Krell KSA 50 pcb
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henryve
diyAudio Member

Join Date: Jun 2008
Location: Strand
Quote:
 Originally Posted by neychi I think he meant 300mV per device.
Yes. Basically the voltage drop over one Re. So that means the total bias is then:

300mv/0.5R * 2 = 1.2A since there are 2 output pairs on the original KSA50.

 12th November 2013, 06:41 AM #8532 docjoe   diyAudio Member     Join Date: Jun 2003 Location: Paris, France Yes, I've sent Dan the Ve I measured on one device, otherwise it would not make sense, as you usually take the voltage across one single resistor. Ive also questionned the tech that made the check up in june 2011, and he told me to set the bias at Ve = 360mV on turn on, as he said this will decrease as the unit gets warmer. We're in the same numbers. He told me also that with +/- 50V rails on this MkII, the output devices died if fully biased to 50W. __________________ docjoe. Last edited by docjoe; 12th November 2013 at 06:46 AM.
henryve
diyAudio Member

Join Date: Jun 2008
Location: Strand
Quote:
 Originally Posted by docjoe Yes, I've sent Dan the Ve I measured on one device, otherwise it would not make sense, as you usually take the voltage across one single resistor. Ive also questionned the tech that made the check up in june 2011, and he told me to set the bias at Ve = 360mV on turn on, as he said this will decrease as the unit gets warmer. We're in the same numbers. He told me also that with +/- 50V rails on this MkII, the output devices died if fully biased to 50W.
It should not decrease to 152mV though. However, the devices is not suppose to just die if you bias it to 50W, unless there is a problem with heat management. The correct way would be to bias and then to check the junction temperatures of the devices after an hour or so.

 12th November 2013, 08:09 AM #8534 docjoe   diyAudio Member     Join Date: Jun 2003 Location: Paris, France Latest news! Hear hear!!! The Krell A and AA transitors are MJ 15024/15025 sait the tech this morning. Krell told them as supply of A and AA shorted. Maybe it has to do with the reduction of Bias. __________________ docjoe.
dihmels
diyAudio Member

Join Date: Nov 2013

Hello All. I have been dipping my toe in the this hobby as of late and have my first attempt based on the "cheap" Ebay KSA50 assembled board. I'm not sure how close it even resembles a Krell KSA50.?.

Here is the short thread that I have been chatting on: http://www.diyaudio.com/forums/solid...-voltages.html

I have to say it seems to works quite well and is dead quite at idle (600ma bias).

Fun so far. Not sure If I want to build this one a house or experiment with different designs before I commit to all that aluminium.

I have never heard a real Krell so have nothing to compare to. Also, at the price of these boards (< \$40 USD complete) many have questioned if the 1943/5200's are authentic. I have no idea how to truly know. Based on the threads and sites I have researched they look original. I also have 7 sets of them sitting on my desk that I pulled from a dead Arcam AVR250 and they look very similar.

Trying to find out input sensitivity for these boards. If anyone is up to translating the Chinese from the attached schematic I would appreciate it.

Thanks
Attached Images
 naked amp.jpg (972.9 KB, 343 views)
Attached Files
 ????? (1)_CAD.pdf (35.2 KB, 71 views) FSA?3?????PCB??? (2)_Schematic.pdf (117.3 KB, 92 views)

 20th January 2014, 04:49 PM #8536 troystg   diyAudio Member     Join Date: Apr 2004 Location: In a dream... Please don't wake me. Most people get started with a chip amp... But you couldn't have picked a better amp to build classics wise. __________________ Troy Thinking positive doesn't make things better, it makes you a better person.
 20th January 2014, 05:05 PM #8537 dihmels diyAudio Member   Join Date: Nov 2013 I thought I would start with the second most inefficient (single ended winning that race) and then move to the most clean power for the \$. This one helps warm my office over the winter. Any suggestions for a thread on the best class D's?
troystg
diyAudio Member

Join Date: Apr 2004
Location: In a dream... Please don't wake me.
Quote:
 Originally Posted by dihmels I thought I would start with the second most inefficient (single ended winning that race) and then move to the most clean power for the \$. This one helps warm my office over the winter. Any suggestions for a thread on the best class D's?
Hypex nCore... IMHO
__________________
Troy
Thinking positive doesn't make things better, it makes you a better person.

 20th January 2014, 06:56 PM #8539 dihmels diyAudio Member   Join Date: Nov 2013 Thanks troystg! I'll look into that one. I want to build a nice "D" and then compare directly with this class A biased "bomb" as my wife refers to it. I have to say that this amp is missing what I would call mid-bass to mid-mid crack or snap. I guess punch. My speakers aren't monsters (Spendor S5E's) so I'm not expecting theatre level lows but one of my amps is an RTEC (rotel) MPA150 that's a dual mono class AB with 150Wrms per and it makes the low sensitivity Spendor's sit up and put out a little more to my taste.
 20th January 2014, 07:35 PM #8540 troystg   diyAudio Member     Join Date: Apr 2004 Location: In a dream... Please don't wake me. The Krell KSA-50 was well known for a good grip on speakers. Especially difficult loads. I would expect an issue with the physical layout / power supply over the circuits inability to control the speaker before writing it off. Now on the other hand the Rotel (which is a very good company) may have some "character" engineered into the sound of your amp that adds that extra snap. __________________ Troy Thinking positive doesn't make things better, it makes you a better person.

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