Krell KSA 100mkII Clone

Quiet here lately..

Well I've updated the BOM with a few changes and elaborations, plus added quite an extensive Everything You Need To Know About The KSA100 Clone But Too Afraid To Ask section. It's not the basic assembly instructions, but more directly applicable to the KSA100 Mk2 and the boards and can be seen as a parahrased version of most of what has been covered on the thread so far.

Combined with the KSA50 wiki instructions it should be very easy to build.

Any comments or additions will be appreciated :)

[There were some errors with the jumper designators that are fixed now]
 

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PWatts,

I disagree to your comment regarding the 5 Amp bias set level of the mk-II :hot: . Proper bias set level should be 2.5-2.8 Amps depending on % of margin. If you meant 5 Amp peak level I agree to you but what you have specified in the BOM document could be confusing to somebody not familiar to Class-A calculation.

Here I would like to refer to some of the earlier posts designated K-Amps, AndrewT and Stuart, whom discussed the subject and cleared things out:

Stuart is right and supports Kamps. I cannot disagree that Iq=2.76A gives MORE than 100W of ClassA into 8r.

I think we are also agreed that KSA100mk2 will safely deliver a lot more than 100W into 8r. Mark has stated 160W.

I also will not/cannot dispute Kamps measurements and calculations leading to
quote:
690mv across the 1 ohm emitter resistors meant it was biased to 122 watts pure class-A into 8 ohms

On the same basis that both the KSA50mk2 and our 50 Klone will push a lot more than 50W into 8r does not stop us specifying an Iq=1.9A giving about 58W ClassA for an amp capable of a maximum of about 70W to 80W.
I think we are all agreed that our 50 Klone is fully biased to ClassA just as a Klone of the 100Mk2 biased to 2.76A will be fully biased to ClassA.

Further information on this subject is to be find in Post # 96-102

Regards :cool:
 
OK OK fine.. but it should be clear to figure out anyway since the total bias is after all the total bias per transistor added together.. and knowing it's 620mA each it's not rocket science.

From a heatsink perspective it makes sense to refer to the total bias since that is what the sink needs to dissipate, but from the amp side the per rail value is more sensible.

Besides, anyone building the amp should at least know the basics of how to calculate reasonable values for 100W into 8ohms or it's likely to blow up anyway :hot:
 
PWatts said:
From a heatsink perspective it makes sense to refer to the total bias since that is what the sink needs to dissipate, but from the amp side the per rail value is more sensible.


Heatsink dissipates power, not current. Bias current flows from +Ve to -Ve, and it is regulated at one single point (Vbe multiplier). It makes much more sense to me to say that my amp runs 2A idle current at +/- 50V (that is 200 watts of power to be turned out into heat) rather than say I've got 4A idle. I mean, if you measure current anywhere in the circuit, there is no one single point where your ammeter will show 4A, is it ? Same current flows through both branches of output - you can't add them. But you can add voltage, 'cause between +V and -V you do have 2 times 50 volts. The voltmeter will measure 100V between rails. I think it is a bit more than just semantics.

Bratislav
 
Jeez OK I should've stuck to the conventional format I suppose.

Heatsinks do of course disssipate power - but with the voltage a fixed parameter (well hopefully with a proper transformer anyway), current increase will increase power in direct proportion so there's nothing wrong with that statement.
 
don't feel bad...

...there is no single answer that will suffice for all people and all possibilities...and it's clear your answer will have answered some peoples unspoken questions...

Power in the heatsink is a big deal for this amp, giving people more info may help them understand what's proportional to what and thereby gain better insight into their particular build. This is unambiguously a good thing...

...and this is key; except for exact clones, there is a good chance no two of these amps are the same, thus each builder/designer must understand the heat issues, they need to make adjustments and end up with a stable, reliable amp.

I expect we will see the same questions many more times before we are done, and answering them different ways, from different perspectives is needed to give everyone the best chance of understanding...

Stuart
 
thats easy...

2.9 amps, 57 volt rails == 330 watts per channel, with 30c temp rise...you need heatsinking to the tune of 0.091c/watt, per channel.

To give (computer geeks) an idea of what that translates to: A stock P4 cooler (with fan) supplied by intel is slightly better than 0.5c/w, so minimally you'd need 6 of them per channel, with their fans...perhaps 8 might be better, one per transistor...of course 8 fans would be kind of loud...

Unfortunately CPU heatsinks are designed to use fans, they are much less efficient without them...

http://www.overclockers.com/articles373/socketA.asp

Stuart