Why Single-Ended?

Yes! It brings the shield into play as part of the signal. IOW its not just for shielding any more. As soon as that happens, then the cable imposes considerably more artifact.

^^Just FWIW, star grounding is nice but the real issue is how the chassis and circuit grounds are handled!

How much potential sonic performance would I lose by using my SE preamp into the unbalanced inputs of a fully differential amp? e.g., my UV-1 preamp into the SE input of an Atma-sphere amp, or using this preamp with a Pass Labs amp.

If using our amps, the difference essentially amounts to the sonics of the cable, as that comes into play when running single-ended. The amplifier input really doesn't care because the voltage amplifier in our amps is a differential amplifier. It simply amplifies what is different between its inputs. If one side is ground it still works the same way.

I'm not knowledgable about how you  configure your circuits but I'm thinking you do not float the signal from input to output so eventually the signals do get referenced to pin one.

We try to avoid referencing signal to ground as much as possible in our preamps as it decreases the Common Mode Rejection Ratio. One area that is tricky though is the volume control. Since two of the five inputs of the preamp are single-ended only line connections (with RCA connectors), the volume control is built with 4 decks (one for each phase of each channel) and it has to have a ground reference to work right with the SE inputs. 

Home audio, especially 2 channel systems with analog being the primary source will rarely benefit from balanced connections. Adding balanced operation in this scenario will only add more circuitry with no real benefit and likely have deleterious effects.

The only place in my room where I didn't have significant interaction between the room nodes and where the equipment might be set up was about 15 feet from the loudspeakers (there just seemed to be less bass in that spot; a nice place to start if you don't want microphonics affecting the sound). So this has meant either a set of very long speaker cables (28' if I was to keep them out of sight), or moving the amps to a location right beside the speakers and running long interconnects.

The latter was not possible single-ended without audible high frequency rolloff and loss of detail. But when I went balanced, that changed significantly and by also running short speaker cables, I suddenly has more detail without brightness; a more relaxed presentation overall. There was no going back unless I placed the front end of the system between the speakers (where it just did not sound as good due to room interactions).

So the quote above is false in anyway I can make out. In the case of a phono cartridge which is balanced to begin with, its helpful to not be getting any artifact from the tone arm cable. The source is always the best place for things to not get messed up!

 Two for the signals and a third is the ground reference.

+1 on your post above Herman, but I spotted this bit in it and though I might point out that this is a frequent area of confusion: the ground is not a reference in a balanced system (or shouldn't be; if it is, the balanced system isn't being set up correctly). The **reference** is pin 2 is referenced to pin 3 and ground is ignored (used only for shielding). This may be one of the most misunderstood aspects of balanced line operation. 

It would seem so.

In order to support the balanced line standard:

1) pin 1 is ground, pins 2 and 3 carry the signal
2) the signal occurs between pins 2 and 3.
3) Ground (shield) is ignored
4) the system is low impedance.

Again as I pointed out earlier, most high end audio systems don't do so well with 3) and 4) nor for that matter 2).

If they did though, the capacitance becomes a non-issue in lengths of 200 feet or so (which should be practical in most homes- at my place they are only 30 feet).

So, Again. If the equipment supports the balanced standard, you won't hear the effects of the cable. IOW if you can hear the effects of the cable, its likely that your gear does not support the standard.

You forgot that we are discussing Fully balanced topology and not design of particular amp in general.  Setting bias point, as you described, can be done to single ended amp and has nothing to do with issue that we're discussing.  Please tell me how Fully balanced amp topology reduces third harmonic better than single ended amp.

It doesn't. The 3rd harmonic (which is musical to the human ear) occurs at about the same level or slightly less (see below) than the 3rd shows up in a single-ended design (this is assuming open loop).

Because the 2nd is pretty well eliminated, the result is (due to the ear's masking principle) greater low level detail since there isn't a 2nd order to obscure it. That there is more low level detail in such amps is not a subtle thing- its quite easy to hear. Its nice when the measurements and the subjective experience agree.

