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Old 19th April 2013, 01:17 AM   #401
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I picked up a pair of ksa50/ksa100mk2 boards off ebay from Jim's audio in hopes of building a ksa50mk2. In reading a few of the very long threads on this amplifier, I think I'm more confused as to which schematic jim's audio is following. Is this his own rendition? There seems to be many variations of this circuit, his seems to use mosfets before the drivers. To the people who have used his boards, did you build it exactly to his BOM?
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Old 19th April 2013, 05:05 AM   #402
neychi is offline neychi  Croatia
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@MEGA-amp: Jim's audio use exactly the same circuit as original ksa50/100mk2. There was several variations in production since 1980 to 1987 when production stops. The first versions of ksa50/100 were without mosfets, later version use them. Don't worry, amp works perfectly.

Btw., some of the components are obsolete so you have to find substitutions for them. Read this thread carfully and you will find all the answers



@Michael: this looks much better
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Old 19th April 2013, 11:34 AM   #403
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Thanks neychi!! Hopefully I can make it look as good as Kaplaars version.
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Old 19th April 2013, 12:28 PM   #404
AndrewT is offline AndrewT  Scotland
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I think when you read through it you will find that D5 & D6 are NOT diodes.
They are current regulating diodes, or constant current sinks. A quite different component.
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Old 19th April 2013, 02:21 PM   #405
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Quote:
Originally Posted by AndrewT View Post
I think when you read through it you will find that D5 & D6 are NOT diodes.
They are current regulating diodes, or constant current sinks. A quite different component.
I see. I've found this: 1N5309 - AMERICAN POWER DEVICES - CURRENT REGULATOR DIODE, 600mW | Newark. A bit pricey, any cheaper alternatives?
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Old 19th April 2013, 03:50 PM   #406
AndrewT is offline AndrewT  Scotland
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jFET set as current sink/source.

I offered some of the crd as matched pairs when I bought excess to allow matching, but no body contacted me.
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Old 19th April 2013, 04:06 PM   #407
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In Jims BOM, his alternative is to replace D5/6 with 33R, and there are two positions to install LM334 adjustable current source. My thinking is that the LM334 would provide a less noisy regulation than using the crd option. I'm trying to get as close to original as possible, but if the crd option provides better performace, i'm all for it.
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Old 20th April 2013, 12:00 AM   #408
spurlte is offline spurlte  United States
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I used the LM334/33R. ONCE YOU GET PAST THE MISPRINTs AND THE NEEDED JUMPER on the main boards, WHICH IS POINTED OUT BY Kaplaars. He also advised to kill the potential contact (short) to a MJEs' heatsink. Just read this thread completely throughly and repeatedly.
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Old 27th April 2013, 07:56 AM   #409
alibear is offline alibear  United Kingdom
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Hi all, I am building a version of the KSA50 clone using Jans boards as described in the thread started by Bra in March 2004. Although the amplifier is still not completed in it's final form I have had it running for quite some time. I am interested in the PCB that is available from Jim's Audio for the KSA50 / 100 Mk2 but I do not know the differences to the boards I am using already. Has anyone a circuit of Jims board that they could post, so I could compare. Any views as to which is best board to use for my final version of this amp.
many thanks
Alan
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Old 27th April 2013, 03:35 PM   #410
spurlte is offline spurlte  United States
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Default Almost ready to assembly.

Need to cut fan exhaust vents. Will attach out going fans below and outside main chassis plate.
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