Why do most phono preamps lack XLR input even thought cartridges are naturally balanced?

First, it's a longstanding tradition to offer only RCA inputs.  Second, it is not enough to offer XLR inputs alone, in order to take advantage of the balanced nature of phono cartridges; one would have to introduce a true balanced phono circuit internally.  That requires nearly double the parts count, which increases the cost of building the device, which reduces profits.  Some inherently SE circuits do use a transformer interface between an XLR input and an SE pathway, which does glean some of the benefits of balanced operation.  So, there are some phono stages that do offer XLR inputs and do offer balanced circuitry.  There is no "con" view of balanced designs, unless cost is an object.  I have read the rationale in favor of RCA inputs and SE circuitry, and it usually involves a story about colorations due to added parts count. 

I can see one possible problem with true balanced operation.   Gains of both amplifiers have to be exactly the same, otherwise common mode noise will get converted to normal mode signal.  It requires some form of cross-feedback to keep gains exactly the same.  Phono preamp in addition has RIAA equalization that changes frequency response within audio band by 40dB  (100 times).  I suspect, that it would be very difficult to match it in both "legs" of true balanced phono stage.

What lewm said, regardless of source type.

kijanki, To the degree that signal handling by the two phases of a balanced circuit is not exactly symmetrical, you are correct in saying that will reduce Common Mode Rejection, and it does for sure in tube-based balanced circuits, because exact matching of vacuum tubes is not possible or stable even if it's momentarily possible.  (Your argument about RIAA equalization does not hold as much water as does the argument about tube or transistor gain matching, because it is much easier to exactly match capacitor and resistor values, or to tweak the values for good balance, than to match the gain components.) To all of that I say, so what? CMR is reduced from some perfect value to some lesser value, but you still do get CMR.  Whereas, in an SE circuit, you don't. I have two fully balanced phono stages; neither of these ever drove me crazy with hum and noise problems that I read about all the time in relation to SE phono stages. But the OP asked "why" we don't have (more) balanced phono circuits, and I think it's mainly the profit motive.

As @lewm notes, that a phono preamp has XLR inputs doesn't necessarily mean that it is fully balanced. But the inverse is also true - there are differentially balanced phono preamps that use RCA connectors. ARC Ref Phonos, for example.

A cartridge has no ground reference so common mode noise will not induce a signal at the pre-amp except at frequencies well outside the audio band.

Matching gains of gain elements is only critical if sufficient feedback at bandwidth is not used to ensure gain is set by the resistive/capacitive elements and not the gain elements themselves.

@lewm  One advantage of true balanced is to remove reference to GND in order to get rid of wire to shield capacitance, but the same can be achieved with input transformer.  The other is that even harmonics produced by both "legs" cancel, but some people looking for "warm" sound might not see it as particular advantage.

Matching resistors is unnecessary if cross-referencing of both "legs" is used (like in the input stage of instrumentation amp), otherwise it is almost impossible.  As for matching RIAA curve - it is very difficult. Typical good capacitors are 1%.  Matching them by hand is not practical for production, not to mention changes over time (aging).  Phono stage amplifies 60Hz by about 6 times vs 1kHz signal.  As a result of both you will get very poor CMRR @60Hz in order of 30dB only.  Good Instrumentation amp, like one in my Rowland amp, have 90dB CMRR @60Hz (and it is just plain line-in).  My current power amp (Benchmark AHB2) has CMRR=80dB (equivalent to 0.01% gain matching)

If they really don't make balanced inputs for such low level signals, they should.  True balanced is out of the question, IMHO, because of capacitors tolerances, but simple solution would be to use input transformer. Why not use instrumentation amp and drive shield with common mode signal?  It is very common in low level amplifiers.

Interesting subject.  Perhaps Almarg or Atmasphere can chime in?

@kijanki instrumentation amplifiers use laser trimmed resistors internally and/or external precision resistors as well as significant open loop bandwidth to achieve high CMRR and fixed gain levels. If you mean the differential pair / long tailed pair on the input, they also need somewhat matched resistors and in op-amps they are trimmed to provide higher CM range. <<$1.00 op-amps have 100db+ common mode rejection, but not in practical circuit which would be about 70db with 0.01% resistors. Low cost practical instrumentation op-amps with high CM range readily achieve 90db CMRR. Your amps may have a few precision resistors, and/or they are calibrated.


