Why Single-Ended?


I’ve long wondered why some manufacturers design their components to be SE only. I work in the industry and know that "balanced" audio lines have been the pro standard (for grounding and noise reduction reasons) and home stereo units started out as single-ended designs.

One reason components are not balanced is due to cost, and it’s good to be able to get high quality sound at an affordable price.
But, with so many balanced HiFi components available these days, why have some companies not offered a fully-balanced amp or preamp in their product line?
I’m referring to fine companies such as Conrad Johnson, Consonance, Coincident, and Bob Carver’s tube amps. CJ builds amps that sell for $20-$39K, so their design is not driven by cost.

The reason I’m asking is because in a system you might have a couple of balanced sources, balanced preamp, and then the final stage might be a tube amp or monoblocks which have SE input. How much of the total signal is lost in this type of setup? IOW, are we missing out on sonic bliss by mixing balanced and unbalanced?

lowrider57
Your list will grow exponentially if you add components which are not fully differential. Some refer to this as "truly" balanced, meaning identical circuit topology for the + and - legs of both left and right channels.

Many other manufacturers are using single ended topology, but offer balanced connectors. Some are simply adapters built into the chassis, some use transformers to convert the balanced signal to single ended.

Single Ended Triode amps certainly do have quite a following. The reason that manufacturers designs vary is because no one single design has been proven to be superior.
I have owned good and bad components that were single ended and balanced designs.

Just as there is no "consensus" answer for the planar or dynamic speaker design, tube or solid state amplification design, digital or analog source design, there is also no consensus answer for the single ended or balanced design.
John nailed it, +1.   
Just because you have XLR inputs or out puts does not mean yo are balanced

As with John I've heard modest and excellent examples of both single ended and true balanced systems. Needless to say many variables determine the final sound heard with a component or full system. I appreciate the stated advantages of differential balanced circuits. Ironically some of the very finest audio systems I've ever heard were with the simpler (technically inferior?) single ended circuits. Either is capable of superb sound quality. Designer/builder talent, parts quality and implementation are major factors involved.

Charles

The reason that manufacturers designs vary is because no one single design has been proven to be superior.

Designer/builder talent, parts quality and implementation are major factors involved.
+1000!!!  At the risk of beating a dead horse, virtually every design is a compromise.  The "best" designs are those whose compromises have an end result that most closely matches the end user's value system.  And that's leaving implementation (which is equally important) out of the equation altogether. 

Not to be flip, but that's why there is not only chocolate and vanilla, but also Ben & Jerry's and Hagen-Daz.  


We only do balanced

http://pbnaudio.com/audio-components/audio-preamps/olympia-li-lxi

Our power amplifiers have a fully balanced input stage as well and when used as mono blocks the output stage becomes fully balanced as well.

http://pbnaudio.com/audio-components/audio-amplifiers/olympia-ebsa1

Even in our consumer direct line, Liberty Audio the topology  is similar

http://www.libertyaudio.com/products/b2b-2-line-level-preamp-dac

Same goes for the power amplifier

http://www.libertyaudio.com/products/b2b-100-all-mos-fet-stereo-power-amplifier

And the phono preamplifier, obviously you will need two of them just like the power amplifier

http://www.libertyaudio.com/products/b2b-1-all-fet-phono-preamp

Good Listening

Peter



Thanks for the comments so far. When I referred to balanced designs I was talking about fully differential, not simply an XLR connection. I would include Peter’s designs wbere there is a conversion after input stage in the discussion.
In addition to the good points that have already been made, I would cite the following highly technical and abstruse factor: Traditions die hard :-)

Related to that, I'd imagine that a factor in many cases is that designers tend to use approaches they are familiar with, and that build upon their previous work, unless there is a compelling reason to change. And the fact that any given design is likely to be used in many systems in conjunction with associated components that are single-ended would seem to make the case for change less compelling.

Finally, making a design fully balanced adds complexity, and with it presumably more opportunity to go wrong, and more opportunity for the design and development process to become more costly and lengthy than desired. Especially if the designer has not previously used fully balanced approaches.

Best regards,
-- Al
 
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.
Thanks Ralph. Great points and well said.
Post removed 
Thanks for the comments, Al and Ralph.
@atmasphere , on a side note, I discovered the Yr album by Steve Tibbetts in 1980 while working at my college radio station and flipped out over his music. We put it into Heavy Rotation. That's where I got my start in audio engineering, since Syracuse was a top broadcast school, engineers were full-time employees and required to have an FCC license.

