Stereo Guitar Cabinet Switcher

I want to switch from one set of speakers to another 'on the fly' via MIDI control, ideally. I want to do this in dual discrete mono (stereo after the source, the source being a guitar). There are mono versions of this switcher but no stereo version.

For the guitar players - I want to switch a mesa/boogie stereo tube amp from a Marshall 4x12 cab (in stereo) to two 1X12 GK openback cabs, one on either side of the Marshall. The GKs are great for time domain effects (delays, chorusing, stereo panning etc) and the Marshall is great for destructo crunch.

The main issue in design is that the tube amp needs to always see a load, so you can't simply 'throw the switch'. I am not an electronics expert - just a guitar player with a soldering iron. Any thoughts?

OMG! another tube amp afficionado? You're going to get heckled for sure.

HiTech said:

OMG! another tube amp afficionado? You're going to get heckled for sure.

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No, we've no problem with valve guitar amps! - there are sound reasons for wanting the high distortion and low quality, you're not looking to hear an accurate rendition of the guitar.

For the OP, from what I gather you want to effectively switch between two pairs of speakers - all you need is a double-pole double-throw switch (DPDT), or a relay. As you want it done from MIDI, a relay is obviously essential, and you should be able to arrnage a MIDI controlled relay.

There's no problem with the valve amp loading, as you're switching from one load to another, not running without a load - the miniscule time interval of the switching isn't a problem.

Why from MIDI anyway?.

Not an afficionado -just a guitar player - is someone going to tell me I'm wrong and that I actually DON'T like the sound of tubes better?..that would be interesting. It's critical to the design, so we might as well get the Tubes vs Trans disco dance over with.

I'm asuming this is going to be used while actually playing the guitar? If so a relay isn't going to work because throwing the switch is going to cause contact noise similar to plugging the guitar in live right?

What about an SCR? I know they're meant for power switching usually but do they work for small signals like this as well?

This isn't a good project for a complete electronics novice, as since you want to do this via midi you need to either buy a midi controller that has a few custom programmable digital I/O lines which would likley cost an arm and a leg, or program a micro controller to make a custom midi interface. Which isn't incredibly complex, but not simple either.

There's nothing wrong with musicians that like tubes. They are better for getting a desired sound out of some instruments, guitars especially. Although with how far digital processing has come today duplicating the sound of a tube should be possible using a simple DSP filter.

Sceadwian said:

I'm asuming this is going to be used while actually playing the guitar? If so a relay isn't going to work because throwing the switch is going to cause contact noise similar to plugging the guitar in live right?

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No, because you're switching the speakers! - a relay is really the only (sensible) option - and is what is always used.

There is a device which is commercially available. It is complex (to me) it uses some method of timing the switch over from one output to the other so that the contact is made to the 'to' destination before the 'from' destination is broken. There is some discussion (on the product site) about how and why this is done (death of the output trans, decreased tube life). Regarding the use of tubes in instrument setups - the electric guitar has become distinct
form other guitar instruments. In the before-time it was just a way to make it audible -Mr Hendrix more or less changed that forever. The whole signal path is the instrument now - various purists arguing about what can and can't be considered part of the instrument. Almost all guitarists will tell you 'tubes are it' when electric guitar tone is discussed. The idea that tubes do not 'render' the guitar accurately is absurd from the point of view that the amplifier is part of the total 'instrument'. I apologize if I am too off-topic. Thanks for the help!

It's not that off topic =) Tube amps are viewed differently by players as opposed to audiophiles. The only exception I think would be someone that has a master in mathmatics, music, and electrical engineering =) Using the right processing elements if you digitize the signal at it's source (basically an ADC at the guitar) You can make it sound like ANYTHING you want, just by programming it properly. But that's even further offtopic than the standard transistor vs tube argument =)

Nigel, why can't an SCR be used to switch a set of speakers? It's an AC signal. You can get SCR's that have absolutley absurd power levels, even more than any audiophile could want. Two SCR's in a triac kind of config should be able to act as a high current relay?

Sceadwian said:

Nigel, why can't an SCR be used to switch a set of speakers? It's an AC signal. You can get SCR's that have absolutley absurd power levels, even more than any audiophile could want. Two SCR's in a triac kind of config should be able to act as a high current relay?