The main point of differential connections in audio is to eliminate the noise from having ground references which are different at the receiver and the transmitter whatever they may be and how they are caused. In a home audio system, that is going to be predominantly through noise induced through the AC, with the capacitance of the power supply, even EMI caps completing the circuit.


With a cartridge, you only have a ground connection on one end. Equal currents induced in the same direction on each wire (common mode) "induce" the same voltage and cancel each other out (it is a loop), at least at practical audio frequencies. Differential noise, will of course look just like a signal. The cartridge is already "isolated".

Most phono stages, preamp and amplifiers aren’t true balanced. A balanced input doesn’t necessarily mean it’s balanced. My Atma-sphere  mp-1 is fully balanced with XLR phono input. I had Ralph add rca phono inputs so I could use any tonearm without adapter. Not many arms have  xlr connectors . All the arms I’ve ended up with over the years except one has been rca. 

With a cartridge, you only have a ground connection on one end. Equal currents induced in the same direction on each wire (common mode) "induce" the same voltage and cancel each other out (it is a loop), at least at practical audio frequencies. Differential noise, will of course look just like a signal. The cartridge is already "isolated".

That is true, as long as currents flow in the loop only.  If one of the wires go to input while the other goes to GND (unbalanced input), currents in both wires are not even anymore.  Perhaps, that's why floating (for audio frequencies) balanced output, like transformer is not enough and has to be connected to balanced input (not single ended).  Microphones also benefit from balanced input.  

As for Instrumentation amps, yes they have laser trimmed resistors, but front (two amp) differential section has always gain of 1 for common mode signal independently of resistor tolerance.  If you set gain of 100 for this section you get automatically 40dB CMRR independent of resistors tolerance.  It happens because each of two amps is referenced to input of another (instead of the GND). 

https://www.researchgate.net/figure/Fig-Two-Op-amp-Instrumentation-Amplifier_fig1_299514235

That is the only way I can see, for truly balanced amps, to function without converting common mode noise to normal mode signal.  Otherwise matching resistors and keeping them matched to some sensible number (like 60dB=0.1%) is not practical, while adding RIAA frequency correction and matching capacitors to 0.1% is next to impossible.

Thanks for the mention, Kijanki. To add further technical elaboration to this erudite discussion of esoteric matters, IMO the main reason "most phono preamps lack XLR input even though cartridges are naturally balanced" (quoting from the subject line of this thread) is simply what Lew said earlier:

... it’s a longstanding tradition to offer only RCA inputs.

:-)

And of course traditions often tend to be self-perpetuating.

It’s perhaps also relevant that not too many decades ago I believe a considerable majority of high quality turntables had pendant (non-detachable) phono cables terminated with RCA plugs.

Finally, regarding RIAA equalization Ralph’s (Atmasphere’s) MP-1 and MP-3 preamps are of course fully balanced, provide transformerless balanced XLR inputs for their built-in phono stages (RCAs can be added as an option), and are spec’d as having RIAA accuracies of 0.07 db and 0.1 db respectively! And given especially that it is Ralph who has provided those specs, I have no reason to doubt them. I’m not in a position to elaborate on how he accomplishes those numbers, of course, other than pointing out that he uses triode-based differential stages rather than separate signal paths for the two legs. But as far as purely technical considerations are concerned his designs certainly speak to the practicability of accomplishing what the OP has asked about.

Best regards,
-- Al

one would have to introduce a true balanced phono circuit internally.

While the idea of duplicated, bridged, or fully balanced (whichever term you like) is sexy, the idea that this is the only advantage is really not correct.  Professional gear has been using balanced signals long before audiophiles got it into their heads to duplicate circuits.

Having a differential input which is not referenced to ground has a lot of benefits for noise.  And while I don't think we need full-sized XLR plugs, there are mini-XLR plugs which would work a treat for this.  I've often wondered this myself.

Phono cartridges are floating sources rather than balanced, and unless there is a low-impedance connection between phono amplifier ground and both sides of the cartridge signal coil, and/or the common mode rejection of the phono stage input stage is extremely high across a wide bandwidth, there most likely will be substantial pickup of electrical noise from the environment (i.e., connecting the phono cartridge in balanced mode will probably yield worse noise performance than an unbalanced connection).

An input transformer magnetically isolates common mode noise, and is a good solution to building a quiet balanced phono stage.

It's common mode. By definition the currents must be matched. If they are not matched, they are not common mode, they are differential and then you cannot tell them apart from the signal. The coil in the cartridge also completes the loop. It is by analogy the isolated end of the transformer.

