Rebuild of classic Krell KSA50 fan heater

[mandryka]

You say this is the first time you have really heard one if these amps. I shared a flat with a KSA100 and KSA 80B for a good year or more and I assure you running a CD player with variable outs into it sounded like crap compared to an Audio Research (LS something or other) pre. That really surprised me to be honest as I was in the ‘less is more’ camp back then. If you have a decent preamp around do give it a go!

What speakers were you using? Given Jez’s comments about the sound in his system with a passive pre, that’s the obvious line to explore.

The room too could be an issue (was it the same room as the one you had the Missions in?)

Also, maybe you had a bad example of the KSA. If I remember right, the fan was noisy.

Mine’s an early model, and I know that the mark II had new technology for heat dissipation, maybe this makes a difference to the sound and maybe this different technology could have been in your Krells.

These are all ways in which what you say, and what Jez is reporting, could be true. Not to mention different inputs, expectations, tastes . . .

 

[337alant]

Excellent work their Jez and a truly classic amplifier "Drool"

I thought the original caps looked like ITT

Alan

 

[Tony L]

These are all ways in which what you say, and what Jez is reporting, could be true. Not to mention different inputs, expectations, tastes . . .

A passive pre can only ever be an interface between two things, they are never a universal solution, so yes, it could well be the CD player (a Marantz CD17KI) was inadequate to drive the Krell. The rest of the system was fine and serious high-end (Martin Logans etc).

If you google around I very much doubt you will find many (if any) people using a £5 Alps Blue pot as a ‘preamp’ with a Krell power amp! The match with Audio Research valve preamps (even in preference to Krell’s own very decent preamps) was well known and by far the most common pairing both here and in the US. This is no accident to my ears. Jez loves presenting his own opinion as indisputable fact, all I’m suggesting here is to at least try the widely accepted alternatives. IME the consensus view on audio synergy tends to at the least be worth exploring as it is always a cumulative view built on much shared experience, not just the opinion of one outlier. Even if you reject it later at least give it a go if you have the option to!

 

[skelton]

looks a lot like my old one,cant think why ! glad to see it got the love and attention it deserved well done jez (oh and the dealer i bought it from said david wright had worked on it. i suspect/hope it wasnt )

 

[Arkless Electronics]

curious about the weight difference between the capacitors ... perhaps due to electrolyte having evaporated in the old ones?

Maybe but there is no sign of leakage so it would have had to be as vapour... It could be they are just of a less dense construction I guess...

 

[mandryka]

IME the consensus view on audio synergy tends to at the least be worth exploring as it is always a cumulative view built on much shared experience, not just the opinion of one outlier. Even if you reject it later at least give it a go if you have the option to!

This sounds reasonable but it puts me in an invidious position because I don't have an Audio Research preamp available and it's not obvious how I can try one without making a commitment, a big commitment. If anyone has one to lend me, then much appreciated!

 

[Arkless Electronics]

A passive pre can only ever be an interface between two things, they are never a universal solution, so yes, it could well be the CD player (a Marantz CD17KI) was inadequate to drive the Krell. The rest of the system was fine and serious high-end (Martin Logans etc).

If you google around I very much doubt you will find many (if any) people using a £5 Alps Blue pot as a ‘preamp’ with a Krell power amp! The match with Audio Research valve preamps (even in preference to Krell’s own very decent preamps) was well known and by far the most common pairing both here and in the US. This is no accident to my ears. Jez loves presenting his own opinion as indisputable fact, all I’m suggesting here is to at least try the widely accepted alternatives. IME the consensus view on audio synergy tends to at the least be worth exploring as it is always a cumulative view built on much shared experience, not just the opinion of one outlier. Even if you reject it later at least give it a go if you have the option to!

Facts:

There is no synergy between audio components.

There is no match needed between pre and power amps other than in the broadest sense.

Power amps are not "driven" by a source.

