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Krell KSA-50S power amp... Sweet and powerful. (long post....)

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Posted on September 28, 2004 at 16:17:03
AbeCollins
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Well, I posted before about my itch to try the Krell KSA-50S in my system and I finally had my chance today. To summarize, I love the way this 'little' Krell sounds so far.... sweet, transparent, fast, with excellent bass depth, detail, and snap. More later.

Someone commented that the KSA-50S is not 'true class A' biased like the older KSA-50. Well it is but it's done more intelligently with something Krell calls Sustained Plateau Biasing. And I like it because the unit doesn't draw huge amounts of power constantly like most basic full class A biased designs (like my old Pass Aleph that I once owned). Instead, it runs barely warm at idle but heats up and draws lots of power only while you're actually using the amp. When the signal goes away, the amp automatically goes back to a cool running standby mode.

I took some measurements while obseriving the Sustained Plateau Bias feature in action. It's not a gimmick. It's practical and I like the way it works. There are three modes: Standby, Bias Level 1, and Bias Level 2. The LED indicators on the front panel tell you which Bias level you're operating at.

The amp remains in standby mode with no signal present or with a very low-level signal. Unlike most standby modes, the amp will actually pass a signal and play music at low volume levels in this mode. I wouldn't normally listen at this level but might use it for very soft background music in the evenings while reading or working on the computer. In standby mode the Krell KSA-50S draws about 75-watts continuous from the AC mains as measured with my inline AC watt meter.

At moderate to loud (normal) listening levels the KSA-50S steps up to Bias Level 1. At this point the amp is drawing around 625-watts continous with lots of effortless volume with excellent deep bass and transient attack. If I mute the source, the amp continues to draw 625-watts at Bias Level 1 for about 20 seconds before it goes back down to standby mode. 625-watts continuous is a lot of power consumption indicating a strong class A bias. It maintains this level for a 'sustained' period of time even with the signal removed eventually dropping down a notch.

At high volume levels the KSA-50S will step up to Bias Level 2. At this point the amp is drawing about 850-watts continuous. When the signal is muted, the amp continues to draw 850-watts for about 20-seconds before it steps down.

I'm no rocket scientist but it appears to me that a 50-wpc amp drawing 625-watts to 850-watts continuous while in normal operation must be heavily class A biased. It drops to 75-watts continous with no signal or very little signal present. Otherwise it draws a lot of power and runs very hot for a mere 50wpc amp. I like it... runs barely warm when in standby mode and runs true class A sizzling hot while enjoying music at realistic volume levels. I can leave the amp on 24/7 without worrying about the heat or the electic bill. And when the music starts to play, the amp automatically goes into its 'power hungry' class A mode.

Ok, enough of the techie stuff. How does this thing compare to the other amps I've owned? In short, very favorably.

I love the sound of tubes but as hard as I try, I cannot get enough bass with great control. Perhaps with a monster pair of tube monoblocks but not the 50 to 100wpc that I can afford.

I own a very nice pair of AES/Cary SixPac tube monoblocks. They run 50-wpc in triode mode using 6 EL-34 tubes each. This is a very transparent sounding pair with good bass (better than my previous CJ Premier 11a). The SixPacs are wonderful especially with vocals and the shimmer and decay in the treble is outstanding without being bright or annoying. Cymbals sound very impressive here. There is also something special about the 3 dimensional soundstage from the AES/Cary SixPacs - better than any solid-state amp I have experienced so far and even better than the CJ Premier 11a or the ARC VT100mkII I once owned. I just wish the little SixPacs had more SLAM and SNAP.

At the other extreme, I have the 'digital' HCA-2 stereo amp from PS Audio. This thing runs stone cold, draws very little AC power, and it packs more bottom end punch (slam and snap, remember?) than the SixPac tube monoblocks. But... it doesn't have near the 3 dimensional soundstage or the transparency. And although the bass is impressive from such a compact package, it's not quite a well defined or 'fast' as I like. The bass is there and it's good but it's not as detailed and dynamic as I would like. Yes, it is better than the SixPac tube monoblocks but at the cost of soundstage and overall transparency. It's also not as extended in the treble as the SixPacs. A different amp for a different application. I use the HCA-2 mostly for rock and home theater impact.

Ok now for the Krell KSA-50S. This amp is also a bit on the sweet side, not dry or clinical and for a mere 50wpc it really rocks! Thats what I said about the Pass Aleph 3 (at only 30wpc) but the Krell KSA-50S is better to my ears. My room isn't huge and my speakers are fairly modest with 8" drivers 6 Ohms nominal and 91db sensitivity.

The KSA-50S is more transparent than the PS Audio HCA-2. It is more 'effortless' and less congested at higher volume levels and the bass region is fast and more distinct with excellent snap and slam. The Krell is also more transparent with better slam than the Pass Aleph 3. I find that I can play the KSA-50S at higher volume levels than any of the other amps I've owned while still maintaining great clarity with less congestion and it's like the amp has plenty of reserve or 'dyanmic headroom' if thats what its called. The treble is also more extended than the PS Audio HCA-2 or the Pass Labs Aleph 3.

