Big amp question

I just traded my Krell KAV 250 for a massive KSA 100, one of the original designs from Krell. This thing is HUGE compared to the KAV amp designs. Here's my question: The KAV was rated at 250 watts per channel, yet is at least half the size of the 100 watt per channel KSA 100. Why is a higher powered amp like the KAV actually smaller in size? I believe I know the answer somewhat in that the bigger Krell can drive difficult speakers (lower ohms) with ease. Can someone explain what else is going on? I remember the old Radio Shack receivers that were fairly lightweight but had high per channel watt ratings. I can also guess that it has something to do with pure Class A vs A/B designs. For those who know about amp design, feel free to jump in.

By the way, the KSA sounds great. In comparison to the KAV, which is one damn good amp, the soundstage is bigger both in depth and width. The music seems warmer and not as upfront as the KAV was. I also read about being able to fry an egg on the top of this thing, but after playing it for over 3 hours, the top was slightly warm. The bottom is where the fans are pushing the heat, and even that was warm but not hot. Of course, I realize it's all about my speakers. I'm using Hales Revelation 3s, and while they do not present a load to the amp such as Apogees, the Hales still go below 4 ohms from what I am told. Heck, my KAV got hotter than this thing.

 

The KSA 100 made their reputation. Some say this was their best design. Being a 100w Class A amp it probably has a much more massive heat sink structure.

I own a Metaxas 100w Class A amp, and attached across the whole front panel are these huge chimney-style heat sinks - they work so effectively that the amp itself does not get very hot. It's not very elegant, but it's well designed. Perhaps that's what the Krell has.

But I did not know the Krell had fans.

It's not really "all about my speakers" - Class A amps run hottest when idling, and run cooler when playing music.

 

Thanks for the reply. Concerning the fans, yes, the early KSA 50 and 100 had them. They are very quiet. I'll attach a picture.

 

Thanks - I had never seen a shot of the inside like that

 

I just picked up a Krell S550i integrated. So far I am enjoying it, still in the break in phase and sounds good.

 

IIRC, the KAV 250 uses newer designed output transistors, which are more efficient and consequently, generate less heat.

 

The 550i is a great integrated!

 

I listened to more vinyl last night with which I'm very familiar with the sound, having heard these recordings for years with my KAV 250a. With the KSA 100 in place, all I can say is "Wow." There is a difference. The KAV is 250 watts per channel vs the 100 watts per channel of the KSA, but the KSA is giving me sound I've never heard from my system before. Bass is now so deep through my Hales Revelation 3s, with a nice musical warmth to everything I listen to. Yes, there was obviously bass before with the KAV, but not like this. And it's not just better bass coming through. Contrary to what many say about Krell amps, the mids and highs are glorious. Voices are better centered with greater clarity and depth. You can hear well into the musical details throughout the soundstage. Recordings that were somewhat bright are now clear but listenable. The harshness, even with analog, is gone. A lot, I'm sure, depends on the match between one's preamp and speakers when evaluating amps. I use a tubed Audible Illusions M3B that appears to be an outstanding match with Krell's solid state design, and Hales Rev. 3s, which I feel are quite musical themselves. I've read some reviews of Krell products where people match them with something like Thiel 3.6s, which to me is not a good match. Those speakers can be unforgivingly forward and bright with the wrong amp and preamp. Something like that needs tubed amps to properly match with.

The bottom line is that I now understand the thought process behind the design of large amps to fully take control of a pair of speakers that are not efficient. You can't power my speakers with a triode amplifier like you can with say large horn speakers. I wonder how highly efficient speakers like that sound with a massive design like Krell?

I'm very happy with the old, but still great sounding KSA 100.

 

It is considered a classic for a reason.

 

So far, so good! It only has maybe 10 hours on it and I'm already happy with it. Integrates into my HT system effortlessly too.

 

Please explain.

 

Mmm - that is what I always thought was the case. For an amplifier to be classified as class A the standing current in the output stage must be greater than or equal to the current under load - that means under the load of the worst impedance. Perhaps what I meant to say was that the devices (transistors, valves) are hottest when idling - the actual temperature of the amp probably is the same.

 

This amp is over 30 years old. It sounds quiet with no distortion, but due to it's age, is the amp out of spec? Can one hear this?

 

The older amp had two conventional power transformers, the newer one has a single toroidal-wound power transformer, which is more efficient.

 

The old Krells are hard to beat. But some need to be serviced a bit. After that, you gotta nice amp for not too much $$$.

 

30 years old? Wow. This amp looks great.

One thing that these days can be done better is electroytic capacitors, perhaps even diodes. I have a hunch that those big blue caps can be replaced with some newer Cornell Dubiliers.

 

I've owned a KSA 100 for 12 years or so. They had a terrific reputation right from the start and their competition was ML and Threshold as the top solid state units. And D'Augustino sure knows amplifier design and if there is an audio design hall of fame, he's in it. Actually purchasing products from hall of fame guys is not a poor choice for used equipment. And they don't exactly give away the new Krell or Boulder anyway.

That amp will provide you with years of enjoyment. What pre-amp are you running it with?

 

Good to know, it's a great price at Music Direct and I'm tempted, it's quite a bit cheaper than the other (albeit US built) amps I'm looking at

 

There's a couple of possible answers.

1) There's a lot of silly business in rating amplifier output. Within a company, you don't often see this though.

2) Amplifier circuit topology. It takes a lot more space and weight to make a Class A amp than it does to make a Class D/switching amp.

3) Changes in technology. Toroidal trannies vs old style, size and scale of circuit integration, etc.

4) How those Watts are made. In other words, what combination of voltage and current into what impedance of a load. It takes more space to drive a low impedance load to a high current than to drive a high impedance load to a high voltage. That's an overwhelming simplification, of course.

 

I am quite happy with it. I don't have the educated ears that many here do, but at that price it's hard to beat. I'm running the OPPO BDP to through the XLRs, phono amp to one set of unbalanced inputs and using the HT passthrough from my AVR. Works well, sounds good. BTW, it weighs a ton!

 

Audible Illusions M3B. After listening to the KSA 100 now for about 3weeks, I'm astonished at the difference in sound between this and my old KAV 250. Hardness in any form has gone out the window. Stage depth and width are increased, and low end is much deeper. One can hear deep into a recording. best trade I ever made.

 

I had a pair of KMA 100 monoblocs
The fans were noisy as hell and they were fking ugly
They did not like low impedence Apogees at all
They burst into flames.......
I bought a KSA 250 to replace them,horribly overbuilt and quite a thick sound.
So I was not impressed.
In fact it was the end of my fascination with big american HIFI.

 

Sounds like fake story to me. krell amps LOVE low impedences. "Burst into flames." Yeah, right.

 

KMA 100 s did not love 1 ohm
The Scintilla was a difficult drive
They did burn their output devices,it was not pretty
The KSA 250 drove them OK, but I got rid of them all that year.
Why would I lie ?

 

those things were legendary for melting many an amp!