Tidbit about XLR cables and plugs.
In the late 70's I worked as a salesman at Shrader Sound in the Georgetown neighborhood in NW DC.
Bill Shrader was long out-of-the-picture, and the silent partner who kept the business afloat was Jim Canon, who developed the "Cannon connector", used at the time on lots of professional microphones. When Jim sold out to United Technologies, they made a "Cannon connector" with a plastic insulator ("XLP") and one with a rubber insulator ("XLR"). |
the sound of the interconnect won't be a thing Malarkey!
Assuming balanced circuitry and connections are properly implemented, which far too often they are not, they can reduce common mode noise. FULL STOP.
For
balanced interconnects to be immune to cable, they would have to be
immune to the laws of physics. Balanced lines [and connectors] have
impedance and impedance controls frequency response.
Regarding the full stop, internally in a true balanced circuit in addition to improving CMRR, you can also improve power supply immunity, and since CMRR can be high, you get insensitivity to ground noise. Actually, the way the interconnects become "immune to cable" (sic) is through two mechanisms, all according to the laws of physics. The first is that the balanced system is low impedance- at 1000 ohms (or 600) the impedances are so low that the capacitance and inductance of the cable are swamped and become negligible- and thus inaudible. The second is that the signal is not sent as a ground return through the shield. If you violate either of these tenants, the cable becomes audible. This is easy to prove through both measurement and audition. differential amps tend to be lower noise we don't need as much gain stages to get the job done If number of stages is a criteria, use a transformer. Differential amps per se are all over the map in terms of gain vs noise. The devil is in the details.
Transformers limit bandwidth and make distortion. Without them the circuit is noticeably more transparent. We've been doing balanced line longer than anyone else in high end audio; don't think we haven't tried transformers, and of course we are known for being transformerless :) the other reason for balanced lines is elimination of ground loop noise I'll
wager that 6 9's of 'balanced' home audiophile systems do not lift the
shield at the destination. Depending on amplifier design, there may be ZERO ground loop improvement over an unbalanced system.
In a balanced line system there is no need to lift the ground at one end of the cable. You are correct about the amplifier design issue; IME/IMO many high end manufacturers don't understand grounding and don't understand how balanced lines work either. The balanced line system was created to get rid of interconnect cable colorations The
balanced line system was invented by the telephone company to increase
noise immunity and power transfer over long distances. Nominally 600Ω, but at 1 frequency ONLY! Low frequency performance is abysmal.The 'telephone sound' is a direct result of balanced cables.
:) of course noise isn't a cable artifact, but you forgot to mention the loss of high frequencies, which made transcontinental phone calls impossible prior to balanced lines. If loss of highs is not a coloration, what is?? Yes, the phone company did just that, and the idea was quickly adapted by the recording industry as running microphone signals over a long distances was a similar problem. Through the ability to transfer power the system swamps cable capacitance and inductance (both of which cause interconnect cable coloration). This is the low impedance aspect to which I referred earlier. Our balanced preamps feature miniature power amps as their line sections- they can make a little power. Many balanced devices are bodged to accommodate unbalanced operation and
coupled with generally incorrect balanced wiring, they don't stand a
snowballs chance of optimum operation in unbalanced mode.
If 4+ decades in electronics has taught me anything, it's that if it can be screwed up it will be: - inexperienced engineers
- incompetent sales staff
- ignorant consumers
This has been a beef of mine for decades, but just because this is so does not mean that all balanced line products have these issues. I should have said "Use caution if driving an unbalanced amplifier from the balanced outputs." We run into that problem too. What most people don't understand is that balanced and single-ended operation is inherently incompatible; you can't have 'quasi balanced' or any such nonsense. Either its balanced, or in the case above, unbalanced. In our preamps, since the output floats with respect to ground (no signal return current in the ground) if you attempt to use only one of the signal pins (ex.: pin 2) and ground (pin 1) you will get a buzz. This is because pin 1 has no direct connection to the return circuit of pin 2 and so pin 2 acts like an antenna. To correct this, pin 3 in this situation has to be also tied to ground (and because our output floats, this can be done without damage) to prevent the buzz. But of course then the output of the preamp is single ended, no longer balanced. |
Anyone have any idea if the Cello Palette (the later preamp version) is true balanced out? I have one coming into my possession and trying to decide if its worth the effort to have some Fischer to XLR cables made.
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Why don’t i just plug all my gear into a very good balanced isolation power conditioner (with excellent CMR) and make my life easier fellas? A wise man once said, " Spend in the right places"
Though .....someone mentioned he gets aways with fewer gain stages. But, i doubt all manufacturers make the same design decisions. |
@atmasphere
" You don't need transformers, but without them supporting thebalanced starndard get a lot trickier. We devolopd a means that is direct-coupled and yet floats the same way that a transformer winding does"
I want to know the detail of your means. Could you please explain. Thanks!
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@runwell Yes. We patented the use of a Circlotron output (which is direct-coupled and balanced) with a servo control to prevent DC Offsets from appearing at the output. The Circlotron is a push-pull circuit that allows for entirely symmetrical operation using a pair of tubes to drive the output. In our case we use 6SN7s for that task.
A Circlotron circuit employs floating B+ power supplies and so can have one side grounded or in the case of balanced output, both sides floating with equal impedance to ground, while at the same time not using the ground for anything to do with the signal. In this way it allows a direct-coupled tube output to support the balanced standard, AES48.
