Krell KSA 100mkII Clone

[Mark A. Gulbrandsen]

I would recomend that we try Victoria Magnetics to see what the price would be on a 1KVA with screens as Andrew mentioned. They are always LESS EXPENSIVE and of very high quality! Dr Leach specifies them for his students that are building his amps. I don't necessarily think it has to be in a can and potted though. Some of the finest amps being built today have standard open type toroids. A quality toroid will be virtually noiseless anyway. This should save considerable on the cost. Also is a toroid the best route or should we also consider an E-I type design.... both have their advantages.


I have e-mailed M&M for a quote on the heatsink extrusion and I should have that back in a day or two.

Mark

[Mark A. Gulbrandsen]

If no one here has any objections in the next hour I am going to hijack the old KSA-50 1st board group buy WIKI and turn it into the KSA-100 board WIKI. This is the old original wiki located here and its long dead done and over with. This is not the KSA-50 technical WIKI and doing so will also help conserve server space.

Mark

[PWatts]

Okay, I've adapted the LTP pairs to be back-to-back, shifted the base pin for the few European types that have triangular pinouts, and added a fourth pin for 2SA/2SC types. Hope everybody is happy now. I had to use 0.5mm traces for a small portion but it will not be a problem.

I've also added the extra hole for triangular trimpots, thickened a few traces and holes, changed the footprints for the drivers to the flat-mounted TO220 package and added a jumper for shorting out the DC blocking feedback caps.

What I could NOT do was the diodes or bigger sized feedback electrolytics. Sorry. With a little ingenuity these can be soldered on the back for those who'd want to use them; I don't think they'd be popular enough to warrant serious adaptions to accommodate them. The driver part and all above it is still only preliminary, I'll make it prettier and more efficient and symmetrical later on. I'm also still pondering about where additional copper pours may be beneficial.

I'll try to see if I can adapt the board with the AAVID heatsinks for the predrivers.

There's only one big problem left: as it is now there is very little room left for the driver heatsink. Compared to the original, there's about 8mm less size for the driver heatsink, not a big difference, but the original already got way too hot. To fit flush with the top of the board, the maximum heatsink size is 25 x 120mm. The board and heatsink cannot be made longer as the clearance to the chassis lid is already very small. Wider will get in the way of the outgoing wire pads. Any increase can therefore only be in the z-axis, but cannot be too much or setting the bias will become difficult. The mounting holes can be shifted lower to make the whole thing lower and thus allow a taller board, but it all depends on the clearance to the chassis bottom.

Right now I cannot do much more until I have the details on what to do with this, how the predrivers should be sinked and what the exact board dimensions and location of terminals and mounting holes are.

Attached is a PDF with the the top and bottom side. I'll add the silkscreen layer etc. when the board is closer to being complete. Some of the stuff that appears to be overlapping would be the components that I made provision for different types i.e. only one will be used such as the MOSFET's. The silkscreen is also covered by the top layer in areas, but of course that will not be the case with the actual board.

Off-topic: Mark, even though I like the idea of my work potentially spreading like a ravaging virus into broken and serviced KSA100's , are you sure that Krell will not have a problem with their designs being replaced with clones in repair shops? DIY stuff and servicing friends' amps on a personal level is one thing, but I'm just curious what the situation might be with something like this... given the sometimes rediculous extent of lawsuits in the USA.

Pierre

[pinkmouse]

Originally posted by Mark A. Gulbrandsen
...I am going to hijack the old KSA-50 1st board group buy WIKI and turn it into the KSA-100 board WIKI...

Good idea!

Originally posted by PWatts
Attached is a PDF with three different parts: the top side, bottom side and top silkscreen.

I think you linked to the wrong file!

[PWatts]

And here's the PDF

[Mark A. Gulbrandsen]

Ok, Its here

Also to those of you that are involvd in this if you want to add or change the WIKI around please feel free to do so. I only set it up as a very basic WIKI. I think this is going to b a more limited run than the KSA-50 WIKI was so we jut might want to place the technical stuff and amplifiers built there as well.

You can also click on the link under my name in each post I make.

Mark

[jacco vermeulen]

I doubt that many original KSA50 and/or KSA100 owners would have their amplifier repaired by a Krell distributor by now.
It would probably cost an arm and a leg, and more of these amplifers would end up in the scrapyard or as a case for a Leach or a chippy amp.
A board that can be used to rejuvenate one of these amplifiers will keep more of these classics alive.
Surely, if these boards do not lead to lost earnings for Krell dealers and keep more of the Krell heritage in one piece, Mr Krell can not object.

[pinkmouse]

Don't post to the wiki at the moment, I'm just sorting something out.

[Mark A. Gulbrandsen]

You may be trying to figure out that I changed the KSA-50 wiki and then changed it back. Either I accidentally created a new KSA-100 wiki or someone behind the scenes did it for me while I was attempting to change the KSA-50 header to the KSA-100.... Yes, I need the WIKI for dummies book!

A Question on the driver heatsink...

Do we all agree on #3 or #2. I asked for a quote on #3 because of its larger contact area.

PWatts.. What is the space between the C/L of the driver transistor mounting holes and the top edge of the board? I need to be sure this sink or #2 will work. I'm not worried about radiating area. Krell only had 3 fins on theirs and it was also quite thin. I think with either we will be in better shape thermally speaking. I just need to be sure that one or the other's mounting foot is going to fit between the top of the board and extend down to allow sufficient contact of the driver deices tabs. What color do you all want these sinks anodized? We have a local place thats reasonable and does very good work. Do we want to stick with the orignal blue color?

Mark

[pinkmouse]

OK Wiki sorted, new link is here. Mark, you might want to update your sig.