Krell KAV 250a deader than a dodo

[pinkmouse]

Jim, I would be very keen to see the full schematics when you get time to do them.

Are you going to bring it along to our diy meet in July?

 

[K-amps]

Al: I think the KAV-250 klone will be a huge success...

 

[pinkmouse]

I could certainly do with something that runs slightly cooler!

 

[digitallake]

Are you going to bring it along to our diy meet in July?

If you diy meet is within 50 miles radius of Leedstown ! lol

I think I've got 2 good pairs of krell's I retested them all earlier (with a diode checker) but how to make sure?? I've got a few PNP's that I think are ok but only 2 NPN's.....

 

[digitallake]

I could certainly do with something that runs slightly cooler!

hmm...dunno about that it was getting quite toasty when I had it on test esp. the pre-driver transistors which arn't heatsinked. Also there are 2 x TO-220 packages on TINY heatsinks on the driver board I would of used bigger heatsinks e.g, like the ones on old comp motherboards or psus. No fans either, and the 10 x TO-3 cans on each channel are very closely spaced! I am musing to what originally caused the major fault I am trying to fix.....and whether it's likely to happen again!

Cheers have a good weekend I probably won't be on here till monday doing other things .....

 

[Mark A. Gulbrandsen]

Sure would be nice if you could back engineer the driver board....

Thanks!

Mark

 

[digitallake]

Sure would be nice if you could back engineer the driver board....

Thanks!

Mark

I'll try....I've had a look at it and it isn't as complicated as I thought most of the component side tracks are a ground plane. Check back for updates next week I'll probably do the PSU first.

BTW, how did you manage to sign on here in 1970 !!!

 

[pinkmouse]

BTW, how did you manage to sign on here in 1970 !!!

Mark has powers*, the scale of which even mods can only speculate upon.



* Well, mostly a power bill we can't imagine due to his huge collection of Class A amps.

 

[digitallake]

back after a mad weekend

Hi everyone I'm still here (just!) set up a huge PA over the weekend for a party, busy stripping it down yesterday but I'm back to real work today I'm going to draw out the rest of the circuits this week I'll keep you all informed!

Cheers, Jim

 

[K-amps]

May the Schwartz be with you Jim !

 

[digitallake]

driver pcb update: scans complete!

Have a google at this. I'm using a mirror image of the solder side scan to complete a diagram of both layers of the board.....easier than keep flipping the board over and getting my wires crossed

 

[digitallake]

oh yeah, I won't wait until someone asks the chip is MPQ6600A1 (Motorola) good luck

maybe....? http://www.diyaudio.com/forums/showthread.php?threadid=19547&goto=nextoldest

 

[Algar_emi]

Is this a amp model with variable plateau Krell bias scheme?
Is it possible that this IC is part of the variable bias circuit?

I can wait to see this schematic. Always wonder how Krell is doing it.

Thanks, very interesting thread.

 

[digitallake]

Hi,
As far as I can see the chip is a balanced input stage, or preamp the bias section is in the next block of the circuit but I haven't started the schematic yet that's just looking at it and making assumptions....check back soon for updates should have it complete within the next couple of days.

Cheers, Jim

 

[aparatusonitus]

IMHO the basic topology is based on current conveyor like this one below...and keep up the good work Jim

 

[enjee]

Obviously,the basic topology is NOT based on current conveyor
The input chip is a 4 BJTs or JFETs,I think

 

[AndrewT]

Hi,

IMHO the basic topology is based on current conveyor like this one below...

are q1&7 the amplifier in that schematic? All else seem to be mirrors, but even they are half of mirrors.

 

[aparatusonitus]

Obviously,the basic topology is NOT based on current conveyor
The input chip is a 4 BJTs or JFETs,I think

The input chip consist two NPN's and two PNP's, perfect for input current mirrors. And if a Krell's CAST topology is used, then we have the basics, no global NF only lokals, just throw in some emitter resistors. CAST connection should look like this...

 

[aparatusonitus]

Hi,are q1&7 the amplifier in that schematic? All else seem to be mirrors, but even they are half of mirrors.

Well, I don't know that, but you can fit in as much mirrors as you like, with gain or not, I think...

 

[digitallake]

I won't keep you all waiting too long, promise