Now, getting back to my SE design question regarding CJ, is this a case of the company finding a design that reproduced very high quality sound and stayed with it since their products were and are still are so successful?
@almarg made a related comment...
I'd imagine that a factor in many cases is that designers tend to use approaches they are familiar with, and that build upon their previous work, unless there is a compelling reason to change. And the fact that any given design is likely to be used in many systems in conjunction with associated components that are single-ended would seem to make the case for change less compelling.

Just to mention if I'm correct, seeing no one has.
  
A totally Single Ended design doesn't have a Phase Splitter (driver) tube, as Push Pull ones have.

Cheers George   
I have always wondered why "almost nobody" buys (or even tries) inexpensive "pro" balanced cables, on the "true fully balanced" audio equipment, such as Pass Labs and ARC. They sound the same as the expensive ones IMO!

This topic has been "put to bed" every time it comes up.

Also why do reviewers not "call out" the equipment manufacturers, with "fake" balanced connections?

Seems like most all audiophiles like to waste money, or are just stupid!

This is strange???


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?
Ralph,

"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."  

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.

 Don,

"I have always wondered why "almost nobody" buys (or even tries) inexpensive "pro" balanced cables, on the "true fully balanced" audio equipment, such as Pass Labs and ARC. They sound the same as the expensive ones IMO!"

Me too,  the Canare L-4E6S  wire offered by Bluejeans cable and other makes for a nice set of interconnects.

Good Listening

Peter

Al, Peter, Ralph,

I use a KEF 107/2 KUBE between a Parasound JC 2 BP and JC 1 monoblocks.  The KUBE is single ended in and out, so prevents a balanced connection between preamp and amps.  The amps are adjacent to speakers, with over 10' separation .  Is there a way to use a balanced connection?  My email address is dbphd@cox.net.

why do reviewers not "call out" the equipment manufacturers, with "fake" balanced connections?

That’s true.  We know from the review that the unit is not a balanced design. They could say "this amp has RCA and XLR inputs."




BD,

Probably not, would there be a way to use the KUBE between your source and the Preamp?  of course with several sources this is a problematic solution. Alternatively could you get a second KUBE ?  would require some fancy wiring but the signal would then be balanced, however probably more effort required than it is worth.


Good Listening

Peter
Also why do reviewers not "call out" the equipment manufacturers, with "fake" balanced connections?
Many amps, preamps, and sources have fake balanced inputs and outputs In that they just put in an extra opamp in the signal path to create a balanced input or output.
Where their single ended input/output is better as that opamp is then not in the signal path.

Cheers George
DBPHD, for the benefit of others who may respond I’ll mention that the manual for the JC2 BP states that it "uses a fully differential balanced circuit and its balanced outputs do not require or use phase inverters." Also, while as far as I can tell from its literature the JC1 does not appear to be fully balanced, it is described as using a differential input stage. And the manuals for both components recommend balanced connections where possible.

So what you might consider doing, at a cost of a bit under $600 plus some additional cabling, would be inserting Jensen transformers between those components and the inputs and outputs of the KUBE. Or, at a cost of around $300 plus some additional cabling, only between the KUBE and the power amps.

Those would convert the unbalanced signals to or from a true balanced pair of signals. They would provide essentially the same noise reduction benefit and reduced susceptibility to ground loop effects that a well designed balanced interface between components would provide. In this particular case, however, I doubt that it’s possible to predict whether the net result would be an improvement, or little or no difference, or perhaps even a slight loss of transparency. Reports here by users of Jensen transformers have generally been very positive, although a few, including Ralph, have provided comments that are a bit mixed.

Suitable models would be the PI2-XR at the input side of the KUBE, and a pair of model PI-RX located near the inputs of each of the amps. Here is a good supplier, although they can also be ordered directly from Jensen, at a slightly higher price in some cases.

Regards,
-- Al

The Tim Paravicini-designed EAR-Yoshino tube circuits are all single ended, the pre-amps and power amps having transformers on the XLR/balanced inputs and outputs.
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.