If it is a powered microphone that has an active ground connection, power and signal, then yes, the benefit is there. The benefit is mainly in better shielding for a non powered microphone.

That is true, as long as currents flow in the loop only. If one of the wires go to input while the other goes to GND (unbalanced input), currents in both wires are not even anymore. Perhaps, that's why floating (for audio frequencies) balanced output, like transformer is not enough and has to be connected to balanced input (not single ended). Microphones also benefit from balanced input.  

The differential input of an op-amp does not have a gain of 1. It's a current source into a differential pair, that will share current based on the transistors being perfectly matched, and it will convert that current into a voltage by the load resistors ... who's matching also impacts the common mode rejection of this stage.

As for Instrumentation amps, yes they have laser trimmed resistors, but front (two amp) differential section has always gain of 1 for common mode signal independently of resistor tolerance.

That's not how it works. I think you are confusing something. For a 40db CMRR, you must have gain matching of gain matching between the two channels to +/- 0.5% (1% total), and you must have perfect transistor matching (which they never are).

If you set gain of 100 for this section you get automatically 40dB CMRR independent of resistors tolerance. It happens because each of two amps is referenced to input of another (instead of the GND).

Typically you use op-amps with laser trimmed resistors and/or you calibrate. You of course need tight temperature tolerance matching which is easier at the IC level, since with low power draw, temp will be very consistent between the temperature co-efficient.

That is the only way I can see, for truly balanced amps, to function without converting common mode noise to normal mode signal. Otherwise matching resistors and keeping them matched to some sensible number (like 60dB=0.1%) is not practical, while adding RIAA frequency correction and matching capacitors to 0.1% is next to impossible.

Which would probably be pointless as you pointed out, you are not going to get capacitors to that tolerance.

I perceive this would only be of benefit at frequencies outside the audio range, as within the audio range, effectively the cartridge completes the loop and common mode noise would be rejected.  Do you have examples of commercial products that use this technique and are they measureably quieter?

An input transformer magnetically isolates common mode noise, and is a good solution to building a quiet balanced phono stage.

Nice discussion.  Ralph needs to chime in.
JCarr, You wrote, "Phono cartridges are floating sources rather than balanced, and unless there is a low-impedance connection between phono amplifier ground and both sides of the cartridge signal coil, and/or the common mode rejection of the phono stage input stage is extremely high across a wide bandwidth, there most likely will be substantial pickup of electrical noise from the environment (i.e., connecting the phono cartridge in balanced mode will probably yield worse noise performance than an unbalanced connection)."
In this paragraph, you used the terms "most likely" and "probably" at very key points in your statement.  Have you actually done the experiment and made measurements?  Also, what would you say happens when the balanced phono circuit is floating with respect to ground, just like the cartridge itself?

That's not how it works. I think you are confusing something. For a 40db CMRR, you must have gain matching of gain matching between the two channels to +/- 0.5% (1% total), and you must have perfect transistor matching (which they never are).

Look at the picture I provided.  Each of two amps operates in non-inverting mode and is referenced to inverting "-" input of another amp.  Since voltage at inverting input is the same as voltage at non-inverting input then voltage across R2 is V2-V1.  For common mode signal V2=V1 and voltage across R2 is zero.  It means you could remove R2 (no current flow) and without it you just have two amplifiers with perfect gain of one each (followers) even if R1s are a little different.  R2 plays role only for normal mode signals.  That way you can set any gain for this stage and gain for common mode will always be one. If you set gain of 100 then CMRR will be 40dB.

As for the balanced connection - it is not balanced anymore when you connect it to unbalanced input.  Noise currents induced in both wires will be different and noise will go thru.  The fact that cartridge is floating won't help, unless input is balanced.

The differential input of an op-amp does not have a gain of 1

Nobody said that.  Instrumentation amp is not an op-amp.

I have XLR's out of my VPI table going into Ayre pre....dead silent.

Sorry kijanki, I thought we were talking about discrete level or discrete within an IC circuit, and that the 3 op-amp instrumentation amplifier you showed was a different part of the discussion. The circuit shown is missing the output buffer that would be on a practical circuit and those two output resistors have to be matched as they dominate CMRR in the calculation. I now get completely where you are coming from  :-)


If the noise current induced are not the same in both wires, then they are not common mode, they are differential mode, and a balanced connection only removes common mode noise.

