Krell KSA 100mkII Clone

[pinkmouse]

No.

[PWatts]

Ugh I don't know how many of you have seen this, but it seems like somebody has made an upgraded PCB of that blue Chinese one we saw; a MK2 model. His component choices are rather sane, but he used the IRF510/9510 output devices. Don't know why he didn't at least go for 610's, they're better for this application. Layout is very compact but it does sort of remind one of Elliott's S500 subwoofer amplifier

http://www.diyaudio.com/forums/showt...58#post1025358

That means that if he is willing to share the Gerbers and the components are easy enough to find my boards are only good for those who want the classic look

Anyway, here is some feedback on the temperatures of the MK2. Very impressive indeed. At 660mA bias per output device (i.e. 660mV across each resistor; 110W class-A into 8ohms), the main heatsink measures 60degrees, the output transistors about 75degrees, the drivers about 46degrees (on the transistors themselves no less), the predrivers just around 40, and the MOSFET's were basically at ambiant. The drivers are therefore more than just perfectly happy with the heatsink provided.

Funnily enough the main heatsink doesn't get nearly as warm as the Mk1 - I suspect it may be due to the bottom mounted fans, and the fans being more effective than the old top-mounted plastic ones. The larger driver heatsink also clearly paid off.

With the transformers wired for 240V mains (it gets 230V), the DC rails are between 49-50V.

All in all a great piece of apparatus and a definite improvement over Mk1. Mk1 owners, get a decent Papst fan for better performance and lower noise. Bottom mounting will be possible with some ingenuity too. All those clicky relays also provide some peace of mind, and they do a damn good job - when the sparks flew for a while during the voltage changeover they quickly saved the day

I'm going to do a full set of measurements (THD vs freq, THD vs amplitude, frequency response, SNR, DR, 1kHz spectra etc) and repeat them after I've ripped out the boards and replaced the caps with Black Gate NX's.

[Jozua]

Pierre

Please consider posting what PSU wires had to be reconfigured for any potential other Krell owners faced with a similar problem.

Interestingly I made 6 international calls to Krell and wrote two unanswered e-mails.....



Jozua

[Jozua]

Gentlemen

Last night we wanted to do a quick distortion test on a KSA100 mk1 and hooked it up to the test equipment. At switch on there was a brief crackling sound inside the box then a puff of smoke followed by a burning smell...

Needless to say it was a simple resistor that blew but still a interesting feeling when you see smoke coming out of your amplifier....even worse when you cannot find a screwdriver when you need one!


Jozua

[Mark A. Gulbrandsen]

zly1980,

Where in China can we mail order those circuit boards from?

Mark

[BobEllis]

here http://cndiyclub.com/c_read.php?tid=5353

[PWatts]

That's the Mk1 boards.

[jacco vermeulen]

Those boards are only good if you go passive cooling.

+250 watts of dissipation will need big MF heatsinks, even if efficient later Krell heatsink types can be traced.
Putting such a board on a fan duct means quite a long heatsink tunnel, also implies placing it horizontal.

Separate boards are more flexibel, enable a compact construction, and the front end can be kept away from the heatsink if so desired.
Pierre's board design looks more attractive to me, with a combined device type output board it would be perfect.

[Mark A. Gulbrandsen]

I have a pair of tunnels at least that long. Just want to know wher eI can mail order them from.

Mark

[Zen Mod]

btw apex.jr always have something interesting,at least for tunnel heatsinking


hm-this is zillionth time that I mention his stock.....I suppose that I can earn serious discount but-I'm on wrong side of ocean for that ,hehe