motor 'defeat' switch for echoplex/etc

[themagicmanmdt]

hey tubers - not finding anything much of anywhere, and since at least we're all a strong family of electrical knowledge, perhaps you can help with my conundrum.

i'm trying to make a scenario happen for a friend of mine - creating a motor 'defeat' for an old EP-2 tube Echoplex. this way, he can have the unit on and warmed up and ready on stage or studio without having the capstan motor running and causing all that head wear... plus, it'll make for a fun effect if there's echo there and the tape winds down to a stop if the motor is defeated.

it's super simple in theory - the motor is AC driven - add a nice carling switch as an interrupt to one side of the AC main that's feeding the motor.

alas....

yes, it works, but it's causing a bit of a 'pop' to come through the electronics, by what I'm assuming is due to the sudden current rush demand. the pop isn't as pronounced turning the motor power off as it is when it turns on.

so, anyone have a 'slow start' trick, or something that might help surpress the inrush of current? the first thing i think about is - hey - a resistor with high wattage! almost like having 'sag' on an amp, this would hopefully cause the motor to ramp up a little slower and, as well, prevent the 'pop' coming through the rest of the amp. however...

i haven't attempted it because i just can't risk any negative effects to his old echoplex. if i fried that thing....

since i'm not confident, i figured i'd ask all 'yall about this 'bypass switch effect' of the current inrush, and any way that the loud thud can be navigated around.

is a similar topology in effect in tube amps with a bypass switch for the B+ at all?

thanks for the noodle scratching -

[nigelwright7557]

I had a similar problem with record deck motors causing huge pops throught amp.
I put a 100nf 500volt capacitor across the switch to soak up the arcs.

[Enzo]

If you just have a switch wired in series with the motor, I don't doubt it pops. The playback circuit is very sensitive - it has to amplify the tiny signal from the tape head after all.

A cap across the switch might help. If I really wanted to do this, I might prefer a triac to control the motor, and the switch would control the triac. No current through teh switch means it can't spark.

And for that matter, now 40 years later, really, how much is "all that head wear?" I'd be a lot more concerned about tape wear than head wear. And I am not really concerned about that.

And you might find that the tape, sitting stationary against the record head, is left with a loud artifact on the tape.

[nigelwright7557]

Originally Posted by Enzo

A cap across the switch might help. If I really wanted to do this, I might prefer a triac to control the motor, and the switch would control the triac. No current through teh switch means it can't spark.

Ideally you would need to switch the triac at zero crossing.
Switching on at peak mains will still cause interference.

[HollowState]

I would use a solid state relay. 3-32 volt in will switch up to 240VAC/40A. Find them on eBay cheap.