Anyone Know How to do Baising?

[rick_bravotino]

When we said DC Offset near Zero means: 0.0xxmV

5mV to 8mV is not near zero for DC offset.

Best reading should be 0.0xxmV. (not all amp can be adjusted to this reading, depending type of Trim Plot used in the design. But U can change the Trim Plot to hi-end type for more precise adjustment)

I just learn this from internet research website and Krell Technician. Meanwhile, busy changing parts and servicing the monster power amp...

 

[kptseng]

Hi Rick,

I'm from Singapore too.
I have recently tried to adjust the bias and the transistor runs very hot after the adjustment, any improvement? Not really. I adjusted them back to original state.

I suggest you leave them alone if you are not familiar, or send back to agent for servicing.
Krell should be using quality parts (for that price) and I don't think the bias will drift easily, hence I don't see a need to adjust. If the unit is giving you problem then better to send for servicing.

There is an article in tnt-audio on this topic
http://www.tnt-audio.com/clinica/bias_e.html

KP

 

[audioholik]

70mV of output offset drift with temp and operational conditions is far too high.
What's causing this?
10mV is probably a drift target to aim for from cold start to fully warm and after heavy use.

I set the offset either side of zero. But I generally set the warm offset slightly closer to zero than the start up offset since the first few seconds/minutes is less important in the big picture.

The symasym has about 2mV of drift and after warm up it stays within +-0.5mV offset, always.

hold on, ill try to measure again..
its aleph X clone from Pass Labs (thx to papa)

right now it like dont have enough power to drive proac 2.5 clone (arround 87Db sens) dan also bass are to weak..

from cold start absolute DC offset are arround 1.8V for both side.. after 15mnt they keep decreasing now i measure about 250mV and keep decreasing..

differential offset are about 10-30mv

if u need something like schematic i can attach the picture

thank you 🙂

 

[rick_bravotino]

Hi KP,

Thanks for the reply.

Actually this old amp is about 15yrs old. There is a need to change all Cap and restore to its Original Condition. Last yr, I send for servicing and part replacment to so called "Senior Tech - part time" working for Krexxxx Dealer.

The Cap replaced is Panasonic. I found the sound stage is rough and somehow not up to standard. So I do some research and oso learn some skill from that "senior tech".

To my surprised, two cap is missing in right driver board and the rest of Cap did not changed.

Now, I remove all Cap and change with hi-end Cap.

To be continue... 🙂

[/IMG]
Before

[/IMG]
After - U can see the Cap Size! I have replaced with higher Quality Cap mostly made in Germany, France and UK.

If you do not changed any Electronic Componet, Biasing can only improve alittle effect. However, if you have changed entire componet, Bias and DC offset is a must. This will greatly improve the sound quality. I am oso online communicating with Krell Dealer to get the Service Manual and advice 🙂

 

[rick_bravotino]

Higher Bias or Hottest does not mean good sound stage.

You have to Bias to the require level. Service Manual will tell you that. Different design circuit have different Bias Point.

KSA200 Bias Point is about 400mV. That the design for it.

Cheers 🙂

 

[jan.didden]

When we said DC Offset near Zero means: 0.0xxmV

5mV to 8mV is not near zero for DC offset.

Best reading should be 0.0xxmV. (not all amp can be adjusted to this reading, depending type of Trim Plot used in the design. But U can change the Trim Plot to hi-end type for more precise adjustment)

I just learn this from internet research website and Krell Technician. Meanwhile, busy changing parts and servicing the monster power amp...

In practise, with whatever high-end trimpot you can find, you will see that the value is 0.0xxV. A factor of 1000 higher.

Jan Didden