Amp/Cab switcher patchbay box thingamajig

[Greg_L]

I've been wanting to build one of these for a long time. I have a bunch of amps and cabs. It's a minor inconvenience to reach behind everything to swap around cables from amps to cabs. I use my attenuator as makeshift common junction box between amp heads and cabs, which helps, but it still means I have to physically hook whatever amp I want to use to the attenuator, and then hook a cab to it.

My idea is to build one box with heavy duty rotary switches that everything stays connected to permanently. Then I can just turn knobs to select amps and cabs....which are already all hooked up.

Something like this, using my awesome MS Paint CAD skills.

amp-cab switcher.jpg

I think this would be a pretty cool solution for my self-inflicted first-world problem of too many amps and cabs.

[Tadpui]

I love this idea! I could even use such a thing to avoid plugging and replugging my amps into my Torpedo.

Can you design it in such a way that it still presents a load to an amp that isn't actively flowing thru to a speaker? Just to avoid accidental oopsies when using the selector...

[JD01]

I was thinking the same thing as Tad. If I had something like that I would just end up being a convenient way of blowing up amps.

[Greg_L]

I love this idea! I could even use such a thing to avoid plugging and replugging my amps into my Torpedo.

Can you design it in such a way that it still presents a load to an amp that isn't actively flowing thru to a speaker? Just to avoid accidental oopsies when using the selector...

I was thinking the same thing as Tad. If I had something like that I would just end up being a convenient way of blowing up amps.

I'm sure there is a way. I thought about that, but I'm not sure yet how to do it.

As long as there's always a cab(s) connected, the cab selector switch can be set anywhere. That side will always have a load. So the potential for goofs would be on the amp side. Each amp will be connected to the amp selector rotary switch, but the switch can only connect one amp at a time to a cab. So the remaining amps will have no load if they're not selected. Not a problem if they're not being played, but if I plug into Amp A and the switch is set to Amp C, then that's potentially a problem. The easy solution would be to just not make that mistake. But we aint perfect beings.

For me, since I only use 16 ohm cabs, I think I could use switched jacks and wire a 16 ohm ballast resistor in parallel to ground at each jack, but that would halve the impedance the amp sees. So my 16 ohm cabs would appear to the amp as 8 ohm cabs. I could just set all of my amps to 8 ohms. And in the event that I forget to set the switch to the amp I'm using, there won't be a no-load situation. The amp will see the 16 ohm resistor to ground. An 8/16 mismatch is no big deal, and it's especially no problem for the very brief amount of time that I'd be accidentally trying to force sound through it. That might work. Maybe. I'd have to mock it up and test it out with the multimeter.

[liv_rong]

This is an awesome idea. Have you picked out dials yet? Des such a thing exist?

[Greg_L]

This is an awesome idea. Have you picked out dials yet? Des such a thing exist?

I think I'd need a switch that can handle about ten amps. What comes out of the power tubes of an amp is very high voltage, but low amperage. It goes through the output transformer where it's flipped to low voltage and high amperage. It might only be 30-40 volts at the speaker jack, but it's flowing with high amperage to drive the speaker coil. Most Marshall impedance selectors are like 10A/250V handling switches, and they're some of the most powerful amps going these days, so I figure if I can find a 6-way switch around those specs for my switcher box I should be fine.

I haven't even looked yet, bu surely there's something out there that will do the job.

[Greg_L]

Bam, 5 seconds of Googling.

https://www.allelectronics.com/item/rsw ... tch/1.html

That might work.

[Greg_L]

https://www.mouser.com/datasheet/2/60/h-1382605.pdf

[liv_rong]

Wow much cheaper than I thought. I mean I knew it wasn’t going to be a lot but I figured like $10.

[Greg_L]

Wow much cheaper than I thought. I mean I knew it wasn’t going to be a lot but I figured like $10.

Yeah. Say an adequate enclosure is like 15 bucks.
https://www.tubesandmore.com/products/c ... -470-x-205

That might be a big enough box. The switches aren't huge, but whatever it is it has to accommodate at least nine jacks - 6 in - 3 out - in some kind of array. They can be in-line, or two per side, three on one side, whatever. It just has to take nine jacks and two big switches comfortably.

So like 15-20 bucks for an enclosure.
Maybe 10 bucks total for the switches and knobs.
About ten bucks for some decent jacks.
I have wire and drills and solder and shit already.

