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In Reply to: RE: hot amp switch box posted by cpotl on June 06, 2017 at 19:27:19
Your last sentence is exactly why I think I will try the resistors on each amp. The old KISS principle once again. With the resistors there is no chance of damaging equipment with a dead short or no load. At worst the sound will be funky, but I ought to be able to notice that. If you happen to run across any plans please let me know as my searches have come up empty for a unit that will allow switching with both amps running.
Sorry for the poor image quality, but attached is a sketch of the sort of thing I had in mind. Two ganged 3-way Make-Before-Break switches, wired as shown. I've had a couple of beers (in China right now, where it is evening), but I think it does the job of ensuring neither amplifier ever operates with no load, and that the two outputs from the A and B amps can never be connected together as the switching occurs. The indicated positions of the switches are for Amp. A playing through the speaker. The middle position is neither A nor B playing through the speaker. R would be 8 ohms or so. Of course another 2 gangs are needed for the other channel of a stereo amplifier.
The schematic assumes it is allowable to have a common ground for the outputs from amplifiers A and B. If this is not allowable (e.g. circlotron OTL amplifiers) then I suppose it would need a similar switching arrangement for the other end of the speaker too.
I could imagine there are more efficient ways to achieve the desired goals, but I think this would achieve it (unless the beer was too much!).
I appreciate the effort, but I tried just adding a 10 ohm/30 watt resistor to each set of speaker terminals on the 6bq5 amp and played it that way for an hour or so. Did not notice any major difference in the sound from without the resistor.
Going to have to put the amps side by side with the resistors mounted and then use a regular switch unit between them to go back and forth. Just too much trouble to route all the wires that would be needed to go to a switch from the equipment rack.
I'll do a follow up post when I get everything hooked up and working.
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