Phase has to be inverted somewhere, either for TRUE balanced (XLR cable) or FULLY balanced design.  It involves extra circuitry that does not make sound more transparent.  For short connection, in electrically quiet environment, single ended design might be a better choice.  As for the FULLY balance design - it offers slightly* better common mode electrical noise rejection at very high frequencies and cancellation of even harmonics produced by the amps.  I don't care for both since my connections are short, while shields and twisted pair, in my XLR cable, work really well.  Cancellation of even harmonics, produced by the amp, makes it sounding colder, while odd harmonics, responsible for brightness, are left intact.  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").

* In order to provide good common mode rejection two halves of FULLY balanced amp cannot be independent.  Negative cross-feedback has to be used to equalize gains of each half and that might be far from perfect.
Hello Kijanki,
That was a very interesting and well reasoned post describing some of the inherent advantages of single ended topology. Just as Ralph presents a compelling case for fully differential balanced circuit.   It is quite clear why both topologies  can result in excellent sounding audio components. 
Charles 
+1 Charles.

Regarding this comment in Kijanki’s post:
In order to provide good common mode rejection two halves of FULLY balanced amp cannot be independent. Negative cross-feedback has to be used to equalize gains of each half and that might be far from perfect.
With some fully balanced architectures the need for negative cross-feedback, or even any feedback, can be minimized or avoided. For example, Ralph’s designs employ an architecture based on differential stages, and are typically spec’d as using just 1 or 2 db of feedback. And in the solid state domain many fully balanced Ayre amps employ zero feedback, and I believe most or all fully balanced Pass amps use very minimal amounts of feedback.

Also, as stated in one of the papers at Ralph's site, "for a given number of stages of gain, differential amplifiers have about 50% more parts," rather than being closer to the equivalent of two single-ended amps that are otherwise comparable. Although with some other balanced architectures the parts count may indeed be close to double.

Best regards,
-- Al


almarg, thanks for the advice.

I have a pair of ISO-MAX PI-2xR converters I have used in the past, but it's a bit a kluge.  I hadn't thought to try converting just one side of the KUBE link to balanced -- a half kluge.

An alternative in the manual for the KEF 107/2s is to insert the KUBE in the tape loop of the preamp, but it's not obvious to me how that works.  The JC 2 BP does have a fixed output for recording but no monitoring capability.  I suppose that output could go to KUBE, but where would the output of the KUBE go?  If to one of the JC 2 BP inputs it would become the source.  

The manual for the Ayre phono stage (I use a JC 3) includes diagrams that seem to suggest converting an RCA plug from a turntable to a balanced input, but I may be misreading that.

Finally, the noise level of the system is low enough to be inaudible even with an ear pressed to the mid/HF driver.  My concern is maximizing sound quality of an excellent sounding setup, so maybe it's wild goose chase.

db  
Al, since I don’t see removal of even harmonics (while leaving odd harmonics intact) as an advantage, then the only thing that speaks for Fully balanced amp is better noise rejection in comparison to amp with True balanced input. 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. 

Perhaps it is achievable using differential stages, but unless gain setting resistors are not on the same substrate stable 90dB does not seem possible.  Perhaps he is using very expensive matched resistors, but price of his amps justifies the cost of components.

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. In any case, it is valid for both True balanced and Fully balanced.
Again, I would buy an amp if it sounds good and not because it is Fully balanced. If anything, I would avoid fully balanced amps as too complex (too many parts to fail).

bdp2The Tim Paravicini-designed EAR-Yoshino tube circuits are all single ended, the pre-amps and power amps having transformers on the XLR/balanced inputs and outputs.
This brings up an interesting concept that I have been thinking about. In the case of a SE designed preamp, what would be the preferred way to send the signal to the amp; use unbalanced RCA cables, or go thru transformers with XLR’s which will be converting the signal back to single-ended? And depending on the type of transformer, the gain may be increased on the output, or it may be a 1:1 conversion. Seems like an unnecessary step.

But if the preamp was fully differential, then it would be advantagous to output a balanced signal to the amp’s XLR/balanced inputs.
Am I correct?
Converting single ended - balanced - single ended using transformers, makes sense if you have a lot of electrical noise and connection is long. Otherwise transformers won’t add anything positive to sound. They will introduce some low frequency distortions. If your preamp and amp are both differential you still might like single ended connection more. (my power amp has only balanced input - I had no choice).  XLR cable's shield is grounded on both ends shorting that way chassis and possibly creating ground loops.
DB, yes, it appears that the JC2 BP does not provide a tape loop or anything equivalent, so assuming you have more than one source I don’t see a way of connecting the KUBE into the system other than between the preamp and power amp.

