Lightbox circuit

Nigel Goodwin

Super Moderator

Most Helpful Member

• Saturday at 12:46 PM

• #21

GCook said:

Okay, I see it on the other schematic. I guess you figured out I was just focusing on the input board. I'd like to know why the circuit needs it. I'd say (after looking at the main input circuitry), that C20 is used to block the DC voltage. I still believe the pot on the input board needs a GND connection. I'm waiting for Splitdog to answer my question about the outer pins of the pot.

Click to expand...

C20 prevents the DC getting to the opamp, but passes the cracking caused by adjust the sensitivity resistor.

You're still thinking the pot is a volume control, it's not, it's mostly an adjustable load for the mike, plus a bit of crude level adjustment as well. The input also isn't floating, it's got R45 and R47 preventing that.

 

S

splitdog

New Member

• Saturday at 12:50 PM

• #22

So the pot is not grounded?

 

G

GCook

New Member

• Saturday at 12:52 PM

• #23

Nigel- I'll be quiet, and just sit back and watch.
Splitdog- Your meter says it's not, so I guess it isn't.

 

S

splitdog

New Member

• Saturday at 12:54 PM

• #24

Should I try a jumper with alligator clips from the 3rd leg to sig grnd?

 

G

GCook

New Member

• Saturday at 1:10 PM

• #25

If you have a 1/4 watt, 50K resistor, just jump the SIG input to GND. The successful result will be that the resistor remains cold to the touch, and the noise goes away.

 

S

splitdog

New Member

• Saturday at 1:12 PM

• #26

Could you clarify? I'm not an engineer.

 

G

GCook

New Member

• Saturday at 1:20 PM

• #27

Connect one end of a alligator clip jumper to SIG. Connect the other end of the jumper to a 1/4 watt, 50K resistor. Connect the other end of the resistor to a second alligator clip jumper that you will attach to GND.

 

S

splitdog

New Member

• Saturday at 1:24 PM

• #28

On the pot? Or the inputs and outputs on the board?

 

G

GCook

New Member

• Saturday at 1:28 PM

• #29

The main board. Not the input board.

 

S

splitdog

New Member

• Saturday at 1:30 PM

• #30

So between sig input, and 'neutral'?

 

G

GCook

New Member

• Saturday at 1:33 PM

• #31

On the main board schematic there is a J2 input connector with two terminals (SIGL and GND). Connect there.

 

S

splitdog

New Member

• Saturday at 1:38 PM

• #32

Ok. I have to get one. I'll let you know. Thanks!

 

S

splitdog

New Member

• Yesterday at 10:54 AM

• #33

Any more thoughts?