So I'm thinking about 40 bucks to make something cool and very functional.

Maybe even less. I have some old die cast knurled P-Bass knobs laying around that would probably work perfectly. But I think I'd want chickenheads on something like this.

[SweetDan]

I love this idea! I could even use such a thing to avoid plugging and replugging my amps into my Torpedo.

Can you design it in such a way that it still presents a load to an amp that isn't actively flowing thru to a speaker? Just to avoid accidental oopsies when using the selector...

I was thinking the same thing as Tad. If I had something like that I would just end up being a convenient way of blowing up amps.

I'm sure there is a way. I thought about that, but I'm not sure yet how to do it.

As long as there's always a cab(s) connected, the cab selector switch can be set anywhere. That side will always have a load. So the potential for goofs would be on the amp side. Each amp will be connected to the amp selector rotary switch, but the switch can only connect one amp at a time to a cab. So the remaining amps will have no load if they're not selected. Not a problem if they're not being played, but if I plug into Amp A and the switch is set to Amp C, then that's potentially a problem. The easy solution would be to just not make that mistake. But we aint perfect beings.

For me, since I only use 16 ohm cabs, I think I could use switched jacks and wire a 16 ohm ballast resistor in parallel to ground at each jack, but that would halve the impedance the amp sees. So my 16 ohm cabs would appear to the amp as 8 ohm cabs. I could just set all of my amps to 8 ohms. And in the event that I forget to set the switch to the amp I'm using, there won't be a no-load situation. The amp will see the 16 ohm resistor to ground. An 8/16 mismatch is no big deal, and it's especially no problem for the very brief amount of time that I'd be accidentally trying to force sound through it. That might work. Maybe. I'd have to mock it up and test it out with the multimeter.

It really seems like there ought to be a way you don't have to mess around with a fake load. The idea of how most commercial effects pedal wiring uses a TRS (not TS) jack on the input side to keep the battery from draining when not plugged in sticks out. It's not a well formed idea yet, and I'm not quite sure the same type of wiring pattern would really apply, but there might be something there. Something along the lines of:

- Amp Input 1 -> amp switch -> cab switch -> Cab 2 is the desired path
- Amp 1 is plugged in
- But Cab 2 is not plugged in (Danger, Will Robinson!)
- something about the jack* for Cab 2 is wired similarly to how the TRS input on a guitar pedal is wired
- because there's no plug in Cab 2, the circuit is not complete

All leading to the non-event of your amp blowing up. Nice!


*If it's possible to wire any of the output jacks like this, they'd all have to be wired like that

[Greg_L]

It really seems like there ought to be a way you don't have to mess around with a fake load. The idea of how most commercial effects pedal wiring uses a TRS (not TS) jack on the input side to keep the battery from draining when not plugged in sticks out. It's not a well formed idea yet, and I'm not quite sure the same type of wiring pattern would really apply, but there might be something there. Something along the lines of:

- Amp Input 1 -> amp switch -> cab switch -> Cab 2 is the desired path
- Amp 1 is plugged in
- But Cab 2 is not plugged in (Danger, Will Robinson!)
- something about the jack* for Cab 2 is wired similarly to how the TRS input on a guitar pedal is wired
- because there's no plug in Cab 2, the circuit is not complete

All leading to the non-event of your amp blowing up. Nice!


*If it's possible to wire any of the output jacks like this, they'd all have to be wired like that

There has to be a load though. A tube output section wants to see some kind of impedance. An open circuit on the output is bad. This is all in theory. Not having a cab/load hooked up doesn't always mean sudden immediate catastrophic failure, but it certainly aint good. I've nuked power tubes by not having a cab connected. It's a pretty spectacular light show. But I've also cranked my Plexi without the cab plugged all the way in and nothing happened. So it's a crapshoot that could/should be easily avoided.

I'm no pedal expert, but I think they drain batteries when left plugged in because of the buffer. True bypass pedals don't have this problem because there's nothing going on when not in use. But a buffered pedal is always trying to buffer if there's a jack plugged in, so they drain batteries. I don't know enough about it to see how it could help my amp switcher box thing.

