After several years I have finally finnished my Double LA2A with Silent:arts pcb! Had a hum-problem and found a solution I want to share. When I had adjusted the unit and a repared a fault caused by a wrong resistor I tested with a mic and headphones in my studio. The unit sounded very good but there was an audible hum regardless of the position of the gain-pots in both channels. I tried to remove the on/off (230 volt) switch from the front but no difference. I found that the houses of the four pots on the front panel did not have contact with earth because of the laquer on the inside of the front-panel. Removed some laquer with my Dremel but same hum. I started to suspect the problem could have to do with the AC 6,3 volt glowingvoltage. Did of course use the twisted cable on the underside as showed in several pictures. Everything measured ok, earth was "in the middle"caused by the 100 ohm resistors. I have seen quite a feew guitar-amps using DC-glowing in the preamp-section to reduce hum and wanted a try. I first tried with one channel. Thought I should try with a regulator, but found that the DC-voltage was so low that there was no need. The rectified DC with a 10.000uF capasitor gave 6.3 volt DC with 300mV ripple. And guess what - No hum at all on both channels!!! Will leave it on for some days to see if new problems arise but do really look forward to record acoustic guitar with this unit and my newbuild Equinox/U47/MK47 mics!!!
Finished D-LA2A!
- Thread starter VanGenz
- Start date