A simple Alps Blue Velvet or much better still a cheap switched attenuator will beat ALL active pre amps even if they are £20000. A perfect active pre would sound the same as a passive... some do this but cos they don't "add niceness" they are not revered. It is difficult to make a bad line pre amp. They therefore tend to sound pretty much the same as each other. The ones lauded with praise tend to be the coloured ones that change the sound with some sort of "nice" colouration and are therefore the worst pre amps!

Most "widely accepted" and "concensus views" on hi fi are wrong.... often laughably...

I always say "in my opinion" or "IMO" or "IMHO" if I consider something technical I say to be controvertible. Anything else will be indisputable fact other than very rare occasions where, being only human, I make a mistake. Take it up with the laws of physics....

 

[Tony L]

LOL! Its that absolutism thing again! ;-)

 

[Dougunn]

Love love love this kind of thread - thank you Arkless!

While we are here, can you articulate (in [simple-ish] engineering terms) what it is that makes early Krells like this (and other heavyweight US amps) so special. Is it just power? What is it Krell did/do differently?

I did once hear monster Krell 'reference' amps but in a system so absolutely bonkers (Goldmund Reference TT, Apogee Divas etc) that it was all overwhelming!

I'm fascinated by this one.

Doug

 

[Arkless Electronics]

LOL! Its that absolutism thing again! ;-)

Them pesky laws of physics! Some things are black and white, others are murky grey... In hifi unfortunately one is often mistaken for the other...

 

[Arkless Electronics]

Love love love this kind of thread - thank you Arkless!

While we are here, can you articulate (in [simple-ish] engineering terms) what it is that makes early Krells like this (and other heavyweight US amps) so special. Is it just power? What is it Krell did/do differently?

I did once hear monster Krell 'reference' amps but in a system so absolutely bonkers (Goldmund Reference TT, Apogee Divas etc) that it was all overwhelming!

I'm fascinated by this one.

Doug

Thanks.

Throwing money at a problem often makes it easily solvable

 

[Barrymagrec]

It could be they are just of a less dense construction I guess...

I think that`s it - quite a lot of old electrolytics seem to be much lighter than physically similar (but much higher rated) modern types.

 

[matt j]

Would love to hear one of these in my system with an appropriate pre.

Nice work Jez.

 

[mandryka]

A friend of mine made this comment on the Krell KSA50 - though I appreciate it may be hard to act on it now.

“See if you can arrange to have the fan suck air UP, rather than
blowing it down. Those idiots at Krell made a huge mistake with early
KSA50 amps, by forcing air down, rather than up. (Hot air rises, after
all). This insanity was rectified in later variants.”

 

[Arkless Electronics]

A friend of mine made this comment on the Krell KSA50 - though I appreciate it may be hard to act on it now.

“See if you can arrange to have the fan suck air UP, rather than
blowing it down. Those idiots at Krell made a huge mistake with early
KSA50 amps, by forcing air down, rather than up. (Hot air rises, after
all). This insanity was rectified in later variants.”

The way the airflow is designed in this model makes it best to leave it as standard in that regard. I did think it rather odd mind!

 

[sq225917]

Carpets, that's why they blow down, less dust Ingress.

 

[mandryka]

Well it's home and it's wired up to the Spendor SP1s, the source is a Theta DAC. It's been hooked up for about 5 minutes. The quality is immediately clear -- the reality of the image and the tone.

Jez: thanks for doing an excellent, thoroughly professional job. I was inspired to take this Krell journey by something you posted

Krell, big Musical Fidelity's, Radford valve amps and then only certain models from these brands. There will be others, and I suspect more valve amps as a percentage have "the magic", but although I get to hear a lot of amps I've heard less than I could count on one hand that really do it...

There are very few genuinely exceptional power amps around. Most amps, although they all sound different to a degree, are more united by similarities... in that they balls up the same things in the same ways!

