Yamaha M-4 | Bias Calibration do not last

[Cergei]

Hello !
I noticed that my M4 Bias current needs to be re-calibrated somehow “often”.
All electrolytic capacitors were replaced recently.
Any idea ?
Thanks

 

[bberkom]

How long do you let it warm up after turn on before setting the bias?

 

[avionic]

Bias will drift as unit heats and cools...

 

[Cergei]

How long do you let it warm up after turn on before setting the bias?

I did not pay much attention to the warm up time. How long should I wait? Thanks

 

[Cergei]

Bias will drift as unit heats and cools...

Thank you

 

[avionic]

New bias trimmers may help. But it is still going to drift up and down.

 

[avionic]

I did not pay much attention to the warm up time. How long should I wait? Thanks

15-30 min.for temps to stabilize.

 

[Cergei]

New bias trimmers may help. But it is still going to drift up and down.

probably will be a good idea to replace those, after 40 years…

 

[Cergei]

New bias trimmers may help. But it is still going to drift up and down.

I am thinking to replace the original trimmers by these that the screw goes 25 turns
https://www.digikey.ca/en/datasheets/bourns-inc-3296

What do you think ? Thanks

 

[avionic]

3296P .....

 

[Cergei]

Correct !
I will replace the three of them. Is 0.5 Watt enough ?
5K for the Bias
100 Ω for DC offset
and Digikey Canada does not have in stock the 2.2 KΩ for the +/– 65V adjustment
Will still just 2KΩ be Okay ?

 

[avionic]

Will still just 2KΩ be Okay ?

Probably be close enough.