High Impedance In Booster

[n9voc]

Good day!

I have attached a schematic and pics of a high impedance input (5Mohm) booster circuit.  If I want to play my electric and not worry about imput impedance of the amp, this does the job as a preamp.  As you can see, I have the knob marked at the x1 and x5 positions. 

Enjoy!

[n9voc]

Just wanted to report that this little box works absolutely fantastic for a piezo pickup (a DYI piezo buzzer hooked up as a pickup) on my acoustic nylon strung guitar.

The 5x boost is sufficient that I have excellent signal to noise ratio, and can even run the signal out of the booster into my chorus pedal for an incredibly rich nylon tone!
:tu:

[n9voc]

Corrected Schematic attached!

Sorry folks, I was looking at the schematic for this box and realized that R2 was NOT 2.2 ohms, but rather was 2.2 Kohms.  I also forgot to suppy the value for the LED resistor.

I have attached a corrected schematic to this post.

[Marek]

Nice booster. Can you tell something more about this piezo buzzer hooked as a pickup? I want to do something similar.
I have few suggestions regarding components:
C1 (10 uF) can be changed to 10 nF (due to high input impedance).
I'm not sure whether R1 (10M) is needed. I would at least try to remove it.
C11 (1000 uF) is probably too much. I would use 100uF.
Most probably C4 (330uF) is also too much. I would use 47 uF and increase the R10 pot value to 22k log.
The idea is similar to: http://www.scotthelmke.com/Mint-box-buffer.html

Marek

[n9voc]

Marak,

I used a $1.79 piezoelectric buzzer element glued to the underside of the bridge on my nylon string guitar, near the treble side.  The cable ran from the buzzer was of the RG174 skinny coaxial type, center conductor to buzzer element and shield to brass baseplate.

I am certain the booster would work with the changes you suggest.

I used R1 to eliminate "pop" and the total input Z was about 5 Mohm, that was my target impedance.

the 1000 uF cap across the 9V battery just makes the battery a "stiffer" supply than a 100 uF, besides, I had a bunch of 1000 uF units around! :tu:

I wanted the best possible low frequency response for this unit, and thus the 10 UF input capacitor and the 330 uF output capacitor I use this for other basic boost applications as well as for a piezo.  The pot in the circuit was another "junkbox" supplied pot.

Overall, the booster is overdesigned, and as I stated at the beginning would probably work just fine with the component changes you suggest - which only goes to show that in most  basic audio circuits, there is a WIDE range of components that can be used and still get satisfactory results!

Have a great day!