to design one and you will soon understand why.

balanced I/O´s using transformers?

To say tube amps do not have balanced circuitry does not reflect on all tube manufacturers. Majority of higher end tube manufacturers offer both RCA and balanced connections.

9% is a lunch beer right?

There is too much variation in the output between two of the exact same tubes to be used in a differential sum. You'll have only 30% or less of the input signal.

My subwoofer quivers everytime he ends the video with his subsonic "bye".

There's no such thing as a "P-channel" tube!

A DSP can make better more fine-tuned tube distortion with no degrading performance over time or warm-up issues than an actual tube, but tube aficionados don’t want to hear that🤔 Alright, tubes do look cooler indeed and for analog sources, a DSP isn’t great.

manley have bance input

Well, if it grows like mold on bread, there's only one thing to do: Try to "make penicillin" from it! ;)

Mcintosh C2600 is balanced.

Well, thats just false. Differential input and push-pull, or BTL, are two completely different things.

Unless you're running over 5 metres of cable you don't need balanced, RCA is fine

Waffles..... U r 2 much !

If a product sound better balanced than single ended, then it is bad design, balanced need 2 of everything, making everything double expensive, why not use the money for better parts, also home audio, not much need for balanced, and I own balanced and single ended equipment.

Lol. Tons of tube amps have balanced in.

In all reality balanced in home audio is gimmicky at best ...

The west coast of the usa makes the strongest beers. Some upto 14% and a few up to 75%.

Please don't stoop to groveling for subscribes. Not classy.

....your videos are way too short,....as if you are in a hurry to go somewhere.....10minutes would be good. Listening to some people is so irritating,...but you are definitely not...SO TAKE IT EASY!