Hybrid Offset Issue

[king30]

I have built Joe's hybrid http://www.diyaudio.com/forums/showthread.php?s=&postid=164935 and have fixed the hum and buzzing issues, but my dc offset is giving me some concern. When I initially power up the amp the offset goes to about -35v. Once the amp warms up (about a minute) the offset lowers to about 50mv. Well actually it fluctuates between 20mv-100mv.

I am using two 1k Panasonic FC caps for each chip. Both chips are being driven from a single toroid (dual 25v secondaries and two bridges). The bridges are connected to form a single +/-/gnd connection for both chips.

Any ideas on how to tame would be appreciated.

Thanks...Lee

 

[Nuuk]

I can only guess but I would suspect a poor connection somewhere in the power supply.

I presume that you are using a transformer with 24/25 volt secondary windings.

 

[moamps]

issues, but my dc offset is giving me some concern. When I initially power up the amp the offset goes to about -35v. Once the amp warms up (about a minute) the offset lowers to about 50mv. Well actually it fluctuates between 20mv-100mv.

Hi,

please read the last part of my post (100)
at http://www.diyaudio.com/forums/showthread.php?s=&threadid=9557&perpage=15&pagenumber=7

Regards

 

[king30]

Moamps,
Thanks for the tip. I will try a relay in my circuit. Another thing that occurs once the amp is stable is that the cones on the drivers will move in and out when I change volume. Probably due to dc on the output. Any tips for this issue?


Thanks...Lee

 

[moamps]

Another thing that occurs once the amp is stable is that the cones on the drivers will move in and out when I change volume. Probably due to dc on the output.

Hi,

Check DC offset on input connector (DC from source).
Must be zero.

Regards

 

[king30]

Moamps,


With nothing plugged into the amp (speakers ,source) I get 0mv on the right and 8.42v!!! on the left. With the source plugged in that goes down to .2mv.

 

[moamps]

With nothing plugged into the amp (speakers ,source) I get 0mv on the right and 8.42v!!! on the left. With the source plugged in that goes down to .2mv.

Hi,

something is wrong in left channel. Check it. If you haven't pot in buffer input place high resistance resistor (100k to 1M) between grid and ground.

Regards