As for the balanced connection - it is not balanced anymore when you connect it to unbalanced input. Noise currents induced in both wires will be different and noise will go thru.

In a typical connection of two components, you have multiple paths for current flow which is how CM noise generates a signal. With a catridge/phono stage, you have a single loop so induced common mode noise does not generate a signal. Where it gets dicey, is when you start adding new current paths like shields. Fix your DM noise, and now create CM noise. I think this is perhaps was jcarr was referring too?

Roberttdid,  I would compare single ended phono preamp input to, for instance, oscilloscope.  When you short oscilloscope probe (tip to probe GND) there will be still some noise on the screen - bigger if you touch shorted inputs (in-spite of you "floating").  It is because for electrical noise one of the wires (GND) provides lower resistance path to GND.  Current thru this ground wire causes tiny voltage drop, seen by the input as input voltage (input is referenced to BNC GND and not to end of the cable GND).    Of course scope can be used in two channel differential mode but it suggests that second input is required.  Amp could be truly balanced, but it is overkill, IMHO - costs money and introduces more components in the signal path.  Remaining choice is likely between differential amp and transformer.  Transformer, in spite of some distortions at low frequencies (most likely inaudible) is a clean simple solution.  What do you think?

I had TT long time ago and always had problems with low frequency hum (single ended phono stage).

Stingreen - you stated that your Ayre phono is dead quiet.  It's likely because of balanced input.  XLR cable wires are usually twisted - a very strong defense against electrical noise.  Do you know by any chance what is inside (transformer, differential amp etc.)?

Hmm. Did I just open Pandoras box? Btw, some phono preamp designers prefer to refer to cartridges as a “floating differential” rather than balanced. 

@clearthinker, contrary to your statement of 6dB reduction with true balanced which I’m not sure applies to cartridges, the designer of BAT phono has claimed that RCA offer 6dB reduction in noise over XLR with cartridges. Don’t kill the messenger.

kijanki,

When you short a oscilloscope and probe to ground, you are creating a loop antenna and creating a differential signal which is not to say that common mode noise and/or common mode voltages are not a problem in measurement. That is why Picoscope makes a differential input scope, and Tek and Lecroy sell high voltage differential probes for about $2,000/each (or more). While you are "floating" you are also a big capacitor to ground which creates a path for common mode signals. Also remember that most oscilloscopes probe grounds are also connected to chassis grounds. Floating oscilloscope inputs (battery powered or otherwise), can offer most of the benefits of differential inputs for many measurements (and tend to be much quieter).

And are you assuming the noise was common mode? Are you sure it was not differential mode?

I had TT long time ago and always had problems with low frequency hum (single ended phono stage).

Current thru this ground wire causes tiny voltage drop, seen by the input as input voltage (input is referenced to BNC GND and not to end of the cable GND).

But again, we are talking a cartridge and absent the shielding and other metal structure (and antenna effects isolated by the cartridge itself), it is a loop. Absent the shield/structure capacitance to ground, there is no other current path, whatever current flows in one wire must flow in the other, and hence whatever drop you have on one wire is cancelled by the other.

Transformers are already used for MC coils, so we know they work.

@dracule1, I'm not sure Mr van den Hul, amongst others, agrees with you.  I should like to see BAT phono's explanation of a 6dB reduction in noise using RCA single-ended.  There seems to be disagreement on the issue.

Maybe a point that needs to be made, you don't need an XLR to have a balanced input connection. You can use an RCA and still have a balanced input connection.

BAT incorporates its “Flying RIAA Network” differential circuit here, which the company claims has fewer parts yet because of ease of adjustment at the factory and dual differential common mode noise rejection, produces greater RIAA accuracy, with typical measured error of less than 0.1dB.

Hello, we are now building the first run of phono preamps with both balanced inputs and continuously variable cartridge loading (10 to 1,000) ohms, balanced outputs too.  lit will be available in a couple of weeks.  Barry Thornton, austin audio works.

Gains of both amplifiers have to be exactly the same, otherwise common mode noise will get converted to normal mode signal. It requires some form of cross-feedback to keep gains exactly the same. Phono preamp in addition has RIAA equalization that changes frequency response within audio band by 40dB (100 times). I suspect, that it would be very difficult to match it in both "legs" of true balanced phono stage.

This statement isn't quite correct. To prevent issues with RIAA equalization, you simply do the EQ network in differential mode. This eliminates issues with matching and gain differences.


