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Originally Posted by gtimbers View Post
The capacitor biasing is something that has existed for many years. Tube equipment does it automatically since there is usually a large DC offset between stages. Some early transistor amps/preamps had two polarized caps in series with the center point going to ground through a large resistor.
I personally became aware of this technique for speaker systems through communications with Ed Meitner, currently of EMM Labs. He is a wealth of information regarding these "tricks" to help linearize or improve the sound of passive components.
It turns out that the bias trick actually increases measured IM distortion and the higher the bias voltage, the greater the increase. It is not by a great amount, but it is measureable. The sound imporvement (or change) is very rarely perceived as worse and is never linked with a increase in IM distortion. The sonic effect is one of smoothness, increased spaciallity, detail and stuff like that. IM has a muddling or confusing effect so I doubt that this particular steady state measurement is explaining the sound difference either way.
Simply put, we are striving to create a class A situation but as was just pointed out, depending on the bias voltage with respect to the voltage across the capacitor, we may only have an "A" condition up to a particular drive level. So if it makes you happier, consider the change to be class AB, but heavily biased to A. You must also keep in mind that the voltage across the input terminals of the crossover network does not tell you what voltage or current is applied to any individual component. Some parts block signal and others shunt signal so the loading on a particular part is not obvious. For the most part, the caps are well taken care of with 9 volts, even at healthy drive levels. The obvious choice for 9 volts is the small cheap battery and holders that are available. No current is involved so a smoke detector battery and holder is a natural choice.
We did do one system with 18 v (M9500). Certain of the Japanese reviewers thought it was an improvement. I can't personally tell any difference. I am also told on a regualr basis (again by our Asian customers) that the battery must be changed at least every 90 days and that the sound degrades after that. Once again, I have not been able to "hear" any difference after 90 days and the battery is certainly still good for many years from a voltage standpoint.
What playing around I have done with initial application of a battery to a biased circuit (that has not been previously powered up) is that it takes about 3-5 seconds for the soundstage to change. I have tried to measure the voltage level in that time period and it seems that several volts is all that is necessary to accomplish 90% or more of the improvement. Once a circuit has been energized, it is nearly impossible to return it to zero. You have to individually short out each cap and leave them shorted for a while or else they will creep back up somewhat. If you replace the battery with a short and play the system for a while, the caps will start to bias themselves, although not to anywhere near the same degree.
You can take this opinion for what it has cost you. I have been very pleased with biasing for many years. I use it in all applications that involve a capacitor and I have rarely been disappointed. Results may vary so if it doesn't do it for you that is okay too. It cost a bloody fortune to implement as it requires 4 times the capacitance and double the capacitor parts count. The network size gets huge as well. Inspite of this, I have never heard a capacitor type that didn't improve (or change) including the nearly perfect teflon variety.
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"What you got is a PSA-2. They kick, and sound clean on subs. Durable amp. As for the gain trims on the balanced input card being removed, seems like that might have been an aftermarket mod, some companies took them out, and replaced them with a fixed resistor. Ive seen Showco modded amps this way. I prefer having the gain pot, and being able to do whatever I need to."
Came across this on the 'net:
"I have a pro sound background from 20 years ago. I toured with Showco from '82 to '87 (the Who, the Kinks, Bowie, Motley Crue, Kiss, Missing Persons, Prince, 200 shows with ZZ Top, Bon Jovi, etc.), so I consider myself an amp snob, but I keep that a secret (don't tell, okay). During my time there, I watched the last of Showco's Crown DC-300A's get phased out for the stunning Crown PSA-2's. As I was leaving, the Crown Microtech and Macrotech amps were arriving.
Just for fun, surf over to ebay and check out some completed auctions for "Crown DC-300A." Hmmm, why are these 30-year-old dinosaur amps selling today for $150 to over $300? Because they rock(!), and no pesky cooling fans either. I never saw it, but I've heard stories that Crown would demo these amps by driving them with a 60 hz sine wave tone and connect the ouputs to a washing machine, using it to wash a load of laundry. (I'm told it would swing 68 volts!) Once the wash was done, they would reconnect the amp to an audio system and play some music. Stable beyond belief. Stereo 155 watts into 8 ohms, 250 into 4, or bridge mono 600 watts into 8. I still have mine that I bought from Showco when they were pulled out of service. At 45 pounds, they're built like tanks. They're still serviceable today. I had about $200 of work done on mine about five years ago (caps and output devices), and it's just perfect today. Beautiful low end for days. I know that I can't be the only one lurking on this forum/board with a DC-300A, so I hope someone else can chime in with any comment comparing it to one of the modern XLS amps or the QSC line.
