Amp biasing again...

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germay0653

Re: Amp biasing again...
« Reply #80 on: 5 Feb 2018, 06:54 pm »
PM, with instructions, sent, daven3871.

Magnatest

Re: Amp biasing again...
« Reply #81 on: 15 Feb 2018, 11:08 am »
Hi Germay-

  Will you please send me the instructions for biasing Khartago monoblocks? Thank You.      -Gregg

goingsolo

  • Jr. Member
  • Posts: 25
Re: Amp biasing again...
« Reply #82 on: 15 Feb 2018, 11:18 am »
Hi Germay,

I would like to receive a copy for biasing a pair of Khartagos please.

Thanks.

tubesrule

Re: Amp biasing again...
« Reply #83 on: 21 Feb 2018, 02:27 am »
Could you email me too for Khartargo mono block bias
Thanks

germay0653

Re: Amp biasing again...
« Reply #84 on: 21 Feb 2018, 10:45 pm »
Here you go.  Of the two sets of instructions, the one that refers to From Klaus himself have given me the best results!

Instructions for biasing

The amplifier should be at operating temperature. If you've been playing music, wait perhaps 10-15 minutes for everything to "settle down".

The board is basically two channels, bridged into a monophonic amp, and essentially there are two "sides" to the board corresponding to the left and right channels in the stereo versions.

First check the output offset, which is the voltage between pads 6 (+) and 5 (-). The (+) wire going to the speaker cable terminal on the back of the amp is on pad 6. Set the DVM to 200 mV DC, put the positive lead of a DVM onto 6, negative lead onto 5, and adjust the trim pot way at the opposite end of the board (not the one in the middle) to zero out the offset. Don’t worry about small offsets, say 1 mV or less.

Repeat for the other channel, with the negative lead on pad 5, positive on 7.

Now, go back to the other side, negative lead on pad 5 or other convenient signal ground, and check TP 5 and 6 to see which one has the highest value (they will be slightly different). This time, use the trim pot in close to TP 6 to set the bias, using the TP point that had the higher voltage, to be about -21 mV. Repeat on the other side, checking TP 1 and 2, and use the trim pot near TP 2. Be careful not to short anything to the power transistor case which I think is grounded.

Then check the offset values again as they may have changed slightly, recheck the bias, etc.

The bias controls the "voicing" of the amp. -18 will be colder, -24 mV will be warmer. Klaus recommends -21 mV as a starting point.

Per Klaus himself:

Make sure that you have the red probe on the speaker out, and only use that part of the board for biasing,  as the board is true mirror image...then move the probe into the other post and bias that part of the board...for offset,  probe - goes to opening 7 or 8 (ground of the unused speaker outs on the board)...offset pots are the 2 close to the face plate,  get the offset close to 0 mV....then for the actual bias go only into TP's 3, 4, 7, and 8...ignore the others, and use the one on each side with the higher value....pots are next to the transistors.......20 mV's....again,  PLEASE  make sure that you move the red probe from side to side,  as the 2 sides of the board right through the middle act independently !!!!!!!!!!!!!!

walk away from it, come back after 10 minutes, check, and repeat if necessary until it is stabile........

khoadk2193

  • Jr. Member
  • Posts: 10
Re: Amp biasing again...
« Reply #85 on: 22 Feb 2018, 03:36 am »
I keep the (-) probe of my multi meter in the ground post and use the positive probe to check for TP 3,4,7 and 8. I got all of them around 21 mV DC. Am I doing this right?

germay0653

Re: Amp biasing again...
« Reply #86 on: 22 Feb 2018, 04:18 pm »
-, negative, -21mV

johnzm

Re: Amp biasing again...
« Reply #87 on: 28 May 2018, 05:14 pm »
Here you go.  Of the two sets of instructions, the one that refers to From Klaus himself have given me the best results!

Instructions for biasing

The amplifier should be at operating temperature. If you've been playing music, wait perhaps 10-15 minutes for everything to "settle down".

The board is basically two channels, bridged into a monophonic amp, and essentially there are two "sides" to the board corresponding to the left and right channels in the stereo versions.

First check the output offset, which is the voltage between pads 6 (+) and 5 (-). The (+) wire going to the speaker cable terminal on the back of the amp is on pad 6. Set the DVM to 200 mV DC, put the positive lead of a DVM onto 6, negative lead onto 5, and adjust the trim pot way at the opposite end of the board (not the one in the middle) to zero out the offset. Don’t worry about small offsets, say 1 mV or less.

Repeat for the other channel, with the negative lead on pad 5, positive on 7.

Now, go back to the other side, negative lead on pad 5 or other convenient signal ground, and check TP 5 and 6 to see which one has the highest value (they will be slightly different). This time, use the trim pot in close to TP 6 to set the bias, using the TP point that had the higher voltage, to be about -21 mV. Repeat on the other side, checking TP 1 and 2, and use the trim pot near TP 2. Be careful not to short anything to the power transistor case which I think is grounded.

Then check the offset values again as they may have changed slightly, recheck the bias, etc.

The bias controls the "voicing" of the amp. -18 will be colder, -24 mV will be warmer. Klaus recommends -21 mV as a starting point.

Per Klaus himself:

Make sure that you have the red probe on the speaker out, and only use that part of the board for biasing,  as the board is true mirror image...then move the probe into the other post and bias that part of the board...for offset,  probe - goes to opening 7 or 8 (ground of the unused speaker outs on the board)...offset pots are the 2 close to the face plate,  get the offset close to 0 mV....then for the actual bias go only into TP's 3, 4, 7, and 8...ignore the others, and use the one on each side with the higher value....pots are next to the transistors.......20 mV's....again,  PLEASE  make sure that you move the red probe from side to side,  as the 2 sides of the board right through the middle act independently !!!!!!!!!!!!!!

walk away from it, come back after 10 minutes, check, and repeat if necessary until it is stabile........

that last little bit was what i was missing.

since it looks like many have asked, and i finally have complete instructions, i built an image to help everyone out.
by the way, to adjust the offset it is much easier if you have a ground lead that you can clip into the board. you might want to pick one up before you start.




