AQR Noise Gate

[Kipper4]

Rankot I tried a 1M pot to Gnd // with the 22uf and I was not of much use. Not worthless either.
Depending on playing dynamics and note/chord lengths i can mostly get what I want without the extra pot.

I've settled on a version without the key input or send/return loop.
2 knobs 1 switch should squeeze nicely into a 1590b.
Currently doing a perf build.
My first in a month or so. It's been all learning and modifiying for a while.
Tonight I get to inhale the sweet smell of solder flux.

If I come back in the morning asking for debug tips.... Just run


Great little circuit Adiel thanks.
Rich

[Kipper4]

Only two problems. Envelope ripple and thump when the shunt opens.
Grrrr

[rankot]

Ripple was the reason why I have changed all those things...

[Kipper4]

Can you elaborate please. I'm struggling to see how the decay pot works.

[rankot]

I am not sure, I built it first to original schematic, then noticed ripple at decay. Maybe I forgot to put 470n cap (C6 on your schematic), however, I tried to solve that. Since I didn't build it on a breadboard (I made PCB thinking it will work fine  ), I decided to model it in LTspice and experiment there, to avoid PCB damage . So I did that and started tweaking various parts, finally settling at published schematic. I am currently very busy with regular job, so I can't unbox it and try different options (swell, for example), but I will do that in few days.

However, if you are still in breadboard phase, you can try to alter R10 and R11 and see what will suit your needs - it made ripple gone in my case.

And I forgot why I've changed C4 on my schematic to 1u (C3 on yours)! Sorry...

[Kipper4]

Thanks mate.
I must of made a gaff.
If you still have the sim can you see what the voltages on the last transistors are for me pls.

[rankot]

This is the file so you can try to mess with it yourself. I believe that the most important change is R11 on your schematic, it shall be 100 Ohm, not 100k.

http://www.cad.rs/d/AQR-noise-gate.zip

[Kipper4]

It was the cap hanging off the base of the last transistor that was causing the thump. I made mine 10uf.
Sorted.
If I use a 100 Ohm between the two last transistors it doesnt work as a sweller.
I found the minimum for my application between 22k~47k.
You have to be mindful of the collector voltage when changing the resistors..

[rankot]

Have you sorted out the ripple with those resistors or not?

[Kipper4]

Yes thanks just needed a bigger cap on the base.
I'll write it up when I finish work.

[rankot]

It was the cap hanging off the base of the last transistor that was causing the thump. I made mine 10uf.
Sorted.
If I use a 100 Ohm between the two last transistors it doesnt work as a sweller.
I found the minimum for my application between 22k~47k.
You have to be mindful of the collector voltage when changing the resistors..

Maybe you can use 100 ohm fixed in series with 100k pot for swell controll?

[Kipper4]

I'll come back at the weekend over a cup of coffee or two and write some more.

Since getting back form work I've got one of those annoying little lead cut offs in my toe and given my left pink a second degree burn with the hot melt gun.
Bonus is I've wired up an indicator led and the boards nearly ready to box.
I have one more possible ammendment in stall. I'll see what happens on the breadboard with that one.

I'm off to bed to cry myself to sleep .

          "Night John boy"

[Kipper4]

Heres where I am with the sweller/gate (actual build varies from the breadboard in that charge cap mostly.
It does what I wanted. Not just a gate but a gate as an effect and a sweller too.

[rankot]

Is this C11 really necessary?

[Kipper4]

Real world pcb wouldn't function just with the 470nf.
Might be faulty?

So I tried 470n 1u 2u2 4u7 10u
That's what worked best.
I can't simulate the behaviour on the breadboard.

I tried a series R between cap and gnd. 
Has to be a small value.
Not worth the part probably since it didn't really solve the issue.

Here's some fooling.

[rankot]

My noise gate is without 470n (C11) and I have 10u (not swelling, because my R12 is 100R). So I thought that you don't need C11 at all, since you also have C10 in your schematic at the moment.

[Kipper4]

I couldn't get the range of swell times I wished for without the // cap arrangement.
I could sacrifice the 470n and a 10 but it will limit the range of swell effects.
I'm not sure why it's behaving like this. The breadboard version does not display such behaviour. Although I've had my problems with it.
A 100 ohm will make it work better as a gate.

[highwater]

I've seen several schematics with a small ceramic cap in parallel with a large electro, though usually for power supply filtering.

IIRC, the idea is that the electro could have significant parasitic inductance or resistance (or maybe both? I forget) that cause it to filter poorly at high frequencies.

In other cases, the electro filters the entire supply rail, and *every* IC gets it's own ceramic decoupling cap as close as physically possible to the supply pins. This appears to be nearly-universal in most fields of electronics -- virtually every opamp datasheet suggests it. In that case, I think they're entirely to counteract stability issues stemming from the resistance of the PCB traces themselves.

[adielricci]

My original values were the ones that worked better for me, regarding opening/closing times, as well as swell...

I really like this discussion, as we tend to learn a lot more when things do not match our needs.  Congratulations, boys! 

[megabelkins5000]

Boldly resurrecting this thread as a noob to ask the AQR experts, do you think a TL071 IC can be used in place of the 741?