When I was speaking of the bias point I was not referring to the output tubes, but the bias point at which the voltage amplifier is set. This is not an adjustment; its the value of resistor in the cathode circuit, which can affect the distortion and gain structure of the voltage amp. In the case of a differential amplifier, this resistor is in the CCS circuit and its value can be critical. In essence the value can have an outcome on the kind of distortion the voltage amplifier makes, particularly when it overloads. I prefer to set that value so that the stage is clipping in a symmetrical fashion. This makes for more of a 3rd harmonic rather than a 2nd, but also can have the effect of reducing the amount of the 3rd harmonic.

You cannot eliminate capacitance between wires.  Low output impedance helps to lower effect of it, but it so does with single ended design.  It will be difficult to get rid of shield to wire capacitance since many preamps have balanced output referenced to ground.

I hope you are not suggesting that single-ended cables can run as far as balanced... I'm going to refer you to Wikipedia on this one.
https://en.wikipedia.org/wiki/Balanced_line

I also refer you to AES file 48 which I've mentioned several times. The Rane site has a great little article that should help clear things up:
http://www.rane.com/note110.html

The final statement in the quote above points to the possibility that you did not read my opening post in this thread. I will therefore repeat myself in saying that many high end audio products don't support the balanced standard, such as the preamps to which you are referring in that last sentence.

When the balanced line standard is not supported the interconnect cables become audible and then audiophile tend to spend a lot of time and money trying to eliminate the audible artifacts that result (IMO/IME its simply easier to just support the balanced standard). This is the reason why this debate is still around (as Herman points out) years on after we introduced balanced line to high end audio.

So Ralph, you have come over to the dark side with an SE preamp. There is some hope :>)

Ha! We've been making some variant of that since the company was founded. Not sure that 'come over' is the right phrase...

if you transformer couple it with a center tapped secondary then that would definitely be balanced.

I very much doubt that there even is such a thing as a center-tapped SUT for the reasons I outlined earlier. We have made up SUT boxes that were entirely balanced using Jensen SUTs. All transformers (including SUTs) are capable of operating single-ended or balanced; no center tap required- works better without it.

You could ask the same of Atmasphere. Why don't they offer an SET amp? The reason is they are dedicated to optimizing the topology that they are committed to.

Hm. I think you could be mistaking pragmatism for being dogmatic. Take a look at this:
http://www.atma-sphere.com/Products/#UV-1

I've often defended SET amplifiers on account of they can do something that very few push-pull amps can do: As the output power is decreased, the distortion becomes unmeasurable. The only push-pull amp I know of that does that is our own amps (now you can see why I defend SETs in this regard) although there will be others if the designers take the right steps.

Not sure of that.  Perhaps, since it is done without input transformer there is ground reference for instrumentation amp that is usually connected with higher value resistor (and small cap) to a chassis. Signal is still differential and I cannot understand why would it reduce effect that cable brings.  Cable capacitance, inductance and dielectric absorption are still there.  Do you think that extremely dirty copper would sound wonderful in balanced cable?

The way balanced line eliminates cable artifacts is twofold. First, ground is ignored, so the shield is not part of the sound (nor the is noise to which its exposed; in a single-ended system the shield is part of the signal path).

Second, the source impedance is low and so is able to swamp the inductance and capacitance of the cable.

In fact in our tests and auditions we have frequently used an aged (60 year old) microphone cable that used rubber dielectrics and tin-plated multi-stranded copper, with obvious corrosion on the shield. When driven by a balanced passive control (which did not meet AES file 48) the cable literally sounded broken compared to other cables (Purist, Kimber, Audioquest and also Mogami)- broken enough that you wondered what the heck was wrong with the stereo. When we then ran the same set of cables with a source that supported file 48, the differences between the cables, including the one with the 'dirty copper' vanished.

IOW, what the technology is **for** is to eliminate a problem that audiophiles are well aware of- which is that cables sound different and often not as musical as one would hope. Put another way, if you can hear a difference between cables in an audition, it means that **both** cables are wrong, as everyone knows full well that next year someone (likely the manufacturer of the better cable) will have a newer cable that sounds amazingly better. This has been going on decades (one would think an audiphile would just like to finally get to where that is all going and not have to search for the holy grail anymore), yet somehow recordings made in the 1950s (using balanced lines) just sound better and better as the playback equipment improves...

