Krell KSA 100mkII Clone

I would'nt have any problem shipping the current sources with the boards..... A single current source is so easy to implement. But if a CCS built up out of seperate parts is easy enough I'd be open to it. Would make things all the more flexible....

The original fets were Supertex VN and VP0210N5. I think these can be replaced by Zetex ZVP3310 and ZVN3310 and these are cheap! See if these will fit your spice model.....? In the KSA-80 these devices weren't set up to draw very much current.

Also see THIS THREAD on klonning the KSA-80 in which the Zetex devices were subbed in for the Supertex.
 
OK here are some of the results:
The best results for the LTP were with BC546/556 transistors. Good news since they are easy to get and cheap.

For the FET's, indeed the ZVN3310 and ZVP3310 are a viable option, and they improved measured specs considerably. The only dissipate 32mW each @ 1.5mA, so it should be OK without a heatsink.

Drivers and pre-drivers, MJE15034/5 seems slightly better than 15030_1.

Concerning the current sources, the 1N5309 or J509 yields much cleaner current than basic discrete CCS's. It will have to be a more complex one that would be able to improve on these diodes, that is quite frankly not worth it. In this application the diodes have a ripple of only 0.7uA, or -73dB.

So it seems like the component cost and variation will be fairly low and easily obtainable.
 
Thats good news and pretty much as I thought it would be. Have any of you gotten a board design far enough along that can be posted for us all to pick and pull at and then agree on some basic design? I think thats the next step here..... I was going to build mine on ceramic Tektronix terminal strips until this thread was dredged back up.

Mark
 
The only issue I have with the ZVN/ZVP's are their rather high Rds of 10ohm and 20ohm respectively. Doesn't seem to be a problem and shouldn't be in this particular application but still. Plus in a TO92 package they may get too hot - the original KSA used TO220's with a small heatsink and if I recall correctly they got a little hot still. I think I'll provide support for both TO92 and TO220 so people can experiment with both types, either for sonic evaluation or if heatsinking becomes a problem. Alternatively the DPAK F-package may be good if a proper pad with lots of vias is used for heatsinking.

I was thinking of doing an exact copy of the original MK2 for the layout (as a matter of fact I'm restoring a genuine MK2 within the next few weeks so it'll be easy to jot down the basic layout), and just add the few refinements as Al has made to his KSA50 wrt grounding, PSU bypass caps, separate power supply inputs etc. Any suggestions you felt that Al left out on the KSA50 that should be present on the KSA100? If not, it will be a fairly straightforward design.

I also have to admit that I'm seriously toying with the idea of a completely separate regulated supply for the input and driver stage; it draws only about 120mA. Anybody ever tried it? Comments? It will not be part of the board but would be interesting.

The part that bugs me is the heatsink though. The predrivers can use small heatsinks as in the genuine one, but the four drivers and thermal feedback transistor need a substantial one. I'll try to place the heatsink at the far end so that people can use whatever they want, since a bolt-down type will be impractical for most people to try and accommodate.

In addition, has anybody looked at the MK2 photo? All the components are easy to identify, but close to the feedback electrolytics there are two caps - one silver mica and the other an axial type, presumably polystyrene or related. The latter is the 100nF bypass for the electro's, but what is the silver mica? It's not the 680pF input shunt (that is the blue one close to the input) or the 62pF Miller caps (they're next to the drivers), so what on earth could it be? I'll investigate closer when I strip the one to be restored but it will be a few weeks.
 
PWatts said:
Any suggestions you felt that Al left out on the KSA50 that should be present on the KSA100?

Use both sides of the copper better to increase the thickness of the input and output tracks on the output boards, something I can't believe no-one picked up on. Try and fiddle the input pair closer together so they can be coupled so they see the same temp. increase. Allow a greater spacing for resistors so bigger boutique types can be used if required, and allow for different sizes for the output resistors as well. That's all I can think of at the moment, but I'm sure more will come to me! :)
 
I agree with what Al said. You may just want to follow his general design for the KSA-50 MK-2 boards as they seemed to work out very well for all that have built them. If you use the resistor size/spacing on the original KSA-100 board then we should be fine there. They used Dale/Vishay 1/2 watters everywhere and they are quite large. If I can match input pairs for these amps I don't think distance will be a factor. In a closed in chassis everything seems to equalize anyway and I've had zero problems with DC drift on my KSA-50. I will check with the guy that did the KSA-80 about how the Zetex fets have worked out for him. He used them in a very similar place on the 80 dissipating just under 200 mw with good results. It is very easy to heatsink the Zetex's if needed.

