SHURE FP32 Portable Mixer noise

[Pip]

So this has been brought up in forum before in Mixers... page. But no responses so I will try it here.

I have a Shure Bros FP 32 portable battery powered mixer that is almost new. Bought it from a friend when she was divesting some gear.

The knock on this unit has always been the noise. It has quite a prevalent hiss. Now since these are usually used for film dialogue gathering I suppose that was OK. But I would like to use it for other things.

So is anyone familiar with any mods that have been done to this unit to upgrade its signal path and if so please share.

 

[tubegeek]

Does the hiss affect it at all settings of the limiter? Are you using it with the gain way up and the limiter in? The manual says -128dB EIN, which is not amazing but it's not, like, unusable either. So I wouldn't expect it to be godawfully noisy....

Manual here: http://cdn.shure.com/user_guide/upload/862/us_pro_fp32_ug.pdf

 

[bruce0]

I went looking for a schematic (to no avail).  Having a schematic is one reason I like DIY ( though there are projects where no schematic is provided... argh).

There are a lot of reports on noise on that mixer on the internet, but there are also people saying they are fine with no noise problems.  It makes me suspect a settings problem. 

Anyway (with no schematic) here are some thoughts on debugging the noise.


1) Check the outputs... The outputs are switchable from MIC to LINE (600 ohms).  They should be set on LINE unless you are running it into another mic preamp (which would in itself explain some extra noise).  Having that set wrong could be noisy depending upon the next device in the signal chain.


Assuming those are set right, try to eliminate possible noise sources:

Turn off the Limiter
Turn off the automatic gain control (if it has that.. I couldn' t tell from the manual) and pretty much turn off everything you can.

Still noisy?

Run it on batteries, not wall power (maybe the filter caps are bad) and see if that is quieter.

Still noisy?

The units provide phantom power and T power.  Phantom is often 48V in the studio, but in this case it is 18V-11V and T power I think is 12V but applied differently.  I assume you know what your mic's need, but lets just eliminate power to the mic as an issue.  Turn OFF any T power (so you don't fry the mic) and any phantom power and just plug in a SM57 or SM58 or whatever dynamic mic you have lying around.  If that is quiet, you may have an issue with the phantom/t power circuit or your phantom powered mic may want more phantom than 18V (somewhat rare.. usually work fine with lower voltages).

 

[okgb]

They cruised a long time with the mediocre designs , Sound Devices seems to be the
decent new standard .  any time recently that i had to use the shures if the supplied
headphones were bright like the sony  [ 7506 ? ] I found the hiss almost unbearable
so factor the headphones into the equation

 

[Mike Cleaver]

Shure mixers were never any great shakes in the noise department.
In broadcasting, we usually only used them for remotes, sports broadcasts, etc.
They were fine for that, feeding telephone lines, back in the day.
I still have one of their single channel mic to line battery powered units that I only use with headphones to check out microphones I find in pawn shops, second hand stores, etc.