Harmon Kardon Audio Players & Recorders - Recent Questions, Troubleshooting & Support
Realistic equalizer hum
I've got this equalizer with another product. Testing it revealed there was a hum noise. Investigating the root cause I found on internet that it was related to the power supply transformer. Trying to fix it I burned the primary winding of the transformer. I fixed it this way:
1. I was unable to find an equivalent transformer. Looking at the schematic, original had one primary but two secondaries, but voltages were not there. On the internet I found the values. My solution was to install two transformers on the equalizer. One of them 24V (12-012) and the other 12V (6-0-6). The center tap on the 12V is not used.
2. The main caps on the power supply were not good (470 & 330 uF). I changed them.
After that, hum was reduced considerably. I also added a ground look isolator between the equalizer and the amplifier and now it sounds very good.
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