Mark
 
I haven't had any trouble with the Zetex parts I substituted for the obsolete Supertex. Yeah, the temperature is pretty high, but the whole amp is hot in the steady state. If you make sure there is plenty of copper on the PCB then you'll get satisfactory heat dissipation through the leads.

Watch out for the input grounds in your new design. I had trouble with buzzing using the original Krell ground layout and wound up drilling new holes in the back panel to move the inputs away from the bulk power supply.
 
Supply Rails

Mark A. Gulbrandsen said:
...Yesterday we had the opportunity to compare my KSA-50 MK-2 Klone to Bill WW's Krell KST-100 Class A-B amp. Clearly the KSA-50 clobbered the KST-100 in high frequency end of things... it was much more refined while the Krell KST was colder fomr about 5K up and just a tad bit gritty sounding. HOWEVER... the KST-100 blew the KSA-50 out of the water in the low end department driving my Dynaudios with a slam factor that never seemed to run out...

post 30...I believe the rails of the KSA-100 are at +/- 48 to 50 volts...

Mark, thank you for this report. Could you please describe the power supplies of each amp used in comparison(rail voltages, uF, VA of XFMRs) It would povide another layer of background for me.

Secondly, can someone verify the rails of the orriginal? Would there be some play with the +- of the clone and what would be typical low and high of these rails without changes to the circuitry?

I missed the KSA50 and now I know why.:D

Cheers,

Shawn.
 
KSA 100 vs KST100

I read the KSA-100 was of 80's vintage & the KST-100 was of 90's vintage.

Is there debate as to which model will be selected for the clone. Perhaps obviously the KST because it was newer? Just asking as I find myself stumbling over the varoius model numbers a little as I follow the thread. :xeye:

Cheers,

Shawn.
 
Hi Tom,

Were doing the KSA-100 Mk-2 version or the last version of that amp. At the amp shootout we compared my KSA-50 Klone to the KST-100. Needless to say the KST 100 had incredible low end response and quite decent mids and highs. Everyone there agreed that the KSA-50 does easily beat out the KST-100 in the mids and highs. The 50 has a much warmer sound to it... more tube like. The KST-100 is fully balanced and would be difficult to build... at least as difficult as kloning the KSA-80 as JWB did. The power supply in my KSA-50 Klone is based around a 2KVA toroid with dual secondaries. There is a simple bridge and 56,000 mf per rail. The original 50 had dual trannys that were I'm pretty sure around 400 kva each, Yes, my 2kva toroid is way overkill but it was only 70 bucks. I'm not sure what the supply is in the KST because everything is under one large PCB. I'm sure its pretty beefy though. Let me know if you need any more info.

The photo is of the top of the KST-100......

Mark
 

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The original used +-52VDC rails, dual 1kVA toroidals and 55000uF 80V electrolytics per rail per channel (not sure about the capacitance).

@Mark: How do you sink a TO92 package? Or should the harder to find DPAK package rather be used? I'm still thinking more in the line of the IRFD110/9110. They have a bit larger package and has more or less the same capacitance as the Zetex ones. Plus they're easy to parallel if needed. Check them out if you like.

I've never used the output stage boards (always used TO3 cans), but will increase the copper area. Compared to the boards used on the original for the TO3's I don't think Al's was lacking, but why not add extra conductivity.

Regarding LTP closeness, there are some very nice integrated packages from Intersil if memory serves that will help layout. I'll take a look at them again, provided they're not too hard to find.
 
Aavid / Thermalloy make at least two slip on TO-92 sinks. Digikey stocks them. One is .42 and the other is $1.30, so thats not a problem.

As for the outputs there will have to be a board that will accomodate both TO-3 and TO-3P to effect any group buy... or two seperate OP boards done up. I also prefer TO-3's myself but the majority out there can't work with them or can't get them. I have no problem with adding the extra copper.....

I've never been a big Intersil fan... they seem to let things go obsolete way too fast.

Mark