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Why Do Solid State Amps Run So Hot


thebes

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10watt = 114db

1watt = 104db

.1watt = 94db

.01watt = 84db

.001watt = 74db

.0001watt = 64db

.00001watt = 54db


I dunno... I've never understood or experienced this. To me, loudness and dynamics are completely different, and while my full Juicy Music tube system can play loud, it's not nearly as dynamic as my SS Bryston preamp/amp system. Detail, clarity and tonality are all important, but without dynamics music is lifeless in my opinion, and 10 watts doesn't bring it in my experience. Music designed to wind you down vs. wind you up... sure... tubes, but to continue the automobile analogy, say you've a wife, three kids and a house with a three car garage out in the burbs. On the key rack are three sets of keys... Minivan, F-150 and Porsche GT3 RS. Which set you reach for depends upon what you intend to haul - kids, lumber or a$$. If I'm haulin' the
, SS all the way.
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My question.... compared to what?



You, Sir, are LASER FOCUSED! I like that!

I'mma little whipped tonight, but tomorrow evening I'll run some temps on my pCATs and Bryston 3B SST2. I'll tell you right now, the Bryston runs barely warm to the touch deep into a listening session while the KT88s run to max heat (bloody hot) in just a couple minutes and park there no matter the signal.
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Detail, clarity and tonality are all important, but without dynamics music is lifeless in my opinion, and 10 watts doesn't bring it in my experience.

Just to be clear nothing I have said is just about loudness and the chart very much relates to the variable power needed for dynamic operation of in this example the Khorn. Yes the chart shows what power is required for a certain SPL but it also represents how the power requirements vary under dynamic conditions.

My experience is dynamics and detail, clarity. and tonality are all linked together if one notices flaws in one there should be problems in the others.

I'm also not clear when you say "10watts doesn't bring it" is this with KHorns.?

I also want to note: When I've been talking about class A amps though I've mentioned tube amps I also included examples of ss amp like Pass and First Watt because for the points I've been trying to make it's irrelevent.

Again please understand I really believe to each his own but I caution everyone it's dangerous to lump (generalize) about amps or most anything for that matter. There are good and bad designs in every catagory we can think of.

miketn

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Uh oh, I'm in a contrarian discussion with my mentor and electronic guru. This will probably not turn out well. Especially since he knows what things like "slew rate " actually mean.

Yes all designs have tradeoffs, but it still seems the trade-offs, low distortion versus heat and the need to own your own personal nuclear reactor are not to me, imo, the hallmarks of elegant engineering. The tradeoffs seem too stark. Now as a "no compromise-low distortion" engineering design, I can get behind that descriptive. But elegant? I don't know. Think about it. I'm not an engineer but hundreds, if not thousands of engineers, have similar problems with Class A and it's one of the reasons they keep trying to come up with better solutions than betting the farm on that good first, and very inefficient, watt.

Maybe it's just semantics we're arguing over, but given all of the other topologies invented since those early Class A tube radios, I'm not so sure.

I did read the article on the Krell, by the way, and I'm pretty sure the technical descriptives are not written in English.Big Smile

You know, I agree with you. It may sound good, but it is a pig power-wise. I worked my way up the B&W 800 series and, yea, they sounded great, but I had 700 wpc monoblocks driving them (4 ohms, the speakers dipped way below that).

It actually started to upset me that they designed the speakers to need so much current. I sold the speakers and the amps and I now have a 200 wpc amp driving speakers with a much easier load and I am much happier, same sound quality too.

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You know, I agree with you. It may sound good, but it is a pig power-wise. I worked my way up the B&W 800 series and, yea, they sounded great, but I had 700 wpc monoblocks driving them (4 ohms, the speakers dipped way below that).

It actually started to upset me that they designed the speakers to need so much current. I sold the speakers and the amps and I now have a 200 wpc amp driving speakers with a much easier load and I am much happier, same sound quality too.

Try driving a pair of Apogee Scintillas, one of the most absurdly designed speakers ever made (but they did sound pretty good): http://www.apogeespeakers.com/scintilla.htm

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I know. I have heard a pair, sounded great but yikes.

