OK, so I picked up a Krell KSA-250 locally and lugged this beast into my listening room...I finally had a bit of time to compare it to my Pinkmouse Krell (with 3 pairs Toshiba 2SA1943/2SC5200, 1.2KVA toroid, pool of four 56kuf caps)...interesting comparison.....
Sonically they are both very very similar. They both have that solid bass and sweet HF...a testament to Pink's boards (You ROCK!)..only real downside is they both have a slight hum that is not really noticeable on my ML ESL and Scintillas unless you really seek it out...
Now the KSA-250 pulls a bit over 7 amps from the wall, when playing, and at idle, on my CLS and on my Scintillas. I checked at high volume and increases slightly...why they require a dedicated 20 amp service is beyond me...
Pink's KSA-50 I built is biased to the hilt (till the sinks are 140F) and also pulls 7 amps from the wall, and also doesn't change much on high volume or speaker load either.
Anyway, the question is this. Since both pulling 7 amps from wall, and everything being equal (speakers, wires, preamp, etc) are they both outputting same power to the speakers if both in Class A? I understand my three pairs of output devices are getting pummeled compared to the 12 pairs in the KSA-250...
I also would like to add that when I first got the KSA-250, I was a bit disappointed - Pink's KSA-50 really sounded a lot better, but later I noticed that the balanced shorting pin was not in (single ended RCA from my Aikido Preamp). Once shorted, it sounded much better (duh). Also, I had the amp periodically "fart" on startup. I changed all six of the Soft Start board caps (all brown/discolored, but still speci'ng out fine after checking with my LC meter), and "fart" was still there. I took the amp apart to see of I could see any corrosion on output relay contacts. I then noticed that the Ground wire from PS board to chassis was not connected and just left dangling in chassis (previous owner's lame attempt at lifting ground to reduce hum?). Anyway, I re-screwed it to chassis and have not heard a "fart" since...I am very surprised that the exposed ground wire didn't touch one of the rails and short the whole amp....
I really like this amp - solid!! But also now appreciate the KSA-50 even more...
Sonically they are both very very similar. They both have that solid bass and sweet HF...a testament to Pink's boards (You ROCK!)..only real downside is they both have a slight hum that is not really noticeable on my ML ESL and Scintillas unless you really seek it out...
Now the KSA-250 pulls a bit over 7 amps from the wall, when playing, and at idle, on my CLS and on my Scintillas. I checked at high volume and increases slightly...why they require a dedicated 20 amp service is beyond me...
Pink's KSA-50 I built is biased to the hilt (till the sinks are 140F) and also pulls 7 amps from the wall, and also doesn't change much on high volume or speaker load either.
Anyway, the question is this. Since both pulling 7 amps from wall, and everything being equal (speakers, wires, preamp, etc) are they both outputting same power to the speakers if both in Class A? I understand my three pairs of output devices are getting pummeled compared to the 12 pairs in the KSA-250...
I also would like to add that when I first got the KSA-250, I was a bit disappointed - Pink's KSA-50 really sounded a lot better, but later I noticed that the balanced shorting pin was not in (single ended RCA from my Aikido Preamp). Once shorted, it sounded much better (duh). Also, I had the amp periodically "fart" on startup. I changed all six of the Soft Start board caps (all brown/discolored, but still speci'ng out fine after checking with my LC meter), and "fart" was still there. I took the amp apart to see of I could see any corrosion on output relay contacts. I then noticed that the Ground wire from PS board to chassis was not connected and just left dangling in chassis (previous owner's lame attempt at lifting ground to reduce hum?). Anyway, I re-screwed it to chassis and have not heard a "fart" since...I am very surprised that the exposed ground wire didn't touch one of the rails and short the whole amp....
I really like this amp - solid!! But also now appreciate the KSA-50 even more...
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The KSA-250, iirc isn't truly "Class A" but it's probably biased high enough so that for most situations it doesn't matter much.
You'd want to check the vdrop across one of the emitter resistors, assuming you don't short it out and you can get to one. That would tell you the current per device, which multiplied by the number of devices would show the available current at idle. That can be translated into the available power.
I know that there are many people who really liked and still like the way these old Krell amps sound, but I always found them sonically flavored and somewhat "mechanical" sounding, as opposed to "natural". What they excelled at was throwing power at very low-Z speakers.
You'd want to check the vdrop across one of the emitter resistors, assuming you don't short it out and you can get to one. That would tell you the current per device, which multiplied by the number of devices would show the available current at idle. That can be translated into the available power.
I know that there are many people who really liked and still like the way these old Krell amps sound, but I always found them sonically flavored and somewhat "mechanical" sounding, as opposed to "natural". What they excelled at was throwing power at very low-Z speakers.
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My first ever experience of hi-end was hearing a sales demo of a KRELL driving JBL floor standing speakers at a store in Toronto. I was mesmerized by it, having never experienced such a sound before. Even now, my memory of it is that I have not easily found a way to recreate that sound. It did have one flaw, the sound of violins sounded 'etched'. I didn't have the vocabulary to describe it at the time but that is how I would describe it today. I've never been brave enough to build an amp that burns that kind of power when it's sitting still.....
