JMP-1 encoder mod

[Valvehead]

Ive read in other forums about fixing the data wheel issue in the JMP-1 Marshall preamp. I just got one and the patches jump around when turning the control. I guess this is common in these units . They are adding a de-bouncing chip. No one mentions "how"

here : https://www.mouser.com/ProductDetail/863-MC14490DWG

https://www.mouser.com/ProductDetail...CW1J-C36-CC24L


so the encoder is 3 pins and the chip is 16 pins.

Has anyone done this mod? Is there a scem , or can someone tell me how to do this ??

[Pedro Vecino]

When the encoder ages it tends to be unstable, making the adjustment difficult.
When it is new, its precision is total.
Sometimes I have cleaned them and they work better, but if the degradation due to use is excessive, it is enough to order a new one.

[g1]

"The circuit I used was just the standard circuit in the MC 14490 data sheet, and I attached the PCB to the back of the encoder with foam tape."

http://www.marshallforum.com/threads.../#post-1167049

[Valvehead]

i found some help--thanks though

[Enzo]

Debounce? It didn't need debouncing when the parts were new. Seems like a lot of extra effort to get around replacing a worn control.

[g1]

Apparently the datasheet for the encoder shows a recommended debounce circuit. Not sure if that means it is recommended to use one, or if it means if you are using one, here is the recommended version.