Kijanki, thanks. It’s interesting, though, that the Pass amps which are fully balanced and therefore presumably have minimal even order distortion (for example, John Atkinson’s measurements of the XA30.5 state that its "THD is almost pure third harmonic") seem to generally be considered as having a sonic character that is a bit on the warm side. As always, there are countless factors that contribute to the sonic character of a design, in addition to its basic topology.  And therefore, as you said, "I would buy an amp if it sounds good and not because it is fully balanced."

Best regards,
-- Al

Thanks Al,  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.
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.

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.
 
I don't know your designs, but usually output stage, at least in SS amp has to be doubled, as well as stage driving it.  You can place differential amps in front of it, but most of the expense is already there.

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? 

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?

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 

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.

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

That's great, but it will be also true for well designed single ended amps.   There is no gain difference between topologies that would explain any additional distortions.

I'm not sure why Nelson Pass designs Fully balanced amps.  Perhaps it is market demand, that the tone of OP question suggests.  For the same reason designers still use unregulated linear power supplies instead of line and load regulated extremely quiet SMPS  (Jeff Rowland uses them).  I suspect that in your case objective, since there is no output transformer, might be to get more output power.  Once you have double output stage front is just a small addition.




This is the good side of an open forum discussion. Two obviously qualified people who can clearly (and politely) present strong positions for the merits of opposing technologies. 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!
Charles
I totally agree Charles. I've been following and enjoying all of these well informed ideas and learning quite a bit in the process. Sounds as if both topologies can offer great sound if properly designed and implemented. Kudo's to all the gents that have contributed their vast knowledge in such a civil fashion. I'm looking at purchasing a new pre and amp that are OTL but don't know if they are single ended or fully balanced.....on one hand this discussion makes me want to find out but on the other hand I guess it doesn't really matter since either approach has its merits. 
Mac,
The OP asked why single ended? He's receiving substantive replies. 
Charles 
Thank you Charles.  While not opposing any topology I think less is more.   As electrical noise is concerned, home environment is in most cases benign.  I argue to learn/understand and I have, especially from Al and Ralph.  This forum is great.
Yes Charles, I'm getting much more info than I expected. And very pleased that a discussion about the different designs has happened.
 Glad that some of brightest minds on the forum have joined in.
Jim
dbphd: "The manual for the Ayre phono stage (I use a JC 3) includes diagrams that seem to suggest converting an RCA plug from a turntable to a balanced input, but I may be misreading that."

Ayre products are zero-feedback, fully-balanced designs.

Ayre provides only XLR connection for the phono input on my phono-stage equipped K-1xe and recommends using balanced-configured cables terminated with XLR connectors into the phono stage, thus they provide a diagram on their website to show how to construct a balanced-configuration XLR-terminated phono cable (pin 2 hot), "This is the preferred solution and offers the highest level of sound quality."

The manual shows the option of using RCA to XLR adapters if the user is determined to use a RCA cable: "...this converts the balanced input into an unbalanced input and causes a slight loss of sound quality."

The stand-alone P-5xe phono stage allows for XLR and RCA connection, but Ayre still recommends the using the balanced XLR inputs and outputs for "the highest level of sound quality."

Dave
a very tired topic which has been debated ad nauseam. Ralph always beats the balanced drum as that is what he sells. Others beat the SE drum because that is what they sell, Look through the old posts and find as many of these just like this one as you want.

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

All sound sources are single ended, compressions and refractions.

When you get to the speaker they are all single ended, they move in and out, no balance. 

There are  also a lot of misconception about balanced and differential, two related but different things.

Ayre is misleading you with "zero feedback." It is no global feedback, but all solid state designs must provide some local feedback or they will be unstable.

Bottom line, I've heard many, many, many systems and the best to me have always been highly efficient speakers driven by a minimum number of SE stages. From DAC output to speaker I have 2 tubes both SE  because I only need a few watts of power .... bliss....  It is indisputable that SE tubes operated properly are the lowest distortion (most linear) stages 

If you choose equipment based on topology versus how it sounds you will lose. It is the sound, not the implementation.

