"Mysterious" wire in Krell KSA-50MkII - Page 2 - 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 21st July 2014, 05:09 PM   #11
rayma is offline rayma  United States
diyAudio Member
 
Join Date: Apr 2011
Location: Upper midwest
As an example, Nelson Pass sometimes solders an extra resistor onto the emitter resistors to trim the value in some of his amps to adjust the AC balance. Such fixes are not uncommon in production where the design is frozen.
  Reply With Quote
Old 21st July 2014, 05:43 PM   #12
diyAudio Member
 
LineSource's Avatar
 
Join Date: Sep 2003
Location: SiliconValley
LOOKS LIKE:

1) The output transistors for the KSA50 are located on a physically separate fan cooled heatsink, such that the global negative feedback from the output at the speaker terminal requires a wire to make connection to the differential amp negative input on the physically separate main PCB. You must have this wire on both channels. R8 is the out-to-in global negative feedback resistor.

2) The ratio of R8 / R9 in your schematic sets the amplifier gain.

3) The adjustment Pot1 (R3-R4-Pot1-R6-R5) at the top of your schematic is used at the factory to null out any "native" amplifier DC offset.

4) C3 C4 C5 in your schematic are there to remove additional DC offset that might get generated from you PreAmp.

5) I expect Krell put any speaker fuse or speaker protection relay after this wire connection from "output" on your schematic to final the chassis speaker output terminal. You never want to break the global feedback connection. (output-R8 -diff_pair)
  Reply With Quote
Old 21st July 2014, 06:03 PM   #13
rayma is offline rayma  United States
diyAudio Member
 
Join Date: Apr 2011
Location: Upper midwest
Yes, that seems correct, but then where is the NFB resistor for the other channel?
  Reply With Quote
Old 21st July 2014, 06:05 PM   #14
diyAudio Member
 
Join Date: Nov 2010
That's the mystery

I looked at the other PCB and there are no signs of soldering on that point.
  Reply With Quote
Old 21st July 2014, 06:40 PM   #15
rayma is offline rayma  United States
diyAudio Member
 
Join Date: Apr 2011
Location: Upper midwest
If there are no signs of tampering or desoldering, this could be a factory error, omitting the NFB resistor. Hard to believe, though.
  Reply With Quote
Old 21st July 2014, 06:42 PM   #16
diyAudio Member
 
Join Date: Nov 2010
I don't think it's an error, I saw pictures of different KSA50MK2 and the all have that wire on only one channel.
  Reply With Quote
Old 21st July 2014, 06:52 PM   #17
rayma is offline rayma  United States
diyAudio Member
 
Join Date: Apr 2011
Location: Upper midwest
Very interesting. I think that only Dan D. can explain this. Must be some kind of start up thing.
  Reply With Quote
Old 21st July 2014, 09:03 PM   #18
diyAudio Member
 
LineSource's Avatar
 
Join Date: Sep 2003
Location: SiliconValley
Quote:
Originally Posted by rayma View Post
where is the NFB resistor for the other channel?

PERHAPS, the physical mechanical design is NOT stereo symmetrical.

One pair of output transistors on the shared fan cooled heatsink is close enough to the driver circuit PCB to require just a short jumper, and the R8 NFB resistor connects to this short wire on the circuit PCB for that channel.

One pair of output transistors is on the other side of the shared fan cooled heatsink and requires the longer yellow wire to connect the output with R8 to the negative diff-input. The design engineer might have found that it is superior to put the R8 NFB resistor close to the output transistors to immediately attenuate the feedback signal, and thus allow the yellow wire to just carry a low voltage, low current signal.


PERHAPS, some idiot snapped the yellow wire under the fuse so it would not jiggle.

I own two Krell KSA250 rev2 amps. After re-cap'ing both I like to call Krell mechanical design "idiot-savant engineering" In the KSA250, 0.4" high metal screw spacers are used to stack the driver PCB on top of the output PCB. The output feedback signal travels through a screw+metal_standoff between the two PCBs. The shortest path, but a cheap mechanical connection. "idiot-savant engineering"
  Reply With Quote
Old 21st July 2014, 09:25 PM   #19
SonyFan is offline SonyFan  United States
diyAudio Member
 
SonyFan's Avatar
 
Join Date: Jul 2014
Location: Sunny South Florida
The engineering in high end pieces is usually more questionable than it is in mass market gear.
__________________
"You lose, Rickles!" - Jim Lahey
  Reply With Quote
Old 22nd July 2014, 11:49 PM   #20
diyAudio Member
 
LineSource's Avatar
 
Join Date: Sep 2003
Location: SiliconValley
This Sunday I went to Church and prayed upon your yellow wire.
God told me that Satan is in that yellow wire!
If you fall to temptation and turn the rear switch, Satan will destroy your speakers!!

If you want your speakers free from Satan, you must perform an Exorcism and remove the yellow wire and restore both channels to the standard wiring+feedback. Never touch Satan's switch!!
Can I get an AMEN!



I have seen several Krell KSA50 and KSA100 amps. None had your rear "switch". Your pictures do not show enough details around the switch to trace the circuit.

PERHAPS: A past owner added this switch with the yellow wire and another feedback resistor as a way of setting two different amplifier gains .... two different R8/R9 ratios. i.e. for ONE CHANNEL the switch selects between (a) one resistor = R8; or (b) two resistors in series(or parallel) = R8. This would allow passive Xover circuit bi-amping with different gain for the woofer than for the mid-tweet.
  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


Similar Threads
Thread Thread Starter Forum Replies Last Post
"WTB" "The Wire AMP" Class A/AB Power Amplifier based on the LME49830 with Lateral enantra Swap Meet 3 23rd December 2012 06:36 PM
Building "The Wire AMP" Class A/AB Power Amplifier" wirewiggler Solid State 12 23rd September 2012 03:40 PM
Krell S300i Integrated Amp "Made in China" which Factory? tiefbassuebertr Solid State 10 29th October 2011 09:17 AM
Need help to build "Krell KSA-50" space2000 Solid State 12 7th August 2008 01:53 PM
Any thoughts on these mysterious OEM 8" woofers? Spasticteapot Subwoofers 4 21st January 2007 12:25 AM


New To Site? Need Help?

All times are GMT. The time now is 06:10 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