A bit of audio history since this is relevant: we built the first fully differential phono sections for home use in our MP-1 preamp, introduced in 1989. As such is was also the first balanced line preamp, tube *or* solid state (again, for home use). At the time the XLR connector was the only game in town so that's what we used for the phono input. We had no idea at the time that a product like this should do anything other than support the balanced line standards (AES48) so that is what it did and does.


The correct phono connection is: + and - outputs of the cartridge are pins 2 and 3 of the XLR. The tone arm and turntable ground is the shield of the interconnect cable and ties to pin 1 of the XLR of each channel, so no ground wire is needed. You'd be surprised how many cable manufacturers there are that think the ground wire is still needed :)

This connection is so quiet that we've used unshielded twisted pair with a ground wire (what we've come to call a 'twisted triplet'; but we've also used Kimber braided wire) and its noise-free. But one thing that has been pointed out here that is really important is the CMRR of the input stage. Of course transformers do this really well, but since we're sort of known for transformerless operation, the other way to do it is with an input gain stage that has as high CMRR as possible, combined with the lowest noise.


Obviously opamps work great for this but we wanted to use tubes, so the input circuit is a differential cascode which employs a 2-state CCS (single-stage CCS circuits leave performance on the table). If you want low noise and high CMRR, this type of input circuit (which is common in a lot of solid state circuits as well) is really the only way to go. Because tubes drift and because matching components is tricky, we sorted out the differential mode EQ and as far as I know we're the first to do that by decades prior to anyone else. Differential mode EQ insures that both outputs of the phono section (inverted and non-inverted) will have the same EQ regardless of how much gain imbalance there might be. To prevent common mode noise from becoming differential mode the simple bit is making sure that any ground in the gain circuit is common to both phases- common sense :) In this regard layout plays a role as well, as the designer will find that certain parts in the circuit are best placed as close to each other as possible to maintain noise immunity.


The main downside we encountered was the reluctance on the part of dealers to deal with the balanced input since it meant changing out the tone arm cable; some thought the arm had to be rewired which of course it doesn't :)   The advantage of operating balanced at this point in the signal chain is that as long as the tone arm cable is low capacitance, the cost of the cable isn't important- how its wired is. So you can have a $200 cable sound just like a $2000 cable. Cable immunity was a big incentive for why we developed a balanced preamp. 

Atmasphere,

How much advantage did you find by adding shielding of the XLR over just using a differential input w.r.t. noise?

Interesting on the differential mode filter network. When you say it it seems "obvious", but certainly wasn't when the question was first posited.

Very interesting post, thank you.

Ralph, very interesting.  As roberttdid said about differential filter "it seem obvious", but it escaped me completely, being stuck on "matching". 

Cable immunity may just be the most underated design aspect in all of hifi land...
I mean we all know cables make a difference...but what if that variable were greatly reduced? More budget is opened up to things like better circuit components and implementation- a very good thing.

We are all told that cables make a difference. Absent knowing what cable or that there was a change, my experience in controlled environments says that is the cable is competent, there may not be a difference. Diminishing returns much quicker for interconnects as well versus speaker cables. Noise rejection is important yes.

How much advantage did you find by adding shielding of the XLR over just using a differential input w.r.t. noise?

Almost none. I ran unshielded tonearm cable in my home system for some years. You could crank up the volume and no hum or buzz from the cable, even if grasping it or moving it around. You do still have to ground the tone arm and it works best if that wiring travels with the signal wires. One advantage here is this allows for much lower capacitance in the cable.

As roberttdid said about differential filter "it seem obvious", but it escaped me completely, being stuck on "matching".

@kijanki  I think a lot of people think of matching 'equal but opposite' circuits when they hear the word 'balanced'. EQ circuits might be the best example of that. I once went to see a demo of the new (at the time) Mark Levinson preamp (IIRC the ML-29) which was their first balanced line preamp. But the phono was single-ended. When I asked why, I was told that matching the EQ was the problem the 'engineers' were worried about weird effects if the parts weren't matched really carefully! That was when I knew they hadn't tried it at all.


At any rate if you want to do balanced right with active balanced circuitry, the way to do it involves differential circuitry. That's how you develop power supply noise immunity (Cross-Mode Rejection) and Common Mode Rejection. (As a side note, the CCS is critical and frankly, most CCS circuits I see are pretty terrible.) But what is less obvious but also important is the simple fact that you should do wiring in differential mode too- common grounds and common power supply points being the most obvious examples, and of course the EQ can be done differentially as well. Now we use passive EQ for our phono (based on the formula of Stanley Lipschitz) so imagine dual EQ networks, one for each phase; this made it go easy.

