Active TRIAC

I guess I should say that I'm interested in a very low power TRIAC. I'm not sure if they make these things though as I've only seen high power ones... although I've read that they use low power SCR's in ESD protection.

I guess I should say what I'm interested in doing. I wanted to make a very simple noise gate. I figured I could use a triac to do this quite simply... instead of using a bunch of op amps and transistors. I don't need anything fancy but I'm worried about the nonlinearities of the triac that might end up screwing with the sound.

Hmm, sounds like a silly idea, the triac will cut off every cycle, and I dont dare think how it would work at 20K. The least difficult part of a noise gate these days is the gain element, while the control side involves the most design work, and a good noise gate needs controls so that you can adjust it for the programme material

check out the audiohm link at silonex, or a 4053 mux

martin

But you could use the signal itself to control the gate? That way it won't cut off when the signal itself is strong enough but when its to weak it will. This is basically what a noise gate is and I figure that the real problem is only the implementation. It was just an idea I came up with when I realized that I needed a noise gate. I'm sure there are atleast a million ways to make one but I'm after a quick, easy, and novel one.

It would seem to me that the most simpliest noise gate is a diode... except that it is unidirectional. So then the best is a diac... but then there is no control of noise floor... so then it has to be a triac. My main concern is that it would be hard to implement due to finding the proper components(I cannot find any low power triacs at all ;/).

one could put in a comparator in front of the gate that compares the source with constant voltage and sets the gate if they are close or turns it off it they are not. this way its more of an open and shut thing instead of a gradual change. Maybe the design is not practical though as it might not be very stable.

I'm more interested in making it myself. I don't want it to be to complicated and its really just a small project that isn't important but I figure would be fun to do and to hear the result. Its more like "I wonder if this idea would work" and "I wonder how well it will work" then "I really need a noise gate".

Jon

Not sensibly. That's a way to make sound-to-light effect though.

No. A noise gate follows the programme envelope, not the signal itself on a cycle by cycle basis.

No such thing.

See

Actually, my own gate is much simpler.

Graham

Fine, just hook up a triac to an audio source, turn it on and off, measure/listen to the signal. I guess it will probably have a lot of crossover distortion, if not, you can take it to the next stage.

It's a bit like trying to use a microwave oven as a tweeter

martin

Could you define please what is a "noise gate" ?

thank you, Vasile

It's an audio amplifier that mutes its output when the input signal drops below a specific level for a specific time, say 100mSec.

It is useful when you have a lot of microphones open at the same time, each with its own noise gate, in an uncontroled situation, like a conference table.

When someone talks, the gate will open, on that specific microphone, in say a millisecond or so.

Closely related is the expander, which does not cut but reduces its gain in say a 2:1 ratio, below a certain level

martin

Oh, I see now. This english language has a lot of traps.

One possible design should be a level comparator followed by a retriggerable monostable. As long the signal falls below a set level, the comparator output trigger and start the monostable. As long the comparator output remains unchanged, the time flows on monostable and after the RC period it's changing the output. If the comparator output oscillates because of an input noise, the monostable keep it's output unchanged. The monostabile output could drive the mute circuit.

greetings, Vasile

amp

The more common term is "squelch", not "noise gate".

...Jim Thompson

amp

Yep, prolly in the comms world, but not the little audio world I inhabit. BTW, Vasilie, it is normal to add a few dB hysterysis to prevent hunting around the noise threshold, no need for monostables, just TL074 opamps

martin