The shimmer and decay in the cymbals is still a bit better from the AES/Cary SixPac tube amps and the tube amps also present a better soundstage. But overall I consider the KSA-50S to be outstanding and so far the best solid-state I've ever owned. (I've also had several Classe including the fairly large CA-300, BAT VK200, Pass Labs Aleph 3, PS Audio HCA-2, and a couple integrated amps not in the same league).

I'm not sure how the newer Krells sound but they're way out of my price range. And I've been told that the KSA-50S is one of the better older models. It's getting up there in years but still very impressive.

Krell KSA-50S 50wpc Power Amp


Accuphase DP-65v -> PS Audio PCA-2 Pre -> AES/Cary SixPac tube amps -> Tannoy D500 spkrs

 

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Re: Krell KSA-50S power amp... Sweet and powerful. (long post....), posted on September 28, 2004 at 17:22:34
LoudandClear
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Posts: 411
Location: Canada
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Thanks for the great "review" Abe.

I notice that gthe KSA series are selling off pretty quick on Audiogon. Must be the recent Stereophile article proclaiming the KSA50 as one of the top 10 amps of all time.

Congratulations on your find. I will watch for a KSA as well.

I had a similar experience recently. After having about 10 amps through my system this year, I was beginning to think that there was no more magic to be found. Then a buddy dropped off a borrowed Vecteur Integrated amp. WOW! Synergy in spades. HiFi+ just gave a rave review as well. Impossible to find used. No discounts on new ones. Might just have to bite that bullet.

 

While you are at it try the KSA 150 as well…, posted on September 28, 2004 at 22:50:02
I had them in my system a while back they do sound more powerful than the 50’s with similar smooth top end. Though the midrange is a little grainy for my taste compared to the ARC D-250, however they are quite impressive never the least.

 

Re: Krell KSA-50S power amp... Sweet and powerful. (long post....), posted on September 29, 2004 at 02:02:59
georgemg
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Great review, I heard sometime ago krell ksa 300s, yet today this was the most transparent and dynamic sound I heard, I friend compared this amplifier with two gamut d250 mk3 monobloks and he told me that krell was better in every way, the speakers were B&W 801.

 

I recently purchased the KSA300S and am very impressed...., posted on September 29, 2004 at 05:48:51
Mr Vinyl


 
I will post some comments on it when I get a chance. But based on this amplifier alone I would say that Krell is getting a bad rap from some people. And their customer service has been excellent. They have answered all of my questions and e-mails very quickly and politely, even though this amp was not purchased from them and was bought used. It has been out of warranty for a long time.

 

Could you tell me how you measure the current the amp is drawing at different bias levels?, posted on September 29, 2004 at 05:52:07
Mr Vinyl


 
Sorry if my question is a simplistic one.

 

Re: Krell KSA-50S power amp... Sweet and powerful. (long post....), posted on September 29, 2004 at 10:35:50
vikvilkhu
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Location: Rochester, NY
Joined: January 1, 2002
Abe,
Thanks for your findings, always enjoyable to read about your adventures. I remember you always liking the sound of your old CJ 11a save a paucity in the lower frequencies.

Though it isn't going to beat the Krell in this department, I urge you to just take a listen to a MV60se. I'm playing around with amps at the moment and am very impressed with its bass output. Though I've never heard the 11a, I am told that the MV60se is the 11a with a better bottom end. Just something to think about!
Vik

 

Re: I recently purchased the KSA300S and am very impressed...., posted on September 29, 2004 at 15:46:21
AbeCollins
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I wasn't even considering Krell until I heard a buddy's KSA-50S. It sounded great in his system so I was anxious to try one in mine. I can't speak for the other Krell models but if the KSA-50S is any indication, I'd say any 'bad rap' from Krell bashers is unfounded.
Accuphase DP-65v -> PS Audio PCA-2 Pre -> AES/Cary SixPac tube amps -> Tannoy D500 spkrs

 

The watt meter is called "Watts Up?" See info here., posted on September 29, 2004 at 15:53:20
AbeCollins
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There are less expensive basic wattmeters available. They've become popular with consumers who are into energy conservation or simply knowing what their appliances consume. I've seen these in department stores and mail order catalogs, airline in-flight catalogs, etc. This is not the brand I have but here's a link for you: http://www.ahernstore.com/p4400.html

Mine is a unit call Watts Up? Pro. In addition to a basic wattmeter, it has cost per KW/Hr output, power factor, etc. It also has a PC interface with basic datalogging and charting capability. You can read more about it at the website link below.