Hey Ralph, I've been gone for a few years, interesting to see the same things debated over and over and over
https://forum.audiogon.com/discussions/balanced-is-inherently-flawed

here's a post I started 12 years ago on the same topic. I admit I did it just to start a debate, but shows how this has been ongoing since the beginning of audio and will never be resolved
Herman,
Admittedly there is redundancy of topics on audio forums and we all know the drill.
Tubes vs solid state.
Digital vs analog sources. 
Passive vs active 
High efficiency speakers vs lower efficiency speakers. 
On and on it goes. 
Yet sometimes meaningful debate and perspective can still arise from seemingly tired topics.   This is an example of such an occasion. 
Herman welcome back to audiogon 😊. 
Charles 
Thanks Charles,

One final point. I don't mean to disparage Ralph or anyone else for promoting what he sells, well, other than the crackpot selling magic pebbles, flowers,  and clocks. Ralph's points have  basis in fact and I have no doubt he truly believes in what he promotes. But back to the bottom line... in a home environment I've never heard better than SE low powered tube amplification into highly efficient speakers.

YMMV

Herman,
Ralph has integrity and believes in his product and is thus understandably passionate in his advocacy of differential balanced topology,  fine with me. I happen to share your preference regarding SE low power amplifier choice and matching speakers. Numerous paths to good  sound. 
Charles 
The same old discussions continue because preferences become the basis for a position rather than facts. I see preferences being expressed again here although there are several great posts that do stick to the facts.

The facts are clear - fully balanced XLR is better especially for longer cable runs and especially to help avoid ground loops. There is no way around it - these are the facts.

Fact - a black car will get hotter in the sun than a white car.
Preference - I only buy black cars because I think this colour looks best.
@herman , I appreciate you participating in the discussion, but in viewing the archive threads I did not find an answer to my original question. I wanted to find the reason a manufacturer designs a SE component and why in today’s HiFi environment (which includes many fully-balanced components), does not offer a balanced option in their product line.
I’m referring to fine companies such as Conrad Johnson, Consonance, Coincident, and Bob Carver’s tube amps. CJ builds amps that sell for $20-$39K, so their design is not driven by cost.

I appreciate everybody’s comments and learned that I should have planned out my system more carefully. In my case, I have a balanced source and amp, but my preamp is SE. My next purchase will be a new amp and learned that maybe I should go for SE tubes, rather than one of the many fully-balanced amps that are available.
There has been evidence provided that staying single-ended may be the best direction for me.

I'm with you lowrider57, I'm leaning towards single ended amps with high efficiency speakers like Herman, Charles and many others have. To me there's something magical about that sound. I've heard great sound from all different systems from tubes and SS, single ended and balanced, high or low efficiency speakers, analog and digital......there's a flavor for every taste. Ain't it great? 
Good to see you back here, Herman.

Not sure that I agree with you, though, regarding:
BTW despite what Ralph contends phono cartridges are NOT balanced as there is no ground, no ground pin connection, only 2 lines out.

All sound sources are single ended, compressions and refractions.

When you get to the speaker they are all single ended, they move in and out, no balance.
It is true, of course, that when a cartridge is not connected to anything its output is "floating" with respect to whatever ground reference one may choose to define. However if the two output lines of the cartridge are connected to a properly balanced input of a phono stage, both the impedances and the signal amplitudes of its two lines will be balanced with respect to the ground of that phono stage. In other words, the nature of a cartridge is such that connection of its output lines to a balanced input causes its output to become balanced.

The same goes for a speaker, when connected to a power amp having balanced outputs.

Compressions and refractions (I think that should be "rarefactions") that occur in the air as acoustic waves propagate are a different and unrelated matter, as I see it.

Regards,
-- Al

Lowrider, I see what you are asking

"the reason a manufacturer designs a SE component and why in today’s HiFi environment (which includes many fully-balanced components), does not offer a balanced option in their product line"

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. If Conrad Johnson suddenly offered a balanced amp it would make them look two faced after being adamant for all these years that SE was best. If Ralph tried to break into the SET market it would undermine his position that OTL is best. 

Why doesn't Avantgarde build speakers in boxes like Wilson? They are dedicated to and believe horns are the best solution.

Why doesn't Wilson build horn speakers? They are dedicated to and believe the speakers they build are the best solution.

Why doesn't Tesla build cars with gasoline motors? They believe electric cars are the best solution.