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CECE
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Krell July 07'

Never seen a VPI 19 cleaning machine, nor a VPI HW-19 MK14...where they special order?
A $16600. amp that ONLY puts out something a bit over 1kW...and runs hot as hell ain't so slick. Heat will shorten it's reliabilty, and life. Why don't they use an amazing concept....fan cooling. My AVA/Hafler P500 are about 1400W running mono into 4 ohms, fans kick in high speed, the units are merely warm to the touch, HOT is a fire hazzard. What a poor design. Fans make a bit of noise, but the fire trucks make even more noise. Why would such an expensive amplifier not use fan cooling. Ya didn't mention how many output devices are in this thing. JA mentioned these things make enough power for any one....nope, disagree totaly, it's just a start...1kW can be taxed easily into speakers at lifeike levels. Slew rate? not mentioned, what kind of thermal protection do they use...not being fan cooled is a poor choice for such a pricey product. The instese heat is certainly not good for the thing, pre amp section, is taking a beating.

bifcake
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Re: Krell July 07'

I disagree about a fan being a viable option in a high end amplifier. You're spending megabucks to get low noise, blacker blacks, higher dynamic range and you're willing to sacrifice that to fan noise? That makes no sense at all. Bigger heat sinks and better heat management is the answer, not fan and its inherent noise.

CECE
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Re: Krell July 07'

do you also turn off the heat or AC in your house while listening. When the music is playing, the fans ain't heard. A $16,000 amp that runs what seems exceedingly HOT is a dumb design. It will certainly shorten it's reliabilty. Long term lifetime. Even rack systems have fans in place checkout most pro setups fan it baby. Smoldering amps and electronics can't sound better than ones that are running cooler with fans. Most fans are black so it shouldn't have any effect on.."blacker blacks" Low noise fans are also available.

CECE
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Re: Krell July 07'

When my fans kick into high...it's a summer breeze a hot summer breeze when all 4 are pumping out all that wasted heat energy. But my amps ain't frying themselves into an impending doom. Chassis are merly warm, the room is very warm..all wasted energy heat. Convection cooling even with larger heat sinks won't work in many installations. Fan it, like the grand pubahs of past. I actually have to run teh ceiling fan above to get some air down to the lower amps, it works fine...fans, what a concept

rmck818
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Re: Krell July 07'

Your post is a good example of information being used out of context to make a point that is biased in its conclusion. For example, the amp is overheating and dangerously hot. As I recall JA' informal method of temperature determination, he was unable to keep his hand comfortably on the amps chassis and heat sinks, which he usually states is about 80 degrees C., 176 Farenheit. Warm, and perhaps dangerous to a persons touch but certainly not hot enough to start a fire, the ignition point of paper being 450 F for example. But why is the amp at this temperature, playing music at one watt? No, it has just pumped out 100 watts RMS for one hour, per FTC testing standards. After that regimen, most amps tested are at that temperature, or have shut down before the hour had elapsed. The new Class D amps are not stressed by this test, but otherwise the reaction of the FBI was quite normal. To characterize the amps reaction to the FTC conditioning as an indication of its normal funtioning is just plain wrong.

Overheating is a relative term, a vacuum tube is not normally touchable in use, is it overheating? Are light bulbs dangerous if they cannot be touched while in use? I have touched voltage regulators on CD players and DACs that were uncomfortably warm, but operate at that temperature in normal operation. My Krell preamp has voltage regulators that run very warm and has done so for years without problems. I read that the wear and tear semiconductor devices undergo from heat is not caused by the heat itself, but from the repeated heating and cooling cycles it experiences when powered on and off. Fan cooling works of course, but is not used much because of fan noise and the need for maintenance. Check the insides of your PC and its power supply to see the build up of dust that will occur. I have a Crown amp I use on a subwoofer in a HT system, it has a fan that I can hear the moment the soundtrack changes from loud to quiet. Fan noise has long been an issue.

