Hissing when input cable is unplugged from overdrive [SOLVED]

[LB801]

Hey everyone, this is my first post on this forum.

I have designed my own simple overdrive pedal on a PCB and it sounds pretty good. My only problem is when the input cable is unplugged with the 3PDT is switched to use the PCB, and the pedal is powered on, there is a very loud hissing noise.

This happens while using a wall power supply and a 9v battery. The hissing does go away when I connect the input straight to ground, bypass is selected on the 3PDT, or when a cable is plugged into the input jack.

Is there any way to fix this? Thank you for the help!

[mozz]

Schematic would be nice to see. Do you have a resistor to ground on the input?

[antonis]

Hi & WELCOME..!!
(@ mozz:  )

Do you utilize a stereo input jack with power switch-off when unplugged..??

[LB801]

This is the wiring I used for the 3PDT.


This is the wiring I used for the PCB I made.


I do not have a resistor going to ground from the input, what value would you suggest I use?

[LB801]

Hello! The input uses a stereo jack and the output uses a mono jack. What do you mean by having the power switch off when unplugged?

[antonis]

If input uses a stereo jack, you shouldn't hear ANYTHING when unplugged..!!
(POWER OFF - NO SOUND at all..) 

P.S.
A 1M resistor (or so) between R1 & C1 should be OK..
(although, by grounding IN when bypassed, you don't need it..)

[LB801]

Hey I connected the 1M resistor from input to ground and the noise is gone! Thank you for the help.

[duck_arse]

we're not finished yet - your circuit diagram shows the 1uF output cap drawn backwards, the (+) should face the op-amp. also, there shows no supply connections to the op-amp, how have you arrainged them?

and also welcome, lest antonis does green-face at me.

[LB801]

Thanks for pointing that out, I'll swap the cap around when I get the chance. I uploaded an outdated diagram because I didn't have a pic of the current one at the time. The opamp is connected at pin 4 and 8 for ground and power respectively.

[duck_arse]

well now, pin 8 is supply connection for a dual opamp, so I goes back and squints at yer dia again, and see TL0x2 - and that brings up the next qustion - how did you wire the unused half of that opamp?

[LB801]

Pins 5, 6, and 7 are all not connected to anything. Should I do something with them?

[bluebunny]

Pins 5, 6, and 7 are all not connected to anything. Should I do something with them?

Definitely.  Connect pins 6 and 7 together (to make it a buffer) and connect pin 5 to V_REF (the midpoint between R3 and R4).

[PRR]

> 5, 6, and 7 are all not connected to anything.

If I don't tie-up my dog, he gets into trouble. Digs up wires, chases skunks, barks at trucks.

Same for HIGH gain opamps. Your "hiss" was probably this untamed amp going crazy chasing its tail 69,000 times a second (with sidebands into audio). Marc's connection makes it stand still at half mast, a perfectly natural state.

[LB801]

I just connected those pins and everything seems good. Thank you for the tips!