When I startup the amps in a cold condition within a couple of minutes they take 2.8 Amps each at at 230 Volt line. Temperature rises to 53 degrees Celcius measured at one of the last screwholes (strange word!) within an hour. After that it slowly over the hours falls to 1.7 Amps and 50/51 degrees Celcius.
You can touch the heatsink but it's not comfortly.
My friends Krell FPB-600 becomes even hotter when he's playing moderate to loud on his Acoustats. I'm curious what happens if he plays loud for a couple of days with this amp, besides developing an hearing impairement.
I was very sceptic (that's my nature I think) about this operation but I must say that the amps really improved and not only when playing loud but also to my surprise at much lower levels. There's is more presence, more texture, inner dynamics I think, and it it seems the "noise level" has dramatically sunken unveiling or even better cleaning up the sound.
The KMA-200's were not biased a 1150 Watts each but 580 Watts as Jacco cleared up. The KRS-200 was almost 1150 Watts but could hold it's Class A output even at 40 Volts @ 4 Ohms.
Thanks for the info, all of you!
Loved them too! Magical sound but ran out of steam on my Acoustats too soon. Idled at 400 Watts (I believe, must be careful now was corrected before) and most of it had to be shared by the four convectionmodules at the back with only 8 transistors in total. The two convectionmodules at the front were the regulators. At 1976 you had to pay 3,500 USD for a pair and that's what you still have to pay at least for them nowadays. Sold mine after a recap and some work at the regulatorcard.
People prefer that old MLAS stuff nowadays much more then the new Levinson gear.
Somehow they lost it....
The ML-2 was a real benchmark for other highend audiocompanies not in the least Krell.
Maybe you should stick to a proven concept and designer (I know Mark Levinson was the visionaire not the designer, Curl and later Colangelo were).
People prefer that old MLAS stuff nowadays much more then the new Levinson gear.
Somehow they lost it....
The ML-2 was a real benchmark for other highend audiocompanies not in the least Krell.
Maybe you should stick to a proven concept and designer (I know Mark Levinson was the visionaire not the designer, Curl and later Colangelo were).
They were fantasic with the original Quad. I found them not so fantastic with the ESL-63, and they ran out of steam, so I sold them. But, they were also very good on the ESL-63, do not think otherwise, however, the gap to other amplifiers at that time (I had them from 86 to 94 or so) was not big (with the ESL-63).
BTW I bought my old ML-1 back, I found that more enjoyable than the ML-7. But, it will be placed on a shelf as soon as the B-1 is ready.
Friend of mine drives his HQD system with eight of them. One for the Hartley woofer. one for the Decca tweeter and one for each ESL-55 so four for one channel. Should be our guy for the upcoming Climateconference in Kopenhagen Denmark!
I'm sure they're gonna tax new Class A amps severly in the near future. You should buy your Passlabs XA series amp before this taxingprogram is in effect!
Success with your B1.
I'm sure they're gonna tax new Class A amps severly in the near future. You should buy your Passlabs XA series amp before this taxingprogram is in effect!
Success with your B1.
Well, I cannot imagine class A amplifiers being such a problem, compared to automobiles, people traversing the globe in jetliners, unneccesary lighting, cheap gizmos of all kinds produced in China, shipped to the West, and thrown in the bin after a short time/after they break.
But probably someone still will ban class A amps. Expect silly rules like oh, well... you get the point.
Ran my Thresholds SA/1 without problems the last month. They idle at 72 Watts RMS and the heatsink (temperature rod in the last screw insert) just reaches 50 degress Celcius. My friends Krell FPB-600 becomes even hotter when he's playing at moderate listening levels. I wonder what happens if this amp is driven to it's max output for a considerable time and stays at its highest biaslevel, meltdown?
Well they probably covered that at Krell Industries.
Very nice indeed Jacco, Rockwell (the original manufacturer) of the B1
Well they probably covered that at Krell Industries.
Very nice indeed Jacco, Rockwell (the original manufacturer) of the B1
Yep I know that but I ment his Krell FPB-600.
This Krell becomes pretty hot when only playing moderate levels.
I wonder if this Krell is asked to deliver high amounts of power and is not allowed to shift back to a lower level of sustained bias what happens.
I also wonder how the Anticipator circuit can be quick enough to react to a sudden increase in inputvoltage when it's just downshifting. It seems to me that it has the same fundamental problem as the Negative Feedback techniques of leaping behind the facts all the time but maybe I'm wrong.
I also saw somewhere on this Forum that you liked the early designs of Krell, maybe you could elaborate why that is.
Thanks for the reaction
I'm not sure about this, but if the ML-2 is the amp I recall, it predates the existence of Krell by quite a few years, maybe even a decade... and wasn't the ML-2 a John Curl design??
_-_-
_-_-
Even assuming that the anticipator circuit exists, there will
always have to be a discontinuity when the bias changes
suddenly.
😎
Did I miss something?
The first samples of the ML-2 were delivered at the end of 1976.
Krell amps, the KMA and KSA series with there forced cooling were introduced in 1980.
John Curl is credited for the JC-3 (prelimenary schematic for the ML-2) but parted with MLAS arguing about intellectual property rights with Mark over his earlier JC-1 and JC-2 designs. Hence the JC-2 preamp was renamed to a ML-1 with no major designchange as I recall.
The JC-3 was brought to its final conclusion as a ML-2 by Tom Colangelo long time
Could you point out any potential form of discontinuity in your current designs or is theren't any? How did you solve this problem in the Threshold 800A sliding bias amp?
Hello Nelson ,
Would this also apply to the S500 . My S500 Series -2 (non optical bias ) runs cold at idle and at moderate levels ( barely any heatsink temp ) i only see heatsink temps in the 47 C range if played at above moderate to high levels for at least an 1 hr or 2 , Is this normal ?
Nelson, I am late contributing here, but of course, your calculations are correct. It is in the ease in which one slides from Class A to Class A-B that is important to me, these days. It need not be abrupt.
The Threshold Standard Biasing Procedure (posted on this forum already) from 1991 stipulates that the non-optical versions should run at an idlingtemperature of 42 degrees Celcius and the optical biasversions at 49 degrees.
So that's certainly not cold when idling.
You should be able to touch the heatsink when all warmed up (one hour) for at least 10 seconds for a 'S' version amp. With the 'SA' versions it's becoming uncomfortable after a couple of seconds.
You can acces the blue biastrimmer from the back of the amp but take care it probably a oneturn version, so a to turn too great can result in a blown railfuse.
Twenty to twentyfive degrees Celcius above ambient temperature is a safe setting. Twenty percent of it's rated output at 8 Ohms in Class A (peak value)is the standard value for the 'S' versions I believe.
So if you put an MM measuring amps across one of the railfuseholders (fuse out of course ;-)) it should be between 1.2 and 1.3 Amps after an hour.
In the beginning it should be a lot higher because of the faster warmup feature in the Series II.
Success!
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