[YoungDave]

I see from the Feb Sphile (Krell KAV-400 on the cover) that:

1.  Sphile just cannot bring itself to say that a component is bad; although at least JA takes measurements and is willing to call a unit's behavior "odd" (p.91).  We've seen this before, as in the high-distortion $150,000 WAVAC amp that the subjective reviewer loved, but that made more than 1% THD at 1/3 of its rated output.

2.  I don't think the Krell KAV-400 is worthy of subjective listening evaluation as it fails my minimum quality/engineering standards. Too bad SPhile won't say such a thing about a major advertiser's product. I note specifically:  

The amp will not make 1/3 power for 15 minutes!  I know this is a popular-priced model, but I think Krell could easily spend another $5 for a sufficient heatsink & still make a profit.  There may be $250 worth of parts in the thing (although I doubt it)...why not make it $255 so that it can make the power that Krell advertises?

The output impedance is very high (.35 ohm), twice the advertised value which is itself moderately high.  This impedance yields a damping factor of 22.  Damping factor is perhaps not terribly important, but the unit under test ought to meet or exceed every one of the manufacturer's specifications in every case.  The fact that it doesn't makes me exclaim, "What in the world happened at Krell?"  It looks like they are giving phony specs - what else is phony about this amp?

The amp's distortion spectrum contains a lot of low-order harmonics and the amp's intermodulation performance is rather poor, too, at high power anyway.



All this makes me think about my minimum standards for audio amplifiers, as I have never made a comprehensive list.  I figure if an amp meets the minimum standards, then it is worth an audition - otherwise, I cross it off my list as there are plenty of well-engineered amps to audition.

I guess I would start with

1.  An amplifier must be able to make any output up to its rated output power continuously, both (or in the case of multichannel, all) channels driven, without thermal problems.

2.  An amplifier must be stable with all conceivable loads.  Note - "stable", not necesarily "optimal."  It should not be capable of being driven into oscillatiion with any known speaker load.  A bench test that any amplifier must pass is to run it up to rated output and then short the outputs together for 5 minutes without damage.  I reckon every amplifier is going to encounter a shorted output at least once during its lifetime.

3.  An amplifier must have useful self-protection to prevent thermal runaway or other common malfunctions causing a complete self-destruct, and it must have effective speaker protection circuitry, e.g., it must positively disconnect the speakers quickly upon sensing DC at the output.

4.  An amplifier must meet or exceed all specs without special tweaking to get it in spec.That is, specs should be realistic and not inflated to make it more appealing.

5.  An amplifier must be robustly engineered (Krell used to be known for this) to provide years of trouble-free service even with hard use.

Anyway, that's my minimum standards list, at least a start on one.  I'd be interested to hear anyone else's additions or comments.

Cheers

[warnerwh]

Good points. I couldn't believe I read that review and it was a Krell.  Guess they're trying to make money is all but for less money you could buy better, it just won't say "Krell" on it.  It looked like a piece of junk to me.  
Please don't blame the magazines too much as they do have to make a living in a rather cool economic climate. Without advertisers there'd be not much. Also the fact they do publish the measurements is good. I like that.  I get sick of the poetic bull shit all the time.

[tkp]

Such an amp existed but not some thing I want to own.  The reason is simple.  What you described is an amplifier to meet its specs and operate reliably for many years without any regard for sonic quality.  There will always be a trade off between sonic quality and reliability.  Analog amp designs has changed very little over the years.  With the same design topology, amplifier with less protection will sound better because of less parts in the signal path.  To name a few protection circuitry being used for long term reliability but has detrimental effects on the sound.

-  DC block cap at input to prevent DC from preamp to blow speakers and destroy amp.
-  Zobel network at output to prevent oscillation due to RF
-  DC servo circuitry

For example, amplifier that is based off The TDA7294 power opamp will meet all your requirements but it will not sound as good as some with less protection in place (I know quite a few but will not name the amps here).

There are two amps I have owned which meet almost all your requirements (except for the 5 minutes short test) and sound good.  I am hunting down an amp that potentially meet all your requirements plus excellent sonic quality.

[Florian]

Could it be that they received a faulty unit ? All Krell equipment i have seen so far and the own i own are extremely high quality pieces. I have heard the 400i on a pair of Maggie 1.6 and liked it a lot.  

-Flo

[John Ashman]

I don't think it's any secret to most non-Krell fans that Krell has been more about marketing that product quality for the past 10+ years.  Stereophile "made" Krell. Without them, Krell would just be some small little operator.  Looking inside, they don't appear to be doing anything much, if any better than, say, an NAD, Adcom, Rotel, etc and certainly nothing as exceptional as a C-J, BAT, YBA, Meridian, etc.  I had a 300i for less than $1000 used and everyone wanted to try it and everyone brought it back because they hated the sound of it.  Finally sold in on the 'net.  Other folks had newer versions and had lots of issues including hum.  I just don't see why people love the brand so much.  In fact, every time I trade in an older Krell and tell my Krell fans about it, the reaction is always the same "oh, that unit.  Yeah, that wasn't very good, but the NEW ones are awesome".  And then later, when those got traded in, those "NEW ones" suddenly weren't so hot.  So, I continually scratch my head and think "well, if Krell built all this 'crap' according to Krell fans, exactly how did they get their reputation?"    All too strange for me.

[JoshK]

Florian, don't stress, your amp is from the days when Krell made kick ass amps, things have changed it seems.   The KSA series you own are said to be the best sounding amps Krell ever made.

[Florian]

Well my KSA-150 is about 12 yrs old. I have heard many many amps incl the ones i cant afford, and found him to be absolutly amazing. Sounds better to my ears that the big new H2O amp. I see a lot of people which have systems where "money is no object" that have the big Krell amps (exept the 1400lbs MRA)  

All i have heard so far from them, and seen is wonderfull. The service is great, and build quality is exellent. Maybe this only effects the "cheaper" modells.

I have noticed a huge Krell bashing on the AA. I wont jump on that band waegon. I have heard the Adcoms and H2O amps, and they all seem to miss alot. Anyways, thats just my view.

-Florian

[Florian]

Florian, don't stress, your amp is from the days when Krell made kick ass amps, things have changed it seems.   The KSA series you own are said to be the best sounding amps Krell ever made.

Thats a relief      I only heard a few of the new ones and saw a MRA sitting on a floor, which was pretty darn cool. I cant comment on the newer ones. My friend, has had trouble with a 400i too.

-Florian

[tkp]

I used to own a KSA150 amp.  It runs fairly hot but not as hot as the Plinius SA250 MK IV.  It sounded decent but not spectacular in my book.  On the other hand, it sounded quite a bit better than a lot of today hyped amp.

[Florian]

Well i havent really had a chance to try many different ones (21yrs). I had 2K for a AMP. I looked around and listend to Pathos, Jeff Rowland, Krell, McIntosh, H2O and some other ones. After planning on selling the 3.6R, i thought about trying a Apogee but gave the RM30 a shot. I bought the KRELL because i havent found a AMP in my used price range that can drive any load with ease, has tons of dynamics, detail and cold brute speed. Plus always since i started in this hobby i wanted either a Mark Levinson or a Krell    
Now i have one, and love it. He can warm my feet too