Balanced vs RCA preamps

As for @atmasphere, he simply won't accept that his opinion that the only proper way to build a balanced component is to make it consistent with the AES48 standard is simply his opinion. It's one that most of the high end community has rejected but he disputes that too, arguing that maybe they've never heard of the "standard." Those are the simple facts and I'll grant him the last word.

Ralph's issue is confusing his opinion with fact. No more, no less.

@cleeds Please read this thru to the end; you might see there's another explanation.

You might have to be a member of the AES to view this document:

https://www.aes.org/publications/standards/search.cfm?docID=44

At that link:

Abstract: This standard specifies requirements for the termination, within audio equipment, of the shields of cables supporting interconnections with other equipment, taking into account measures commonly necessary for the preservation of EMC (electromagnetic compatibility) at both audio and radio frequencies. The shielding (or screening) of audio equipment, cables, and microphones can be critical for EMC. The improper connection of these shields can cause common-impedance coupling in equipment.

You should be able to see something at the link on that page entitled: 'Downloadable Preview'; on page two at that link you'll see an interesting list.

Opinion vs fact... where your argument falls apart is where you say the 'high end audio' industry rejected AES48. So hang with me just a bit as there is some history first:

You have to jump thru some hoops design-wise in order to support the standard. Traditionally in the 1950s when hifi was getting started no-one thought there was a need since home audio devices weren't built to the same standards as recording/broadcast equipment, no-one thought there would be a need for long interconnect cables and no-one thought RCA interconnect cables might influence the sound if kept short.

Back then, to drive a balanced line you needed a line transformer and they cost about as much then as they do now ($500-$1000/channel) once adjusted for inflation.

So traditionally all home audio has used single-ended connections. Please keep this in mind.

Its that issue about an output transformer that has most tube preamp producers stymied about driving balanced lines. They cost a lot so will raise the price of a 'balanced' preamp by $1000-$3000 depending on how the manufacturer sets pricing. You could use a solid state circuit that's a lot cheaper but tube preamp producers and their market tend to disdain that idea. Or you could use our patented method but we're a small player and to this day a lot of the high end community doesn't know who we are and if they do, don't realize that we are more about balanced line than we are about OTLs (IOW we're still known for OTLs despite the fact that our preamps have traditionally been our best selling products). If they do know this about us, the other problem is in high end audio designer's don't like to use ideas 'that weren't invented here'.

Add to that the simple fact that many are simply ignorant of AES48 and you have a nearly perfect storm. I knew there were standard practices for balanced line back in the 1970s but I didn't learn about AES48 until about 10 years ago (it was codified about 2005); and yet we were the ones that pushed harder for balanced lines than anyone else in high end audio worldwide with the first fully differential balanced amps and preamps made back in the 1980s.

So from my perspective its hard to see yours. We influenced ARC to do balanced line; Dave Gordon (who might still be at ARC) and I were visiting the same dealer in Studio City CA back in the early 1990s after CES and he saw that we had figured a balanced connection between a tonearm and preamp. He asked how we did it so I sent him a copy of our MP-1 preamp owner's manual which details how its done. A while later ARC produced their first balanced phono section, later discontinued as they found out that dealers didn't like that because they had to change a cable to play it and that sort of thing could cause a customer to walk. 

I think the rejection argument isn't quite right; here's something we've not yet discussed:

When you have a balanced preamp that does not support the standard, it will play nice with single-ended equipment (in particular, a balanced preamp driving an amp with a single-ended input; this because single-ended and proper balanced operation are mutually incompatible, which means if you try to hook one up with the other you can get a buzz problem) and will also cost less.

Occam's Razor suggests that between two explanations for a given situation, the simpler one is probably the correct one.

So your explanation that 'high end audio has rejected AES48' needs some nuance. I'm also thinking my idea of ignorance isn't quite correct either (although I know of examples where that is clearly the case). 

I think the simplest explanation is AES48 is inconvenient because it complicates equipment compatibility (solvable but can be an additional hoop to jump thru) between single-ended and balanced, which means dealers will have objections (this is one we've dealt with a lot) and its more expensive. Both of those are money issues; that is the simplest explanation.

It’s a red herring, really and you’ve already acknowledged that AES48 is not commonly accepted in home audio. You describe your MP-1 preamp as "featuring Balanced Differential Design®" and state it’s "still one of the very few preamps to support the balanced standard (AES48)." You then go on to insist that only AES48-compliant designs are "proper" balanced designs.

