AQR Noise Gate

[rankot]

I've seen this interesting noise gate made by Adiel here: http://www.diystompboxes.com/smfforum/index.php?topic=116919.msg1103734#msg1103734, and after some Googleing I found schematic and some PCB on Brazilian board, here: http://www.handmades.com.br/forum/index.php?topic=9870.0

Build was a success, it started working immediately, but soon I've noticed some problems. First of all, it had a nasty habit of tremolo-like decay, second, it worked very strange with bass. So I decided to improve it a little, and this is the result:



I've changed C4, R11, R2 and Sensitivity pot, added Decay pot and removed swell switch.

[rankot]

This is the finalized pedal:

[Kipper4]

Did you try any other transistors?

[rankot]

No, why? I believe you can use almost any NPN, only use low noise NPN for input buffer.

PCB for anyone interested to build this, I hope it will fit in 1590A 

[Kipper4]

C4 and C5 are back to front. your drawing.


Well Heres what I've made of it so far on the breadboard.
Subs
All jellybeans used are 2N5088.
Some value are changed arbitrarily depending on what was left over in the breadboard parts box.


I didnt like the way your decay pot futzed with the transistor.
So I removed it.

I added a 10k (Attack) resistor R17 (my drawing)this changed the time constant and made the transistor on/ off smoother.
I'm guessing this is what you were trying to achieve with your decay pot.

You can futz with this some more if you wish.
Maybe a series R + Attack pot wired as a varable resistor in the place of R17.
Maybe 1k+B10k pot?


You note that I've also tried some different values for C12 (mine) this had a similar effect to the new R17, ie changing the time constant as before.

I made a switchable swell feature (with two swell times) similar to that seen in the designers drawing.

I also added a noiseless biasing network for the op amp rather than the one the designer used  (2x 100k)
Probably futile and a waste of parts on my behalf, but I'm happy with it.
I've no doubt I could have biased the Q1 with it, but it's not really saving any parts.





Rich

[Kipper4]

It is quite a noisy circit too.
I forgot I swapped out the sens pot to a B1M.

[rankot]

C4 and C5 are back to front. your drawing.

That's how my drawing app shows capacitors, those two are not electrolytic, so it is not important how are they rotated.

I didnt like the way your decay pot futzed with the transistor.
So I removed it.

I had probably the same problem without it - vibrato style decay

I added a 10k (Attack) resistor R17 (my drawing)this changed the time constant and made the transistor on/ off smoother.
I'm guessing this is what you were trying to achieve with your decay pot.

You can futz with this some more if you wish.
Maybe a series R + Attack pot wired as a varable resistor in the place of R17.
Maybe 1k+B10k pot?

Interesting, I'll try that too.

What it the effect of that swell? I can't remember how it sounded, but I presume I didn't like it or thought that it is affecting decay stability, so removed it. It was one month ago, and I can't remember

[rankot]

It is quite a noisy circit too.
I forgot I swapped out the sens pot to a B1M.

Interesting, I didn't find it noisy at all? Maybe using BC550 for buffer is really that important?

[Kipper4]

Looks like you left the swell cap ,22uf on the drawing......
Also is R2 really 100 Ohms.

[rankot]

Yes, I left one of those swell caps, can't remember what happened when using another one? According to LTspice, it shall affect attack?

I made R2 100 Ohms beacause it seemed to work the best, at least in simulator.

I've also changed R16 to 10k to have less noise. Also, C11 should be at least 1u, for better low freq response.

[rankot]

If I remember well, this combination of R14/C6 was necessary to have LED indicator working well.

You can find LTspice file of this gate here: http://www.cad.rs/d/AQR-Noise-Gate.asc

[adielricci]

Interesting, I didn't find it noisy at all? Maybe using BC550 for buffer is really that important?

Yes, the BC550 is an ultra low noise device.  That's why I recommend using it.

I've also changed R16 to 10k to have less noise. Also, C11 should be at least 1u, for better low freq response.

1uF for C11 might change the time response, as well. My intention was to provide a simple circuit to suit my needs, not having to resort to rare or expensive components.

I am really glad and honoured it may serve others, and I am going to try all of your nice suggestions here, as soon as I have some free time.

And Rankot, the pedal and the layout are great, congratulations!  I am flattered! 

[Kipper4]

https://youtu.be/m4G_WlM37U8

[Kipper4]

I've been having breadboard problems hence the distortion. It's been a lot worse off camera.
I now have a functioning gate/sweller on the breadboard.
Thanks firstly to Adiel for the design and share.

I've made a few changes I hope you don't mind.
To better suit the swellers needs. Ie having a degree of control over the gate shutting.
So I added a few features, renamed a few, even added an untested decay mod.

R13 (below) is new. Still not sure of its usefulness until i scope this.
I tried 100k,220k. no go
560k that worked so I went 1M as I say I'd rather see the results before I'll commit.

The addition of the "sens" (envelope gain) just gives a bit more control over the gate shutting, not so Important when swelling long sweeping chords but for the fiddly diddly stuff we need a gate shut to order.

The two swell caps on the switch are for long chord swells 22uf
                                                            and short swell 4u7.

I wouldnt bother going much above 22nf for the envelope charge cap C5 (below)


I added a small cap to the envelopes NFB too.

Some voltages included

Thank you both great thread.

Edit. Erratta. theres a 1uf NP cap missing between gate pot wiper and Non inverting input.

[Kipper4]

Heres an updated drawing with side chain.
C4 is bigger. Thanks for the advice Stephen.


The side chain may need a series 100k + series diode on the input depending on the signal fed.

[Kipper4]

[rankot]

Just to ask - why've you removed gating indicator LED?

[Kipper4]

I figured it would be pretty moot on the breadboard.
A distraction. I'll probably try it before I think of doing a layout.

Did you find any of my findings useful.
I tried a few send return effects and that would need some more tweaking.
As would a key input, you never know what someone's gonna plug into it.

I was pretty interested in the swell feature
It's just a shame the amp has some distortion and noise.
It does some nice long chord swells to short note swells.
Bonus is, it's a fair gate too.

[adielricci]

Kipper4, thanks a lot for the nice ideas.  When I tried C4 (last schematic diagram) at 10n, the gate seemed to take too long to close, letting some noise pass through.  That's why I settled for 2n2.

The 3-position switch is a clever touch, I did not have a small enough switch at the time, to fit in a 1590LB...

External triggering reminds me of the Gator, from Craig Anderton. Great idea!

[rankot]

Kipper4, I have already boxed my gate, so I am kind of lazy at the moment to experiment (really hate unboxing and boxing again), so why don't you try to add 1M pot instead of swell switch and use only one 22u capacitor? How would it work?