Switching speakers on the same amp in real time

[pjd3]

OK, so the challenge is going to be how to clearly describe this.

If you wanted to safely be able to switch speakers at a gig on the fly, what are the electronic considerations that you would need to tend to?

Say for instance, you wanted an American and a British speaker in the same cabinet, and wanted to switch them during a song to compliment the various sections.

Just off the top of my head, what comes to mind is"
-never create a situation where there is no speaker load on the amp
-Identify if there is any kind of inductive spike that occurs should one speaker immediately connect/go in parallel with the other speaker.
- Have high current switching system that is able to keep a fairly constant load on the amp during switching.

Of course, this is off the top of my head but, with my modest understanding of higher current switching of inductive loads, coupled with the safe load requirements of tube amp output sections, I'm encouraged to think that impedance should only ever shift very minimally (meaning never a "no load condition) and, the prospect of both speakers being connected momentarily causing an inductive spike that could stress the output section. As I understand it, its usually not the instant connection of an inductive load to an active circuit that is problematic but, the disconnection of the inductive load that needs to be addressed, where there is a collapsible magnetic fields on the inductive load this is being disconnected from the circuit, and most critically if it is disconnected relatively instantly - which possibly makes timing of the switching a consideration in the implementing of a well considered switching mechanism.

I was laying in bed thinking how cool it might be to one day have a reliable speaker switching feature that doesn't cause stress to the output components. I think it could be very useful in certain situations, and surprised I haven't seen it anywhere.

Thanks,
PJD3

[pdf64]

I think that commercial amp / speaker switching systems are available.

[pjd3]

Thanks pdf64,

I'll take a look!

PJD3

[LOUDthud]

Simply palm mute the guitar strings for the instant the switching takes place. If you are still worried, place a resistor, perhaps 180 Ohms 10W across the amps output so it is connected all the time.

[pdf64]

Simply palm mute the guitar strings for the instant the switching takes place. If you are still worried, place a resistor, perhaps 180 Ohms 10W across the amps output so it is connected all the time.

I recall an amp build whose OT used a terminal board, rather than flying leads. It had a switch on the back panel to flip between secondary taps.
When testing, I used the above logic, that it would be fine to switch between taps with the amp idling, master volume at minimum.
Plus I’d taken my standard precaution of a safety resistor, 470R as per the Vox AC50.
When I flipped the tap switch, a spark jumped across the primary terminals!
I realised that the safety resistor was the wrong side of the switch, at the point of switching, the standard break before make action left the secondary open circuit.
With the resistor moved to be directly wired across the 16R secondary winding, switching was spark free.

[R.G.]

Use a make-before-break switch.
These switches are designed to connect the "new" side before opening the "old" side. There is no time in the switch operation when the common is not connected to one or the other poles, and a brief moment in the middle where the common is connected to both at once.
There are fancier and probably cheaper ways to do this electronically, but the MBB switch is a quick solution.

[CraigGa]

I was looking at the schematic for a Toneking Imperial which uses switchable secondary OT taps to provide attenuation and it has a 1000pF 3kV capacitor across the OT primary.
I'm guessing that providing a similar function?

Craig

[WhopperPlate]

The future is now

https://reverb.com/p/radial-tonebone-he ... ntent=1655

[neskor]

[sluckey]

The future is now

I don't think this future is what pjd3 is looking for.

[WhopperPlate]

The future is now

I don't think this future is what pjd3 is looking for.

My bad , cab switcher not head switcher , doh

[Reeltarded]

In the studio we use a huge relay triggered with a momentary switch but that is on AdComs I would never switch a tube amp outputs like this.

I also don't mix speakers in cabinets and I don't use ten close mics while recording, so.. I'm from the wayback.

[pjd3]

Hey everbody, geez I didn't think I'd get this much attention! I'm humbled.

To be specific, I'm just thinking about how nice it might be to have an amp that when you footswitch from an American sounding preamp to a British sounding preamp, that the speakers would switch with it, say in a 2 x 12" combo. People really start of have an idea about what speaker they want with what amp so, it could obviously be a nice boon to have your favorite speakers match the channel that you switch to.

Without knowing yet in practice, it seems like there is a chance of say, a 16 ohm speaker going to the 16 ohm tap, and an 8 ohm speaker going to an 8 ohm tap, and a relay that is make before break each way that would switch the taps. At least that way something would always be connected to the output transformer and there would never be a very significant shift in impedance that might cause a big fly back voltage to occurr, or some kid of audible click or pop. I don't know this yet to be true but, I suppose with a couple of speakers and an amp I could set up to simply look at some things on the scope while using a mechanical switch to connect and disconnect speakers in parallel, series, on differing taps, etc... Using the single shot on a scope you could even see what's happening at the first handful of nano-seconds following a speaker switch of the various configurations - see what's better, worse, out of the question or acceptable. I just may have to try that soon. And I will follow up with a report of the findings.

Sound like a good idea?
Thanks everyone,
PJD3

[pjd3]

And to add, if there was anything undesirable happening electrically during switching, I would take my home scope shots into work, and let all the electronic engineers squabble over what the best solution might be based on the waveform type, the impedance and power of the output section. We design and manufacture defibrillators so, a huge part of their design intentions are to identify waveform spikes and how to alleviate the problem (MOV"s, suppression diodes, and lots more).

PJD3

[GerryJ]

I was wondering about using a simple passive DOD A/B switch to alternate two separate cabs. Head is an old Traynor, they're pretty indestructible, but iirc someone wiser than me said this still may be risky to the output transformer.