A TRS-type switching jack and dummy load could be useful though. Say the dummy load is engaged when the jack is closed (not in use), then it's disengaged when the jack is used. That would work, but it defeats the purpose of the switcher box. My idea is to leave everything plugged in all the time so all I have to do is turn knobs. I want all of my amps and all of my cabs plugged into this box at all times so all I have to do with the box is select and amp and select a cab by turning two knobs. The danger is accidentally trying to use an amp that has not been selected resulting in it "seeing" no cab load.

[SweetDan]

...A tube output section wants to see some kind of impedance. An open circuit on the output is bad...The danger is accidentally trying to use an amp that has not been selected resulting in it "seeing" no cab load.

Ok, I didn't understand the danger from that side of things, but it makes sense: the amp is still going to do work, even if there's nowhere for the signal to go. Going along with you're picture, you're trying to prevent the case where the switching box is configured "Amp 2 -> Cab 1", but the guitar is playing into Amp 1. BAM! Signal goes out of Amp 1 and ...?

Regarding the case of not ever unplugging things, yes, you might not...but what are your band buddies going to do with the box when you take this thing to rehearsal to show it off?

So, really, I think in general there are two dangerous situations to avoid: un-loaded signal at either input or output side. A possible solution could be routing everything to a dummy load -- all the amp inputs and all the cab outputs -- unless explicitly selected. So, TRS jacks all around, wired so that any jack in the unplugged position routes to the dummy load, but routes to the next component when plugged in.



Disclaimer (for all the rest of the internet; I'm not worried about you Greg or any of the regulars 'round here): I'm not an EE; any commentary regarding electronics made by me is not an indication of suitability for any purpose; use at your own risk; blah blah blah.

[Lt. Bob]

cool project.

It ought to make some things a lot easier.

I recently read an interview with ............ can't remember .... it was someone high profile like Zak Wilde or Van Halen or someone.
Anyway ..... they had their own studio and a shitload of amps.
What he did to keep from accidentally running any of his old delicate marshalls without a load is he had only one power cable so he'd have to change that to get any amp tp run. So it would always remind him.

But your switching box is way better and will be easier to deal with.

[Greg_L]

Ok, I didn't understand the danger from that side of things, but it makes sense: the amp is still going to do work, even if there's nowhere for the signal to go. Going along with you're picture, you're trying to prevent the case where the switching box is configured "Amp 2 -> Cab 1", but the guitar is playing into Amp 1. BAM! Signal goes out of Amp 1 and ...?

Regarding the case of not ever unplugging things, yes, you might not...but what are your band buddies going to do with the box when you take this thing to rehearsal to show it off?

So, really, I think in general there are two dangerous situations to avoid: un-loaded signal at either input or output side. A possible solution could be routing everything to a dummy load -- all the amp inputs and all the cab outputs -- unless explicitly selected. So, TRS jacks all around, wired so that any jack in the unplugged position routes to the dummy load, but routes to the next component when plugged in.



Disclaimer (for all the rest of the internet; I'm not worried about you Greg or any of the regulars 'round here): I'm not an EE; any commentary regarding electronics made by me is not an indication of suitability for any purpose; use at your own risk; blah blah blah.

The thing I think maybe you're missing is nothing will ever be unplugged...until I take some of this stuff to a gig. At home, all amps and cabs will be joined through this box. When you use an amp head and a separate cab, they are connected by a lowly speaker cable. So I'm taking six of my heads and connecting each one of them into this box. Then on the other side of the box, three cabs will be connected. Six speaker cables coming in one one side, three going out on the other side to cabs. So everything is always connected, but each head and cab has to be selected by the rotary switches.

The issue is the amps that are not selected. The cabs don't matter. Forget that side of the box. Cabs don't care. They're just a box of speakers. The amps though need to be connected to some resistance when being used. The potential for danger is turning on an amp to use, cranking it, banging a chord, and not having that amp selected on the switcher box. The signal goes to nothing and jumps across output transformer windings. That's bad. It has no connection to a speaker load because the amp selector switch is set for a different amp. So I need to think of a fail-safe for that scenario. The TRS switchable jack idea is good if there's nothing plugged into the jack. A simple mod to any amp is to use a switchable speaker jack that shunts the output signal through a resistor to ground in the event that a speaker load is not present. The OT still sees a load. But in my example there is always something plugged into every jack on the switcher box. So I'd need to make those connected but not selected amps see some kind of load in the event they try to get used without being selected. There's the rub. Actually, I don't need to do it because I won't make that mistake, but the potential is there and it's a neat brain exercise to figure it out.