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@ atmasphere
Are you talking the connection between RCA preamplifier and XLR power amplifier ? or the circuit inside the amplifier?
I just want to have a solution between RCA pre and XLR power amp, it seems the transformer coupled is the simple way to go.
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I just want to have a solution between RCA pre and XLR power amp, it seems the transformer coupled is the simple way to go.
It is. A set of Jensen ISOMAX line transformers should do the job. They make one that has RCA inputs and XLR outs.
https://www.jensen-transformers.com/home-theater/audiophile/
They make them to order too- so you can get RCA in and XLR out although you don't see that on their site.
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@ atmasphere
Thanks! I put the order a few days ago and will receive very soon.
So finally it goes down to the transformer isolation,it seems the usual way even the XLR output from the pre,they usually get the rca signal first and use the transformer to get the inverse signal and consist the XLR sigjnal.
Am I right?
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In a balanced line system there is no need to lift the ground at one end of the cable.
Try not doing it in a large multi-room facility like a sound stage, dubbing room. It may not be required with the AES-48, but until all gear is to that standard, prudence takes precedence over valor.
Most XLR gear is not transformer coupled. Not all is actually balanced.
In transformer gear, an unbalanced signal is fed through the transformer. The output can be XLR, banana, TRS, multipin, etc., etc.
While the Jensen transformers are excellent, they, like all transformers, still have a sonic signature.
Depending on the issue, adding transformers with the screen carried may not solve the problem.
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So finally it goes down to the transformer isolation,it seems the usual way even the XLR output from the pre,they usually get the rca signal first and use the transformer to get the inverse signal and consist the XLR sigjnal.
If the preamp has both RCA and XLR outputs its quite rare to see a transformer used for the XLR output.
In high end audio in particular, in a situation like this the RCA is one of the phases of the XLR output (which has an inverting and non-inverting output). The problem with this approach is that ground is being used to complete the circuit, and this leaves the circuit vulnerable to ground loops. One of the goals of the balanced line system is to eliminate ground loops.
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@atmasphere
" The problem with this approach" Do you mean Transformer coupled approach?
As far as I know transformer coupled way is to solve the ground loop.
That's the reason we use the transformer isolation instead of RCA to XLR cable,right?
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The way to solve a ground loop is to purchase properly or fix improperly designed equipment. Adding a transformer is a bandaid. Bandaids fall off.
My company wired recording and film studios in Los Angeles and New York in the 1980s & 1990s. We had transformer and electronic balanced and unbalanced equipment to interface. Hundreds of connections that could be reconfigured into literally millions of combinations. Correctly done, there is no ground loop.
If you detail out your equipment and connections, perhaps we can solve your issue. By detail, I mean brand, connection, electrical power etc. Since we can now post images, draw a sketch.
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" The problem with this approach" Do you mean Transformer coupled approach?
@runwell No. If you are dealing with a ground loop, the transformer can fix that, but take @ieales' post seriously.
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My Ayre electronics sound better using the differentially balanced outputs/inputs than the RCA's
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@atmasphere
You suggest to use transformer isolation and you deny the way to use it.
What is your opinion?
Audio Research reply directly that I should use transformer coupled to connect RCA pre with their XLR only power amplifier.
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You suggest to use transformer isolation and you deny the way to use it.
What is your opinion?
Audio Research reply directly that I should use transformer coupled to connect RCA pre with their XLR only power amplifier.
@runwell If you are using a single-ended preamp, using a transformer might be the only way to drive certain power amps with a balanced input. ARC is often one of them. I'm not familiar with their current lineup, but it was only 5-6 years ago that some of their gear was only offered with a balanced input, but that input had a poor CMRR (Common Mode Rejection Ratio) according to a personal friend of mine who used to work there (Kalvin Dahl). Apparently it was only about 20dB. This meant that if you tried to drive it with a single-ended source, the distortion of the amp was very high and the output power was much lower. So a transformer was the only game in town if you had a single-ended preamp with that amp (which otherwise got good reviews).
If you have an ARC amp and a single-ended preamp, from what I've seen of their circuits I would advise the use of a transformer like the Jensen to do the conversion from single-ended to balanced, so I agree with ARC's advice above.
I don't like using transformers in the signal path which is why I designed a direct-coupled circuit that supports AES48. But transformers have their place; most of the classical LPs or CDs of recordings from the Golden Age of stereo (1958 to 1963) have several transformers in the recording signal path. Jensen and Lundahl arguably make some of the best transformers for this purpose.
Based on what you've told me so far, I would use the transformers!
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So that's it. I will feedback when I receive and install the transformer in my system.
I tried the direct RCA to xlr cable before, and I can hear the soundstage is not good.
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Just connect the ISO MAX transformer in between my RCA pre and XLR power amp,The sound is changed too. It is not very active as it before and Sound volume is not gain +6db,but become a little small. Totally different sound. I just remove it from connection. No good for thus isolation transformer.
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@runwell
Just curious what RCA pre and XLR power amp connected via ISO MAX transformer?
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Rega Cursa 3 pre and audio Research VT100 Mk III ( this model has rca input and I just do the test and if ok will move to Audio Research Ref 75se.)
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