Krell is known for running their amps in class A or with high bias current that keeps the transistors running in class A. Class A operation means high heat dissipation. They've done that for years, and given their five year warranty coverage and the cost of shipping those monster amps around, they must not have many problems with heat damage.

It would be interesting to see how your AVA amps would react to the FTC conditioning procedure. Mosfets (used in your amps) are known to increase their internal impedance as their temperature rises, which limits how hot they will become (as well as their output capability.) Yet they still need fan cooling? I wonder what temperature they would be at after one hour at one third power? We know the Krell amp will survive, would the AVA? A mystery. . .

CECE
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Re: Krell July 07'

Not a mystery at all. The Krell was just putting out 100W. come on, that's a friggin car radio! I regulary have my 4 amps cranking for hours and hours loud...fans going full speed. Well past any FTC 1/3 power test for a mere 1 hour. AVA stuff works and keeps working. And since my OmegaStar EX ckts are based inside teh Hafler pro 500 chassis , it has the great Hafler desinged heatsink with 12 Mosfets (16 on the XL-600_ the heatsink is terrific design, lotsa surface area in a compact size inside with teh fan cooling it through it's center...Hafler knew what he was doing. AVA took the great design, and updated teh driver boards, the Mosfets replaced with modern, more linear, faster ones from Exicon. All great stuff, reliable, robust, and priced for mortals. AND much more powerful and musical than some extremely expensive Krell. Where is teh Krell assembled, anyone know? If it's not made in a country with people who get paid a living wage, I'd be sure as heck wondering, why the insane price tag? An educated consumer is some of AVA's best customers. The AVA OmegaStar EX in Hafler Pro 500 is delivering about 1200-1400W RMS mono...anything less is underpowered It takes 4 in mono to get some realism going. 4800W RMS capable or so, brings it alive, and will pass any FTC 1 hour 1/3 test. Didn't some extremely expensive amp miss about 500W? So much for FTC amp power rating conformity. Yet it was given a great review....Me thinks that is WRONG!

CECE
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Re: Krell July 07'

YES, light bulbs are dangerous!!! Leave a 100W lamp on, too close to an old dried out paper shade, or do you read any news about how some extremely HOY halogen lamps in some poor fixtures where over heating buring up places, do some investigation...Put a 100W lamp in a fixture that says 60W MAX, as many dopes do....fire time. In recessed cans, table lamps, that's why they had to make recessed cans idiot proof and have thermal cutouts to prevent RETARDS from doing dumb stuff, like relamping with a too high a wattage lamp. CFL's solve that issue, since the bases are keyed and most are not interchangeable. Except for it's specific watt type lamp. Amps running uncomfortably hot to the touch are just dumb. Just shows they musta cut corners in heatsinking. But it's good Stereophile brought this issue out in it's test. this kind of stuff is reality based reviews, not subjective mumbo jumbo about hearing stuff that doesn't exist.

bifcake
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Re: Krell July 07'


Quote:
do you also turn off the heat or AC in your house while listening. When the music is playing, the fans ain't heard. A $16,000 amp that runs what seems exceedingly HOT is a dumb design. It will certainly shorten it's reliabilty. Long term lifetime. Even rack systems have fans in place checkout most pro setups fan it baby. Smoldering amps and electronics can't sound better than ones that are running cooler with fans. Most fans are black so it shouldn't have any effect on.."blacker blacks" Low noise fans are also available.

I actually do turn off AC while listening. I find the AC noise to be extremely distracting. I have no problems with fans in a low to midfi systems, but if you're going to be paying a gazillion dollars for an integrated, there shouldn't be any fan noise associated with it. Otherwise, you may as well pay a lot less for a cheaper integrated because you won't be able to hear all the subtleties that a 16k integrated will be able to recreate.

