FET DI impedance mod?

Support for JLM Audio Kits

Moderator: Joe Malone

Post Reply
prhunt
Posts: 14
Joined: Sat Jan 28, 2012 1:08 pm

FET DI impedance mod?

Post by prhunt »

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?

User avatar
Joe Malone
Site Admin
Posts: 2068
Joined: Wed Jan 24, 2007 11:35 pm
Location: Brisbane, Australia
Contact:

Re: FET DI impedance mod?

Post by Joe Malone »

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.
Joe :-)
JLM Audio
Capturing Audio without Injury

prhunt
Posts: 14
Joined: Sat Jan 28, 2012 1:08 pm

Re: FET DI impedance mod?

Post by prhunt »

Perfect! Thanks Joe 8)

Paul

Post Reply