Speaker Switch That Protects Tube Amplifier

The box of parts has been passed to the EE in case he gets time before we get time to overlap. Two dad's with small kids means very little free time and even less overlapping free time.

As I suspected, my buddy couldn't contain himself and I have the completed switch on my desk at work this morning. I should have time to install it tonight.

One of our design criteria was to only use components that don't require a break-in period. Also, all components have been room temperature heat treated for the best possible performance.

Viridian - Thanks for the information.

My Yaqin MC-30L is rated for about 50 watts per channel is ultralinear mode. So using a 100 watt load resistor should do the trick, right?

I'll clarify that when using my Mac and iTunes as the source, the source of the Yaqin is really a DAC fed by an Apple Express and the source for the Integra is an Apple TV. iTunes just has the option to send the music to more than one zone. The switch would only swap the speakers leaving both amplifiers with a source signal at all times.

Can you describe the circuit layout you are thinking about?

True. Just gathering as much info as I can. There is always more than one way to do things.

I think we have the details worked out on the switch circuit. We'll be using an 8 Ohm 100W Non-Inductive Dummy Load Resistor from Part Express to load the tube amplifier when the speakers are switched to the receiver. I just need to measure the space in the cabinet so that we can get the right sized project box. I think all internal wiring will be 10 AWG to match my speaker cables.

I had thought about the possibility of using relays, but I think I prefer the passive route. In any case, the parts are on order. Thanks for the idea.

The plan is break before make with each channel on a switch. Should I be concerned with the tube amp not being loaded for a instant when the switch is toggled?

Each channel will effectively have three parallel switched toggled by a single physical switch.

Imhififan - Your responses and link to the other thread made me dig into things a bit more. Thank you.

The revised plan is to use a heavy duty 4PDT toggle for each channel. The solid state receiver will be on/off, the tube amplifier will be off/on, and the 8 ohm 100W non-inductive dummy load resistor will be on/off. To bridge the instant between the speakers and the dummy load resistor on the tube amplifier we will also add 150 ohm 5W or 10W resistors on each channel based on the recommendation from the Niles manual that was linked. I'm not worried about my receiver as I often have it passing sound to the TV via HDMI with the speakers disconnected and hooked to the tube amplifier.

I'm interested to hear how the final switch box "sounds" as it will obviously add components to the signal path. Being completely objective may be a challenge in contrast to the negative placebo of knowing that the signal path has been compromised.

Almarq - I was hopeful that you would provide input as I value your opinion. The revised plan is to use the dummy load resistor (a parts express item) on both inputs and also put 150 ohm resistors on both inputs to make it a fail safe design for a tube amplifier. I'd rather not have to keep track of the tube safe input. Each channel will have its own switch because it would take at least a 6P or 8P switch to do what we want.

My current solution is to have two sets of cables at my speakers that I manually switch depending on the amplifier that I want to use. To this point the tube amplifier has always been shut off (though not always at room temperature) before disconnecting the speakers. The receiver has been used to pass the audio to the TV via HDMI without the speakers connected many times.

My ultimate goal from a fun perspective is to be able to do live A/B switching as any other delay makes it virtually impossible to accurately "remember" what it sound like for comparison. It will likely be a gimmick type of event at first that eventually becomes rare. I

The long-term improvement from a practical standpoint will be that I can have the tube amplifier on for listening, switch to the receiver for watching something with my wife, and then go directly back to the tube amplifier without having to turn it off. As a general rule I don't turn the amp back on until it's cool and because the sound is much better with everything warmed up short power cycled listening just isn't the same.

This sounds like a great alternate solution that someone else may choose to use. I have some of the parts in hand and almost everything else is in the mail. The only missing piece is some 10awg cable from Blue Jeans Cable as the stuff that we got from Parts Express didn't turn out to be what we wanted.

@therandyman - Here you go.

It's been in my system almost constantly since it was built and has worked flawlessly.  It gets flipped on average more than once a day.  I like that I can use the TV while letting the stereo amplifier stay on and effectively hooked to inaudible speakers.

If memory serves, it toggles between my speakers and the dummy speakers that are part of the switch with a resister in the circuit to provide a load during the switch.