mic Hum

[tINY]

Have you checked continuity on pins 1/3 of your mic cable?

If one or the other doesn't make connection, there could be hum.





-tINY

[piper]

The cable is good because if I switch out the 990 for a 603 (identical electronics) then the hum vanishes.

[Torea]

I had a hum problem when I did my first mods. Touched the body, went away, let go, big hum. Redid the joint between the black wire from the capsule and the board. Fixed it; I guess my previous soldering job had been shoddy.

[tINY]

OK, then the next thing to check is that both (+) and (-) are actually putting out a signal. If one side is shorted to ground, you'll get hum.

After that, check for grounding of the headbasket.



-tINY

[RickS]

Originally Posted by piper

I have an MXL 990 that hums. I have checked that there is continuity from pin 2 to the body, and there is, but I have no idea what to do next. What parts are most likely to cause hum?

Pin 2?
I'm a pin 1 kind of guy when it comes to ground.

[tINY]

Originally Posted by RickS

Pin 2?
I'm a pin 1 kind of guy when it comes to ground.

Yeah - kinda reflects my point on the grounded signal pin.

...then, some people see 100 ohms as "connection".



-tINY

[Haz-Mat-Strat]

Originally Posted by piper

I have an MXL 990 that hums. I have checked that there is continuity from pin 2 to the body, and there is, but I have no idea what to do next. What parts are most likely to cause hum?

Pin 2 should not have continuity with the body. If pin 2 is grounded that may be the issue. Trace the wires and check the voltages on pin wire 2 and 3 (at the circuit board) they should read around 48vdc. Pin 1 is ground = 0vdc

Make sure the body is screwed on tight. You can also sand the edge of the body to get a better connection.

.

[piper]

I think I meant pin 1. I'll check that and the other tips this weekend.