CECE
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Re: Krell July 07'

Crazy. Nothing like sweating to the oldies. Sweat dripping off my forehead is much more distracting. Shivering is too. When they recorded it the heat and AC where on. Live events also have AC and heat if indoors. If outside there is a breeze. Or rain if you are in Central Park N.Y....Woodstock had lotsa open air natural effects. Never been to a live event that didn't have ambient noise. Listening to music in a vacuum is unnatural. Pristine quiet enviorment is not real. So why spend $16,000 on a amp running way too HOT and yuou un naturally restrict the listening enviorment with no noise. Not audiophile at all. Music is meant to be listened to in REAL enviorments, you are therefore masking the music by having things too pristine. Ain't that defeating the purpose of an expensive amp in teh first place. So teh amp heats up the room, due to it's overheating, it gets hotter and hotter, at what point do you call it all off. AND, you forgot teh temperature increase ifs probably effecting teh speakers, so you are defeating the purpose of an expensive amp. Audiophiles are a looney bunch ain't they? Nothing natural about how audiophlakes try to reproduce music to be natural and REAL!! Give me FANS, give me FANS. Live muis chas lotsa FANS, both in the audience and in the equipment.

bifcake
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Re: Krell July 07'

I don't like outdoor concerts because the acoustics suck. I prefer indoor venues. I don't hear the AC at a live event indoors, so that doesn't apply.

I usually listen to music at night, so I turn off the AC during the time I listen. If/when it gets too hot, I stop, turn on the AC, cool off the room and then resume my listening. I want to experience the recorded environment when I listen to a recording, not my own environment intermixed with the recording venue. Hence, I minimize the effects of my room, I pick out audio components that do not detract from my listening experience, I minimize noise within my equipment and my listening environment. If you're not willing to do that, then I see no point in spending so much money on audio equipment that strives extract the Nth amount of detail and ambiance from the recording and take the noise level down to imperceptible using power conditioners, cables, etc, etc.

High end audio is about getting the last 5-10% out of your recordings. If you're not willing to minimize extraneous noise within your listening environment, then you're just wasting your money on high end equipment. At least in my opinion.

CECE
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Re: Krell July 07'

Everytime I upped the equipment the sound got better. With the AC on while I listen. From bi amping from single amp, to quad bi amping into better speakers. the minutia of the miniscule things you try to perceive in your listening are not worth the effort. High end is about top quality reproduction of the recording. It becomes insanity when you try to dig out stuff that is just about some weird perceptions. Every update I did/do are so dramatic that the AC on or off don't change the improvements. Outside live events are fine, you just ain't been to any good ones then. Live outdoor events eliminate any room qualitys that blur the sound, like too loud, boom, etc. Open air is fine. If your system sounds are influenced by teh sound of a fan cooling teh room, you need to upgrade better for more dramtic improvements that will make you ignore a fan. changing a cable is not an upgrade for any audible things that matter. high end is about 100% top end sound not some inane 5% minutia. If you change an amp from 100W to a 200W amp, there is no improvemnt. going from 100W to 1000W will result in a improvemnt you will hear without being a trained, listener trying to pull stuff out of teh imagination. Try upgrades that go beyond what are disrupted by an AC cooling teh room.

bifcake
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Re: Krell July 07'

Perhaps if you turned off your fans and your AC you wouldn't need cascading amplifiers supplying 12 megawatts of power into your speakers.

Seriously though, I think that room noise defeats the purpose of a high fidelity musical reproduction. Noise is still noise no matter how you try to mask it.

martin_n
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Re: Krell July 07'

Transistors fail between 150C and 175C. What you should consider is not just the temperature of the heatsink, but the temperature of the semiconductor junction.

For instance, in this example you could roughly assume that the transistors connected to the heatsink will have a temperature gradient of around 1C per watt. So if the amp has say 2 transistors in its output sage, and the amp is dissipating say 50watts then each transistor is getting rid of 25watts
This means that the junction temperature will be 25C above 80C or 105C.

How does this shorten the amps life? Well MIL217 is a book primarily written for the US military. It is a set of equations that is used to predict MTBF (Mean Time Between Failure)
As a transistors junction temperature approaches its failure level then MTBF reduces exponentially!

