will a dc offset affect a speaker?

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At the risk of being flamed again, I do believe that when that voice coil is being lifted off the stop by the positive peaks of the electrical signal that is sent to the speaker, the acoustic signal that comes out of the speaker will have side-bands that are not present in in the electrical signal that is sent to the speaker. In essence, the DC turns the speaker into a nonlinear device, and that nonlinearity creates severe distortion.

I would not, however, call that "DC causing sidebands." If I replace a little 2W speaker that is on the stops at a particular DC level with a big 1KW PA speaker, the distortion will pretty much go away. If I use a speaker with the excursion soft-limited at the perimeter of the speaker instead of at the coil, the nature of the distortion will be radically different. I would say "DC causes speaker nonlinearity, speaker nonlinearity causes acoustic sidebands" or perhaps "DC indirectly causing sidebands."

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As opposed to your subtle diplomacy?

You haven't even got the wit to be rude without being scatological. It's as pathetic as your attempts to pose as a pedant.

-- Bill Sloman, Nijmegen

A John Field's subtlely would be an oxymoron, comparable with "military intelligence".

I'm afraid that you have been exercising what little imagination you've got in a futile effort to look slightly less less like a Texan oaf.

Do try to stick to plausible lies - making implausible claims just makes you look even more ridiculous.

-- Bill Sloman, Nijmegen

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Its the only thing Bill is good for.

The operative word being 'transient'.

NO. Not in any competent design.

Graham

Quite, but I've witnessed this in a VS-Musician bass amp and an MA150 PA amp. The bass amp was a combo and the speaker was blown by the fault; the MA150 was switched off before it damaged speakers. I have never known what provoked the latch-up - cycling the power removed it.

Chris

Any competently designed amplifier will NEVER 'latch up'.

Should you choose to buy an inferior one that's YOUR problem.

I could give you a lecture on pro-power amp design, I've been doing it for 28 yrs but would you believe me ?

Graham

Quite so, I don't disagree.

Theyr'e not ones I had bought personally.

I might believe you but I wasn't seeking a lecture. The reason I posted about this observation was because (a) a symptom was that it applied a large DC offset to a speaker and (b) I wondered if anyone else had witnessed the same with HH amps in the past and might have known what provoked it.

Chris

Very strange. I've never seen that. Some op-amps can do weird s*it when overdriven though like invert phase which could latch up. I had a mic amp circuit do that on me and it puzzled the heck out of me until I realised it was exactly that op-amp behavior. A couple of inverse parallel diodes across the inputs can do wonders if the circuit topology is suitable.

Graham

The op amp problem is caused by a big positive common mode input that turns off the entire p-channel input stage, which in the 1970s designs caused the output to rail high, which works like a weird kind of positive feedback. The parallel-diode trick doesn't help that--it actually makes it worse, since the output can then pull *both* inputs to the positive rail.

An inverting topology is one good cure, and making sure the input CMR is wider than the output swing is another.

Cheers,

Phil Hobbs