It does not make sense.  I understand how even harmonics are eliminated but don't know of any mechanism that would remove odd harmonics in fully balanced amp.  Remember we're talking about Fully balanced amps in general - not only your designs.

I get that it does not make sense for you. But that does not mean it does not make sense. The idea here is to remove distortion sources (now this is strictly my opinion). If you can't use feedback to get rid of distortion, how do you get rid of it? Eliminate distortion sources! A common complaint about tubes: 2nd harmonic (ask any solid state guy). OK- fully balanced differential design gets rid of the even orders. Now we are left with the odd orders. To reduce them, we set bias points in the voltage amplifier such that it cancels the odd orders. Then design the circuit to use as few stages of gain as possible (in our amps there is only one stage of gain, making them a simpler signal path than an SET). Use triodes throughout. Get rid of the output transformer (which may or may not add distortion). Take care to avoid obvious diode issues (proper metallurgy) in component selection. Stuff like that.

Kijanki, you have made one of the most reasonable cases for the sonic advantages of the single ended circuit and its simpler design. This positive perspective is rarely seen. Well done gentlemen!

For the most part I agree, however just for the record as I pointed out above, our amps have only one gain stage with no phase inverter circuit. They are a simpler signal path than most SETs. This should be possible with any **fully** differential circuit- it does not have to be an OTL.

BTW despite what Ralph contends phono cartridges are NOT balanced as there is no ground, no ground  pin connection, only 2 lines out.

This statement has long been debunked. Herman, take this from someone who has apparently made a career of balanced line operation, who also understands single-ended (I've built many SE amps; type 45, 2A3 and 300b):

Any source that employs a magnetic pickup, like a phono cartridge, dynamic microphone or tape head, is an inherently balanced source. The proof of this is simple: reverse the connections to the device and all that happens is you reversed the phase. If it really was a single-ended source, reversing the connections from it would get you a whole lot of hum and buzz!

The reason is simple- all of those sources are simply a winding.

Now I think I see where the disconnect is happening: you probably think that balanced line requires three connections, and that somehow something like a cartridge would too. It does not work that way. If you refer back to my initial post in this thread, you will see that a balanced line **ignores ground** (and so uses two connections, not three, as ground is only used for shielding).

To put that in perspective, let's take the example of a transformer driving a balanced line. I suspect you think that such a transformer would use a center tap for the ground, but that is not the case. The reason is simple: you want the best Common Mode Rejection Ratio you can get. If you use a center tap of a transformer, the CMRR will be degraded because the center tap can never be placed perfectly in the center of the winding). Instead the winding of the transformer floats- its output (or input) is merely tied to pins 2 and 3 of the XLR and nothing else. No ground connection- that is only for shielding and the chassis and is not tied to the transformer, cartridge, tape head or dynamic microphone.

So only two connections are needed, and in many cases you can operate a balanced line without the shield (sometimes its actually lower noise this way, particularly in shorter runs of less than 3 feet). IOW you don't need three connections to be balanced.

One thing here I like to point out:

Running balanced lines is an entirely different matter from having an amp or preamp that has a fully balanced differential circuit! By this I mean that you can have a single-ended circuit but run balanced lines outside the box and retain all the advantages of balanced line as it pertains to cables (a good example of this is the venerable Ampex 351 tape electronics, which is almost entirely single-ended, but runs balanced line inputs and outputs; many fabulous recordings exist in many audiophile's libraries that were recorded on those electronics). 

IOW its important to not conflate the two.

Now as it happens, there are advantages to running a fully balanced circuit. I think that one of them is the simplified signal path. For example in our preamps we have three stages of gain from low output moving coil input to the line stage output (which can drive headphones). In the amps we have one stage of gain. That's about as simple as a signal path can get!

I too prefer higher efficiency loudspeakers with an amplifier of simple design and signal path. So that is one thing that Herman and I have in common.

Also, FULLY balanced amp has practically two amps inside and costs much more.  I could buy much better single ended amp instead. That's why I would never buy FULLY balanced amp ("Fully" is not always "Better").

