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Originally Posted by Volkum /img/forum/go_quote.gif
I'm positive there is $100 minimum order.
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Good to know they've changed that policy.
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Originally Posted by TheShaman /img/forum/go_quote.gif
Did you have a chance to compare their performance/measurements?
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They're wildly different amps. A head-to-head test wouldn't be any kind of scientific.
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| I'm trying to choose between the two "schools of thought" on the matter (those recommending separate PSUs to minimize EMI/RFI etc and those insisting that short distances are a must) so your input would be more than valuable. |
This is engineering, not religion: it's all about tradeoffs, not absolute right and wrong. There aren't two schools, just two endpoints on a tradeoff gradient. You probably don't want to be at either extreme.
Let's first discuss the main problem, EMI, due to the electromagnetic field put out by the power supply transformer.
I avoid EMI in the L configuration PPA two ways. First, the YJPS uses a toroidal transformer, which keeps the EM flux concentrated more tightly around the transformer than with other types, hence keeps EMI low. Second, the arrangement purposely puts the transformer in one corner of the case, and the audio circuitry in the other. I have two areas inside the case with nothing at all, on purpose. I've seen some similar designs that try to cram more stuff into the case, ending up using space around the transformer...bad idea if it's in any way electrically coupled to the audio circuitry.
Putting the power supply in a completely separate case and separating those cases with a lot of space is just taking those ideas to an extreme, and it does indeed further reduce EMI.
This is at the expense of raising the power supply's output impedance, however, which is a problem if your audio circuit has any kind of dynamically changing current. (And the only time that isn't true is for toy circuits and pure class A.) If the power supply doesn't have any kind of specially low output impedance or awesome regulation, a few tens of milliohms more output impedance probably won't matter. But since we're talking about Jung super regulators here, it does matter; qusp is right. Remote sensing helps, but that's no excuse to put the power supply on the floor and the amp at desk height.
Note well that I'm only talking about long regulated DC lines here. Long unregulated DC lines are fine if there's local regulation between them and what they're powering. The Creek OBH-11 does this, for example. In terms of my designs, a good setup would be:
unregulated DC wall wart -> [ TREAD -> PIMETA ]
with the brackets indicating a single enclosure. Here, the impedance of the unregulated DC line isn't really an issue...it's mitigated by the regulator's 80-90 dB ripple regulation.
That's EMI. RFI is a whole different ball of wax and hair and mud and hash.
When it comes to power supply issues, virtually all the RFI you care about comes in on the AC line. Keep this in perspective: millions of miles of cable running through a city's worth of RF sources. The YJPS deals with that with the AC line filter. In an EI core based power supply, the transformer is a fair RF filter.
The other distance -- between the power supply and the powered circuit -- is much smaller, and so of much smaller concern. This wire does form an antenna, which does
ipso facto pick up RFI. I have yet to see fixing this problem actually fix an audible problem, however.
First, most audio amps aren't terribly sensitive to "true" RF.
Aside: Some define RF as beginning just above the audio band, but that's arbitrary. The US Navy communicates with its submarines using sub-audio frequency, because it penetrates both earth and water. That's "radio" to me, but not RF in the sense we're dealing with here.
Second, of those audio circuits that do have a wide enough bandwidth to pick up whatever we'd like to fuzzily define "radio" as today, what does it matter? I guess it could be a contributing factor to some kinds of oscillation, but shielding the DC power cable seems like a bad way to fix oscillation to me.
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Originally Posted by zxc /img/forum/go_quote.gif
Tangent, in what sequence would you recommend that the PPAv2 & YJPS combo be powered on?
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I haven't received any reports of sequencing problems with the YJPS yet, and I haven't had any myself. But then, the cost of the thing means there aren't yet as many YJPSes in the world as there were STEPSen at the same point in its history.
Of my two PPA + YJPS combos, only one gets turned off regularly. It has two power switches, one on the rear panel at the AC input, which stays on almost all the time, and the other between the amp and power supply on the front, which I toggle off when not using the amp. This amp has been working like that for years. That DC switch gets toggled almost daily.
