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in a pre amp??
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That is IF the preamp is truely balanced, not all preamps with balanced inputs and outputs are balanced preamps. Also, for optimal results you will require a truely balanced source and amplifier too.
Balanced is louder but not always better.
Should be the correct answers.
If you have ever heard a 3 foot cable make a difference in your system, then you know what I am talking about. In theory, balanced operation means no cable artifact at all.
In practice, you still can hear differences but they are very slight compared to single-ended cables if the standards of the balanced line system are adhered to by the equipment manufacturer.
Unfortunately, in high end audio, adherence is very rare. If adherence was common, single-ended would have long ago been relegated to the entry level of the market.
Here are the standards:
1) pinout: pin 1 is ground, pins 2 and 3 carry the signal in inverted and non-inverted form. USA industry standard is pin 2 is non-inverted.
2) the signal is driven between pins 2 and 3; ground is ignored - instead ground is used for shielding only. Termination standard is 600 ohms.
3) The circuit is low impedance.
#1 is so things hook up right.
#2 is so signal current does not go through the shield. This reduces the artifact of the cable quite a lot, and is one of the areas where most high manufacturers don't keep with the program.
#3 is also to reduce cable artifact by swamping out minor capacitive and inductive effects that are the result of the construction geometry of the cable. This area is also a problem for most high end audio manufacturers. The termination standard is what the preamp can drive; to do that its actual output impedance will be a lot lower.
In effect this means that the cable can also be very long and expense of the cable will have little to do with how it sounds.
Even if the cable is only 3 feet long this can still be a benefit! An excellent example is LOMC phono cartridges, which are a low impedance balanced source- if the cable is set up according to these standards, you will not be hearing any difference between a $200 cable and a $2000 cable.
Try that with single-ended!
The lower noise is obtained both by the common-mode rejection ratio of the equipment (the ability to reject signals that are the same on both the inverting and non-inverting inputs, like a hum field imposed on the cable) and also by the internal noise-rejecting aspects of the balanced circuit. It is also lower distortion as IM is much lower due to superior power supply noise rejection and even ordered harmonic distortion is gone.
So you can expect a fully differential balanced preamp to be very low distortion and very neutral compared to the same topology in a single-ended embodiment.
"In theory, balanced operation means no cable artifact at all."
After mulling that over carefully, I don't understand. What be the theory of which you speak?
Tnx, Rick
of getting rid of cable artifact.
This was done initially to make long distance (transcontinental) phone calls possible. But the recording/broadcast industry picked up the technology for rather obvious reasons - no cable artifact - and this is why Mercury was able to park their recording truck outside Northrup auditorium in Minneapolis, run 200 feet of microphone cable, and get really excellent recordings of the Minneapolis Symphony.
So in short, we are talking about 'balanced line theory and operation'.
The benefits in the home are identical to what they are in the studio and broadcast, even if the cable is only 3 feet.
"So in short, we are talking about 'balanced line theory and operation'."
OK, thanks.
Guess I don't think of the geometry as an artifact but rather as a design attribute. 'Artifact' brings to mind secondary issues like finite resistance, dielectric absorption, triboelectric effects, shielding percentage and all that.
I appreciate the clarification.
Rick
But the whole point of balanced line operation is that the geometry is now made a lot less important, although there are certain things you can do with the cable that can help.
In most cases this simply means that there is a twisted pair that travels together within a single shield.
With single-ended cables you will see all sorts of geometries that all sound different. The main issue with single-ended cables is that there is no termination standard so terminations might be anywhere from 10K to 500K or even one megohm, and there has to be signal current carried in the shield or at least the ground circuit. These two aspects pretty well guarantee that the geometry will be audible.
So my clarification is that geometry and artifact are not the same, but quite often are directly related. With the balanced line system, the two become disconnected- that is to say that the effect of the geometry is really reduced by several orders of magnitude.
"The main issue with single-ended cables is that there is no termination standard so terminations might be anywhere from 10K to 500K"
The cable itself surely isn't matched is it? I used to work with Mic. cables and theater stuff in general in high school to get funds for important things like ham radio and at a guess their 'surge impedance' was in the neighborhood of 100 ohms so there was no real matching going on. I think they relied solely on the transformers and shield to reject RF a little, but not always enough... Of course in-band that hardly counted so the system ignoring the cable was around 600 ohms.
