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Old 12th December 2011, 05:51 AM   #19041
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Hi,

Quote:
Originally Posted by VladimirK View Post
In some less practical cases, like external PS, constant current consumption from PS independent on signal yes/no, one can really succeed in getting no any effect from power cord. Just good screening and multistage filtering with good caps needed, at all reasonable points.
Doing the above helps in some areas, however it does not address the root cause, but merely (possibly) mitigates against some of the symptoms, like slowing down the current spikes when the reservoir capacitors are being charged (most extreme in the use of choke input supplies often found in Tube gear but never in solid state gear) and constant current operation. Such power supply work as extra filtering and constant current operation can however help addressing other issues inherent to the circuitry.

To deal with the sensitivity of equipment to power (and other) cable(s) differences we need to employ a different discipline and we must look at the whole interconnected system, including interconnecting cables, common mode and differential mode impedances, balance of the cables carrying power for differential noise and so on.

It is a problem that remains completely invisible on the test bench testing an individual item of equipment and test gear, simply because decent test gear must, by the force of requirements to measure precisely constructed in a way to minimise these effects regardless of the nature of the device under test.

Take the same device into a real system with multiple sources, pre- and poweramp and maybe powered subwoofers and a raft of problems "suddenly appear" that are tough to solve while continuing to comply with electrical codes and that have a lot to do with observed differences between cabled and nothing whatsoever with the direct design of power supplies.

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Old 12th December 2011, 06:37 AM   #19042
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Use silver fuses if you have them. Of course, fuses can make a difference. They are non-linear in operation, and all the current has to go through them. We have discussed this before.
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Old 12th December 2011, 06:59 AM   #19043
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Quote:
Originally Posted by Wavebourn View Post
But I can guarantee that when an amp is properly designed there is no difference between properly selected computer grade power cord and something you can buy for crazy money.
'Properly designed' means 'fit for purpose' right? So while I agree that from an engineering perspective making an amp immune to power cords is an excellent aim. But the purpose of most amps is to be sold, not just perform according to engineering specs. To get an amp sold it has to be attractive to a dealer and the dealer makes a much bigger margin on cables than he does on amps. ISTM therefore that an amp which is immune to cables won't get sold through any kind of dealer because its less attractive a financial proposition than one which sounds better when partnered with a $1,000 mains lead. Am I missing something?
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Old 12th December 2011, 07:04 AM   #19044
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Vlad, many people here have little experience, and strong opinions as to what SHOULD be important.
Wavebourn, I was designing recording consoles 40 years ago. Please do not think that you are the only person who has faced these problems. How I fixed consoles was to run them from professionally made lab power supplies, and individually buffer each discrete op amp with its own pair of capacitor multipliers. In the old days, I did it with bipolar transistors. Today, I do it with either jfets or mosfets. In any case, even the JC-3 phono preamp, one of my more modest efforts, is double or triple power supply protected, AND for good measure I stuck a 10uf film capacitor across the power supply line where the line cord connects. I try to not leave anything to chance. AND it has worked for me over the years.
For everyone, please empty a little of your 'head' to input new data. Even a PhD does not teach you everything that you need to know. By the way, I hired my first PhD EE in 1974, quite a few years ago. I know when what I need is beyond my educational level, but this does not eliminate EXPERIENCE and feedback from you and your associates' listening impressions. That is critical for successful audio design.
I am surprised that nobody has mentioned circuit breakers, instead of fuses.
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Old 12th December 2011, 07:50 AM   #19045
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By referring to high-power class AB amps, I imply that it is almost impossible to preserve good dynamics of such amps with extensive use of LC and RC filtering in PS. But with standard simple C filter, this C and power cord become included in the signal chain, as well as speaker cables. Even the circuit breaker at house switchboard play a role.
My friend did special reconstruction of power line for audio system, by laying special quality 6mm2 power cable up to transformer substation, and claims it adds to dynamics.
I have choosen another way, low power SE amps with diminishing the role of PS as much as possible, up to 7 RC sections at various places (aimed at HF noise, not at 100Hz ripples). This would immediately kill quality of AB amp, but works excellently for definite kinds of SE schematics.

Last edited by VladimirK; 12th December 2011 at 07:55 AM.
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Old 12th December 2011, 07:57 AM   #19046
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Quote:
Originally Posted by VladimirK View Post
By referring to high-power class AB amps, I imply that it is almost impossible to preserve good dynamics of such amps with extensive use of LC and RC filtering in PS.
And with tubes such filtering is OK?
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Old 12th December 2011, 08:09 AM   #19047
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And with tubes such filtering is OK?
For low power devices could be OK, but Yuri Makarov puts few farads per channel at his 3W tube amp, just to remove effects of LC RC sections.
Only for shunt-like output stages (load in parallel to active device) one is free for any fantasy in PS.
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Old 12th December 2011, 08:14 AM   #19048
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Do you know the circuit diagram of Audio Research D400 power supply?
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Old 12th December 2011, 08:25 AM   #19049
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John,

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Originally Posted by john curl View Post
Use silver fuses if you have them. Of course, fuses can make a difference. They are non-linear in operation, and all the current has to go through them. We have discussed this before.
I'm afraid this explanation, while reasonable, seems in need of rejection as hypothesis.

In AMR gear we eliminate all fuses except those mandatory for electrical/fire safety by design. Initially we used to have more, but we instead went to self protecting transformers (as we have several in parallel and in theory would need one fuse per transformer).

Now here is the cracker, in the case of the CD-Players all power supplies that feed something variable are CCS fed Shunts and all analogue stages are Class A SE as well (and Tube rectified to boot on the big one).

Incidentally, I use these CCS fed Shunts almost religiously - they do help to keep signal/noise currents contained into controllable loops without having to cut ground planes, offer defined low impedances into the 100's of KHz, keep an absolutely constant load on the power supply transformers and even cure cancer, okay, they don't do the last thing, but they do do all the others...

So there is clearly no variation in current draw whatsoever, no matter what the device does. Yet the one single fuse in the IEC Mains Inlet which must remain has audible effects. I am severely stomped at any explanations and "They are non-linear in operation, and all the current has to go through them." really does not cut it for this case. I am rather puzzled by the why...

Ciao T
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Old 12th December 2011, 08:44 AM   #19050
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Quote:
Originally Posted by PMA View Post
Do you know the circuit diagram of Audio Research D400 power supply?
You mean that it is with RC filtering?
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