Sorry I misread your post so I am re writing...
The power dissipated as heat in the amp under use could be radically different depending on a number of things such as if one amp is optimized for a 4 ohm load and the other for an 8 ohm for example.
Also if one amp is a high-biased class AB amp the current draw from the wall will increase as the volume is turned up.
You would then be comparing apples to oranges.
The power dissipated as heat in the amp under use could be radically different depending on a number of things such as if one amp is optimized for a 4 ohm load and the other for an 8 ohm for example.
Also if one amp is a high-biased class AB amp the current draw from the wall will increase as the volume is turned up.
You would then be comparing apples to oranges.
I don't think that's quite what the OP meant.
Yes they draw the same power, but power output is different.
The KSA50 has 45 Volt rails, so good for c. 100W RMS p chan. if fully biassed for class A then total power consumption will be a bit above 400 W. (Say around 450W).
It will get very hot and expire due to heat stroke before too long.
If it is drawing 800 Watts then that is way too much and you can expect a meltdown accompanied with lots of smoke.
I believe the correct bias for these is in the 1A per channel area, with a consumption of around 200 odd Watts in total. Then it has a chance of aquiring old age.....
These amps are, therefore, class AB.
The same applies to the 250, but I'm not sure at what piont the A/B level is set.
Yes they draw the same power, but power output is different.
The KSA50 has 45 Volt rails, so good for c. 100W RMS p chan. if fully biassed for class A then total power consumption will be a bit above 400 W. (Say around 450W).
It will get very hot and expire due to heat stroke before too long.
If it is drawing 800 Watts then that is way too much and you can expect a meltdown accompanied with lots of smoke.
I believe the correct bias for these is in the 1A per channel area, with a consumption of around 200 odd Watts in total. Then it has a chance of aquiring old age.....
These amps are, therefore, class AB.
The same applies to the 250, but I'm not sure at what piont the A/B level is set.
The rails on my Krell Clone are +/- 36V. The two channels are in a chassis that has four 12" x 10" x 3" heatsinks arranged like a Aleph amp (actually initially built for an Aleph 2 monoblock)
As I said, biased until sinks got 140F. I use it quite often and built it 4 to 5 years ago...if I remember correctly, 620mv across .68 ohm emitter resistors, so right around 1A each, but three pairs instead of original two pairs...
As I said, biased until sinks got 140F. I use it quite often and built it 4 to 5 years ago...if I remember correctly, 620mv across .68 ohm emitter resistors, so right around 1A each, but three pairs instead of original two pairs...
I have a very early Krell KSA 100 with MJ 15024 outputs with +/- 48 volt rails and 4 devices per polarity biased at 625 ma per device for a 2.5 amp total bias current. 2.5 amps x (.7071 x 48VDC ) = 84.5 watts Class's A bias. It used an EI core Western Electric transformer with an extra ground lead making me think it has an electrostatic shield - Krell soon moved to torroids under Japanese market pressure. I also recently got a KSA 250, but I haven't looked inside or measured anything - yet 
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OK, I checked again and the KSA-50 Clone I built is actually drawing 5.25A (inline meter indicating 500 watts / 630VA) not 7 A...still seems odd that the KSA-250 only drawing 7A???
A pic of the two....I have to say the Clone sounds a bit clearer / focused than the KSA-250....
A pic of the two....I have to say the Clone sounds a bit clearer / focused than the KSA-250....
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The 8 amps from the wall is NOT the same as the actual bias on the amps... it's related and maybe even close, but that is not certain depending on details of the power supply and how much current it takes to keep the cap bank charged.
8 amps for the KSA-250 seems about right. But you can likely find the spec online, or in an early review (Stereophile?).
_-_-
They are biased pretty high, iirc...
8 amps for the KSA-250 seems about right. But you can likely find the spec online, or in an early review (Stereophile?).
_-_-
They are biased pretty high, iirc...
The KSA 200 pulled 12 amps idling , i would speculate Krell did not want the public to feel the 250 was inferior by refering to the reduced bias and the 20 amp breaker is standard fare for any big Krell, i have used the same on all Krell's.....
Your 250 may need re-capping if not done already , this has been my experience on older Krell's ...
Hi,
As far as I know the Krells used a fast attack ramping up bias
topology with a slower release down to lower bias levels.
They were also built to produce prodigious current into
stupidly low impedance loads, like Apogees speakers.
The static current draw does not reflect the bias topology.
rgds, sreten.
I can't be bothered to find out, but I think the Krells use
used fast multilevel switching to increase the bias levels,
and a slower regime to drop back down the levels.
As far as I know the Krells used a fast attack ramping up bias
topology with a slower release down to lower bias levels.
They were also built to produce prodigious current into
stupidly low impedance loads, like Apogees speakers.
The static current draw does not reflect the bias topology.
rgds, sreten.
I can't be bothered to find out, but I think the Krells use
used fast multilevel switching to increase the bias levels,
and a slower regime to drop back down the levels.
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