Here is what bothered me, I was at a point where I was going to run a few dedicated circuits for my equipment. I got to thinking and the proverbial light bulb lit above me head. It is amazing that it took me years to figure this out.

Think Homer Simpson, "Hmmmm, I can run two dedicated circuits to drive this equipment or I can just get different equipemnt. Doh."

When you turned the system up (I rarely did), it hit a flat spot where it seemed like lots more power was going in, but not getting much louder, kind of like riding a Harley Davidson [:|].

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Mike, don't get me wrong, I'm not being dismissive of the first watt, just wondering why it has to be that way. As you know my Marantz 8b, a push/pull design, has only modest wattage, doesn't do everything well, yet still makes utterly entrancing music.Yet I found that giant SS Class A brick to be utterly beguiling, with tighter bass, an expanded sound stage and great cohesiveness. If it wasn't for the underlying SS distortion that I can feel in my stomach, I'd probably be saving up for one right now.

I guess what's still holding me up is why can't the audio engineers do somethings audio wise, or circuit wise within a Class A amp to make use of all that wasted power that's simply being rendered out as heat. Again, I'm referring to those 200 watts a side SS jobbers with the monster coke cans for caps,not those itty biddy SET amps. It's more of a supposition than anything, since I lack the technical background probably even to understand why it has to be that way.

I mean, could the path to global warming start at the doors of earnest, well healed audiophiles equipped with several thousands dollar Class A bricks?

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Mike, don't get me wrong, I'm not being dismissive of the first watt, just wondering why it has to be that way. As you know my Marantz 8b, a push/pull design, has only modest wattage, doesn't do everything well, yet still makes utterly entrancing music.Yet I found that giant SS Class A brick to be utterly beguiling, with tighter bass, an expanded sound stage and great cohesiveness. If it wasn't for the underlying SS distortion that I can feel in my stomach, I'd probably be saving up for one right now.

I understand where your coming from Marty and I'm glad your exploring different amplifiers cause there is nothing like first hand experience to know what works in your unique system/room.

Marty if by some chance you get an opportunity to hear a Pass Aleph 30 or possibly other Pass design give it a try you might find the answer to the SS distortion you described.

I guess what's still holding me up is why can't the audio engineers do somethings audio wise, or circuit wise within a Class A amp to make use of all that wasted power that's simply being rendered out as heat.

Marty what you are asking for is why I pointed you to the Krell design..!

note: the Krell design principle address the wastefull problem (idle pwr issue is mainly the issue you have been bothered by) that you have brought attention to and again it could be used for any size class A amplifier but where is the demand for it..? The range of 10w to 50w class A amplifiers of high quality design just doesn't get the attention we dedicated horn guys need. Think of the Krell design as a variable power class A amplifier...ie if you need 20watts it smartly adjusts itself to operate at that level and if the music demands and you need 100w it again adjust to provide 100w class A.

miketn [:D]

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Marty I thought you might find this interesting as a comparison because for instance the Bryston 3b SST2 mentioned in another post idles at 127W and is rated at 150W per channel into 8 0hm and operates in class AB versus the Krell's idle at 120W.

"This "Sustained Plateau" biasing scheme is said to offer the sonic benefits of pure class-A without the massive energy inefficiency and correspondingly huge, hot heatsinks. The energy-conscious KSA-200S idles at 120W. If it ran in pure class-A, it would have to idle at around 1kW—over eight times as much wasted energy drawn from the wall."

The following comments in quotation are from this interview: http://www.stereophile.com/interviews/1203dagostino

"After doing a lot of research, I decided it was feasible to build a 100-watt, pure class-A amplifier. I didn't think anything smaller was big enough power-wise, and anything bigger became more of an engineering monster."

Comments like this are why I point out that the amplifier industry (SS designers mostly) largely ignores high quality amplifiers in the 10w - 50w range that would serve horn devoted listeners.

