Josh Snider wrote:
Ok here's my query. I've got an Eela Audio console S191 from about 1985.
When I plug my Radial DI into it, I've got no issues at all. Everything
sounds just the way it should, however, upon plugging a cheaper condenser
into it (MXL 990) there was a horrible 60hz hum, which got louder upon
gaining up, and was also audible through the headphones as well as the main
monitoring desk. I disassembled the mic, and noted that pin 1 was tied to
the chassis, disconnected that and the problem got worse, reconnected and
noted that while I was touching the chassis the hum was notably louder.

What does an SM-57 in the same input do? What happens when you turn the
phantom power on and off with an SM-57? What do you hear with no input?

Is your cable good?

Does it happen on all channels or just one?

Now this is a European desk, however it was operating in a Canadian
broadcast station for years before I got it, and I believe had been phase
flipped (at least the mic inputs, the line inputs had not as I came to
find), and it IS a cheap condenser but can anyone tell me what the possible
source of this hum is and how to eliminate it. I don¹t have another mic to
swap out with it at the moment, but the Radial (Passive) DI has no issue
with it so I assume it could be a phantom power issue (although I do measure
+48V across the to legs of the power supply), but it may also be a grounding
issue between the mic and the input, or possibly the signal ground is tied
or leaking to the chassis? Any help would be much appreciated. I'd hate to
have this sitting here useless.

It could be any of these. Get a dynamic mike and see what happens with
the dynamic mike with and without phantom.

Also I was wondering if anyone could tell me what the wiring convention was
for this desk, I'd like to know which colour wire went to which pin on the
XLR input so I can double check to see if this desk HAS been phase flipped
or not.

Why does it matter? As long as it preserves phase, it doesn't matter which
pin is hot as long as the input and output are the same way.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."