krell ksa5 klone

[jboehle]

Did the bottom of any of the original PSUs or amp have vents?

[jboehle]

I am making more progress on my power supply & amp boards.  I checked to make sure the TO-3 insulators in the PSU were doing their job and the TO-3 cases were not connected to the big heatsinks, unfortunately my meter shows .3 ohm (it shows .2 ohm shorting the leads together), doh!  I guess some of the jaggies from the heatsink poked through the (absurdly thin) mica insulators I got?  What TO-3 insulators do you guys use?  Unfortunately I was a dumbass and already soldered the TO-3 leads so I'm going to have to desolder those to replace the insulators, ugh.

[kevin gilmore]

I use the thermasil ones. you use insulators to get good thermal transfer. The heatsinks

are isolated from everything, so you don't even need insulators, but if you use thermasil

or other conforming ones you get better thermal transfer. Even if there is a short between

the case of the transistor and the heatsink its ok, as long as you don't touch the heatsink

 

I'm pretty sure this is the one I used mouser part number

567-175-6-310P

Edited March 26, 2014 by kevin gilmore

[jboehle]

Thanks Kevin.  I am a little worried about accidentally touching the heatsinks either with a probe or to a part of the case but I will just try to be careful.

 

I couldn't find any Thermasil ones stocked at Digi-Key or Mouser.  BTW the ones you spec'd in the - "thermal washer   739-A15038003  2" - are for TO-220, not TO-3.  The TO-3 insulators I was able to find in stock at Mouser are 534-4662 (mica), 534-4667 (mica), 534-4636 (mica), 567-175-6-310P (Kapton), and 739-A15036002 (Tgard 500 - some kind of thick silicone one).

 

Also, are the MJF1503x in the new PSU supposed to have any heatsinking?  It doesn't look like they did in your pic but thought I would make sure.

[kevin gilmore]

mjf parts do not need heatsinking

[GrindingThud]

Holy shit....that did not take long:

http://www.ebay.com/itm/KRELL-ksa5-Class-A-headphone-amplifier-kit-/161267038245?pt=US_Amplifier_Parts_Components&hash=item258c43b825

Looks like it's missing half the caps and squished a PS on the board too...... My gut says what a turd, but curious to hear it.

Edited April 4, 2014 by GrindingThud

[kevin gilmore]

you bet its a turd.  But its only $79.99

 

For that price it still beats the crap out of anything 20 times that much money.

 

The real klone sounds a fair amount better.

 

And that is what I get for releasing the schematics and making it easy to copy.

 

I wonder if I release the liquid gold schematics if they would do the same thing

[wink]

Do it.......

[luvdunhill]

Even the Chinese have standards...

[spritzer]

Tempted to buy one for shits and giggles.  A bit funny to think this came from some Sunday afternoon boredom on our part... 

[Zashoomin]

I was also thinking about buying one to compare to the current one that I am building.  Does look like I would need a different transfromer though. Apparently there is one that comes with it that is 220V.

[Remolon]

Schematic posted on June 2010:

http://www.diyaudio.com/forums/solid-state/109618-krell-ksa-5-a-4.html

[kevin gilmore]

and that schematic is both incomplete and wrong

[jgazal]

(...)

 

I wonder if I release the liquid gold schematics if they would do the same thing

 

 

Even the Chinese have standards...

 

Hong-Kong may have higher standards.

 

Some Korean manufactures just throw away any failing pcb because SMD service is challenging for their affiliated electronic services.

 

That is easy to understand if your facility has automated routines and extremely low rate of failure.

 

I just wonder if such model is economically viable with manmade PCB's (which failure rate would one need to break even?).

[Remolon]

You are right. The bias adjustment is missed, as well as other controls and adjustments.

It is just a curiosity that shows the interest of people on this design.

[DefQon]

Do it.......

+1.

 

Would love to build me a Liquid Glass amplifier. 

Edited April 8, 2014 by DefQon

[ang728]

small question here .

 

Can I use 2n5565 to replace 2n5564 JFET?

[kevin gilmore]

I'm sure the 2n5565 will work. Some people are using lsk389

[jboehle]

Finally got my SumR transformer.  Any precautions powering up the new PSU to test?  Any problems testing it unloaded (not hooked up to the amp)?

[GrindingThud]

PSU works fine with nothing attached. If it is the old one with early board runs....make sure you have the grounding error fixed discussed earlier in the thread.

[jboehle]

I am using the newer one.  I have one of the older boards with the error but currently have no plans to build it.

 

PSU seems to be working great!  I am using BB OPA227 op-amps.  Measuring some temps around the board, the op-amps are the warmest at ~50C.  Probably a useless measurement since the PSU is not under any load right now.  The TO-3 cases are ~27C.  Going to let it run for a bit and check voltages again.  After about 5 minutes I had +23.12V, -22.94V on the outputs.  Using a SumR tx 50VA 2x27V secondaries.

 

EDIT: After running for a while longer, I saw +23.26V, -23.11V at the outputs.

[jboehle]

Trying to finish up my amp board.  Was doing a test fit of the heatsinks with the trimmer resistor between them and the Bourns ones that were spec'd earlier in the thread from Mouser are a little wider than the ones I've worked with before.  You can see in this pic, that on each side of the board, the side of the resistor is right up against and touching the side of one of the heatsinks.

 

http://imgur.com/s6EKcY4

 

Will that be a problem? 

[jboehle]

Okay, so I looked at the specs and it says the temp coefficient of the 3299W-1-501LF is 100ppm/C.  So that would mean that even if the heatsink (and thus the resistor) went from 22C (room temp) to 65C, the resistance would only increase by ~2.15 ohms.  Anything to worry about?

[spritzer]

The 3296 line would be a better fit in that spot.  We never do the BOM's so no control over them...

[kevin gilmore]

mine are right against the heatsink too. works fine.