[Greg_L]

cool project.

It ought to make some things a lot easier.

I recently read an interview with ............ can't remember .... it was someone high profile like Zak Wilde or Van Halen or someone.
Anyway ..... they had their own studio and a shitload of amps.
What he did to keep from accidentally running any of his old delicate marshalls without a load is he had only one power cable so he'd have to change that to get any amp tp run. So it would always remind him.

But your switching box is way better and will be easier to deal with.

I used to do exactly just that. One power cable and while I'm back there, make sure a cab is connected. It's a good idea and it works. But it got old and my laziness and demand for convenience has taken over. And the fact that this is a problem of my own creation is not lost on me. I have too many amps and cabs. I created this monster. But I think this would be a cool device to make it all easier to deal with.

I mean , look at this....


Now imagine taking all of that and having it all almost immediately accessible with a twist of two knobs on one box. Instead of reaching behind all that and moving cables around, you just pick an amp, pick a cab, and go. It's all already connected through the switcher box. That would be awesome!

[Lt. Bob]

best amp up there is that purple gregAmp beauty!

[Minerman]

The thing I think maybe you're missing is nothing will ever be unplugged...

This is exactly why I've been interested in something like this...
Even if I only have 2 measly little amps, compared to Greg's Angus & Malcolm setup he has over there...

Really, a simple A/B/Y pedal would work just fine for me...

[SweetDan]

The thing I think maybe you're missing is nothing will ever be unplugged...

I'm not missing that. I don't believe you, though. Quoth the Greg, "Nevermore!", but then went on to say "...until I take some of this stuff to a gig". lol

(And try as we might to protect our gear, and tell the wife and the kids DON'T TOUCH THE GUITAR STUFF, there's always that snot-nosed tow-headed kid wandering off from his family who sneaks behind us and starts poking at the apparently irresistible tangle of amps and cables and power cords and shiny things while me and the band are playing a gig on the patio of the wine bar last week...good thing the rhythm guitarist caught the little pecker before he did any damage! *He* might unplug one of the cables or move the switch on your box; but I digress)


So, anyway, I realized there was a flaw in my suggestion, and you nailed it on the head here:

...But in my example there is always something plugged into every jack on the switcher box. So I'd need to make those connected but not selected amps see some kind of load in the event they try to get used without being selected. There's the rub. Actually, I don't need to do it because I won't make that mistake, but the potential is there and it's a neat brain exercise to figure it out.

Not being an EE myself (insert disclaimer/CYA here), I'm not sure if there's a solution to this problem. If there is, though, it might look like:

1a. connect the fake load to every input
1b. BUT wire the input selector switch so that it disconnects the fake load for the currently selected input
2a. connect the fake load to each output jack
2b. BUT wire the jack such that the fake load is disconnected

I'm fairly certain 2a/2b are achievable in the same way a "true bypass" (not sure about buffered) effect pedal is wired to keep the battery from draining. (http://www.tdpri.com/threads/can-someon ... in.622670/)

However, steps 1a/1b I'm not sure about, but are the trick to making this "foolproof". I have a friend (the rhythm guitarist, in fact) who is a (retired) EE; I'll ask him at our next rehearsal if there's a way to wire up jacks and a switch like this.



BTW, I know you'll do it however you want, and it will be fine, and you won't blow anything up. (Probably. Watch out for that wandering kid, though.) At this point, I'm only still thinking about it because it's an interesting intellectual problem...plus, if I ever built one myself, I'm less confident I wouldn't blow something up. When and if I build it, I can refer back here for the wiring diagram.

[Tadpui]

I used to do exactly just that. One power cable and while I'm back there, make sure a cab is connected. It's a good idea and it works. But it got old and my laziness and demand for convenience has taken over. And the fact that this is a problem of my own creation is not lost on me. I have too many amps and cabs. I created this monster. But I think this would be a cool device to make it all easier to deal with.

I mean , look at this....


Now imagine taking all of that and having it all almost immediately accessible with a twist of two knobs on one box. Instead of reaching behind all that and moving cables around, you just pick an amp, pick a cab, and go. It's all already connected through the switcher box. That would be awesome!

Dammit Greg, stop posting these lurid and lascivious pictures on this innocent forum! I totally did the cartoon wolf "aooooga!" thing here.