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Old 20th January 2014, 08:43 PM   #8541
esgigt is offline esgigt  Netherlands
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Among the regular KSA 50 boards on the internet with 2 pairs power transistors, I've found this one.

Free Shipping! 1pcs KSA50 Class A amplifier PCB gold seal plastic speaker protection integrated generic version-in Other Electronic Components from Electronic Components & Supplies on Aliexpress.com

Having 6 pairs of power transistors it seems to me more likely to push out some 50 watts in Class A quality. I've seen this one assembled to @ $190 per channel.

Does anyone know more about this board?
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Old 20th January 2014, 09:39 PM   #8542
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Good points Troy. I'll have to look a little deeper. Not sure that using the Arcam as a pre-amp is a good start.
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Old 20th January 2014, 10:56 PM   #8543
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esgigt.

0.50A bias pr device and 3 pairs in push-pull configuration is 36Wrms at 8ohm.
peak class A current is twice the bias. so 3A peak. (.5a*6devices)
3*0.707=2.12A rms
2.12*2.12*8ohm = 35.95Wrms in class A at 8ohm speakers.

(Math courtesy of AudioSan. Hope I didn't butcher it )
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Old 20th January 2014, 11:08 PM   #8544
esgigt is offline esgigt  Netherlands
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Quote:
Originally Posted by dihmels View Post
esgigt.

0.50A bias pr device and 3 pairs in push-pull configuration is 36Wrms at 8ohm.
peak class A current is twice the bias. so 3A peak. (.5a*6devices)
3*0.707=2.12A rms
2.12*2.12*8ohm = 35.95Wrms in class A at 8ohm speakers.

(Math courtesy of AudioSan. Hope I didn't butcher it )
Thank you for the correction!
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Old 20th January 2014, 11:15 PM   #8545
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Quote:
Originally Posted by dihmels View Post
esgigt.

0.50A bias pr device and 3 pairs in push-pull configuration is 36Wrms at 8ohm.
peak class A current is twice the bias. so 3A peak. (.5a*6devices)
3*0.707=2.12A rms
2.12*2.12*8ohm = 35.95Wrms in class A at 8ohm speakers.

(Math courtesy of AudioSan. Hope I didn't butcher it )
Close - the total bias is only 1.5A because the same current flows through the the N and P devices in each pair. So peak class A current is 3 amps, then the rest of the math is fine.
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Old 20th January 2014, 11:24 PM   #8546
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Originally Posted by BobEllis View Post
Close - the total bias is only 1.5A because the same current flows through the the N and P devices in each pair. So peak class A current is 3 amps, then the rest of the math is fine.
I though I used those numbers. Do you mean that peak is 1.5 amps because the same current flows through the N and P device? I'm not sure I understand.
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Old 20th January 2014, 11:27 PM   #8547
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Yes, with 3 pairs there are three channels for current. So 3 pairs @ .5A each is 1.5 A total bias.
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Old 21st January 2014, 12:18 AM   #8548
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So 1.5A or 1.5 *.707 = 1.06Arms
1.06*1.06*8 = 9Wrms in class A.

Mine setup runs 2 pair at 600ma quiescent current. So I have 1.2 amps peak or 1.2 * .707 = .848Arms. .848 *.848 *8 = 5.76Wrms in class A?

I stand corrected esgigt.

In my setup each rail has an idle load of 2.4 amps for left and right.
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Old 21st January 2014, 12:27 AM   #8549
esgigt is offline esgigt  Netherlands
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Quote:
Originally Posted by dihmels View Post
I stand corrected esgigt.
Well, isn't that the way we learn?
I learned that the actual Class A output is distant from a real Krell...

"Having 6 pairs of power transistors it seems to me more likely to push out some 50 watts in Class A quality"

Also proved to be overly optimistic I also stand corrected
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Old 21st January 2014, 12:52 AM   #8550
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I think the idea behind more sets is that they can share the load. So if you had 6 pair per rail or 12 devices you could run 3.5 amps of quinscent current and produce just under 50wrms in class A. So each device carries the 1/6 of the load and will dissipate 1/6 of the watage in heat.

You would need a couple of 600va toroidals



Or go bqk in time and get the Mr. Fusion from the DeLorean.
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