CECE
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Re: Krell July 07'

Amazing, yes there is science in electronics. Yeah, if teh heatsinks are hot to the touch, just how hot it the component that managed to heat up teh mass of metal to that temperature. them transistors are cookin'. Poor design, poor heatsinking, for such a pricey item. Nobody has said yet where it is made? If it's a country with highly underpaid workers (which just recently are now wising up, demanding raises, didn't take long!!!) then how do they justify the price? thick front panels? they shoulda' put more metal in teh heatsinks, less in the front panels....Vietnam is now getting work that is too expensive to do in CHINA!!! Wow how things change so quick....Pretty soon there will be no countires left to exploit for cheap labor? Only Africa left, but what will the company policy be on Lions eating the employees, will that be considered a non approved day off from teh assembly line? Will it be covered by medical insurance...Is a $16K intefrated really any better than say a"cheap" $2,000 one? For teh same power ratings? Is it audible...or is it just hype? Glaring differenes, or those indistinct verbage things writers droll on about things that really have no meaning...pace, tempo, etc. since those are physical things, how does a electrical product change what they did in the physical action of playing an instrument? That is bizzare. Pace tempo, rhythm..physical not sonic You know, white people ain't got no rhythm. It's a physical thang, if you play a non rhytmic white thing through a amp that is claimed by some creative writer, to have rhythm, is something gonna improve? Or if you take some Rap hip hop crap, and play it through an amp with rhythm, pace and tempo, will that rap crap suddenly become musical? If it don't then it proves you can't have electrical products changing physicla attributes of music. I conlcude then, the terms used by creative writers in thier reviews are just that creative writings of the imagination. Measuremetns matter, since they are based on science and electrical characteristics.

Elk
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Re: Krell July 07'

Thanks, Martin. Interesting info.

rmck818
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Re: Krell July 07'

Yes, Krell has a very strange business model. Create products that self-destruct from heat damage and make them extremely heavy and expensive to ship, so the cost to do so is so high it uses up all the profits when they must be constantly repaired and shipped back and forth during the warranty period, and subsequently the company goes belly up. Once past the warranty period, the customers will be angered by the high cost and difficulty of shipment, not to mention repair, thus creating a disatisfied customer base that won't buy Krell in the future. Apparently this model is not working, as they have not closed their doors and have continually expanded their product line to include HT components and loudspeakers.

My ten year old Krell amp had a problem in one channel one day, as a small puff of smoke rose from its chassis vent upon turn on. So, did a cascade of component failures in a domino affect occur within the amplifier, or fuses blow or were wild AC waveforms or a DC power supply surge sent to my speakers? No, it quietly shut itself off with no further harm. If I tried to turn it on again, it would just shut down with no trace of any other component failure. The problem turned out to be . . . an electrolytic capacitor, a small one on an amp board. First time it ever had service and never has since.

I'm sure you'll spin this into some terrible design flaw or who knows what else. I'm pleased for you that AVA amps will never die and their impeccable design and performance is at the pinnacle of the amplifier art and all else are the equivalent of a boom-box IC amp chip taped to a beer can heat sink (polypropylene tape of course). So enjoy, and meanwhile I'll try to start a new thread regarding the FBI's review.

Elk
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Re: Krell July 07'

Gosh, bi-polar, how do you live with the day to day disappointment of an amp that just keeps working and working while producing excellent sound? It must be exhausting.

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Re: Krell July 07'


Quote:

Transistors fail between 150C and 175C. What you should consider is not just the temperature of the heatsink, but the temperature of the semiconductor junction.

For instance, in this example you could roughly assume that the transistors connected to the heatsink will have a temperature gradient of around 1C per watt. So if the amp has say 2 transistors in its output sage, and the amp is dissipating say 50watts then each transistor is getting rid of 25watts
This means that the junction temperature will be 25C above 80C or 105C.

How does this shorten the amps life? Well MIL217 is a book primarily written for the US military. It is a set of equations that is used to predict MTBF (Mean Time Between Failure)


Quote:


As a transistors junction temperature approaches its failure level then MTBF reduces exponentially!