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Why would you want to?, a relay is perfect - it's low cost, simple, reliable, and has no effect on the sound. Using SCR's or TRIAC's meets none of those criteria.

Not sure if the OP wants to switch while he's actually playing which is the impression I got, you couldn't do that with a relay, there would be a audiable click/pop when it switched and a couple ms's of contact bounce.

Sceadwian said:

Not sure if the OP wants to switch while he's actually playing which is the impression I got, you couldn't do that with a relay, there would be a audiable click/pop when it switched and a couple ms's of contact bounce.

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He's switching the SPEAKERS - this doesn't give the audible 'plops' etc. that capacitors charging through preamps does. It may make a very slight noise, but nothing of any concern (assuming it's even audible?), and certainly nothing of any concern to a guitarist using a valve amp!.

cabinet switcher

Yes, audible-audio-crapola (snap, crackle and pop) is of concern even to us admittedly uninformed and lowly users of valve amps. (sheeesh!). The switcher is intended to be used on the fly, while playing - a smooth, unnoticed, transition is desired. Thx.

Depending on your distance from the amp and cabs, I don't see why a hardwired push-toggled dpdt switch in a stompbox enclosure wouldn't work as well.

agent420 said:

Depending on your distance from the amp and cabs, I don't see why a hardwired push-toggled dpdt switch in a stompbox enclosure wouldn't work as well.

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You mean like I suggested in the third post of this thread?, although it couldn't be midi controlled - but he's never replied to my question about that requirement.

Nigel Goodwin said:

You mean like I suggested in the third post of this thread?

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Yup Somehow missed the simple answer in the midst of all the other stuff

cabinet switcher

Hi - the thing that scares me away from this idea, which was my own first thought is; the commercially available switcher employs much more complex technology - I don't think they do it to bamboozle the marketplace. I think they do it because it's needed to keep from destroying the horribly overrated and erroneously valued TUBE Amplifier (strains of 'there I said it again'). I don't want to destroy my tube amplifier..I LIKE my tube amplifier. I don't know what the rules are here on this site regarding the mention of product websites. If it's OK I can direct you to the site where I am getting this info?
Or-if you feel adventurous , you can google 'cabinet switcher' and get there yourself. The MIDI requirement is not an absolute requirement, simple latch/unlatch kind of a deal is fine - the need for that is to switch cabinets based on a preset - so that a full set of instructs is passed as easily as possible. The MIDI controller that I use has this capability. During a performance, where the aesthetic takes precedence, it is not desirable to be tap-dancing amongst the control boxes. Usually, one has about 1 beat To go from sound A to sound B- so depending on the tempo of the piece...you get the idea.

Would it be the "Radial Tonebone Cabbone EX Speaker Cabinet Switcher 300 Watt"? - a HUGE price for something very simple!. There's no problem posting relevent links - and that would have been VERY relevent.

I'll say it again, there's no problem switching the output of a valve amp to two pairs of speakers using a DPDT switch, or a DPDT relay - the switching is so fast as to be near enough instantaneous.

It's certainly much, much faster than it needs to be from a damage point of view (and I've been repairing valve amps for 35 years), it's not even a consideration!.

Noise wise there's also very little concern - obviously you're going from nothing to something on the speaker you switch in, but it will make very little (if any?) audible noise. Buy a DPDT switch and try it!.

If you want it completely 'in-audible' you would really need to modify the amp, so you can mute it (preferably ramp it down, rather than a sudden mute), switch the speakers, then ramp the amp back up again. But even this would produce the mute 'effect', probably more noticable than a direct switch.

cabinet switcher

Why then, in your opinion, do they (ToneBone) go to such lengths to do the switching? Would one employ two DPDT relays to do the switching in stereo? I also assume there is some sort of electrical way to activate the switching or is that where the relay comes in? I am a 100% dangerous novice when it comes to this stuff.
Thanks

GtarPlaya11 said:

Why then, in your opinion, do they (ToneBone) go to such lengths to do the switching?

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Not for any technical reason!, they go to such lengths to relieve you of large sums of money!.

You only need a single DPDT relay or switch - or you could use two SPDT relays.

Depends on the kind of contact bounce you get from the relay or switch you use, especially if there's any active output at all. Guess you'd have to try it to see if it'd be okay.