The PSA-2: the self-analyzing amp. 265 watts into 8 ohms stereo, 450 into 4, or 900 bridge mono into 8 ohms. These things were simply awesome, beautiful, bulletproof, heavier than anything, and we loved 'em. Stable, stable, stable. They're not as common as the DC-300A's over on the 'bay, but when you see one you'll be surprised at the prices they fetch. There's one on a fixed price classified ad site right now for $795, which may be ambitious, but I've seen them fetch $600 in the last year. Cooling fans. Front panels that you'll either love or hate the looks. I love the way they look, but they're like loyal old friends.
Both the the DC-300A's and the PSA-2's were 4-space (7 inches of rack space) amps. The Microtech amps changed that with their 2-space chassis, but my goodness those things were deep! Power? Stereo 250/8, 350/4, and 1,000 bridge mono into 4 ohms! And this was back in 1984! When they arrived, Showco used the PSA-2's for the subs and lows with the Microtech's for everything else. I think there were three PSA-2's and two Microtech's in each amp rack. Who wants to go load the truck?! Heh, heh, heh!
When I joined the Bowie (Serious Moonlight) tour as it arrived in North America in July '83 after the European leg, Showco wanted to try some Carver amps. As far as I knew, nobody told Crown, but after a day or two there were Crown reps swarming all over the place asking all of us Showco guys if we were happy with their amps (okay, it was maybe a couple of guys from Crown, but it was obvious they wanted to protect their interests). The Carvers weren't exactly what Showco needed (amps that would work without fail night in and night out for months on end), so it wasn't long before Showco was once again 100% Crown. We were always told that Showco actually owned more Crown amplifiers than Crown owned, which was a little surprising at first until you stopped to think that Crown was in the business of selling them, not owning them.
When Showco realized that our AC distribution systems (208 volt 3-phase "y") used such long cable runs that we often saw only 110 volts or less at the amp racks, Crown devised a modification for the PSA-2 that would produce rated power at 100 volts. If you ever see a "PSA-2XH," snatch it up. The "XH" designation is for "Extended Headroom," and is one of these specially-modified amps. Sweet, sweet, sweet!
The Microtech amps were problematic when they first arrived, although right now I can't recall the specifics. In fact, I can't recall if I saw the Macrotech's before I left Showco at the end of 1987 (let me know if you want a refund for what I said above ;^).) Since that time, Crown has perfected the design, and the Microtech and Macrotech amps are as good as any you'll find. Again, check the 'bay for some completed auctions, where you'll find beat up examples selling at a premium. Again, ask "Why?" Because they rock, and their rep' is known all over! I think someone mentioned earlier in this thread that it's just not possible for Crown to legitimately rate their new I-tech amp at 8,000 watts in a 2-space chassis and 28 pounds. I can tell you that Crown has always rated their products very conservatively."
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Lucinda MacKethan ? Hollins University
How can this not be a hate crime. And how are we not all guilty when we do not persistently call out those who try to make intolerance a virtue, from Fraklin Graham to Rush Limbaugh to Fox and Friends to Tom Goolsby of our own NC state legislature. We did not think it could happen here, a massacre of 3 of our best: young Americans, North Carolinians, High achieving, service oriented students at our best universities. Oh, they were Muslim? How can we allow their religious beliefs to lead to their deaths. In this country. Here, where we thought we were better.
Reply ?
? 30 minutes ago
Larry Rochelle ? Top Commenter ? Writer of the Palmer Morel Mystery Series at Self-Employed
The FBI Set Up the "Lone Killer" Scenario:
1. They set up Oswald.
2. The FBI set up Sirhan Sirhan.
3. The FBI set up James Earl Ray.
4. The FBI is not an investigating body. They are "fixers." They make killings go away by blaming just one crazed nut.
Reply ?
? 42 minutes ago
RALEIGH: FBI launches new investigation into Chapel Hill killings, as thousands mourn in Raleigh | Crime | NewsObserver.com
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Descend, bold traveller, into the crater of the j?kull of Sn?fell,
which the shadow of Scartaris touches (lit: tastes) before the Kalends of July,
and you will attain the centre of the earth.
I did it.
Arne Saknussemm
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#randomquotes
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https://www.youtube.com/watch?v=dpUYahrXi7k
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http://images.volcanodiscovery.com/index.php?eID=tx_cms_showpic&file=fileadmin%2Fphot os%2Findonesia%2Fbromo%2Fbromo_0211%2Fbromo_i43223 .jpg&title=bromo_i43223.jpg&width=1500m&height=500 m&caption=Another+powerful+explosion+throws+a+barr age+of+bombs+onto+the+outer+flanks+of+the+cone.+On ly+few+of+the+ejected+blocks+are+actually+glowing. +%28Photo%3A+Tom+Pfeiffer%29
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