JLM AUDIO

I am starting to experiment with some piezo strip pickups, which need to be loaded with about 10Mohm or higher.

1) how would I modify the input impedance on the FET DI?
2) could this be made switchable?

prhunt wrote:I am starting to experiment with some piezo strip pickups, which need to be loaded with about 10Mohm or higher.

1) how would I modify the input impedance on the FET DI?
2) could this be made switchable?

Easy the two 2M2 resistors marked with a * work in parallel to make 1.1Meg input impedance.

Changing both of them to 200Meg resistors would make 100Meg input impedance.

If you fit the highest value resistors you can then switch low impedance resistors directly across the TRS jack tip and sleeve to lower the impedance.

eg set with 2 x 200Meg to get 100Meg and switch 1Meg across jack to get 1Meg input etc.

Perfect! Thanks Joe

Paul