acousic booster?

[rogerinIowa]

got a design problem here-

A friend of mine is in an acoustic band. He and the other guitarist both run direct to the board, and both want simple booster pedals to raise their volume levels when soloing. They both use martin acoustics, with one guy using a pickup in the soundhole of his guitar, and the other using an under the saddle piezo pickup system. The questions I have are:

1) have any of you built a booster for acoustic?

2) if so,  what is the best design out there ( mini-booster, LPB, mini-amp, etc),

3) what would he have to concider with the differences between his acoustic soundhole pickup versus the piezo pickup used by his buddy?

They both want the "cleanest"( a misnomer I know) boost possible for their respective acoustic rigs. Would some booster design offer more clean volume increase versus an overdrive type tone ? Have any of you had good results using boosters of any variety with acoustic guitars

thanks in advance for all constructive input!

Roger in iowa

[Gilles C]

This one is a standard.

http://www.muzique.com/schem/mosfet.htm

[niftydog]

if all you want is a slight volume boost, I would go with an op amp with modest, adjustable gain.

[rogerinIowa]

I have never worked with Piezo pickups and was wondering if there are any considerations when building a booster for use with a piezo equipped guitar...anyone have experience with this matter?  I am hoping to get by with building the same simple booster design for each of the 2 guitarists...the guy using the piezo and the guy using the regular soundhole style pickup. I like the look of the Mosfet boost Gilles suggests, and had looked at others as well ( I use a modified stratoblaster with my prs and older boogie, but these guys are strictly acoustic). I'll be looking at op-amp boosters now too.

thanks

Roger in iowa

[niftydog]

you want a really high input impedance, and ideally very little stray capacitance. For this reason, I would use a non-inverting op amp buffer followed by a gain stage (either opamp or mosfet or whatever).

PS: I have simulated (using Protel) a non-inverting buffer design that had an input impedance of around 850 Gigohms!

[petemoore]

The thing about boosting accoustics is after so much boost [you can probably already do this with the vol knob] they feedback because of the guitar body resonation enhanced by amplification. Maybe the one with the pickup in the sound hole will be slightly more or less prone to this.
 Perhaps they want a touch of grit but just never tasted it to know, Minibooster comes to mind.
 The EQing can make a big difference in the sound / volume level before feedback, by cutting some lows, and adding just a touch of grit, the level before feedback may seem louder.
  This is a sensative application compared to boosting a hardbody guitar, also depending on the pickups natural tone, different booster effect and choice of voicing caps might be a good idea to test around on. maybe socket the input cap and try both guitars while swapping caps to see what works best.

[cd]

PS: I have simulated (using Protel) a non-inverting buffer design that had an input impedance of around 850 Gigohms!

Explain, please

[niftydog]

software simulation of real circuits.

Protel is a schematic design, simulation and PCB layout package.

I simply design the schematic with "simulation ready" components, add a signal source (like a 1kHz sine wave) and the simulation will tell you all kinds of things like input and output impedances, power, currents and voltages, noise, frequency response etc etc. of individual components and points in the circuit, all displayed in a graph.

For more info, google "Spice" and "Pspice". Most software simulators are based on this protocol. A simulation ready component is one that contains spice data that the sim. software uses in it's algorythms.

[rogerinIowa]

I really appreciate everyones input...I'm getting some good ideas here!  Petemoore hits on another fear that I have with boosted acoustics, that being feedback. Hollowbodies are bad enough! ( try to imagine being Ted Nugent with those birdlands in the 1970's!)

I agree that most people think they want a "Clean boost", but in fact may want some grit. That slight bit of dirt could help these acoustic players to get better sustain and such. After all, they are soloing.We've all seen that sort of revelation on this very site: I for one could never understand the need for treble boosters until I used one into my already distorting amp. It became apparent at that point the differences between the name of a circuit and its practical use.

I'm going to give Niftydogs idea about NI opamp buffer into Mosfet or maybe Jfet gain stage.

It really helps to bounce ideas of folks who are alot more experienced than me ( I'm still  newbie at best)

rogeriniowa

[Gilles C]

I know you are now decided on an op-amp thing, but I'm posting this one I forgot to post before anyway.

http://www.jensen-transformers.com/as/as098.pdf

What I found as my best mix is this kind of input buffer (FET, discrete, etc...) to get more signal with the least noise possible, and a lower output impedance to present to the following stage, (an op-amp, an effect or whatever).

The Fishman preamp I have in my accoustic guitar is only a FET preamp with a high input impedance that came with the piezo transducer I bought.

But that's my own taste...

Gilles