Post by JohnH on Nov 28, 2009 0:20:45 GMT -5
This is a design for a gadget to blend two pickups to give one active output. It was designed for combining an active magnetic and an active Piezo pickup on an acoustic guitar, but it could equally blend two passive magnetic pickups, or one active and one passive source. It works by feeding the inputs from each source through a 500k linear pot, to a JFET buffer which has a high input impedance and a low output impedance. The output is intended to drive long cables if required with no tone loss, and can go to either a guitar amp input, or a line level input on a mixer.
EDIT - the unit can also be used as an active Volume control.
The original discussion and development with treguiers was on this thread, and he has successfully built it.
guitarnuts2.proboards.com/index.cgi?board=acoustic&action=display&thread=4567&page=1
Blender Module
Here is the blender module, constructed on Veroboard, and mounted on the blender pot. The board is shown from above, as if transparent and the copper strips are underneath.
www.jocidapark.com.au/circuits/GN2/ActiveBlender191109.gif
The pot should be 16mm diameter so lugs match the strip spacing. The board is only about 23mm x 21mm, so should fit most potential applications including use in guitar control cavities.
Installation
And this is the overall wiring, specific to these two Fishman pickups, but the principles are general:
www.jocidapark.com.au/circuits/GN2/activeblenderinstall281109.gif
On this installation, the magnetic pickup was originally running on 3V, so part of the wiring was to allow it to run off the same 9V supply as the piezo preamp, hence the 12k resistor and 10uF cap. On the magnet pickup the white wirewas the signal output while on the piezo output it was red wire.
Use as a Volume control
After completing this successfully, it was decided to add a master volume control after the output, using a second similar module. This can be done by grounding IN1 and using IN2 as the input. If the second volume module is after a previous active stage (such as this blender module), the volume pot can be 100k. Or use 500k if it is being fed by passive pickups. The easiest way to ground IN1 is to omit the track break adjacent to that lug, which leaves it connected to the ground rail.
Current draw and Battery life
The current required by one module is about 0.2mA, and it is not very sensitive to battery voltage. If one module was used on its own, a 9V battery should last at least 1500 hours.
Note that if the system is not required to drive a line input, but only a guitar amp input, the 33k resistor (R3) can be increased to 68k with no ill effect, to halve current draw. This could also apply if two modeules are used (as here) for blending then volume, the first can have this higher value resistor for lower current draw. Either way though, it uses little current.
regards
John
EDIT - the unit can also be used as an active Volume control.
The original discussion and development with treguiers was on this thread, and he has successfully built it.
guitarnuts2.proboards.com/index.cgi?board=acoustic&action=display&thread=4567&page=1
Blender Module
Here is the blender module, constructed on Veroboard, and mounted on the blender pot. The board is shown from above, as if transparent and the copper strips are underneath.
www.jocidapark.com.au/circuits/GN2/ActiveBlender191109.gif
The pot should be 16mm diameter so lugs match the strip spacing. The board is only about 23mm x 21mm, so should fit most potential applications including use in guitar control cavities.
Installation
And this is the overall wiring, specific to these two Fishman pickups, but the principles are general:
www.jocidapark.com.au/circuits/GN2/activeblenderinstall281109.gif
On this installation, the magnetic pickup was originally running on 3V, so part of the wiring was to allow it to run off the same 9V supply as the piezo preamp, hence the 12k resistor and 10uF cap. On the magnet pickup the white wirewas the signal output while on the piezo output it was red wire.
Use as a Volume control
After completing this successfully, it was decided to add a master volume control after the output, using a second similar module. This can be done by grounding IN1 and using IN2 as the input. If the second volume module is after a previous active stage (such as this blender module), the volume pot can be 100k. Or use 500k if it is being fed by passive pickups. The easiest way to ground IN1 is to omit the track break adjacent to that lug, which leaves it connected to the ground rail.
Current draw and Battery life
The current required by one module is about 0.2mA, and it is not very sensitive to battery voltage. If one module was used on its own, a 9V battery should last at least 1500 hours.
Note that if the system is not required to drive a line input, but only a guitar amp input, the 33k resistor (R3) can be increased to 68k with no ill effect, to halve current draw. This could also apply if two modeules are used (as here) for blending then volume, the first can have this higher value resistor for lower current draw. Either way though, it uses little current.
regards
John
