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Double Bass amping an AMT mic

G

greitzer

Jul 25, 2002
437
1
72
Near Berkeley, CA
#1
I wonder if somebody who knows electronics can explain this surprising discovery. I've got an AMT mic (the kind that comes with the premium pre-amp, I forget the model number). Using it in my GK MB150 combo amp, I've never been able to get more than a whisper from it, with or without additional external pre-amps. It's been sort of the "my bass only no louder" concept. Tried all kinds of different placements, angles, settings, etc. No usable volume.

Today on a whim I plugged the AMT into my little practice amp, a Crate B10 that only has 10 watts (compared to the GK's 100-to-150 watts). Presto! It sounded great -- loud enough to actually use on a gig! I also tried it through my Fishman pre-amp into the Crate B10, but I lost some volume that way. I got the loudest, most powerful and roundest sound plugging the AMT directly into the Crate B10.

Who'da thunk?
 
#3
In both cases (GK and Crate), I plug the mic into the AMT pre-amp that came with it, and plug this directly into the amp. I can't plug the AMT mic directly into my amps, because the mic itself has its own kind of a four-pin connector that won't plug directly into an amp. The mic will only plug into the AMT pre-amp. This then goes into the amp.

When I use my Underwood piezo pickup instead of the AMT mic, the GK 150 amp WAY outperforms the Crate. Louder, better, more, etc. But with the AMT mic, the Crate gives me more sound.
 
#6
If you search around the threads hear you will find a lot of my posts about the AMT mic. Too things:

a) The AMT preamp is really more of a power supply and a signal processor than a preamp. The output level from the AMT preamp is quite low - the designer said it is supposed to be equivalent to a Shure SM58. You definitely need to plug the AMPT preamp into a preamp - the signal definitely won't be hot enough straight into an amp. I am guessing that the Crate preamp has more gain than the the GK150 preamp assuming you were in fact going into the preamp stages in both cases.

b) There is a trim pot inside the AMT preamp. You can use this to adjust the permanent output level. Remove the screw from the preamp and slide the internals out and look for the trimpot. You'll need a small flat screwdriver to adjust it.
 
#9
Adrian, Chris and Ray -- I appreciate your responses on this. I knew this was going to be a difficult problem to explain on the forum, and it will be a difficult one to solve.

Regarding the use of a preamp, I do use one (the Fishman Platinum Plus Pro EQ), so that's taken care of.

Regarding the cables, I appreciate the suggestions but the cable works fine (as evidenced by the fact that the AMT mic can be heard at a reasonable level when I plug into the Crate amp, but not the GK amp -- using the same cable -- and by the fact that when I use the same cable to plug my Underwood pickup into either amp, it works great). So it's not the cable.

It seems, to me, to be something about the interaction between this mic and the GK amp, but not being an electronics guy, I'm in the dark.

Very strange . . . thanks again for trying.
 

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