Let me add my 2 cents in layman's interpretation....

Increased Operating Junction temp of 10 deg C above 85 deg C will reduce MTBF ( Life ) by 50% !!

Lets assume that a Power Transistor has an MTBF of 500,000 Hours ( not untypical )

If it is operated with its junction temperature of 20 deg Centigrade above 85 deg C, the Power Transistor MTBF will drop from 500,000 hr to 125,000 hours

Assuming that a Power Amplifier has 5 Pairs of output transistors in parallel per channel ( a total of 20 Output devices ) the MTBF for the Amplifier will be :

125,000 divide by 20 = 6250 Hours

That is just 260 days of continious use ( which could also translate to just 260 days of being left powered on, for a Class A amplifier... even with No signal.

THis example is NOT related to any specific commercial product, but is given to show that Heat KILLS ... rapidly, if temperatures are not adequately controlled by passive or active heatsinking.

Cheers

CECE
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Re: Krell July 07'

HEAT is one of the biggest enemys of any electronics. Not just audio phoilble land. After hours and hours of CRANKIN' my 1200-1400W AVA/OmegaStar EX/P500 amps are merely warm on the entire chassis. Driving 4 ohm speakers that drop even lower at some freqs. A superior design, both mechanically (heat disapation, cooling) and sonically, and electrically. High temps are for cooking, not listening to audio. The beauty of the Hafler heatsink in the larger amps P500, P505, DH500 models where that unique heatsink, lotsa surface area, in the smallest size,inside, not a large plate out back BRILLIANT!!!! It keeps 12-16 MOSFETS cool and long lived. And yes, never ever, had an AVA failure ever. Superior design, simple, priced for mortals. Simplicity is genius, ya know who said that? All electroncis benefit from keeping it's temperature down from self destruction.

gkc
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Re: Krell July 07'

I do the same thing, Alex. I cool the room, then listen. Outdoor concerts? Not unless I'm overpowered by reefer madness. I attended my last Hollywood Bowl concert about 15 years ago...the sound of a bad AM radio. I attended my last Rolling Stones concert about 20 years ago, at the Oakland Coliseum. I didn't go there for high-end sound, but for the publicly naked babes and the, er, casual atmosphere.

DUP, your AVA stuff is no better or no worse than anything else out there in a similar price range. If you need that much grunt to "move air," you need some science to verify air movement as a measurement criterion. Here is what I suggest. Put a couple of anemometers in your room, and scatter a few wind socks around your listening chair (in a pinch, you could mount condoms on sticks). Then wear a propeller beanie, tied down with a chin strap, as you ramp up the velocity. Chart the results. How many watts does it take to get you airborne? Did the wind socks (or condoms) change directions with frequency? You could be a pioneer. This may be your last shot at fame and fortune -- you sure as hell ain't gonna win any spelling bees.

Happy tunes, all.

Elk
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Re: Krell July 07'


Quote:
(in a pinch, you could mount condoms on sticks)


Be sure to keep track of the style and brand of condoms; it matters.

Does AVA make condoms?

gkc
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Re: Krell July 07'

Yes, Elk, I am sure they do. I have heard that the bigger models are hybrids, with tubed output stages and fans.

There once was a man at Assizes
Whose balls were of different sizes --
The left was quite small,
Of no consequence at all,
But the right one was large,
And won prizes.

Elk
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Re: Krell July 07'

CECE
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Re: Krell July 07'

Hybrid pre, my amps are MOSFETS only....MOSFETS are king. Fans rule, electroncis proeprly cooled rules. Hot running amps are not cool.

CECE
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Re: Krell July 07'

anotehr live event over teh weekend..my frined ..and Gary U.S. Bonds on stage....Lotsa Crown stacks and stacks, some really amazing QSC stuff. Rather small speakers stacked up nicley really did a great job in an open air, outside venue... QSC does make a lot of reasonably priced stuff, that work real good. For some reason, stacks and stacks of CROWN amps as usual.

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