krell ksa5 klone

[GrindingThud]

I can shrink em and just upload here.....fixed.

Got the PSU up and running after some minor troubleshooting. The big caps I used were snap ins and the hole in the PCB was a hair tight. When I opened the holes up a little to fit them, I inadvertently removed the through plating, leaving them ungrounded (doh).

...now on to finish the amp

Edited December 15, 2013 by GrindingThud

[GrindingThud]

I'm getting close to the point where I'm able to power up the amp. I've got the trim pots set in the middle (250Ohmz).....any idea how close centered is to the desired bias point? I'm assuming 125mv cold is across the 2ohm output resistor test points.

Btw there is an ebay unit up for sale again....2999..

ok, so the krell documentation is a little questionable, but when they measure the bias they

do it from emitter to emitter. so the number is twice as big as the two test points I put on the board.

 

specifically its 250 millivolts emitter to emitter cold, and 180 to 200mv hot.

 

so at the two test points provided its 125 millivolts emitter to output no load cold a,d 90 to 100 millivolts hot.

 

which sounds about right.

[fishski13]

I'm getting close to the point where I'm able to power up the amp. I've got the trim pots set in the middle (250Ohmz).....any idea how close centered is to the desired bias point? I'm assuming 125mv cold is across the 2ohm output resistor test points.

Btw there is an ebay unit up for sale again....2999..

 

 

you could take the trimpots down a bit more, counterclockwise a few more turns, assuming you have them soldered in correctly.  i started half way and measured about 350mV across the 2R emitter resistors.

Edited December 17, 2013 by fishski13

[GrindingThud]

• oo, thanks!  exactly what I was looking for. 

   

  you could take the trimpots down a bit more, counterclockwise a few more turns, assuming you have them soldered in correctly.  i started half way and measured about 350mV across the 2R emitter resistors.

   

Edited December 17, 2013 by GrindingThud

[GrindingThud]

Did a trial power up this evening....no smoke. Test points measured in high like you said. Took about 5 turns to level it out to .125

Did not get to listen to it yet.....the audio inputs, volume, and outputs are not wired.

Edited December 19, 2013 by GrindingThud

[GrindingThud]

Ummmm, WoW, and that's an understatement. Thank you to all involved with this project. This is just an absolutely crazy good sounding amp. I'm not done putting together all the packaging and grounds but just had to jack into it with some ad-hoc jumpers.

Outstanding!

Edited December 20, 2013 by GrindingThud

[fishski13]

congrats!

 

i tried the Alps, TKD and GoldPoint in this amp.  my favorite was the GP, but i could live with the Alps. 

 

yes, a big thanks to KG, Bigir, and Lil Knight for making this project possible!

[GrindingThud]

How immune do we think the design is to TRS jack shorting? I plan to depower when jacking, but just in case....

[nopants]

powering down before jacking? I power up when jacking off so I don't know what you're talking about

[GrindingThud]

[spritzer]

It can handle the short circuit for  brief moment just fine.  The Krell amps all shipped with TRS sockets...

[GrindingThud]

Thanks, I figured as much, especially with the servo....but I thought I'd check.

It can handle the short circuit for  brief moment just fine.  The Krell amps all shipped with TRS sockets...

[GrindingThud]

Here's another one with some measurements:

http://translate.google.com/translate?sl=auto&tl=en&u=http%3A//bbs.hifidiy.net/thread-866039-1-1.html

someone over at a Chinese DIY site has a working KSA5 clone based on the schematic Kevin posted.

He used his own boards, replaced mpsa06/mpsa56 with BC546/BC556, and changed the cap values a bit.

He seems to like the sound (obviously.) Right now.. he is playing with different caps.

 

Here is the link.

[fishski13]

most awesomest translation.

[GrindingThud]

Ok, I have a chassis ground question. In a two chassis build, with the power supply and transformer in one chassis, and the amp in another, what is the best ground scheme? I mimicked what was done in the β22, and tied the PS chassis to IEC earth ground. Took +V, C, -V and carried through the umbilical directly to the amp board. Shielded RCA inputs float through the volume pot to the amp board inputs. I tied the amp chassis to Common at the entry....I also tried doing it at the RCA jack, but things seem quieter tied to common. I noticed this resistor jumper I circled in this KSA5 photo.....thoughts on doing it this way vs tying other things to chassis?

Edited January 4, 2014 by GrindingThud

[kevin gilmore]

on the original power supply chassis ground connects to iec ground, but not to power supply output ground.

[GrindingThud]

Cool, thanks. That's where I ended up this afternoon.

My 1st iteration I had them tied, which was not good when I attached other components to the line level chain.....still wondering about that resistor on the amp side....10ohm? I have mine straight jumpered right now.

on the original power supply chassis ground connects to iec ground, but not to power supply output ground.

Edited January 4, 2014 by GrindingThud

[GrindingThud]

Finally hot a chance to bring this to a meet. Seemed to be received very well and got a lot of good comments on power/transparency. Was able to hear it with the LCD-2 and LCD-X...pretty satisfying to hear it drive the LCD-2 so well.

[nopants]

had the chance to listen to this recently on some hd800s. I prefer it to the beta 22

[jose]

For the LCD2 don't is a bad amp, but I prefer use it with Monitor 10 or the HD6X0, DT990, DT880...

 

IMHO, the Beta 22 or Dynahi balanced is best option for the LCD2.

[zorning]

Here's another one with some measurements:

http://translate.google.com/translate?sl=auto&tl=en&u=http%3A//bbs.hifidiy.net/thread-866039-1-1.html

 

lol, i posted that thread, and you found it! 

the blue pcb I used almost has the same layout as KG's layout, only use different protection circuit. 

and my power supply is based on lm723/mc1723.

[GrindingThud]

I see you're in Baltimore. I'm in Leonardtown. You should bring your amp to the next MD/VA/DC meet over in VA next time they schedule one. It would be fun to have them side by side.

lol, i posted that thread, and you found it!

the blue pcb I used almost has the same layout as KG's layout, only use different protection circuit.

and my power supply is based on lm723/mc1723.

Edited February 23, 2014 by GrindingThud

[jboehle]

Are there still boards for this available?

[spritzer]

You can just order some for yourself.  I have plenty of the older style PSU boards for sale though.   

[jboehle]

I got a set of boards (amp + new & old PSU) from a member that decided not to build theirs.

 

Ouch, the shipping for 2x LSK389 from Trendsetter is more than the chips themselves.

 

Was the "new" power supply used with the real KSA5 as well or was it used for some other Krell product?

 

Is it worth ordering extra transistors for matching or not?  I see earlier in the thread that not much luck was being had in matching.