Buzz/Hum from Audiosector LM3876 board itself - no buzz in speakers

dakku

Member
2013-10-30 5:05 pm
I have a distinct buzzing/hum from the actual amp board. Its like the hardware is making the buzz, but I do not hear it in the speakers, just directly from the amp..

For the starground I have joined the ground wires from the following to a single point (not connected to the chassis):

Mains Ground
PG1+ and PG- (rectifier)
Left amp OG
Right amp OG

Any ideas?
 
The concept:
DimbulbSketch.jpg

image by antiqueradio.org
The bulb is incandescent, both standard and halogen work, and 25W fridge bulbs and 40W clear oven bulbs remain widely available.
 
Last edited:
my 2 cents (of euro)...

... Its like the hardware is making the buzz... Any ideas?

Hi dakku... as you already disconnected the speakers... some ideas :

- transformer vibration (toroidal no tight enough, DC component on the 120 or 230VAC...) ?
- toroidal incorrectly mounted on metalic surface with metal screw creating a kind of secondary short-circuit ?
- defective chemical cap or cap enclosure in contact with a rigid structure ?
- inverted polarity or alternative current (bad diode) on cap...