@cleeds How is that a red herring?? The topic of this thread is "Balanced vs RCA preamps" so my comments about balanced operation are relevant.

I do describe the MP-1 and the MP-3 in that manner. I’ve described other high end preamps in that manner too. 

The emphasis added bit is false.

Nor am I claiming they are The One True Way (in fact listed a couple of other ways including links in prior posts which you seem to be ignoring) nor did I say any competing balanced line product isn’t ’proper’. Please stop trying to put words in my mouth; when you do so you commit a logical fallacy called a Strawman; logical fallicies are false by definition...

Regarding the use of ’proper’ I was talking about driving a balanced line ’properly’. I didn’t say anything about some balanced line product not being proper. Do you get the distinction??

Again, for like the 4th time already(!), this is what I claim:

if AES48 is not supported, then you loose a lot of the benefit that balanced line operation offers: immunity to ground loops and reduced or non-existent cable coloration/interaction issues (this being the ’cable makes a difference’ phenomena).

Nowhere in that is any comment about anyone’s particular balanced preamp or the like. Its a simple statement about balanced lines themselves.

It cannot possibly be a "standard" ("something established by authority, custom, or general consent as a model or example") yet at the same time not commonly accepted.

@cleeds   That's the thing: it is commonly accepted (would you like an industry list?); not sure if high end audio designers chose to ignore it or are simply ignorant of it.

Just so we're clear, other than our own, I've never put that trademark on any website. As far as I know, that sort of thing might be considered a violation of forum rules. 

If you want a speaker to work right you have to pay attention to Thiel Small parameters, for a USB cable you support the USB specs, for balanced line its AES48.

No, balanced lines can work quite nicely and still reject AES48. You're welcome to listen to my mostly-ARC system and judge for yourself, @atmasphere.

Thanks!. Just to be clear though, I never said or implied that if you don't support AES48 that it won't sound 'quite nicely'. What I did say was

if AES48 is not supported, then you loose a lot of the benefit that balanced line operation offers: immunity to ground loops and reduced or non-existent cable coloration/interaction issues (this being the 'cable makes a difference' phenomena).

My DAC at home sounds 'quite nicely' but it doesn't support AES48. So I keep its cables short to minimize cable colorations.

But it is just as opinion, and one which many of the world's foremost manufacturers of audio equipment reject.

@cleeds I'm not sure that's true; AES48 is an industry standard but you'd have to check with them to see. As far as I can tell, a good number of them don't know what AES48 is. I've seen manufacturers state their gear supports AES48 but then you found out it really doesn't. That makes me wonder if they know what it is.

You mistake my reason for being active on threads where balanced line is discussed. The simple fact is I've been doing this longer than anyone else and I've seen an awful lot of misinformation online. Apparently if I don't say something, the chances are high that no-one else will step in and set the record straight. Would you prefer that I just don't participate?

Just to be clear WRT to the 'one absolutely right way' remark,  I didn't make this stuff up. We use a direct coupled technique in our products, transformers have been in use for the same purpose for the last 70-some years and That Electronics makes a chip at the link that is an example of the other way to drive balanced lines properly. There may be more ways but I am not aware of them and would love to be enlightened- after years of doing this, these three methods are the only ones I know of.

You are correct that my way isn't the only way. Before we introduced balanced lines to high end audio the only balanced products you came into contact with was studio gear. To be clear, the innards of the product doesn't even have to be balanced. My Ampex 351 tape machine was single-ended inside. That machine was the recording industry workhorse from about 1957 to well into the 1960s. 

I am not denigrating anyone else's work; I think you misunderstand. Instead what I am saying is that if AES48 is not supported, then you loose a lot of the benefit that balanced line operation offers: immunity to ground loops and reduced or non-existent cable coloration/interaction issues (this being the 'cable makes a difference' phenomena).

No-one would argue stating that you don't have to support the USB standard for cable because such a cable might not even work. Balanced lines are different in that they will still play despite the standards being ignored, much like speakers in this regard; you can throw some drivers in a box but unless you did your homework its unlikely to sound right. If you want a speaker to work right you have to pay attention to Thiel Small parameters, for a USB cable you support the USB specs, for balanced line its AES48.

The resulting voltage is the so-called differential voltage, which is twice the amount of the individual phase voltage. This explains why the voltage from an XLR port is twice that of its RCA counterpart.

@lanx0003 Actually this isn’t true if the source is AES48 compliant.

