On your 50 you are fan cooling at that bias right?
I use 3 pairs also at 40 v loaded with 800va toroid and use fan cooling. (Mono blocks)
The 250 doesn't have enough heat sink ( convection) to run much more bias without some way to keep it cool and hence to lower bias and quicker ab transition
Knowing the way the 50 reacts with low impedence loads, I don,t think it will work well with 79 db 1 ohm scintillas.
Are you getting the 4 ohm version of the scintilla?
Regards
David
I use 3 pairs also at 40 v loaded with 800va toroid and use fan cooling. (Mono blocks)
The 250 doesn't have enough heat sink ( convection) to run much more bias without some way to keep it cool and hence to lower bias and quicker ab transition
Knowing the way the 50 reacts with low impedence loads, I don,t think it will work well with 79 db 1 ohm scintillas.
Are you getting the 4 ohm version of the scintilla?
Regards
David
No, I have passive cooling - the sinks are 12" x 10" x 3" and there are four of them like an Aleph 5. Like I said, I biased the hell out of it and sounds great.
The tranny is 1.2kv, and I have four 56,000uf caps on power supply. It should be able to drive the scinnies. This amp has been up against some pretty nasty ESL loads and never had an issue...
The scinnies are 1 - 4 ohm, and set for 1 ohm. Still waiting for them to show up...
The tranny is 1.2kv, and I have four 56,000uf caps on power supply. It should be able to drive the scinnies. This amp has been up against some pretty nasty ESL loads and never had an issue...
The scinnies are 1 - 4 ohm, and set for 1 ohm. Still waiting for them to show up...
I always wanted a pair also and missed out a couple of times. I,m always keeping an eye out for a pair also.
Everyone says the 1 ohm sounded best, but never heard it personally.
Please post your listening results when you get them.
Regards
David
Everyone says the 1 ohm sounded best, but never heard it personally.
Please post your listening results when you get them.
Regards
David
Sustained Plateau Bias, aka automatic bias, bias goes up/down with input signal.
Full (constant bias) class A at that level, without fans, would require an amp chassis the size of a washing machine.
Hmmm, I did not know this amp was the Sustained Plateau Bias - I thought the KSA-250S was Sustained Plateau Bias, while the KSA-250 was constant bias...drats!
So the harder I drive it, the more bias? Don't expect too much at low levels?
So the harder I drive it, the more bias? Don't expect too much at low levels?
Krell didn't call it ''sustained plateau bias'' yet when they introduced the KSA250, but it does have automatic bias adjustment.
The model before , the ksa200 was biased at 14 amps draw , it was a full 200 watt class-a at 8 ohms and ran hot enuff to require a recap every 5-7 yrs.
@John,
You want to run the Scinnies direct with their 1 ohm settings , i expect a big difference between the two at 1 ohm, the 250 will need freshening up to be its best. The Ksa200 sounded better to me drivng 1 ohm loads after we recapped it and lowered the class-a bias from 14amps to 5, ran cool as a cucumber and had plenty speed and attack , the jump factor was so good , i could not listen to the Thresholds or my other amplifiers afterwards, this was not the case before ...
Lowers only at idle , the bias raises as you raise the output above idle , lowers after when the amp sits idling....
Interesting reading this exchange and then looking at the Stereophile article. Are you sure its pulling 12 A from the wall? That's about 1500W - wow. My sx-amp runs at 700mA per pair for a total bias current of 1.4A and I've rated it at 15W class A and up to 25W class AB. Certainly class A has a magic sound to my ears, and especially so when I drive book shelf speakers. I imagine the Krells, with that additional supply rail headroom must sound fantastic.
I've done some work on auto bias BTW - pretty easy to implement with a handfull of passives and a mosfet. The amp is biased into class AB normally and when the music starts it goes into class A in about 100 us with a long time constant (2-3 secs). When the music stops, it goes back to class AB.
Heatsinks on my amp run at about 65C (I think thats also about 140F)
You'll need class A with the weather you guys have over there right now . . . dont stay too cool 😉
I've done some work on auto bias BTW - pretty easy to implement with a handfull of passives and a mosfet. The amp is biased into class AB normally and when the music starts it goes into class A in about 100 us with a long time constant (2-3 secs). When the music stops, it goes back to class AB.
Heatsinks on my amp run at about 65C (I think thats also about 140F)
You'll need class A with the weather you guys have over there right now . . . dont stay too cool 😉
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I read that 12A on some review, but it is really only pulling around 8 - 9 amps from the wall. Wonder why the hell they recommend a 20A service if idle is 8 - 9 amp, and really never gets a whole lot higher...
OK, so I pushed it a bit and it does sound a lot better when driven harder. The KSA-50 just sound sweet ant any volume...i was kinda expecting the same... not as disappointed as before...actually a little happier...just wish those Scinnies would show up...
And yes, it is freaking COLD!!
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No, it is not.
The KSA-200 is biased at 325mV across the 1R emitter resistors, 325mA per power transistor. (Krell issued number, btw)
The power amp has 3 blocks of 6 TO-3's per channel, 18 times 325mA makes 5.85A.
That is a little over half the nominal continuous power in class A, or 274W peak.
(the last bit of quiescent current doesn't count, as one enters the cross-over region there)
Full 200W class A would require at least 3.5 amp quiescent current, with 75Vdc loaded rails that equates to some 550W dissipation per channel.
Even at half the nominal continuous power in 8 ohm in class A, the heatsinks of the KSA-200 are underdimensioned.
Most of the time, they were running well over 140F.
Most serial manufacture class A power amps that have been produced were only part biased.
Only FULL class A biased Krell models are the KSA-50, KSA-100, and KMA models. (till 1990-1991, when Krell went bias hopping)
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No way!! I thought you were in California - we discussed my Krell Clone once. I am on Taylor...don't tell me you do too!!
We measured , it was drawing 14amps at idle, i had two 20amp breakers installed to feed the system and yes it ran too hot, melted itself down a few times over it's 20 yr career, the last time it was re-capped it was rebiased and had a totla draw of less than 5 amps, it sounded it best to me then ...
It's freezing , you bwoys should put all yuh Krells together and have a space heater party .... \
even the mighty krells of old can't content with this cold.
brrrrrrr ....
but we have hope, it's almost 4pm and i see it's 3 (uhm, that's POSTIVE 3) degrees; we are out of the negative zone!
mlloyd1
brrrrrrr ....
but we have hope, it's almost 4pm and i see it's 3 (uhm, that's POSTIVE 3) degrees; we are out of the negative zone!
mlloyd1
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