Weird gate

[Kipper4]

Cheers I'll try those.

[Kipper4]

Heres where I'm at.
it gates but the gate comes on really fast. too fast for use.
primeraly this is the issue.


I tried inverting the comparator and using a jfet tried 2n5458, j201, J113 similar results to before
I tried a pnp mosfet BS250 similar

Any ideas on how to control the note decay to switching a bit slower?

other things i tried for kick
a 1n914 from drain to gate
a 1n914 from source to gate

a 1n914 from D3 cathode to gnd both ways round

the comparator input is taken from the input buffers output through a 100nf cap.
would changing the cap value here help?

Thanks for your time

Frustrated country boy
Rich

Edit
further suggestions and ammendments are welcome
Schmitt trigger will this be useful. Switching chips ?

[slacker]

The time it takes for it to gate once the input falls below the threshold is set by C7 and pot2, try making C7 bigger.

[samhay]

>it gates but the gate comes on really fast. too fast for use.
I'm guessing it is supposed to be a noise gate. If so, then it is supposed to come on fast.

Is the issue more that it is too twitchy, such that it keeps cutting out/back in again?

[Kipper4]

Will do Slacker
Thanks

[Kipper4]

>it gates but the gate comes on really fast. too fast for use.
I'm guessing it is supposed to be a noise gate. If so, then it is supposed to come on fast.

Is the issue more that it is too twitchy, such that it keeps cutting out/back in again?

Sorry I should have been more specific.
If pot2 is at full rotation the gate is on. I hear zilch.
If pot 2 is at 4pm it's glitchy. On off on etc
I can play with the other pots but that only somewhat shifts the position in which it gates ie 3 to 4pm maybe.
I have built the dod fx 30  (it's a modded one) the schematic's over at the other place.
Tuneable enough for me threshold and sensitivity. But this beast is not tunable.

This is a valuable lesson to me. I'm just getting my head around how the comparator works after a quick browse online earlier today.
I still have a lot to digest in this hobby.
Cheers

[PRR]

The comparator has HIGH gain.

The MOSFET may have HIGH gain.

Between the two, the on/off action is too abrupt.

Maybe lower the comparator's gain (actually work it as a linear gain stage, not a comparator).

Is this your own invention or plagiarized?

[Kipper4]

Thanks for the response PPR.
Not plagiarised it came from here

http://techniguitare.com/forum/realisation-montage/tranquility-noise-gate-malheur-composants-t8976-90.html

It was apparently an updated version of the Hot Amp Noise Gate that was floating around on the net somewhere.
I can't find it now I want to of course.

I'll look into lowering the (comparators) gain and mess with that.
All help great fully received.

[Kipper4]

Right having looked over the schematic (post1) I can't figure out how to lower the gain of the comparator.

I'll refer to it as comparator for the duration of the thread so we all know to which bit we refer even if it is n fact a linear gain stage.
Thanks for that PPR.

Since normally the gain of an op amp (in distortions) is set by the input resistor versus the feedback resistor.
In this arrangement there's no feedback resistor. I'm gonna google differential op amps mean time and see if I can figure it out.

I only have one other fet to try and I think it's a power mosfet (lrf520) so I doubt it's gain will be lower than a 2n7000 or BS170.

What y'all think.

[garcho]

power MOSFETs are for high current/voltage, not extra gain, no?

[Kipper4]

Could be a candidate then thanks Garcho. I'll go over the datasheet thanks.

Since PPR said it was a linear etc. I looked up comparators and a lot of the ones I've seen have dual
Bjts on the output.

Like the single power supply comparator equivalant circuit here..

http://home.cogeco.ca/~rpaisley4/Comparators.html

What's that all about?

I looked up differential op amp circuits and now understand that a comparator and differential are differant beasts. One more bit of knowledge helps.

[garcho]

https://bytebucket.org/intelligentagent/replicape/raw/6a578f24a5f4e12c159f60fb76229215ae0ee9aa/Doc/Literature/sloa067-1.pdf

not sure if that will help, but while it's on your mind...

[Kipper4]

Nice read thanks

That explains Pauls comment.

