Krell KSA 100mkII Clone - Page 235 - diyAudio
Go Back   Home > Forums > Amplifiers > Solid State

Solid State Talk all about solid state amplification.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 4th June 2009, 09:32 PM   #2341
Fix is offline Fix  Sweden
diyAudio Member
 
Join Date: Feb 2008
After some problems... and smoke...

I've monted one channel in the chassi.
And everything is working Perfect...

I've been playing music on One channel for 3h now...

One funny thing, or shall we say HiFi thing..
Is that you can't listen on MP3 in bad quality anymore...
IT SOUNDS CRAP... I thought there were a problem with the amplifier...

Soon as I played a normal CD it sounds great...

So the details is great..
I've never heard it so clear before as now.

There is NO Way I can stand listen to those MP3's again.. :-)

Will mount the other channel next days...
  Reply With Quote
Old 4th June 2009, 09:41 PM   #2342
Fix is offline Fix  Sweden
diyAudio Member
 
Join Date: Feb 2008
There are some questions I have,


When setting bias:

What is the correct way ?
No signal and no speaker ?


When setting DC offset:
It's no problem to get 0mv...
But If I measure are other side on the pcb board I then get ~20mv...

Shall I set DC so I get same reading on both sides ?


Bias:
When starting up the bias will first go up, and after 5-10 min it will come down again.. Guess this is normal.

I also should wait 1-2h before setting the final bias...
This is what I did...

But now I've been playing 3h and the bias is comming down... 1mv a time..

I set the bias at: 625mv... then it goes upp to ~660... then back down to ~625... but after 3h, it's down to 599mv...

Shall I wait longer before setting the bias ?!

Guess this is the last things I need to know to get everything perfect...
  Reply With Quote
Old 5th June 2009, 10:13 AM   #2343
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
The small changes in bias are of no consequence.
Big changes that keep moving in the same direction are of much more concern. It could indicate that the thermal stability of the output stage is suspect.
You have no concern here, the readings look fine.

Set the bias and the offset with the input shorted and the output with no external load.
Check the offset does not change when you connect your source in lieu of the input shorting link. If it changes significantly then a redesign is in order.

I found the circuit is very sensitive to the addition of tiny caps on the output terminals. Adding 100nF instantly blew both F5A supply fuses.
The only way to solve this was to increase the Cdom value. Then it sounded terrible, no detail, no sparkle, =not acceptable. I have been waiting almost two years for someone to catch up and assemble another Klone in the hope they can find me a solution. In the meantime my mono is sitting in the corner of the workshop.
__________________
regards Andrew T.
  Reply With Quote
Old 5th June 2009, 11:35 AM   #2344
Fix is offline Fix  Sweden
diyAudio Member
 
Join Date: Feb 2008
Quote:
I found the circuit is very sensitive to the addition of tiny caps on the output terminals.
Sensitive to what ?
Damage to caps when connecting speaker ?


- - -

About Bias..

Yesterday I found out that after 4h the bias got stable, +/- 2-3mv
Guess it need 3-4h before getting real stable :-)

Quote:
Set the bias and the offset with the input shorted and the output with no external load.
OK... But where on the cirrcuit shall I measure...

DC Offset: Signal In (shorted) and depending on where on my design I measure, ( Can measure on 4 TP's I get different readings... ) On Output NPN/PNP side...

I've measured on all points and have now set it to 10mv.

If I set it to 0mv on Output on PNP side, same side where I have my cable to the Outputterminal I get ~25mv on the other NPN side...

Will check if the DC Changes when connecting source.


BIAS:

I've measured on each emittor resistor for similar readings.

Approx: .625, .630. .650 .630
I used resistor where speakar cable is connected as reference on both channels.

Will post pictures if needed....

More pictures will come tonight on rest...
  Reply With Quote
Old 5th June 2009, 12:29 PM   #2345
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Quote:
Originally posted by Fix


Sensitive to what ?
Damage to caps when connecting speaker ?
adding a small value capacitor to the speaker output terminal blew the PSU fuses when the amp is idling with no input signal and the standard Cdom is fitted.
Quote:
Originally posted by Fix

OK... But where on the cirrcuit shall I measure...

DC Offset: Signal In (shorted) and depending on where on my design I measure, ( Can measure on 4 TP's I get different readings... ) On Output NPN/PNP side...
measure output offset at the speaker output terminal.
There can be only one speaker output terminal on a monoblock amplifier, not four.
__________________
regards Andrew T.
  Reply With Quote
Old 5th June 2009, 12:57 PM   #2346
Fix is offline Fix  Sweden
diyAudio Member
 
Join Date: Feb 2008
Quote:
quote: Originally posted by Fix Sensitive to what ? Damage to caps when connecting speaker ? adding a small value capacitor to the speaker output terminal blew the PSU fuses when the amp is idling with no input signal and the standard Cdom is fitted.