This statement is false. A fully differential amplifier does not have twice the parts and is not nearly two amps inside! This is a very popular myth.

Our amps tend to be less expensive than SET amps with a fraction of the power, and yet we have more bandwidth with lower distortion (without using feedback). As any transformer designer can tell you, a good SET Output transformer is a bit of a trick! Its very hard to make them in higher power levels- for this reason you can easily build push-pull amps that outperform them for less money.

Of course, we have the added benefit in the cost department of no output transformer...

Balanced input of my amp goes to instrumentation amp (THAT1200) that has CMRR of 90dB@60Hz and 85dB@20kHz. I don’t believe that it can be achieved without cross-feedback in Fully balanced amp. 90dB would be equivalent to overall gain setting (all stages) resistors matching to 0.003%. This cannot be done (be stable) even with multiturn trimpots, etc. Perhaps Fully balanced design offers better rejection at higher frequencies, but I doubt it - frequency response of both halves would have to be identical.

We tend to get about 87-92db CMRR without feedback of any sort. The key is proper Constant Current Source design and I can safely say that most CCS circuits I see in most amps are terrible. Hint: a good CCS design will employ two stages. It simply isn't possible for a CCS with one stage to work right.

I can hear the difference between different XLR ICs - perhaps Ralph was talking about matched 600ohm input/output designs that I’m not familiar with.

If this is the case its probable that your gear does not support the balanced standard. Let me guess- you can run the signal single-ended just by disconnecting pin 3, right? IOW what I am saying is that in your gear, the non-inverted signal occurs between pin 2 and ground (pin1) and the inverted signal is pin 3 and ground. If that is true, then the gear does not support the standard as ground is not ignored, and all of a sudden the cable becomes audible. This is a very common design error and to give you an idea of how common, I saw that mistake being made in a piece of Audio Precision test equipment 20 years ago! I don't know if they ever fixed that...

Third harmonic, that supposed to be euphonic, will be the same in fully balanced or single ended design.  Removal of the even harmonics cannot make amplifier sound "warmer".  It is achieved by reducing higher order odd harmonics produced by the amp.  It is likely related to excellent design and not topology itself.

This harmonic structure thing is another myth. How it works is, if the circuit is fully differential and balanced, the primary distortion product will be the 3rd harmonic, at a diminished level (IOW much less than you would see of the 2nd harmonic in a tube amp). This is true whether the amp is tube or solid state! The implication here is that the topology in fact plays a huge role. In a tube amp the higher orders will be absent given proper design.

When you think about it this makes sense. After all, triodes are quite linear so why should a tube amp make more distortion than a solid state amp? The answer has a lot to do with topology and how much feedback is applied. We don't use much in the way of feedback as we are trying to avoid higher ordered harmonics (and its the feedback that contributes to that in most designs).

One thing you are not taking into account is how distortion compounds from stage to stage. If the gain stage just does not make the distortion, it can't be compounded by the distortion of the next gain stage. We only have one stage of gain in our amps, so higher ordered harmonics really don't play a role. This allows the amps to be very relaxed.

Some one please explain to me how an SET amp can be fully differential. I see some SET amps that are offered as balanced. Could one of you explain the circuitry in the amp that makes the use of XLR connections advantageous?

All amplifying devices are differential in nature; a tube or a transistor. This is so since if the signal is the same at both inputs to the device (in the case of a tube, the grid and  the cathode) the device will not amplify. This is because it looks at what is different between its inputs.

Most designers don't take advantage of this or don't realize it, so on nearly all SETs the XLR input is not balanced (although some, like the Viva, have input transformers and so can operate either way). However it should be obvious that it is possible to set up the amplifier to use the other input (which will be the cathode of the input tube) by tying it to pin 3 of the XLR while the grid of the tube is tied to pin 2 of the XLR. This technique is not balanced, but it is certainly differential and retains many of the advantages of balanced operation (such as noise rejection). The cathode input is relatively low impedance and some preamps may not be able to drive it (although ours have no difficulty in this regard).