Watts Up? Pro wattmeter / datalogger. This is what I used

Accuphase DP-65v -> PS Audio PCA-2 Pre -> AES/Cary SixPac tube amps -> Tannoy D500 spkrs

 

Thanks for the post, posted on September 29, 2004 at 18:37:25
Biencfg
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It's hard to get good information about Krells...they stir up too much controversy. Really good to read a levelheaded account.

 

Wow, thanks a lot. (NT), posted on September 29, 2004 at 19:23:43
Mr Vinyl


 
NT

 

Re: Krell KSA-50S power amp... Sweet and powerful. (long post....), posted on September 30, 2004 at 08:22:34
sogood
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Location: Flint, Michigan
Joined: September 30, 2002
I have owned an old Ksa-250 for a good while..also another classic IMO. Driving my Apogee Duetta Signatures, very powerfull yet smooth as butter in the all important mid-range.

This amp mated with my tubed (Audioprism Mantissa) pre-amp is exactly what my tastes call for. While I'm sure there are tons of better stuff out there (at least I read that)...I never seem to find it when I go for a listen? SO, amp upgrade stays low on my list.

You have made a great find and of course now know that everything we read is not always true for some of us.

A link to my system, the room is new so still very plain with no acoustic tweaks as yet.

 

A KSA50S (not mine!) just got listed on AG (nt), posted on September 30, 2004 at 11:17:25
LoudandClear
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.

 

Niiiiccce........., posted on September 30, 2004 at 20:41:28
Marc Bratton
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I've always lusted after a big Class A amp like your Krell, or the bigger Class Coda's. I agree with you that a good tube preamp with a heavy Class A SS amp is a damn intelligent compromise, and hope I can try one of the all Class A Krell's one day.

 

Re: Krell KSA-50S power amp... Sweet and powerful. (long post....), posted on September 30, 2004 at 20:54:52
AbeCollins
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Nice room! Wish I had more space. Everything is a tight fit in my room.
Accuphase DP-65v -> PS Audio PCA-2 Pre -> AES/Cary SixPac tube amps -> Tannoy D500 spkrs

 

Not mine either. His price is a bit high too (nt), posted on September 30, 2004 at 21:46:31
AbeCollins
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.

Accuphase DP-65v -> PS Audio PCA-2 Pre -> AES/Cary SixPac tube amps -> Tannoy D500 spkrs

 

Re: Niiiiccce........., posted on October 1, 2004 at 03:01:48
sogood
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Agree on the Coda's Marc, great sounding amps!

Dave

 

Are those the normal "feet" that come with the amp in your picture?, posted on October 1, 2004 at 10:25:12
Mr Vinyl


 
If not what are they and are they still available.

Thanks

 

No, those are my 'cheap tweak' coasters...., posted on October 1, 2004 at 23:32:57
AbeCollins
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Those 'feet' are just coasters for coffee cups, etc. I got them in a set of 4 from "Bed Bath and Beyond". I've also used wood cutting boards as amp stands. Hockey pucks ($1.00 ea ) can also make for nice 'cheap feet'. It's interesting what you can find in the kitchen wares department or at a sporting goods store. ;-)
Accuphase DP-65v -> PS Audio PCA-2 Pre -> AES/Cary SixPac tube amps -> Tannoy D500 spkrs

 

Re: No, those are my 'cheap tweak' coasters...., posted on October 2, 2004 at 06:41:54
Mr Vinyl


 
They look good in the picture. Krell used to sell what they called Acoustic Mass Damper feet. They are no longer available and I thought that is what was in your picture (I have never seen them).

By the way, I ordered the WattsUp meter you mentioned. I purchased the pro version although I am not sure I needed it. It wasn't much more money. In any case it should be interesting to see what my KSA300S is putting out at different bias levels. Who knows maybe the meter will save me in electicity bills over the long run.

Thanks for your reply.

 

Re: No, those are my 'cheap tweak' coasters...., posted on October 2, 2004 at 09:08:33
AbeCollins
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Let us know about the KSA-300S power consumption but be careful. At it's highest bias level, I bet the KSA-300S comes close to exceeding the limits of the wattmeter. I believe the meter is capable of measuring up to ~ 120VAC/15A, 1800-watts maximum.
Accuphase DP-65v -> PS Audio PCA-2 Pre -> AES/Cary SixPac tube amps -> Tannoy D500 spkrs

 

I assume you didn't do any serious listening/evaluating with such a device in the chain? nt, posted on October 4, 2004 at 15:01:21
bjh
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.

 

Re: I assume you didn't do any serious listening/evaluating with such a device in the chain? nt, posted on October 4, 2004 at 23:51:00
AbeCollins
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The wattmeter 'in the chain' has zero effect on the sonics as best I can tell. It's not like the device is in the 'audio chain'. It's inline with the AC power cord.

But to answer your question, for most of my listening evaluation the wattmeter was not inline. It was there only to measure power consumption at the different bias levels.
Accuphase DP-65v -> PS Audio PCA-2 Pre -> AES/Cary SixPac tube amps -> Tannoy D500 spkrs

 

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