"D'Agostino: It came from a desire to make larger class-A amplifiers. With [conventional] sliding bias, you're turning the transistor on really hard, then turning it off in conjunction with the incoming musical signal, which creates very unusual and nonlinear distortions in the output stage. What's wrong with it is that it's changing with the music. What's right is that, at idle, it's not drawing a lot of current. I thought about a lot of things, and one was the sustain pedal on a piano. When you push it down, the note hangs on. I asked myself why I couldn't ramp up the bias to the level of class-A that I needed and just hold it there for a period of time. And if another signal comes in that's higher, go up another level and hold it there. And if the level goes back down, after a period of time, which is usually 60 to 90 seconds, go back down as needed. So you get the amount of class-A you need, never more or less. And you're not changing the output stage with the musical signal. Sustained Plateau Bias allowed me to get huge amounts of class-A power for short periods of time."

Basically if the shifting into different bias levels is done in a manner that is inaudible under musical conditions you have your green class A amplifier Marty.

Very innovative engineering that address the green issue for sure.

miketn

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The largest, most efficient Klipsch speaker I own is the forte II - around 98ish db as I recall. I often wonder the percentage of forum members who do own the Khorn, since new they are $10k and in excellent used condition they languish in the Garage at anything over $3k.

From Mark's web site:

The challenge was this: How to take the magnificent sonic qualities of the BlueBerry
design and extend that into a power amplifier. We love the sound of SET amps, but we
didn't like the small output power. The answer is the Pure Class A Triode or "pCAT." An
all up design that provides effortless lifelike clarity and cohesiveness of SET amps, but
with 25 to 50W of output power.

I know some guys use "flea powered" amps with their Khorns and love them to pieces. I've never listened to a Khorn, so my experience is limited to the aforementioned pCATs and forte setup. Back to cars - a Chevy Cavalier will eventually get to 100 mph, but a Z06 Corvette will do the same much more dynamically. I guess my biggest frustration with tubes (and while out of production, I consider the pCAT a "modern" design) is that the designer tests for a compliment of tubes that is likely to suit the largest population of enthusiasts and that also doesn't wind up costing more than the amps themselves. Rolling is encouraged however, and therein lies the slippery slope - things can either sound much better or much worse and cost a lot in terms of money and time spent. I like what I hear from my tube system, it just lacks the dynamics of the SS system. It's entirely possible it's a tube issue, and it's entirely possible I'll never figure it out. With sand amps, you heat it up for an hour and that's it - you get what you get.

KT88 after five minutes...


tube.png

Bryston 3B-SST2 after several hours...

SS.png

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Hey AnalogWave

Power demand jumps very quickly and I can understand someone wanting more than a 25w amplifier on Forte or Cornwall and especially if they are in a large space or really cranking it.

Just to point out again to get a perceptable doubling of volume from a 10w input to a speaker will likely take 100w and another doubling would be 1000w.

I've never had a chance to listen to Bryston amps but would sure like to especially because I do like alot of the priorities they place in their designs.

I did get to listen briefly to the KSA 50 amp in the early 90s that you mentioned on KHorns but unfortunately their had to be something wrong with the guys setup because the imaging and tonal balance just wasn't right.

I don't know about you guys but I believe I've been beating this horse long enough..[:D]

miketn

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  • 4 years later...
On 7/5/2012 at 4:24 PM, thebes said:

Ah that's it. Thanks guys. That must be it. It draws about 6 amps at idle at 122 wall volts according to the meter on my variac. In contrast, my tubed Bogen MO100A, 100 watt tube monos, draw only about an amp and a half at idle.

Maybe it's me but it sounds like Class A is an inelegant engineering topology, an insult to proper engineering.

On the off-hand chance you still have that inefficient, poorly designed POS let me know and I'll come over and take it off your hands.  I'm in Annandale.

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The amps are doing fine compared to speakers, most of which dump 99% of the signal to heat.

The automobile V8 dumps enough heat to warm a four bedroom house when it's 15 degrees below (don't try this at home).

 

On a more philosophical note, I think concerns about the "inelegance" of things that seem overly hot is a persistent human projection. Metal is not uncomfortable at 250 degrees despite a strong tendency to think that it must feel least stressed at room temperature. Car engines are designed to operate well over 200 degrees, and tubes need some of their elements to be thousands of degrees. The Earth is not inelegant because its core (268 billion cubic miles of iron) suffers a high temperature, and the Sun feels no pain or shame.

 

... some things need to be hot.

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