This technique was originally used by George Philbrick who is generally credited with designing the first practical opamps, which were vacuum-tube (as a side note he was not the inventor of opamps although he often gets credit for that too).  

You can feed a single ended signal into a fully balanced preamplifier, ground the negative (inverting) amplifiers positive input - connect the two negative inputs of both amplifiers (non inverting and inverting) together and a balanced signal will appear at the output of the preamplifier and the signal would be fully balanced from here on.

This is certainly true- we do it with our preamps all the time, but its a simple fact that the preamp is accepting the input as a single-ended signal, with the weakness that the cable becomes part of the sound. The preamp then converts the signal (via its differential operation) to a balanced output. So you can see that in this example that the signal was either single-ended or balanced, but never both at the same time.

We were the first company to produce a fully differential balanced preamp and power amp for high end audio. The amp was in 1986 and the preamp in 1989.

The reason we did it is because I had exposure to recording gear while playing in several orchestras in high school, college and after college. I saw that the microphones often had cables that were over 100 feet before their signal arrived at the tape machine. Somehow that didn’t seem to hurt the sound. About 1977 I also met Robert Fulton of FMI, who is the founder of the modern high end audio cable industry. As all of you know. At least if you didn’t, you do now.

Obviously he was claiming that cables made a difference, and he could prove it. But what I saw when my orchestra was being recorded was something different- the cable didn't seem to affect the sound!

That difference was the difference between balanced and single-ended. Turns out the phone company had to deal with sending audio over long distances and found that balanced was the way to do that; the recording and broadcast industries picked up on that pretty quick in the late 1940s and early 1950s, which ushered in the age of high fidelity.

During the 1950s home audio was seen as audio on a budget and so the use of the line transformers often used for balanced operation seemed an extravagance, especially when the signal needed to only go a few feet. So home audio became exclusively single-ended operation.

The thing is, during the 1980s high end audio really go going; ARC and others were building monoblock amplifiers and suddenly there was a home application for balanced operation. So at the end of the 1980s we introduced the world’s first balanced line products and that’s how it got started.

The thing is, there’s actually always been a standard for balanced operation! We were aware of it because of my exposure to recording equipment (Steve Tibbetts recorded his second LP in my basement recording studio in the late 1970s). So I knew the standard existed and made sure our gear conformed.

The standard was updated in the 1980s and is now known as AES file 48. Most high end audio equipment with balanced connections does not conform to the standard and as a result does not get all the benefit of balanced operation. That is why there is a conversation about which is better.

The balanced standard is:

1) Pin one is ground
2) the signal occurs between pins 2 and 3
3) ground is ignored by the source and what follows (this is done to avoid ground loops)
4) the balanced source shall have the ability to drive a low impedance; perhaps 1000 ohms or less (600 ohms was the old standard which our gear supports)

items 3 and 4 are the main areas of non-compliance with most high end audio manufacturers.

Please note that balanced and single-ended are inherently incompatible! You can’t be both at the same time- its either one or the other.

In a nutshell, if your gear is competent and conforms to the standard there will be no going back to single-ended. It sounds better even if the cables are only a foot long because there is more to it than just being able to drive long distances. But the first sentence of this paragraph is crafted the way it is because competence is a huge issue. It plays a huge role as well as the ability of balanced lines to eliminate cable artifacts does (which means that a cheap cable and a really expensive one will sound remarkably similar and by that I mean also really good if the balanced standard is used).

Of course, some manufacturers are merely placing the connectors on their gear for convenience while others are really serious about it. So like so many other things in high end audio you just have to audition it and sort it out for yourself. Sorry for so much verbiage on my part for what others have said in a single sentence...

How I see it is I can totally use a 30 foot pair of interconnects in my home (which might cost about $300 for the pair and yet sound as good as a set costing $1000/foot), allowing me to keep the amps right by the speakers with short speaker cables. In this way I minimize the effects of the cables in my system. That is what the balanced standard brings to audiophiles.

In addition, phono cartridges and tape heads are balanced sources. So part of the development of the preamp (the MP-1) was to accept the phono signal in the balanced domain. That in turn eliminates the artifact of the tone arm cable. For those into analog, this is a nice boon.