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MC2105 Speaker thump

cuboid

cuboid

New Member
Hi all

I've got a well-loved but frequently-serviced MC2105. The current concern is that when it's powered on, I get some major speaker thump. Though it's just a single oscillation and my speakers are now pretty high power, they're now too expensive for me to risk damaging them from something that might be avoidable. It's also possible I'm overthinking it, but I don't want to risk it if I don't have to.

Notes on the power amp: It's recently been fully recapped and cleaned up by a local shop I love, and earlier last year the speaker switch was bypassed by them as well, though my understanding is that there's no speaker relay in the switch (could be wrong!) and so that wouldn't have much of an effect either way.

I'm open to any fixes, aftermarket suggestions or thoughts and prayers if it must come to that

Thanks, as always
 
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You need some type of delay circuitry. That speaker switch they bypassed would be nice, you could have the speakers off and then turn them on after the amp has been powered on. You could use an outboard speaker selector like a Niles. Anything to cut the amp output from the speaker input until the amp has had a chance to power. There are after market speaker protection relay boards with built in delay out there. A couple options, any reason why they bypassed the switch?

Dan
 
Try plugging one of those 1/4" to 1/8" stereo headphones adaptor plugs into the headphone jack at start up. This should switch the output to the headphone jack instead of the speakers. Once the MC2105 is turned on and settles down, remove the plug. This is a problem with some vintage receivers and integrated amps. Some do this with the Marantz 1060 integrated amp. There is a thump at turn on. I've never experienced it with mine though.
 
Looking at the schematic, the headphone jack doesn't break the speaker connection on this amp. That's why they included the speaker switch.

If you are really worried, there are speaker protection kits out there for not much money. You would need a power supply to use one externally. A 12v AC wall wart would do. Probably not the greatest quality or the fastest reaction time if you were to lose an output device, but better than nothing.

https://www.amazon.com/gp/product/B08HW93N9D/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1
 
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