So I was adjusting my bias today and apparently I had shaky hands. The temps were around 44c and I wanted to bring them up to 50-52 which I did.
In the process of measuring, I touched the bottom lead of one of the resisters to a ground contact which made a nice spark. I have to say, it was a high quality spark. I used to weld so I was impressed. Part of the ground pad under a nut is MIA though.
After adjusting the bias and almost lighting the house on fire the amp sounds really nice!! It is amazing how durable these things are.
Should I have any concern now that I have done this?
This brings me to the DIY portion of this post. I meguivered these fancy screw drivers because the bias pots are hard to access. After some more research and development I realized that I should add an electrical insulator so I shrinkwrapped my creation.
The steel is very hard and brittle so I heated it until it was red hot with a torch and hammered the tip to a 90 degree angle with my hammer. I then ground the tip with my bench grinder to form a flat head screw driver tip. I may make some more at other angles. Took all of 10 minutes to do both. I may make some more.
I didn't know if anyone has made screw drivers like this for adjusting bias on these S series amps so I wanted to share.
In the process of measuring, I touched the bottom lead of one of the resisters to a ground contact which made a nice spark. I have to say, it was a high quality spark. I used to weld so I was impressed. Part of the ground pad under a nut is MIA though.
After adjusting the bias and almost lighting the house on fire the amp sounds really nice!! It is amazing how durable these things are.
Should I have any concern now that I have done this?
This brings me to the DIY portion of this post. I meguivered these fancy screw drivers because the bias pots are hard to access. After some more research and development I realized that I should add an electrical insulator so I shrinkwrapped my creation.
The steel is very hard and brittle so I heated it until it was red hot with a torch and hammered the tip to a 90 degree angle with my hammer. I then ground the tip with my bench grinder to form a flat head screw driver tip. I may make some more at other angles. Took all of 10 minutes to do both. I may make some more.
I didn't know if anyone has made screw drivers like this for adjusting bias on these S series amps so I wanted to share.
Last edited:
Quote--- " I touched the bottom lead of one of the resistors to a ground contact which made a nice spark " , have you checked the value of the resistor to see if its still the same ?
right-angle screwdrivers | McMaster-Carr
right-angle screwdrivers | McMaster-Carr
Quote--- " I touched the bottom lead of one of the resistors to a ground contact which made a nice spark " , have you checked the value of the resistor to see if its still the same ?
right-angle screwdrivers | McMaster-Carr
I will check the resister. Thanks for the suggestion.
I know about right angle screw drivers. I tried one that I have and it was to large to fit in that space also not long enough.
enthusiasm smileys
Is this the spot where you are supposed to measure the temperature? I am measuring it right on the head of the screw. I have heard multiple things all of which give a variety of different temperatures.
Last one I read was put your hands at the top of the heatsinks which is about a 7 degree Celsius difference. if that is the case, I really need to raise my bias quite a bit.
Thanks!
It scares the crap out of me when I do that. Or discharge a cap. Even small ones pack a nice spark and makes the wife check that my life insurance is paid up!
I agree. That is why I made the heat shrink screwdriver, that way I don't have to worry about it. I was good at doctor when I was a kit but many years have gone by...
Okay thanks. I figured out why the temp was so different. With my A/C on, one of the registers on the ceiling was blowing on the amp which accounted for the temp difference. Without that the temps are only about 1 degree different.
I plan on building one of your amps after I mow through some other projects that I am doing. Thank you for making all of this available to us.
I plan on building one of your amps after I mow through some other projects that I am doing. Thank you for making all of this available to us.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
- Home
- Amplifiers
- Pass Labs
- Threshold Adjusting Bias Touched Ground