Those networks should use a common ground of course, but if you think about it, you don't need the ground at all. And if you got that far, then you can see that resistor values are in series as are capacitors- meaning that only one resistor need be used, only one cap (of half the value; you can see where this is going) and now there's one network instead of two. Much, much easier and all you're doing at that point is trimming to the values you need, rather than a Sisyphean task of matching to some extreme; pointless when you have tubes or semiconductors that won't come anywhere close to a similar match. A nice result is you don't have to do crazy amounts of tube matching yet the EQ will be spot on from both phases even as the tubes age. As far as I know, we were the first to do this (1990) and I think it was only about 8 years ago before I spotting any circuits that did the same thing- apparently its not common knowledge even today.

Good you mentioned no advantages with the shield Ralph, I was about to send this in the morning before you even answered in the thread and I think this although been mentioned before it is largely overlooked.
I had 1st a Hifi digital system and then I started getting into serious and educated analog. The digital audio community was introduced to a concept to improve SQ on digital rigs, specifically on DC connectors which basically states that a shield on a cable, not connected to any ground but looped at the ends of the DC cable will improve SQ, John Swenson was the engineer mentioning the concept, if it works or doesn't up to you to decide, I don't take sides, with the exception some people started applying this concept to all sort of cables, USB, digital interconnects and SE and XLR interconnects, some reported improvements, I tried these and notice nothing but since there is shielding involved I thought (at the time) it was great.
Fast forward 1 year, got a new preamp from Ralph (Atmasphere) and there is an accentuated buzzing sound on my tweeters, could be heard from 8 ft away, very annoying, my entire rig is balanced XLR. Started analyzing and graphs showed peaks on 120 Hz, 180, 240 and 300 Hz, AC harmonics of course, some of these 15 db peaks some others 30 - 40 db, very annoying. Turned off the entire house, got into a fight with my wife for it, moved things around, added some power conditioners, buzz was there, called Ralph, he suggested an isolation transformer, got one, some improvement, minor, buzz was still there. Ralph asked me to do a few things and he very nicely sent me some plugs and attenuators (at no cost), attenuators worked taming the buzz but at the cost of power as you could imagine,  because of the gain on his pre and amps is high still got plenty of power on the preamp for my speakers so all good there. But me I can't rest until I figure what was wrong, got my spectrum analyzer and scanned the entire house and even the neighbors, nothing out of the ordinary. Got a long extension cord (daisy chaining 4 extensions) and connected my entire system to a neighbor on the other side of the street (with his consentment), same results.
Talked to Ralph on the phone about something else but me being me (annoying asking things) and Ralph being Ralph (willing to explain and educate you with his great knowledge) we mentioned cables used, I use Mogami which he recommends but the topic stayed lingering on my mind for several days.
Sorry for the long rant, getting finally to my point, playing with the Mogami interconnects I noticed no hum, not even the faintest hum with the XLR in place BUT when unplugged one of the XLR's from the preamp and amp on, disconnecting from the pre there was a nasty hum, this is not supposed to happen, then I remembered when ordering these Mogami's interconnects everyone said better to be shielded and at no cost I got them JSSG (looped shield at the ends), there was one guy don't remember where online which told me before all this, for balanced interconnects never get these shielded but since it was only ONE guy I did not.Replaced the balanced interconnects (between pre and amp) with unshielded ones and when unplugging one end the hum was gone, but the buzz was still there.My source DAC was connected to the pre via XLR shielded, looped interconnects and even with the DAC OFF there was buzz, replaced these and the buzz was gone almost completely, turns out not all the balanced XLR equipment out there is "fully differential" or following the balanced standard, Atmasphere's are but the DAC wasn't.
Summarizing and my conclusions.Shielded cables with tricks like loops etc. have A LOT of capacitance, truly balanced equipment won't care but better to have no shields as there are not needed because of the design of these circuits, single ended equipment will suffer from high capacitance with hum, buzz etc.Of course this is what Ralph's have been saying for decades so not so much new here except that now I don't want any capacitance near any of my cables.I'm sorry Ralph I don't think I told you these findings directly but I just discovered this over the last month or so and since it came up publicly in this thread I thought it was best to share.Luis

Forgot this, I understand with turntable to pre interconnect a shield is recommended if single ended or single ended to balanced adapter cable, I am in the process of setting up this, I guess I will find out. Ideally I would like to go straight from the cartridge balanced to my preamp but we will see.