FullRangeMan

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Re: Amp biasing again...
« Reply #88 on: 28 May 2018, 05:28 pm »
Thanks John for taking time to post this image.

88man

  • Jr. Member
  • Posts: 36
Re: Amp biasing again...
« Reply #89 on: 4 Jul 2018, 02:23 pm »
How often should the Stratos amp be rebiased? I rebiased mine 2 years ago. The amp is getting real hot again, and the sound is becoming sibilant and bright. Dual Mono is a real pain as the 2 boards are stacked on top of each other and you have to lift up the board while you balance the probes on the bottom board.

Dishman442

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  • Posts: 26
Re: Amp biasing again...
« Reply #90 on: 7 Jul 2018, 09:22 am »
Could please send bias instructions for Khartago mono amps?  It doesn’t appear Klaus will be able to get to an upgrade any time soon so I want to tune them up. (Just bought them used)  They already have been upgraded once and have the newer board should that matter with biasing.

My email is jstclair442@msn.com

If someone could do a YouTube we would all be eternally grateful!!

Arcticdeth

  • Jr. Member
  • Posts: 233
Re: Amp biasing again...
« Reply #91 on: 5 Apr 2020, 08:56 pm »
Kismet pair.

Any more photos w step by step instructions. ..

Probst.

ServerAdmin

Re: Amp biasing again...
« Reply #92 on: 6 Apr 2020, 02:56 pm »
Arcticdeth, change your profile now please.

germay0653

Re: Amp biasing again...
« Reply #93 on: 7 Apr 2020, 05:37 pm »
Kismet pair.

Any more photos w step by step instructions. ..

Probst.

Instructions are the same for mono and stereo.  Mono bridges the L & R channels so you need to adjust both, regardless of configuration.

anirudh19oct

  • Newbie
  • Posts: 1
Re: Amp biasing again...
« Reply #94 on: 8 Sep 2020, 02:36 pm »
Need some help. Tried measuring the bias in between negative lead on 5 with positive lead on TP1, TP2 and TP5, TP6 on my newly acquired (used) Kratos. The value on the DVM set to 200mV reads somewhere in between -2 and -5 on both sides. Shouldn't it be around -18 to -23 as suggested? DC offset says around -3 to -5 when checked with the instructions above mentioned for both channels.

Looking for some advice on this.

SoCalWJS

Re: Amp biasing again...
« Reply #95 on: 9 Sep 2020, 10:43 pm »
Kismet pair.

Any more photos w step by step instructions. ..

Probst.
I should probably look into adjusting mine as well (Kismet in Khartago cases). Bought used and never checked.

But I’m a chicken  :green:. I’m afeared of zapping myself. Has anybody ever made a good tutorial (pictures, video) on this INCLUDING all of the things one need to do to avoid ZAPPING oneself? The above photos are helpful, but don’t have enough info for me to think about giving it a shot.

I’ve been “bitten” by electricity a few times and I want to avoid that having that experience again.

WarmColors

  • Jr. Member
  • Posts: 90
Re: Amp biasing again...
« Reply #96 on: 10 Sep 2020, 04:11 am »
I should probably look into adjusting mine as well (Kismet in Khartago cases). Bought used and never checked.

But I’m a chicken  :green:. I’m afeared of zapping myself. Has anybody ever made a good tutorial (pictures, video) on this INCLUDING all of the things one need to do to avoid ZAPPING oneself? The above photos are helpful, but don’t have enough info for me to think about giving it a shot.

I’ve been “bitten” by electricity a few times and I want to avoid that having that experience again.

I've been "bitten" by electricity once and it wasn't fun at all!!!!
Lately I have been getting shocked due to static electricity it's really annoying me. I need to buy those bracelets that remove the static.

arfan

  • Jr. Member
  • Posts: 10
Re: Amp biasing again...
« Reply #97 on: 18 Oct 2020, 04:36 pm »
Hopefully I'm not beating a dead dead horse on this topic, however, I haven't read a response on biasing a stereo Odyssey amp and measuring neg. values on TP1&2 and positive values on TP3&4. The same on the other side for TP5/6 and TP7/8. It appears that Klaus uses TP3/4, and TP7/8 points and indicates a positive 20 mv. I'm understanding that most use  TP1/2 -TP5/6 and adjusting to the neg. voltage. Has anyone had experience using the positive readings on the TP3/4 and TP7/8 points. I understand that the procedure is for monos, but should apply for stereo amp.

tripwire1964 in a old previous response has asked the same question on a mono amp, I'm biasing a stereo amp to a new house and voltage.

klaus@odyssey

Re: Amp biasing again...
« Reply #98 on: 18 Oct 2020, 05:30 pm »
Plus,  minus...doesn't make a difference,  changes when you change probes....it is essentially the same with stereo amps on the bias,  just the offset is different in that you use the 2 binding posts on each side....







AGAIN,  AND AGAIN,  AND AGAIN  !!!!!!!!!!!!!!!!

Guys,  I don't have a problem with you optimizing the amps,  that's why I have the info out there....however,  please don't go completely neurotic like some have,  and ALWAYS  make sure that you use the left and right part of the boards and the CORRESPONDING  binding posts,  or otherwise pop goes the weasel.