On another topic, you posted the other day something along the line of balanced amplifiers having lower NF's than single ended and I don't think that's necessarily the case. Using two amplifiers for a given amount of power gain can have lower noise to the extent that their intrinsic noise is uncorrelated however you can achieve the same thing single ended by using parallel stages. But if you were talking about overall noise SUSCEPTIBILITY that's a different matter, at least for in-band noise energy...
It takes a lot of qualifiers to clearly communicate by writing, doesn't it?
Rick
No, the cables aren't matched. Microphones are usually set up to drive about 150 ohms at the input of the mixer, line level is usually 600 ohms.
With regards to parallel sections, you can of course do that with balanced differential as well. That is why I was careful to use the word 'topology' in the post you referred to. We use paralleled tube sections in the front end of our MP-1 preamp to help get lower noise, plus we have a 2-stage vacuum-tube CCS. I have found in differential circuits that you must have a 2-stage CCS or you just will not get the performance out of the resulting voltage amplifier. So as a result, it takes a total 8 tube sections (4 twin triodes!) to execute the single stage of gain at the input of our phono section in the MP-1.
Be aware that a 3-pin DIN connector does not guarantee a balanced circuit design has been utilized. They can be wired in place of a standard RCA connector, just as external adaptors can be used.
"For a nominal service fee,
you can reach nirvana tonight."
One thing you need to realize is that in order to get the most (any?) benefit out of a balanced preamp, you also need to run your amp, (and if possible, your sources), as balanced as well. (And they need to be truly balanced, not the pseudo balanced that some manufacturers add on as a convenience to the customer.) If you don't run completely balanced through your system, then running balanced merely through your preamp does not really accomplish anything, as you would need to convert from single ended to balanced going from your source to your preamp, and then from balanced to single ended going to your amp.I run all balanced, from my cartridge (tonearm cables are terminated with XLRs), through my preamp, (Ayre K-1xe), to my amplifiers (Lamm M2.1 monoblocks). I am extremely happy with the results.
FYI, Read Ralph's response below, as he is VERY knowledgable about balanced equipment. (I believe he actually designed and built one of, (if not the), first truly balanced preamps.)
Edits: 07/24/12 07/24/12
So, instead of your signal being amplified once, it gets amplified twice.
I guess you could call that an advantage? But I'm not sure how.
Hukk
Often repeated, always incorrect.
Yeah I see what you're saying. Clumsy wording on my part. However, I will stick to my first statement, two amplification stages. When they come together at the output, I don't see how additional distortion can be avoided when you compare to a single-ended amp.
Hukk
The way distortion is avoided is that even orders cancel in each stage of gain if the preamp is internally balanced. So instead of having more distortion it will have substantially less!
In addition, if the preamp is fully differential, it is incorrect to say that the signal is going through more gain stages. It isn't! Yes, it may take two tubes or transistors to construct the gain stage, but its only one stage of gain nevertheless- and one with less noise and distortion than the same circuit executed single-ended.
So imagine that you have a tube preamp that is fully differential and balanced. Theoretically you have 6 db less noise per gain stage, work that out over 2 or 3 stages of gain and you see that there is considerable potential for a lower noise preamp- so much so that you may indeed be able to operate with less gain stages overall. In practice this can be the case- it certainly is with our preamps which operate with low output MC cartridges and can drive any amplifier made, but only have 3 gain stages overall to do it.
With less gain stages its a there will be less distortion and greater bandwidth. In addition, the circuit will be far more immune to power supply problems, so IM distortion can be expected to be lower too. IOW, its win-win with regards to single-ended.
a) Any noise picked up by the cable gets cancelled out, you get 50-80dB common mode rejection as compared to nil with single ended;
b) the signal is a lot hotter (11.79dB) than the signal in a single ended cable thus requiring less gain at its destination.
The benefits become very clear if you are in an environment with RFI pollution and/or have long cable runs.
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