An output transformer is a good way to look at this if you understand how they work. In the case of a an output transformer driving a balanced line, there is a simple secondary with no taps. One end of the secondary output is tied to pin 2, the other end to pin 3. Pin 1 is typically tied to chassis.

Now if you want to run this output single-ended, pin 3 is tied to pin 1. You’ll note that the actual output Voltage is unchanged as is the output impedance. IOW either way the Voltage and impedance of the source is the same, which is to say there’s no 6dB increase when running balanced as opposed to single-ended. The transformer doesn’t care if one side is grounded or not. Your conclusion in the quote above is false WRT AES48 compliant sources, such as our MP-1 or MP-3.

Now if you have a non-compliant source (such as a Topping DAC or ARC preamp) then your comment is true.

But that isn’t how balanced lines are supposed to work. Here is a link to a Neumann microphone. Note the output impedance and the load its expected to drive (1KOhm). This mic is set up to drive balanced lines properly. A device that behaves as you described above does not.

Put another way, the idea that the output impedance of a balanced source is twice as high is true only if the balanced source isn’t designed properly to drive balanced lines!

To understand this issue better take a look at this page on the Rane website- its a quick read. If you scroll down to the ’Absolute Best Right Way To Do It’ you’ll see I’m not making this up. You might also read portions of this book by Bill Whitlock who designed most of the Jensen transformers. It gets more relevant to this discussion on page 13; if you look at the diagrams which show balanced connections, you’ll see no connection to ground except when it goes single-ended (such as driving an opamp in the case of an input transformer). Page 15 shows a microphone input. Page 16 shows a line output. I think you’ll see what I’m talking about.

Where did you get this from? Have you done your homework before taking 10 seconds to write this? Let me do some homework for you, and you can do the rest to see if you can find anything to support your false statement.

DAC	XLR	RCA
Topping Pre90	40	21.5
Schiit Freya+ F / Kara	600	75
Audio Research LS17 SE	600	300
Audio Research 6 SE	600	300

 

 

@lanx0003  It is a fact in high end audio though that most producers of balanced line products pay no attention to AES48 (the balanced line standard), or the use of dBm levels (more later). That is part of the reason there is a balanced vs RCA debate.

You have to be careful about things you read like the specs above! I own the two of the Topping DACs; The 40 Ohm value is actually the two 20 Ohm output impedances put in series when really they should be in parallel, which would be about 10 Ohms.

WRT to the ARC stuff they are doing the same thing. FWIW ARC preamps in general tend to have high output impedances.

IOW this is a nomenclature issue, not an output impedance issue.

The standard for balanced line studio line level input impedance is 600 Ohms. Common accepted good design practice is that the circuit driving a load like that will have an output impedance about 1/10th of the load impedance. So we can assume that the source impedance will be 60 Ohms or less. That's a lot lower than most single-ended preamps...

Balanced line levels are usually expressed in dBm. dBm is the VU reading you would get on a VU (Volume Unit) meter when the meter is across a 600 Ohm resistor. So its a measure of power; that requires the output impedance to be even lower. There are two levels that are standards in use: -4dBm and +10dBm; 0dBm is one milliwatt dissipated into a 600 Ohm load.

My Neumann U67 microphones are designed to drive a 150 Ohm load. That implies an output impedance of 15 Ohms.

Our MP-1 preamp can drive 600 Ohms directly at +10dBm despite using a vacuum tube output. This also suggests a low impedance and in fact they will drive 32 Ohm headphones.

My old Ampex 351 studio tape machine was designed to drive 600 Ohms and also supported +10dBm.

Most tube preamps will fall flat on their face trying to drive loads like that. In fact most solid state RCA preamps will too.

My Otari MX70 1" tape machine has 600 Ohm inputs which expect at least -4dBm. You need a low impedance output to drive that.

I designed the first balanced line preamp offered to high end audio back in the 1980s so yes, I researched this quite a lot prior to saying what I did , and yes, balanced outputs generally are usually lower output impedance unless the manufacturer had no intention of supporting common balanced line practices.

To the OP, Balanced Audio Technology (BAT) makes several tubed preamps. Most of their models are solely balanced. Heck, "Balanced" is even in their brand name.

@mammothguy54 You might be interested to know that one of the founders of BAT, Steve Bednarski, was a customer of ours before BAT, and owned one of the first production Atma-Sphere MP-1 preamps.

