Hi really nice job with your amps.I completed my KSA-50 build in 2007. It took longer than I had planned and, combined with a job change and added daily commute time, I never put the final touch in the mono-blocs’ appearance. I decided they would get a makeover for their 10th anniversary, starting with a thorough cleaning of all the aluminum parts which still had Sharpie markings from the cutting and drilling steps. The makeover would also add long output boards to better use the length of the heat sinks, and front panels, which I never got to make back then.
After I had taken the units apart and cleaned up the aluminum panels, Troy posted this:
Krell KSA 50 pcb - Page 355 - diyAudio
I decided to take pictures of the makeover and post them, so he can hopefully enjoy them.
I designed a longer output PCB to better use the length of the heat sink. I made it so a single design can be used in either side of the case. Here are the new output boards next to the original ones, which I never used.
Output boards populated and then mounted on the heat sink.
The aluminum brackets after the cleanup, mounted on the heat sink.
The bottom plate really clean (yeah, I went a little crazy on that one.
The best way I found to mount the bottom plate is to flip the heat sink and assemble everything upside down.
I then installed the front plate and the rubber feet.
Next I reinstalled the capacitors and redid the wiring.
Just ordered a set of boards from ebay and want to make 2 mono block amps like this.
I have been offered 4 x heat sinks 300x132x40 £80 second hand would these be large enough to run in full class A 2x50w.
Not sure weather to get these or buy T-03 heatsink and make fan heat sinks.
Also I really like the longer transistor boards.
Thanks Dave.
I buy aviation grade aluminum (6061-T) remnants that usually have minor scratches. After drilling and counter-sinking all the holes, I use 3M Imperial wet/dry sandpaper, starting with 600P followed by 800P, 1000P, 1200P and finally 1500P. If the aluminum pieces have deeper scratches I may start with 320P or 400P. After all the sanding is done I wash the pieces and buff them with Mother's Aluminum polish.
I am trying to decide what transistors to order for my krell clones.
My pcbs that I have started to put together come with T03 type transistor pcbs but I also have pcbs from another kit I decided not to use.
It would be easier to fit the pcbs with MJL21193/4 to my heatsinks but have noticed that the T03 pcbs have places for diodes.
Would I need to add diodes if I use the MJL21193/4 pcbs.
Which is the best choice transistors for sound quality T03 LM21193/4 or MJL21193/4.
Thanks for any imput.
My pcbs that I have started to put together come with T03 type transistor pcbs but I also have pcbs from another kit I decided not to use.
It would be easier to fit the pcbs with MJL21193/4 to my heatsinks but have noticed that the T03 pcbs have places for diodes.
Would I need to add diodes if I use the MJL21193/4 pcbs.
Which is the best choice transistors for sound quality T03 LM21193/4 or MJL21193/4.
Thanks for any imput.
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Its safe to use either version of them. I used MJ21193/94 in all my KSA50 and 100 builds. I had a ton of used but good ones from doing gobs of QSC amp rebuilds. The amps all sound awesome and they are all still going strong after many years. Mine were TO-3, but I have also used the plastic version on flat backed heat stinks with the same sucess. Not one of the Krell Klones,I built has ever failed. The diodes are likely the commutating diodes and should be installed near each output stage. I think they are 1N4004's or 5's.
Those output devices are multiple emitter devices and are very good for class A amplifiers.
Mark
Those output devices are multiple emitter devices and are very good for class A amplifiers.
Mark
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Thank you for your reply.
I was going to use passive cooling but I won a pair of used but new heatsinks on ebay that can have fans fitted and have decided to make two mono block amps.
PC Boards
Hello. I built a KSA-100, way back when this thread started and noticed your boards look very much different. May I ask where did you get them and are they still available?
Mine has high rails thata re right around that voltage, and three output devices per side on each channel. Also a 1.2 KVA toroid. You can see mine in the picture. I built it back around right when the Pink Mouse boards came out. The heat Stinks are smallish but force air cooled. This is an ex AB Systems 6 channel amp chassis.
Mark
Mark
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I am for sure its not over 2 amps per rail at about +|- 46 volts. I also remember there was a mistake in the original spread sheet that was found later on, so if anyone used it then you are off a bit. Mine beats factory specs by quite a margin, so I've always just left it as is. The bottom end it produces is incredible.
Mark
Mark
My issue with SMPS is they have an absolute ceiling on current supply... So your peak power output might suffer because of it... I built a 250 wpc digital amp using a big surplus SMPS and was never really happy with it.. Not only was the SMPS limited but digital amps also have an absolute maximum level.
Mark
Mark