M 1202 VLZ Mystery

[jetgraphics]

Greetings.
My problem is somewhat complex. I decided to set up an AV studio with my computer.
I resurrected my "old" MZ1202 VLZ mixer (1990s vintage), mics, etc, and noticed several issues with my equipment.

[] Persistent hum (which could be attributed to large amount of computer hardware in close proximity, or the lighting)
[] Bizarre response from Audio Technica ST90 (not MKII) dynamic microphones (hardly any bass response - from both mics)
[] Normal response from a guitar synth plugged into a stereo input
[] Normal response from a guitar plugged into one of the single channel inputs
[] Normal response from a webcam mounted condenser microphone via USB input (not connected to Mackie - a "control" reference)

Can dynamic microphones "go bad" with age?
Can a balanced microphone pre-amp work fine with unbalanced input but exhibit high pass behavior otherwise?

I double checked the output using a software spectrum analyzer which confirmed the spectrum was way off on the dynamic microphones.

Any suggestions ?

[Greg C.]

While it's possible for a dynamic mic to go bad from age, it's unlikely. I think it's more than likely it's just a terrible sounding mic. Specs list the MKII version as having a low frequency response down to 100Hz which is pretty poor. Find or borrow an SM58 and compare. If that sounds off, could be a mixer issue. As for the hum, it could be a ground loop or a board problem. Quickest way to found out if it's the board is to unplug everything except for power and plug in some headphones. If you have a buzz then, the board is faulty. FWIW, I find that Mackie mixers don't age well. And if they're left sitting around with little use, the pots and switches oxidize from lack of use and get noisy.