Years ago I was yacking with Mr. Internet, Kevin Deal (he does know his stuff) and he said on the RCA/XLR question that component build quality is what matters.

Recently I swapped in/out RCA/XLR cables from source to pre and from pre to monos. My data set of one could hear no difference.

@wsrrsw If the balanced equipment doesn’t support AES48 you may well have heard no difference or even a degradation compared to the RCA connection.

I’d argue that noise reduction is the primary benefit of truly balanced circuits, which can offer high CMMR.

@cleeds Unless it doesn’t... I’ve seen some (shall we say) sophomoric ’balanced’ products offered in high end audio that had almost no CMRR at all. -Almost as if the designer didn’t understand what that Common Mode Rejection was all about.

Balanced equipment that isn’t AES compliant isn’t necessarily "improper," it’s just different. For example, the balanced ARC gear isn’t AES compliant, yet using the balanced connections yields improvement that you can measure and hear.

This is true. But you’ll hear cable differences, the system will be subject to ground loop possibility and you won’t be able to drive long cables. These problems were solved over 70 years ago! Imagine a recording studio where you may have 20 different audio devices connected together (although usually not all in the recording chain at one time). If you have a ground loop buzz it could take weeks to sort it out! Ground loops are an audio menace many audiophiles have dealt with; AES48 prevents that happening.

Imagine not having to worry if an interconnect cable is going to sound right- just plug and play with no worries. That too is a benefit of balanced lines if done right (usually you have to support being able to drive a 600 Ohm load).

I designed “balanced interconnect” by adding out and in fully isolating ground transformers, typ 50Ohm unbal. <=> 600Ohm bal. systems with RCA/DIN unbalanced outs and ins with excellent results!

@westcoastaudiophile +1 The venerable Ampex 351 tape machines (which were used to record a lot of the RCA Living Stereo catalog) were internally single-ended but used input and output transformers to interface with balanced connections.

@emergingsoul I like it

I have one of our MP-1 preamps driving about 35 feet of balanced cable which connects to the amplifiers. The tonearm has a balanced connection to the preamp as does the DAC. My tuner is old school so its a single ended connection to the preamp. The speakers are Classic Audio Loudspeakers model T-3s which are 98dB 1 Watt/1 meter, 16 Ohms and flat to 20Hz.

First of all, they do not exist for tube equipment, maybe there is a hybrid out there I am not aware of, but for all practical purposes anything with XLR connections is going to be solid state.

@billstevenson This statement is false. You might be interested to know that the first balanced line preamp offered to high end audio was the Atma-Sphere MP-1, which we still make. It has an all-tube signal path. FWIW, balanced line equipment first appeared in the 1950s, although back then output transformers were used to produce the balanced inputs and outputs. Our MP-1 is transformerless- we patented a method of direct-coupling instead.

When using XLR connectors be aware that Japanese audio manufacturers use a different configuration for pin for ground.  

@toronto416 Its more likely they have pin 2 of the XLR wired as inverting and pin 3 non-inverting (which is opposite of US products). In all countries pin 1 is always ground.

The only potential adverse impact is that the output impedance of the XLR connection might be 2-3 times high. If you have an amplifier with low input impedance, such as a valve amp, you might run into impedance matching issue.

@lanx0003 Usually XLR outputs have considerably lower output impedance than RCA outputs. Its typical in a balanced line setup to see input impedances as low as 600 Ohms (which most modern opamps can drive) although in high end audio input impedances can be 10K to 100K. Our tube preamps can drive 600 Ohms no worries. 

balanced in my view relates to when you have really long cable runs which many of us do not.

@emergingsoul The reason to use a balanced connection should be to eliminate ground loops and cable artifact. A proper (AES48) balanced connection will do that. Its worth noting that a lot of 'high end audio' balanced equipment does not support AES48 even though it's balanced. The benefit is there even if the cable is only 6" long.

My understanding is, by definition, single-ended-triode (SET) operation involves amplifying the entire signal with only one output device. A balanced circuit cannot be built this way. But I may be incorrect.

@dseltz Actually an SET has a differential input (but isn't balanced). Most of the time that input amplifies what is different (hence the name 'differential) between the RCA jack and ground. In case you're wondering, the other input to the input tube is the cathode. One way you can tell the input is differential is that if the grid and cathode are tied together there will be no amplification. If your preamp has a balanced output and has an output impedance low enough to drive the cathode, it is possible for the SET to receive and process both phases of the balanced signal. It won't be balanced, but it will be in the differential domain.