Almost all share the same lack of ability to keep everything separated out properly when there's lots going on. It all becomes a bit of a "wall of sound"...

With the best power amps, music seems to leap out of the speakers rather than be pushed.

You will hear very clearly that those quiet backing vocals are 2 men and a women and are about 20' back rather than "yeah I can hear the backing vocals somewhere over there".

The harmonics of instruments are correct which gives the correct timbre to instruments (a disc I have always sounded like there was a flugal horn present until I heard it with a truly exceptional amp which revealed it very clearly to be a flute!).

Things like gently strummed acoustic guitar which were obviously there during the quiet intro are revealed to not in fact disappear from the mix when the whole band comes in but stay there, very clearly and without "having to listen out for it".

The difference between say a Naim/Quad/Exposure/"insert most amps here" and one of the few that gets it right is quite a revelation when you hear it and could have one thinking that maybe the power amp is the most important link in the chain after all...

If you get the chance to buy a Radford STA25 MkIII or a Musical Fidelity NuVista 300 then sign that cheque!

Well first impressions are very promising indeed, and I am indeed starting to think that

maybe the power amp is the most important link in the chain after all...

Now I need to get two more -- anyone got a cheap Radford STA25 MkIII or Musical Fidelity NuVista 300 they want to offload in my direction? I'm ready to

sign that cheque!

 

[Arkless Electronics]

Well it's home and it's wired up to the Spendor SP1s, the source is a Theta DAC. It's been hooked up for about 5 minutes. The quality is immediately clear -- the reality of the image and the tone.

Jez: thanks for doing an excellent, thoroughly professional job. I was inspired to take this Krell journey by something you posted



Well first impressions are very promising indeed, and I am indeed starting to think that




Now I need to get two more -- anyone got a cheap Radford STA25 MkIII or Musical Fidelity NuVista 300 they want to offload in my direction? I'm ready to

Thanks! I'm missing it already....

As I said in a PM it's only during the last 6 hours or so of its tenure with me that I felt I was really hearing what it is capable of, after changing from a 50K passive to a 10K passive... It became a completely different power amp, so it seems that TonyL was at least partially right about it being unusually sensitive to what drives it... even if it didn't need an active pre!

With the 50K it sounded like a very good valve amp with unusually tight bass...(I was surprised how much it sounded like a Stereo 20 on steroids!) with the 10K, totally, bizarrely, different. It was then very similar to the MF Nu-Vista 300. Incredible hear through transparency, pin point imaging and sound staging, seemingly unlimited dynamics and rabbit punch tight bass. No one would call Spendor's "pipe and slippers" with this powering them! I can clearly see what all the fuss was about, with reviewers buying the review sample and all that back in the day! A quick listen to this Krell KSA50 really makes you question if there have been any advances in the state of the art of power amps in the last 35 years!

 

[Copperjacket]

Well given the current heatwave, I suggest you put it into the hearth instead of the grate!

 

[herb]

Thanks! I'm missing it already....

As I said in a PM it's only during the last 6 hours or so of its tenure with me that I felt I was really hearing what it is capable of, after changing from a 50K passive to a 10K passive... It became a completely different power amp, so it seems that TonyL was at least partially right about it being unusually sensitive to what drives it... even if it didn't need an active pre!

With the 50K it sounded like a very good valve amp with unusually tight bass...(I was surprised how much it sounded like a Stereo 20 on steroids!) with the 10K, totally, bizarrely, different. It was then very similar to the MF Nu-Vista 300. Incredible hear through transparency, pin point imaging and sound staging, seemingly unlimited dynamics and rabbit punch tight bass. No one would call Spendor's "pipe and slippers" with this powering them! I can clearly see what all the fuss was about, with reviewers buying the review sample and all that back in the day! A quick listen to this Krell KSA50 really makes you question if there have been any advances in the state of the art of power amps in the last 35 years!

Details of source components and music used would be appreciated please Jez