MKS-70 with 60 Hz Hum - Fixed!

Post by **synthRodriguez** » Sun Nov 23, 2014 1:01 am

Bought a MKS-70 from a first-owner, nice shape. Problem upon arrival (there's always one) was a 60 cycle hum on all the outputs. Pretty bad at unity gain; definitely unacceptable. Power input for the mains is the older two-pin Roland setup, no ground. Since I already had all the parts, recapped the power supply, no real improvement.

Symptom was: amount of hum didn't change with raising or lowering volume, just always there. Ok, it's not in the audio boards, it's actually sitting on top of it all. That sounds like induced hum, not a ground loop. Started shoving wires around and could hear a change. With a good look could see all the low voltage wires running next to the transformer.

Did a quick re-routing of wires got some good improvement. Did a full-up re routing of everything keeping all wires as far away from the transformer and 120 VAC lines as possible. Plugged it in and no hum at all, even with everything cranked waaay up past unity gain. Sweet.

Looks like the factory routing sucked. The s/n is 720561 and had a V.1.03 rom installed (now updated). Moral is, if you have hum in your MKS-70, take a look at the wiring. Easy fix.