Based on your two posts Ralph (which I just bookmarked because reading it slow makes a lot of sense) I will be using unshielded twisted pair CAT6 on my phono interconnects, not any other audiophile expensive cable, not even Mogami and will see how it goes.

@luisma31 Make sure the turntable/tonearm ground is tied to pin 1 of the phono input XLRs.

Almost none. I ran unshielded tonearm cable in my home system for some years. You could crank up the volume and no hum or buzz from the cable, even if grasping it or moving it around. You do still have to ground the tone arm and it works best if that wiring travels with the signal wires. One advantage here is this allows for much lower capacitance in the cable.

@atmasphere  Wire to shield capacitance should play role only if either output or input circuit is ground referenced.  I thought it was the advantage of fully balanced, not ground referenced (floating) configuration.  There is still wire to wire capacitance (increased by twisting), but there is no wire to shield capacitance, making even less expensive cables to sound better.  I agree that shield does not improve much, since twisting wires makes them very immune to electromagnetic or capacitive pickup, but it should not cause buzzing.  What lusima31 described sounds like ground loop.  XLR cable shield is grounded at both ends, but shells shouldn't be, since it might create such loop.  I've read that in recording studios they often have problems with that and fix it by cutting shield at one end.

@kijanki note my cable is not "grounded" at either end, just looped into itself, hence the crazy capacitance

@atmasphere  thanks for your clarifications. I am using an Ayre P-5xe which has balanced phono inputs.  I was bothered that if one uses the rca inputs to customize resistor loading ( I do not) that the use of one resistor per channel might indicate it was not truly a balanced input. Your explanation of the differential connection clarifies that worry.I have wired my own balanced DIN to XLR phono cables (refusing to pay $600+ for something so simple). Of course pins 2 & 3 are signal, and pin 1 is shield on the xlr ends only. I have a drain wire to the center DIN pin as a drain  connecting to the P-5 ground. Is this correct? I have no hum.

@atmasphere I'll try to have not even a ground but direct balanced all the way from TT to pre

@oldears

DIN to XLR phono cabl e

I thinkg this is what I'm trying to accomplish and this would be "truly balanced" 5 pin DIN from TT to 2x XLR balanced on the pre

luisma31, If it is not grounded at either end, then capacitance to what? To electrically floating object?

@oldears  If its not humming I would not worry, but I suspect there is no need for the 'drain' wire, as the preamp is likely electrically grounded via the ground connection of the AC power cord.

We've been making DIN to XLR phono cables for decades; we just tie pin 3 of the DIN (ground of the arm) to the shield which is pin 1 of both XLRs.

@kijanki

luisma31, If it is not grounded at either end, then capacitance to what? To electrically floating object?

honestly I don't know, I'm not an EE, but the effect of the hum is similar to what high capacitance cables will do, and since capacitors are isolated (just like this cable) I think HIGH CAPACITANCE is right on target

luisma31, It might be true, but I've never heard of hum caused by high capacitance of the cable.  I've heard of output oscillations and frequency roll-offs, but not hum.

Just be aware in my case, with balanced interconnects, the hum was present ONLY when unplugging the connector from one side as I described, when both ends were plugged there was no hum. Replacing the interconnects with no shield cables no hum no matter what.

luisma31, Unplugging connector?  You probably mean - disconnecting shield?  If you had no hum with shield connected at both ends, then why to change it?  I would guess that disconnecting shield at the Phono side only left TT ungrounded with floating antena (shield), while unplugging on TT side or both sides should have less of an effect.  How is your TT grounded? 

Please read my initial post again, I have described my digital rig not TT connected (yet)

I described hum with a shielded balanced cable when unplugged from the pre side, when an unshielded cable was used there was no hum, my understanding is the shield adds capacitance and IMO is not needed and undesirable.

luisma31, sorry, I got confused with initial post about TT problems.  You keep saying "unplugged from pre side" but you probably mean that shield was disconnected, otherwise what are you listening to if nothing is connected to pre?  I suspect that cable might create ground loop.  Lifting shield on pre side might still produce buzz if shield touches connector shell.  Anyway, there is very little chance that anybody can help you if Ralph couldn't.  I use XLR cable grounded at both ends between DAC and power amp and it is dead quiet.