The bass has EMG active magnetic pickups and piezo bridge pickups, which need a buffer amp. I wanted each pickup to have its individual volume control so that each could be adjusted independently and have a seamless blend of piezo and magnetic pickup. Most basses that I have looked at, which have piezo pickups, have very separate controls. I decided to include an active tone stage with treble and bass controls. It would not have meant much more work to add in a mid stage but modern amplification has ample equalisation and I did not want to have too many knobs on the bass.

 I designed the circuit around a low power quad op-amp, LN324. The electronics, including the active pickups, draw just below 2mA with an 18V supply. This should give me 75 hours battery life using two rechargeable PP3 batteries.


I was unsure about the correct overall frequency response for the system. I looked at several commercially available active circuits. They all appeared to have a centre frequency at just below 1kHz. So I have gone with the flow and done the same. The frequency response of the tone control stage is shown below.


I initially tried out the electronics and magnetic pickups holding them close to a Jazz Bass. It sounded well.

All the components for the electronics were purchased from Maplin Electronics