MXR Noise Gate attack control, how?

[Fp-www.Tonepad.com]

Can anybody suggest a way to add a variable attack control to the MXR Noise Gate?

Here's the schematic/etc:

http://www.tonepad.com/project.asp?id=18

A quick look makes me think that the 1uF cap going from Q2 colector sets both the attack and release... I could be very wrong though!

Help!

Fp

[Aharon]

There's two noise gates at Hammer's site.I think they either have or talk about how to implement attack/release controls.
Might be interesting to check them.
Take care Fp
Aharon

[Fp-www.Tonepad.com]

Thanks A,

I'll check them out.

Fp

[Mark Hammer]

Pardon me for sounding impudent, but is that schematic verified to work?  I'm loking at it and looking at it and I can't for the life of me figure out how it would work.  IC1a obviously forms the sidechain for detecting the envelope, but there is nary a diode to be seen, so how does it know when a note is on?

I've also had a hard time grappling with the momentary switch thing. I used to have a Noise-Gate Line Driver back in 1978, but that baby was as latched a switch as you could get.  Is this a different model than the old 1590B type pedal?

The only thing I can see that might affect timing is the 1uf cap by the switch on the right, but that would likely only have an effect on decay time, not attack time.

Can somebody explain a little more about this circuit.  It really looks unlike any use of a sidechain and FET that I've ever seen.

[Fp-www.Tonepad.com]

Hi Mark. The schematic is verified, actually I have redrawn the whole schematic to try to make some sense out of it by 'defining' the circuit blocks. The circuit has been successfully built and I also have it on the simulator, and it works there too...

Here's  my take at what makes this one tick:

Vbias is provided by the 22kohm/5.1vzener/10uF cap...

Input to transistor buffer is split in two singals, one going to the envelope detector and the other one to the actual signal path.

The 500k pot sets the threshold of the gate, amplified / filtered... how the envelope is extracted is beyond my understanding.
When the voltage at the gate of the FET is high, the signal that was split before is grounded (to vbias) thru the 10uF capacitor (FET is conducting). BTW, I think the 10uF capacitor is oriented wrong.

When the voltage at the gate of the FET is low, the FET opens and signal passes tru 0.01uF capacitor, is biased by the 1M resistors and feeds the second half of the opamp, going to the output. (which is what happens when you engage the switch)

The momentary switch is just suggested as that in all the MXRNG schematics I've found. All the MXRNG schematics are available thru aron's 'schematics2'. (I think)

I'd really like to figure this pedal out.

Fp

[Ed Rembold]

Francisco,
Does this design really work well or just "function"?
It seems to me,  like it would be prone to "chattering" as the signal decays.
Looks like IC1A is gonna make a square wave out of the input signal , which is HP filtered.  Looks like the fet Q3 sees this and the output signal at its gate at the same time,  and shunts the signal to ground (through Vb) by doing some sorta comparison between the 2 signals.
I dunno.....I remember Robert Strand talking about this sometime back- I should have paid more attention-  Maybe it's in the archives?
Nice schem....
Ed R.

[Fp-www.Tonepad.com]

Ed,

The design works quite nicely, check out the Build reports.

What Rob mentioned was that because the original circuit used a 741, the better high freq response of the 4558 could induce oscilation, which was fixed by adding a small ~50pF cap across the 1M resistor in the neg feedback.

Fp

[Ed Rembold]

Wow Francisco!
Those build reports are excellent-  forgive me for not
checking those out-
I think I'm gonna a least bread-board this thing-
but, leave out the "momentary" switch,
I'm thinking that is not real necessary.
Thanks,  Ed R.

[Fp-www.Tonepad.com]

Ed,
I hope you do get to at least breadboard this one.

I've added attack and release controls based on the article at Mark Hammer's page... Thanks A, you set me on the right track!!

You can download the latest pdf which has the mods on page2 here:

http://www.tonepad.com/project.asp?id=18

A disclaimer: I haven't performed these mods, I've only tried them on the simulator, so procede at your own risk.

Fp

[Ed Rembold]

Thanks, Francisco-
Nicely done,  I will breadboard this thing and post back.
It's hard being a high-gain fool,  and hating "hissss",
I had a Hush Super C in my rack days,  but I was never happy
with it.  When set to silence the hiss,  it would clamp off
my sustaining notes and delay trails.
We will see-  I'm even more fussy now than I was then......
Thanks again.
Ed R.

[Fp-www.Tonepad.com]

Hi Ed,
If you try the attack and decay controls I'd like to hear how they work.

I was thinking I may need to add a 'max attenuation' and a level control (adding gain, before, of course), because of the possibility to make this one a volume 'swell' kind of thing (using a long attack time)

... Adding those two knobs to the 3 already there will make it 5... and it'd be cool to have a sort of band pass filter or something that will let you 'gate' only some frequencies... making this one a 6-7 knobber...!... but that's just a possibility for the future.

Remember to locate the noise gate right after the noise making device in your rig... I wouldn't have it after a delay because of the reasons you mention. More like: Distortion (noise making), Gate, Delay.

Fp