Need switch to mute line to DI box for bass player changes

[ggunn]

If you run an A/B box, you don't want to just leave one input open, as that will give you a nearly infinite output impedance to whatever you're plugged into. Instead, buy a 1/4" TS "mono" connector and solder the tip and sleeve together, and insert that into the unused input. This will allow whatever you have the A/B box plugged into to see a zero-Ohm output impedance, which will prevent a high impedance input from amplifying noise/hum. Otherwise, you're going to end up with "open guitar cable buzz."

Not necessarily. I use a passive A/B switch and sometimes I only have one bass plugged into it. When I select the empty input it doesn't buzz at all. That buzz of which you speak mostly happens when that you have a cable plugged in and the other end is lying around where the tip can contact something ungrounded and conductive which acts as an antenna for all the 60Hz RF that surrounds us.

 

[line6man]

Not necessarily. I use a passive A/B switch and sometimes I only have one bass plugged into it. When I select the empty input it doesn't buzz at all. That buzz of which you speak mostly happens when that you have a cable plugged in and the other end is lying around where the tip can contact something ungrounded and conductive which acts as an antenna for all the 60Hz RF that surrounds us.

The tip terminal of the instrument cable would be shielded by the Faraday cage of the pedal enclosure, doing a better job at keeping out RFI/EMI than if the cable were simply lying on the floor unconnected. However, an infinite impedance at the instrument end of the cable is still not the proper way to go about when attempting to fully mute the signal. Ideally, you want a zero-Ohm impedance, which effectively prevents an input gain stage from conducting any electrons, except what can be induced to flow within the equivalent series resistance between the ground potential and signal. This impedance is likely to come down to fractions of an Ohm, so things will stay dead quiet, unless the gain stages in your amplifier are noisy themselves. How much effort will be required to create a near zero-Ohm output impedance, and how practical is it to do so? All you have to do is grab an old cable, cut the connector off the end and solder it's tip and sleeve together. Then you plug the connector into the A/B box and forget about it.

 

[walterw]

some store-bought A/B boxes have resistors in them to reduce the noise from an open connection.

unfortunately, those same resistors can be tone sucks with passive instruments.

the right way to wire an A/B box is so that the un-selected side automatically shorts to ground; it's also the right way to wire true-bypass pedals, and for the same reason:

while you're at it, you can stick a tuner in the unused side, for true-bypass silent tuning with any tuner.

 

[ggunn]

The tip terminal of the instrument cable would be shielded by the Faraday cage of the pedal enclosure, doing a better job at keeping out RFI/EMI than if the cable were simply lying on the floor unconnected. However, an infinite impedance at the instrument end of the cable is still not the proper way to go about when attempting to fully mute the signal. Ideally, you want a zero-Ohm impedance, which effectively prevents an input gain stage from conducting any electrons, except what can be induced to flow within the equivalent series resistance between the ground potential and signal. This impedance is likely to come down to fractions of an Ohm, so things will stay dead quiet, unless the gain stages in your amplifier are noisy themselves. How much effort will be required to create a near zero-Ohm output impedance, and how practical is it to do so? All you have to do is grab an old cable, cut the connector off the end and solder it's tip and sleeve together. Then you plug the connector into the A/B box and forget about it.

All I know is that in my setup it's not necessary. I know the theory (I have a BSEE) but the real world trumps it.

 

[ggunn]

some store-bought A/B boxes have resistors in them to reduce the noise from an open connection.

unfortunately, those same resistors can be tone sucks with passive instruments.

the right way to wire an A/B box is so that the un-selected side automatically shorts to ground; it's also the right way to wire true-bypass pedals, and for the same reason:

while you're at it, you can stick a tuner in the unused side, for true-bypass silent tuning with any tuner.

You could also wire it with shorting jacks so that if nothing is plugged in to an input it is shorted to ground. That oughta keep line6man happy.

 

[line6man]

You could also wire it with shorting jacks so that if nothing is plugged in to an input it is shorted to ground. That oughta keep line6man happy.

Yes, 1/4" TS jacks with break terminals tied to the ground potential will do the job nicely. That takes more effort to rewire than simply shorting a 1/4" connector and plugging it in, however.

Note that in Walter's diagram, the jacks are shorted when they are not wired to the common. This works great for keeping the unused output quiet when selecting from a single input, but it doesn't really do anything in this application, where two inputs are switched to one output, with one input needing to stay quiet.

I don't know how much difference it truly makes in the real world, but given how simple it is to satisfy the theoretical concern of noise, I'd rather do it proper for the peace of mind. You guys are making too much of this, lol.

 

[ggunn]

Yes, 1/4" TS jacks with break terminals tied to the ground potential will do the job nicely. That takes more effort to rewire than simply shorting a 1/4" connector and plugging it in, however.

Even simpler is to just plug in and try it. If it's not a problem (it isn't for me) don't worry about fixing it.

 

[line6man]

Even simpler is to just plug in and try it. If it's not a problem (it isn't for me) don't worry about fixing it.

