Crown GLM-200 high pitched feedback -> faulty?

[CHYC]

I have for many years owned a Crown GLM-200 from new, to amplify a double bass. It has this really really annoying tendency to feedback at a horrible frequency of around 6.5kHz. I had put this down to the nature of the mic and dialed it right back and let a piezo do the heavy lifting, with the microphone to add a little string detail. It's not an ideal sound but I've lived with it.

Chain is GLM-200(+Full circle) -> Fishman pocket blender -> Any amplification available but usually an Acoustic Image Coda R.

You cannot buy a Crown GLM-200 new any more so when I saw one second hand I thought I'd take a punt at having a backup just in case my main one went awry. This has opened my eyes somewhat: no feedback whatsoever and I can get to gigging volume using just the microphone, and with all other equipment untouched (save for volume which is now usable.)

So, given that I have two seemingly identical microphones but one has a really nasty feedback and the other doesn't, is this something that's fixable with my faulty microphone? What could be causing it? I try Googling but I haven't found anything conclusive. This isn't feedback like I know (and love), this really is a horrible high pitched squeal and there's nothing I can do to stop it save turning it down to almost inaudible levels. Phase switching does nothing.

 

[Old Garage-Bander]

Well if one mic has feedback and the other does not... AND everything else in the chain is the same, the feedback mic has a problem.

Sorry to sound like Capt. Obvious, but want to be sure that the only thing changing in your setup is the mic.

If we are on the same page... AND you are using a new, fresh battery (not one that just tested as good) in the feedback mic, you'll probably have to send it back for repairs.

 

[CHYC]

Thanks for the response. Literally the only thing changing is the microphone. The cable plugged into the mic is the same, as is everything else past that point.

It's a very old microphone, and I thought that Crown microphones didn't exist any more. However, I can see they were bought by AKG so there's a small chance I may be able to get it serviced. If there's no obvious quick fix then that may be my only recourse.

 

[Mouldy]

I have for many years owned a Crown GLM-200 from new, to amplify a double bass. It has this really really annoying tendency to feedback at a horrible frequency of around 6.5kHz. I had put this down to the nature of the mic and dialed it right back and let a piezo do the heavy lifting, with the microphone to add a little string detail. It's not an ideal sound but I've lived with it.

Chain is GLM-200(+Full circle) -> Fishman pocket blender -> Any amplification available but usually an Acoustic Image Coda R.

You cannot buy a Crown GLM-200 new any more so when I saw one second hand I thought I'd take a punt at having a backup just in case my main one went awry. This has opened my eyes somewhat: no feedback whatsoever and I can get to gigging volume using just the microphone, and with all other equipment untouched (save for volume which is now usable.)

So, given that I have two seemingly identical microphones but one has a really nasty feedback and the other doesn't, is this something that's fixable with my faulty microphone? What could be causing it? I try Googling but I haven't found anything conclusive. This isn't feedback like I know (and love), this really is a horrible high pitched squeal and there's nothing I can do to stop it save turning it down to almost inaudible levels. Phase switching does nothing.

I used to use the GLM200 with the Fishman BP100 pickup through the pocket blender and mine also did the high pitch feedback...without any warning...from new. I remember I used to have it directly over the F hole and that goes against what is recommended by fishman. When the Full Circle pickup was released I felt that the sound was so good that there was no reason to use the GLM200. That was 10 years ago. Now I am wanting to revisit a microphone, dug my GLM200 out and found the zener diode missing. Do you have any info on what diode it is? My intention would be to have the GLM200 between the bridge and the f hole. Hope some of this info helps.