simple optical noise gate!!!!

[deadastronaut]

ive been thinking on uses for led/ldr's again.....oh no!...

what about a 'simple' optical noise gate....ive rigged up the usual 386 sound to light and the darklight, it works...sort of...

but loses a lot of volume, but thats ok it can be made up later, hopefully with the same 386 for extra tinyness.......any thoughts!.....no schemo at the mo!....just tinkering!...

[ddpawel]

Maybe you could use something like http://www.mif.pg.gda.pl/homepages/tom/misc.htm#szumy
For example "Rys.1", part with H11F2 before your volume control and "Rys.3" to control gate.

In summary - buffer, parallel effects loop and gate control, H11F2, volume control and output buffer.

[deadastronaut]

thanks,15v?...    i'm trying to keep it really simple!...ive seen demos of the classics, mxr/dod etc, but they don't really seem up to the job really...too slow to gate etc...

[Gurner]

the 15v is more than likely becaUse 15v was up for grabs from elsewhere in the circuit.

The key part - the H11F2 - works down to about 2.1V ...you simply adjust the series current limiting resistor to suit your particular supply voltage

[deadastronaut]

ahhh i see cheers G.

[electricteeth]

Maybe sending the signal through a buffer, then split the signal sending one through a ldr and then to the output and the other to a comparator circuit which triggers an led once signal reaches a certain voltage. The led lights up and lowers the resistance of the ldr, allowing sound to come through, then when not playing, the led shuts off and increases resistance therefore blocking signal. This may even work more instantly with an optocoupler instead of the ldr/led combo. (in theory this would only require one dual opamp) Love your pedals mr. astronaut!

[Perrow]

Dual op amp. One part of it boosting the signal. The other half in comparator mode "detecting" any signal over the noise floor and lighting the led. The ldr either limits the gain of the op amp or allowing signal to pass in some other way.

Come to think of it the comparator could probably be set up reverse, i.e. turn off the led when a signal is detected.

[deadastronaut]

cheers guys,

the comparator is something ive never dealt with... ,

@pelle, could you elaborate on the tl072 idea?...


at the moment i have a split input to ldr and 386... the signal lights the led, and lets the signal through, when off it cuts it, and is then fed into another 386 to make up level loss , it works sort of, but i guess your suggestions would be a better
solution....

[nexekho]

cheers guys,

the comparator is something ive never dealt with... ,

@pelle, could you elaborate on the tl072 idea?...


at the moment i have a split input to ldr and 386... the signal lights the led, and lets the signal through, when off it cuts it, and is then fed into another 386 to make up level loss , it works sort of, but i guess your suggestions would be a better
solution....

I'm looking into building a noise gate custom design too!  DC bias->Buffer->Rectify->low pass->555 as schmitt trigger->out and discharge running a low pass RC->MOSFET to ground on signal is what I had in mind.

[Perrow]

Ops, didn't read the whole thread. Sorry.

[deadastronaut]

just found this....looks easy....too easy i guess!..

http://500circuits.blogspot.com/2010/10/noise-gate.html

[Perrow]

cheers guys,

the comparator is something ive never dealt with... ,

@pelle, could you elaborate on the tl072 idea?...

I've never actually used one but it's an op amp with (in theory) infinite gain. It's a standard negative op amp circuit without any feedback resistor. If the signal is over less than the positive input you get all the op amp has to give on the output and if the signal is over positive input you get nothing. I'm on a train right now and should get off in about three minutes, so forgive me if I wont say more right now. After the kids gone to sleep tonight I'll return

[deadastronaut]

okey dokey, cheers man!.....ive got to cook dinner!...

[Gurner]

just found this....looks easy....too easy i guess!..

http://500circuits.blogspot.com/2010/10/noise-gate.html

Correct! (for the life of me, I can't see how that can 'gate' noise!)

For a noise gate to erhm 'gate' you need to extract the signal 'level' from the AC signal (therefore rectify it/then LPF the guitar signal)....once you've a DC voltage level representation of the AC guitar signal you then need something to 'trip'/trigger at your preferred threshold (ie your gate level, which would be just above your noise threshold) - that's where a comparator comes in to play.

Comparators are very simple - you set a static DC 'trigger' voltage on one input pin....if the other pin (ie your extracted DC from your guitar signal outlined above) goes above/below that set level, the comparator output flips ...therefore you've got a situation where the comparator output can only be high or low....you then use this high/low voltage as a control voltage to trigger/switch something else (opto isolator, FET shunt...whatever).

So signal chain is....

Signal-> buffer/amp-> rectifier-> low pass filter-> comparator-> opto fet shunt or LED->LDR etc.

(the above should really be a side chain ...ie you have two paths...one for your signal & one for the gate's 'workings')

I'm sure there'll be someone along to contradict me, but IMHO 'simple' & 'noise gate' aren't normally bedfellows! If you want simple as in low parts count, a basic 8 pin PIC would greatly reduce the parts count/complexity but I realise amongst hard core analogue types, that's a hard sell!

[DavenPaget]

just found this....looks easy....too easy i guess!..

http://500circuits.blogspot.com/2010/10/noise-gate.html

Correct! (for the life of me, I can't see how that can 'gate' noise!)

For a noise gate to erhm 'gate' you need to extract the signal 'level' from the AC signal (therefore rectify it/then LPF the guitar signal)....once you've a DC voltage level representation of the AC guitar signal you then need something to 'trip'/trigger at your preferred threshold (ie your gate level, which would be just above your noise threshold) - that's where a comparator comes in to play.

Comparators are very simple - you set a static DC 'trigger' voltage on one input pin....if the other pin (ie your extracted DC from your guitar signal outlined above) goes above/below that set level, the comparator output flips ...therefore you've got a situation where the comparator output can only be high or low....you then use this high/low voltage as a control voltage to trigger/switch something else (opto isolator, FET shunt...whatever).

So signal chain is....

Signal-> buffer/amp-> rectifier-> low pass filter-> comparator-> opto fet shunt, LED->LDR etc etc.

(the above should really be a side chain ...ie you have two paths...one for your signal & one for the gate's 'workings')

I'm sure there'll be someone along to contradict me, but IMHO 'simple' & 'noise gate' aren't normally bedfellows! If you want simple as in low parts count, a basic 8 pin PIC would greatly reduce the parts count/complexity but I realise amongst hard core analogue types, that's a hard sell!

Well ... I did see the innards of my Noise Gate pedal before ... ( It's actually a NF-1 / NS-2 )

[electricteeth]

+1 on the PIC!