Harman Kardon A-402 speaker protetors no relay

sssboa

Super Member
Hi

HKs have those spekaer protectors and no relay.
Do they require cleaning (is it possible)? Are new (modern) drop-in replacements available?

HK1.jpg HK2.jpg
 
Circuit breakers- thermal resetable ? I can't make out the make and model number in your photo.
 
Do these OEM breakers have a reset button on them ?

Good question. According to my catalog, they are available as auto reset or manual reset.

Edit, I should have mentioned that my catalog does not show that exact part number, but does show similar devices.
 
They are 2.5A and they are pretty reliable.

If you want to test it, hook it up to to a small NiMh battery pack- it should trip really fast.

HK used to use push to reset circuit breakers and then moved to auto reset at one point, before dropping them altogether.

The Owner's Manual for the A-402 has this:

a402.JPG

It says it needs a manual reset when tripped, but I would confirm that. The buttons should protrude from the back panel when tripped.
 
^^^^^Good information.


My catalog shows pictures that look the OP's picture for both auto and manual reset, of course the auto reset does not have reset button.
 
Good question. According to my catalog, they are available as auto reset or manual reset.

Edit, I should have mentioned that my catalog does not show that exact part number, but does show similar devices.
So does mouser and digikey.
 
Again, that is good information. I have not looked there, but from the pictures in my catalog, it looks like he might be able to find an exact replacement, depending on this measurements.
 
Do you guys think these switches guarantee safety for speakers? I mean in comparison to a usual relay.
 
Less safety for the speakers, more protection for the output stage.

Those breakers trip with excess current- not voltage, so transients can pass without premature tripping. Excess current can come from too many paralleled speakers, low impedance speakers turned up too high for too long, or simply a shorted speaker lead.

The 'usual relay' you mention can be various things. It can be simply a delay at turn on, an overpower/overcurrent arrangement or detecting and protecting against DC (output stage failure) and, most often, a combination of all three.

HKs implementation using circuit breakers is valid, reliable, and simple. In the case of the A-402, there is no DC protection implemented, however there is turn-on delay thump protection implemented by a simple AC detect/delay which turns on the differential pair (input stage) after a few seconds.

HK's attitude was always to protect their amps, not your speakers.
 
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