Acoustic guitar signal boost for tuning on loud stage...

[hairyandy]

I've done some searching around on the board and I think the AMZ Mosfet Boost might be the best way to go, but I thought I'd put it out for discussion and see what you all think.

I'm a guitar tech and I have to deal with tuning acoustic guitars on a loud stage all the time.  I've got a new tour starting in two weeks and I thought that I'd finally solve this annoying problem by building something.  I've seen other techs use GE-7 EQs and the like to boost the signal, but I'd like to make something small that I can permanently mount in my workbox and use for  acoustics, electrics and basses.  Basically just a full-range, clean-as-possible boost that won't kill the front-end of a TU-2 or a Peterson VSII but will override the vibrations coming from the back of the PA and the backline.  Any ideas other than Jack's Mosfet Boost or is that the best way to go?

Thanks for the consideration,

[petemoore]

Might sound funny, a padded bag on the box.
The PA sound can be 'forceful' enough to introduce Alot of 'stray' harmonic input, through the air, caught' by the bodywood of the guitar, and transferred Directly into the pickup.
I suspect the signal level may not be the function killer, but the fact that the tuner is not recieving 'clean enough string information [you could record the guitar output under loud PA conditions and probably hear the 'extra' tones the pickup is putting out].
Boosting will not separate the 'needed' info, [string vibration frequency] from the 'unwanted' stuff the PA is 'injecting into the body/pickup.
Damping the entire outside of the guitar would help. "Bagging' the body 'sounds' wierd, but is the only way I can think of to isolate the string input to the pickup from the PA's....of course the bag would have to allow string openness. Some kind of padding.

[vortex]

shoot, almost any booster would do. If you make the Mosfet I think that you will find the highimpedance works well with piezos, other pu's too. I think you are on the right track.

[remmelt]

It sounds like Pete is right here. The band I was in had another guitarist with an Epi 335, and he had a tough time tuning with noise around, not because the output was too low but because the (semi-)open body would pick up and amplify the surrounding sound.
You might want to try one of those rubber pads you can put over the guitar's hole to dampen feedback.
For a simple booster I can recommend the beginner project, Gus' NPN boost. Haven't tried AMZ's mosfet boost, so I cannot compare the two.

[hairyandy]

Thanks for the replies guys.  Although Pete's idea may have some merit, I think a booster may be the way to go if not just for practicality.  I have to be able to run on stage at a moment's notice so something physically over the guitar might not work so well.  I have feedback busters in all of the acoustics which does help a bit but sometimes it can be so loud that it just doesn't matter.  Mostly it all depends on how close I have to setup to the PA.  Some days are better than others.

Thanks again,

[petemoore]

Something that just slides on/off...

[niftydog]

you need an old fashioned strobe light tuner. Haven't seen one in ages, but mine is still going strong.

You could probably make one. Mine is just a square wave oscillator with a 6 position switch to set the frequencys (555 maybe?) Then, a simple circuit to drive two small neon bulbs at the oscillator frequency which slide underneath the string being tuned. (I suppose you might even be able to use LEDs.)

When the string is in tune it appears stationary with the strobe light behind it. Simple optical illusion!

It's completely unaffected by sound pressure waves, you don't have to unplug to use it (or, god forbid, have it in your signal chain!) and as a bonus, the oscillator leaks into the pickups if you hold it close enough and then you can tune by ear as well!

[petemoore]

I thought about making one, first the high spec balanced clear wheel with all the lines on it, I'd want to buy one of those, then there's the motor that drives it at a speed determined from the 60 cycles wall power supply.
 The guitar driving the bulbs would be the easy part.
 BTW how hard is it to get a bulb to light at precise reference frequencies? Not sure how those tuners tune, there must be a reference frequency used.

[petemoore]

Install a magnetic pickup and figure the PA doesn't alter the string frequency, completely mute the other strings, "use short sustain?"

[Bernardduur]

I use a compressor for that job..... never had any problems.

[lion]

Just an idea - phase cancellation.

Wouldn't it be possible to design the booster circuit you are looking for - but also incorporate a sidechain, picking up the disturbing sound - turn the phase 180 degrees - and mix it back in. Thereby cancelling (at least to some degree) the unwanted 'noise' - leaving you with a cleaner and boosted guitarsignal to the tuner.

Erik