Whether or not it is a problem is something that is subject to change, as there are several variables involved.
The input impedance of the gear you choose to plug into, the presence of electrical and magnetic field noise and sources of/proximity to their emission, the volume at which you play, the amount of background noises (People talking, etc.) masking stage amp/monitor and PA noises and many other factors come into play, which may be different from gig to gig.

 

[Dave W]

Plugged output to amp, input to bass. Made sure it was muted (tuning mode) and unplugged. There was a slight low-frequency pop.

It may do this because my bass has active pickups. I haven't tried it yet with the output to the DI box.

Whether the bass is active or passive doesn't make a difference. I use both very regularly with a few different tuner pedals with no issues.

A TU-3 is a good pedal and that shouldn't happen. Is it still under warranty?

 

[onosson]

I still think one of those cables with a mute switch built-in to one end is the best solution given the situation you describe. It involves zero extra gear, as it replaces your existing cable, needs no modification, and has the shortest signal path from instrument to amp.

I have a friend who runs an acoustic open mic night. He uses one of these for the various guitarists who want to plug into the board - one cable for everyone, no switches or boxes necessary.

 

[ggunn]

Whether or not it is a problem is something that is subject to change, as there are several variables involved.
The input impedance of the gear you choose to plug into, the presence of electrical and magnetic field noise and sources of/proximity to their emission, the volume at which you play, the amount of background noises (People talking, etc.) masking stage amp/monitor and PA noises and many other factors come into play, which may be different from gig to gig.

Theoretically. In practice I have been using this setup for eight years in a wide variety of situations and not once has there been the slightest problem. There is more (far more) noise from the passive bass I sometimes plug into it than has ever been sourced from the open input.

In order for noise to be generated across that virtually infinite resistance, an AC differential voltage must be present across the terminals. Within a closed, grounded metal box, that isn't that likely.

Do whatever makes you happy, but I'm leaving well enough alone. As I say, I am an electrical engineer, and if there were a problem, I'd solve it.

 

[line6man]

Theoretically. In practice I have been using this setup for eight years in a wide variety of situations and not once has there been the slightest problem. There is more (far more) noise from the passive bass I sometimes plug into it than has ever been sourced from the open input.

In order for noise to be generated across that virtually infinite resistance, an AC differential voltage must be present across the terminals. Within a closed, grounded metal box, that isn't that likely.

Do whatever makes you happy, but I'm leaving well enough alone. As I say, I am an electrical engineer, and if there were a problem, I'd solve it.

Alright, this might not be as big of a concern as I'm thinking it could be.

In any case, the use of an A/B box should present a quick and easy option for the OP to mute his bass. That's all that matters.

 

[ggunn]

Alright, this might not be as big of a concern as I'm thinking it could be.

In any case, the use of an A/B box should present a quick and easy option for the OP to mute his bass. That's all that matters.

If it were I (and I am in the same situation as he is), I'd just plug both basses into an A/B and be done with it. But he knows that.

 

[line6man]

If it were I (and I am in the same situation as he is), I'd just plug both basses into an A/B and be done with it. But he knows that.

Exactly what I would do, as well. The OP has expressed a disinterest in going about this way, however, because it means having more cables on the stage floor. Personally, I think that's a bit silly, but whatever floats your boat.

 

[walterw]

i switch between two guitars all night long in one band, and between guitar and lap steel in another; if i had both instruments with their own cables plugged into some kind of switcher, the two cables would be a tangled knot halfway through the first set

it's pretty easy to have a stomp-mute setup of some sort (you should have one for tuning anyway, right?) and just unplug silently.

 

[walterw]

Note that in Walter's diagram, the jacks are shorted when they are not wired to the common. This works great for keeping the unused output quiet when selecting from a single input, but it doesn't really do anything in this application, where two inputs are switched to one output, with one input needing to stay quiet.

why not? turned around to have two ins and one out, the unused input is shorted to ground, and so can generate no noise.

(oh, and i didn't make that diagram, i just dug it up on the google.)

 

[line6man]

why not? turned around to have two ins and one out, the unused input is shorted to ground, and so can generate no noise.

(oh, and i didn't make that diagram, i just dug it up on the google.)

Dammit! How did I miss it this whole time?
I was thinking about using the A/B box to select two inputs, since the OP had mentioned the A/B switch for two inputs, but all you have to do is run it the other way around, as an amp selector. The bass can go to the common, and the amp to one side. That way the outputs get shorted when they are not connected to the commons.

 

[ggunn]

i switch between two guitars all night long in one band, and between guitar and lap steel in another; if i had both instruments with their own cables plugged into some kind of switcher, the two cables would be a tangled knot halfway through the first set

To each his own. I switched between a Strat and a Les Paul for many years with an A/B switch and never had a problem. I put the Paul on a stand on one side of my amp and the Strat on the other. I always put the one on the stand before picking up the other and my cables never got tangled.

But there are obviously multiple ways to skin this particular cat.

 

[walterw]

I put the Paul on a stand on one side of my amp and the Strat on the other.

that makes sense; i don't always have the luxury of that much space

 

[ggunn]

that makes sense; i don't always have the luxury of that much space

Even if you have both guitars on a combo stand, if you get in the habit of racking one before you pick up the other, the cables won't tangle. If you are trying to do it with a single stand... well, no wonder you have problems.