1 Ohm resistor volume reduction

[12milluz]

I want to make a killswitch pedal where there is always a 1 Ohm resistor(since electricity takes the path of least resistance) in the line but when the button is pressed, it shorts to the ground and kills the signal without hum. Will a 1 Ohm resistor take much volume off?  What are some other ideas?

[Paul Perry (Frostwave)]

A piece of wire would work even better.
But, where is the signal coming from? Because, I hope it is something that doesn't mind being shorted to ground.

[12milluz]

No, just straight from my guitar. I was going to use a normally open switch;) Which is why I'd use the who resistance part.

[jonathansuhr]

That should work for pop-less killswitching

[R.G.]

Your guitar pickups have about 4K to 10K of resistance and from one to six HENRIES of inductance inside them that can't be gotten rid of. This is why almost all amps and effects have an input impedance of 1/2 to 1M of impedance so that the impedance of the pickup inductance will not cause treble losses - the infamous tone sucking you hear about. In order not to not "take much volume off" the series resistor just needs to be small compared to the input resistance of the amp or effect. In practice, anything up to about 10K works fine EXCEPT (!) that you need to use a low noise resistor because you'll be amplifying its noise as well.

Now, as to being pop-less. It's not pop-free. No mechanical switch can be.

Any time there is an abrupt change in voltage levels, your ear hears that as a "gritch" of the high frequency components that it is. When the signal waveform does this all by itself, the ear blends this into an ongoing buzzy sound. When it happens once, you hear a pop. Well, OK, since it's only signal level, a "tick". Mechanical switches "make" instantly when the metal contacts collide. Then they do it again as the contacts bounce. Then again, then... so you get a few ticks as the switch bounces. Some switches bounce hardly at all. Some bounce a lot, depends on the switch.

If you happen to have the switch make contact right when your signal is already at 0V, then there is no "tick". If you happen to have the switch contact at the moment that your signal is at a positive or negative peak, then the discontinuity is as big as your signal, because the switch makes it instantly zero volts from where it was, and your ear senses the "tick".

This is why most silent switching setups are not mechanical. They go from almost completely open to almost completely closed over a few milliseconds, and this is slow enough to fade the signal down or up, not producing an audible tick. Some Japanese-designed stereos have about half the circuitry being low-rce bipolars and their drivers to make for silent switching. A really great way to do this is with an H11F1 (or -F2 or -F3) LED/FET module. The FET makes an almost ideal variable resistor for guitar-level signals for muting, and the LED controls the FET in a way that does not itself cause ticks and pops. You put the FET side of the device across your signal/ground and cause something like 10ma to flow in the LED when you want silence. It's tick-free both muting and un-muting.

The aforegoing (that's lawyer speak for "what I just said") is only true if your signal has no DC level with the AC that you can hear. If there is a DC level on your signal, any switching that you do will cause a sudden change in signal and a pop. Your only chance at getting a silent switching transition with DC is to switch so slowly that it can't be heard. Otherwise, you need to DC block the signal first to take any DC off the signal.

There is an article at GEO for an mike-muter based on these principles. It uses a burglar alarm mat that you step on when you step up to the mike to un-mute the mike, and then to mute it when you step away. Handy on a noisy stage.

[zachary vex]

H11F1 (or 3 or 2) optoisolators are FET-based and sound awful on a high-fidelity audio signal.  If you are going to spend that much money on such a device, go all the way and get a VTL5C9 vactrol, which sounds perfect.

[johngreene]

H11F1 (or 3 or 2) optoisolators are FET-based and sound awful on a high-fidelity audio signal.  If you are going to spend that much money on such a device, go all the way and get a VTL5C9 vactrol, which sounds perfect.

But he's talking about just shorting the signal to ground (muting), not passing audio through it. I would be surprised if the 300Meg resistance and 15pF capacitance in the off state would affect the signal.

--john

[12milluz]

Thanks guys!

[R.G.]

H11F1 (or 3 or 2) optoisolators are FET-based and sound awful on a high-fidelity audio signal.  If you are going to spend that much money on such a device, go all the way and get a VTL5C9 vactrol, which sounds perfect.

The point is not to listen to the audio passing through the FET, but have the FET completely off - many megohms to ground, and very, very linearly off, or completely on, a few tens of ohms to ground, and also very linearly so. The in-between is where you get the distortion, and you don't get to listen to it all that long in the few milliseconds of fade in/out.

For switching, LDRs have a much more limited range of resistance than photoFETs, so it's not as fully on or as fully off. LDRs have their own distortions, they're just fairly benign ones. Many LDRs are quite slow to respond, so you have to know enough to go pick the fast ones to have a chance to switch instead of fade.

It's almost like there's nothing perfect, and you have to know the limitations of what you're working with and work within them - or choose a different beautiful reality. 

That's putting aside the whole issue of high fidelity sound not being what guitar effects is all about. 

Hey, zv, I understand from a friend that some of your pedals are using the Millenium Bypass now. Howzat working for you?