[slacker]

You could try replacing the comparator with the gain stage from something like the nurse quacky http://www.home-wrecker.com/nurse-quacky.html I think this is basically what Paul was getting at with "actually work it as a linear gain stage".
Whip out everything from the bottom left of the schematic up to and including the diode on the output of the comparator Splice in everything from the sensitivity pot on the nurse quacky up to and including the LED on the output of the lower opamp, the sensitivity pot become the threshold control.

[Kipper4]

Got it thanks Slacker.
Thank you all that will give me something to play with tomorrow on the breadboard.
Thank you for your patience.

[PRR]

> power MOSFETs are for high current/voltage, not extra gain, no?

MOSFETs cover the range from small (30V 50mA) to huge (1,000V 100A).

They are handy for BIG work because they have "almost" as much gain (low drive requirements) as BJTs, but are much more robust (no second-breakdown).

They are handy for small work because the gain is more linear than a BJT, and they can conduct both-ways which a BJT isn't as good as.

_I_ think that plan is flawed. When any signal peak exceeds the comparator threshold, that MOSFET will flip all the way to ON. That's too abrupt for music. We want a small but non-zero delay before opening-up, to ignore minor noise-crap. And a lingering after sound "stops", of course, so tails are not chopped. It wants an envelope follower, not a comparator. I'd advise studying all the noise gates you can find. (Sorry, I don't have a good example; they all have flaws.)

[Kipper4]

You could try replacing the comparator with the gain stage from something like the nurse quacky http://www.home-wrecker.com/nurse-quacky.html I think this is basically what Paul was getting at with "actually work it as a linear gain stage".
Whip out everything from the bottom left of the schematic up to and including the diode on the output of the comparator Splice in everything from the sensitivity pot on the nurse quacky up to and including the LED on the output of the lower opamp, the sensitivity pot become the threshold control.

this was the nearest ive got to getting it to playball with the above.
trouble was once the mosfet went off it wouldnt reopen when notes are played so i figured it must be the transistor holding its charge/discharge. something i read led me to put a shunt resistor to ground from the gate. that didnt work either. no matter how i twiddled the knobies i couldnt make it work properly.

i tried a Duck Arse envelope detector intended to light an led in the last op amp stage and did the mosfet switch as per schematic page one. No dice

i tried a fet as a series switch driven by the same DA env detector that was a fail too.
mmmhhh

Six hours on the breadboard and im no nearer to succes.
I'm jacking it in calling it a night maybe tommorow ill succeed.
Update/rant over

[Kipper4]

Update 2
I set it back up on the Breadboard as per schematic but inadvertent left out the 470k on pot one.
Setting the pot 1 so the voltage on the wiper is 0.036v seem to work better. It still cuts off stark but will allow low notes to decay before gating, however it's a bit tricky with the higher E string. Suspect because it's a lower strength signal. I'll do some more tweeking with the pot 1 and see if I can't overcome it.
It's looking like I'm gonna have to use a 25 turn trimmer for pot 1.
On I go.

[Kipper4]

Question for the knowledgable.
would a dedicated comparator chip such as LM393, LM311 be more useful than the op amp as a comparator in this circuit
thanks

https://www.fairchildsemi.com/datasheets/LM/LM393.pdf

http://www.ti.com/lit/ds/symlink/lm111-n.pdf

[Kipper4]

Oh and I'm getting a bit of switching noise

a ploppy compressed note sound on playing and sometimes a doddery on off on off when the gate closes (on)
suggestions for the elimination of this would not go astray.

ive changed the charging cap to a 4u7
the comparators bias network to +9v >100k > 100k pot > inverting input. seems like i have a more useful range on turning the pot.

Im using a 2k7 shunt resistor on the mosfet gate.

changed the value of pot2 to 1M

Changed R4 to 1M

and as before Im using a 1M resistor from Vbias to the input buffer NI input

the comparators NI input is fed from the input too as opposed to the earlier suggested buffer output to comparator input

Did I say I'm using an lm358 op amp?

I'll post up a drawing later if i get the chance
My better half is making me a Honey Do list as I type....... Happy days.........