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DC offset level to avoid speakers damage-

Dear All would you help me to understand this?
My actual power amp has very low DC offset.

I understood that Pass aleph renomated amps that i am targeting have a quite high offset in the range of 50mV.
Something to be worried about ?

Which is the max tolerated level from a speaker ? Which kind of damage can occour ?
Any speaker is more sensitive ?
Tks
ad010685
gs5556
1,235 posts
 
The maximum dc offset tolerated by a speaker is a percentage of the linear excursion of the driver that is acceptable, usually 10 to 15%. The formula used is:

Vdc(max) = % excursion x excursion x driver impedance/[Force Factor x Suspension Compliance]

All these parameters are found in the manufacturer's spec sheets. Using a Scan-Speak 21W/8555-0 driver, the maximum dc offset at 10% of driver excursion is:

Vmax = 10/100*6.5mm*5.5-ohms/[8.2*1.34] = 400mV.

Most amps specify dc offset at less than 100mV. So a 50mV offset is not "high". And a lot of drivers tolerate up to 500mV.
ad010685 OP
102 posts
 
Tks everybody, very clear reply (as usual I should say)
Cheers
eldartford
4,262 posts
 
Bob_bundas. You found my goofup before I got back to fix it. Yes...divided by R. So it is even less of a problem.

I had occasion to adjust bias only once when I fixed a 60 watt Tandberg receiver output stage. I don't remember what the output bias spec was, but I do remember that I had no problem getting it down to less than 5 millivolts. I think that designers/manufacturers set the spec high because it is not critical.
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