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In Reply to: RE: facing the over generalization posted by Chris O on June 27, 2012 at 12:47:15
My final PS C is an ACS made in Japan, 50uf/370VAC, bought new 2 years ago, never tormented. I always thought they were good, and perhaps are better than a cheap electrolytic. I've used Solens too, reliable.
I say try putting any "good" small (0.05uf-0.001uf) cap across whatever final PS cap and/or cathode bypass cap you have, and tell me what you hear.
Then maybe somebody can talk about what happened: did some frequencies get "boosted" or are the same selected frequencies "faster" or ?
The smear issue has been mentioned numerous times, yet some recommend paralleling smaller better caps across larger caps. I have yet to hear smear. If smear is real then wouldn't multiple by passing (say 5 or 6 total) be disastrous? or possibly return to no-smear?
Anyway, something happens, and it "seems" to show that the ACS cap alone
is maybe 1 or 2 db down in a certain higher frequency zone. My guess is that the same thing I hear would be heard by most of you on whatever cap you have. And if you hear nothing, I want to know what cap you have please. Further, IF "returning to flat response" is what is happening by installing a selected group of small bypass caps, then it would seem then that most large (20uf-100uf) caps are not "flat". IF flatness is not the issue and speed is, then are we listening to different speeds across the audioband? Is that "smear"? Is that worse than non-flat cap response? Are these crazy questions?
What is the makeup of your power supply?
The Mind has No Firewall~ U.S. Army War College.
Nothing crazy about it. The problem is that the best capacitor in the world is really very bad as a linear, wideband, frequency neutral device.
No matter how good, in capacitors, all you get is junk.
Fortunately, some junk is much better than other junk. Is there any one capacitor that is, in fact, wide-band in an actual musical circuit where all parameters are constantly changing, where a single cap can work? NO.
That one cap-- regardless of quality, wants to form a resonant circuit--that is, it wants to tune-in to favor certain frequencies over others, based on the cap value and inductances and resistances in the associated circuit.
In order to get around this unwanted "tuning" effect (defect!), we have resorted to parallelling very high quality small caps with larger caps, coupled with very careful use of R.F. inductors.
In a simple SET amp, these capacitors will cost more than all the other parts in the amp combined-- you will end up using the world's best caps, and that is cheap compared to any usable alternatives.
I should slip-in here that push-pull amps do not have anywhere near these stringent requirements-- they're more wideband naturally, and are much more forgiving.
One or two small caps in parallel with a larger one in a power supply, a cathode bias system, or in a driver plate power supply will cause the amp to sound different, but not necessarily better. Usually, bandwidth will be gained, but incoherencies and hot spots in the frequency range as a whole will appear, rendering the amp pleasant, but not accurate.
Of course, the amp certainly isn't anywhere near accurate with only one cap in each of these places, either.
What we end up with is a requirement for as many as 11, 12, or 13 different capacitors of cascading values, installed at each of these places in the amp. If the right brands and values, and the right lead lengths are employed, there will be no trace of incoherency, and usable musical bandwidth will be widened, as will power supply and cathode bias response to signal. Dynamics will be improved so much that the only thing you can attribute it to is that finally, you have built a fast capacitor-- one that is fast at all the usable audio frequencies.
All of these advantages can and will be negated if any lead on any part of this (stack-up?) is too long, too short, or uses too small a conductor.
Sorry this got longish, and it's quite expensive-- this is what it takes.
"Of course, the amp certainly isn't anywhere near accurate with only one cap in each of these places, either."
This is what I was horrified to discover experimentally, and wished I hadn't, but now would rather "face it".
"That one cap-- regardless of quality, wants to form a resonant circuit--that is, it wants to tune-in to favor certain frequencies over others, based on the cap value and inductances and resistances in the associated circuit."
If this is true, then this supports either finding and implementing
a fix/band-aid, as described or other (?), and/or choosing a circuit that minimizes C's. I like Gary Pimm's idea:
I agree that you want to minimize caps as much as is practical-- but remember-- we can't yet get along without them entirely.
You're going to have to admit the truth, bite the bullet, and make some nice relationships with expensive cap people.
You can start with Mundorf, Dynamicap (Michael Percy Audio is a nice, co-operative source), Reliable Capacitor (wonderful helpful people-- S. Cal.-style), old Hovlands, Sidereals, and whatever else that is really great-- that you can scare-up.
Don't be bashful, and don't pinch pennies! GO RIGHT AFTER the best-- to "H" with the other stuff! This will save you time, frustration, and-- in the long run-- money.
You just can't beat actual performance. Don't try to. Embrace the best and the great people who build it.
Only one cap in the circuit, not very big either. The final C feeding the
300B's CCS is not shown, not sure how involved it is? It seems to be out of the "loop"
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