Strange... I have added a Resistor + Cap as shown in the schematic without any problems at all. ( See pictures few post down... )
I pretty sure that I've started the amp serveral times without any signal / speaker also without any cables at all.
Also I've been connecting Signal cables + speaker without turning off the amp...
I had a problem before where the amp did blow the fuse, soon as I connected signalcable or my oscilioscope..
Problem was that I have a shortage between the Neg - Voltage and Ground... and after 2-3 fuses my 10ohm resistor to ground blew..
Then it did work... :-)

I've fixed that right now, and found out that the 10ohm ground resisitor were bad...
Maybe the Resistor/cap on speaker terminal also burnt ???
Havn't checked that, will do that tonight...

Else I can find any problems...

- - -

Quote:
measure output offset at the speaker output terminal. There can be only one speaker output terminal on a monoblock amplifier, not four.
Look at post 2313..

Orange cable is Output..
Same on other side..

Yes I have 1 cable as output... but if I measure front and back on that side I get different readings..

Totalt 4 TP's ...

I can get 0mv on one side, and 22mv on the other side.
I've set DC to 10mv, then I have 10mv on each TP.

Quote:
standard Cdom is fitted.
What is Cdom
  Reply With Quote
Old 5th June 2009, 01:11 PM   #2347
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
a series pair of resistor+ cap is the output Zobel.

Add a capacitor (alone) across the output terminals, i.e. speaker output to audio ground. Try different values from 100pF to 1uF.
I could get away with 68nF, but the scope showed a very significant change in the wave shape. 100nF blew the fuses.

If I excluded the output transistors from the feedback loop. i.e. feedback from drivers only, the circuit is much more tolerant of output loading variations.

Which pic in post 2313?

Cdom (dominant pole capacitor) is the base to collector capacitor, sometimes referred to as Miller compensation capacitor, that tunes the HF response and thus stability of the VAS stage.
__________________
regards Andrew T.
  Reply With Quote
Old 5th June 2009, 02:14 PM   #2348
Fix is offline Fix  Sweden
diyAudio Member
 
Join Date: Feb 2008
Quote:
Add a capacitor (alone) across the output terminals, i.e. speaker output to audio ground. Try different values from 100pF to 1uF. I could get away with 68nF, but the scope showed a very significant change in the wave shape. 100nF blew the fuses.
Is it needed ?
Will sound be better or protection....

I've tried to drive my test loudspeaker 4ohm, into 4hz without any problem.. The emittor voltage (Bias) went crazy 350mv-750mv (625mv normal..) Looked funny on the speaker...

And my DC Sence PCB didn't brake so I guess there were no problem..


About the cap you talk about, is it used in the original design ?


Shall I remove the Zobel Filter, and add Cap instead ?

- - -

The two last pictures you can see the Orange cable (Output)
It's connected from Front - Back PNP side.. and on NPN side the same.

The Output is connected on both sides...
Depending were I measure I get different readings..

DC Offset: If I measure signal-in to output PNP side, Front I can get 0mv, if I change to back or the NPN side I get 20mv..

I have connected a Speaker cable as shown on the original PNP side...
  Reply With Quote
Old 5th June 2009, 07:06 PM   #2349
first is offline first  China
diyAudio Member
 
Join Date: Nov 2006
Where I can got the PCB.
  Reply With Quote
Old 5th June 2009, 08:52 PM   #2350
Fix is offline Fix  Sweden
diyAudio Member
 
Join Date: Feb 2008
After many many hours of tears, blood and guts... and some smoke...
There is light in the end of the tunnel.

Another Krell KSA-100 Clone is born.

Been playing for the last 3h with both channels everything mounted in the case.

Before testing the amp with my Infinity IRS Sigma speaker I will test the amp ten more hours so everything holds up.

Some fun facts:

Total weight 37kg
Power consumtion: 550-580w @ 2.49-2.69 Amp / 230V
Bias: ~625mv ( depending on outside temp )

And here is another batch of pictures...


First channel mounted... Lots of space left...
Click the image to open in full size.

Click the image to open in full size.

Other channel on it's way...
Click the image to open in full size.

Both channels in place..
Click the image to open in full size.

Click the image to open in full size.

Click the image to open in full size.


Many thanks to all here at the forum for all help.
I will try to write down everything I've discovered when building the Krell Clone.. So others can start building..
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off



New To Site? Need Help?

All times are GMT. The time now is 08:39 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2