will a dc offset affect a speaker?

... or that troublesome transient complaint that HH amplifiers used to get from time to time, where they would latch up and apply lots of DC to the speaker(s). I never really knew the source of the problem but I did wonder about the design of the current sources in the bias chains which showed a remarkable similarity to a unijunction!

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Mike Terrill making his usual sophisticated contribution to the discussion.

I don't know where we'd be without his wisdom and insight.

-- Bill Sloman, Nijmegen

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This seems unlikely.

"Conventional" is much less specific than "digital" - you were simply careless in your choice of words.

"Conventional" is an odd word to use in this context - one doesn't choose to use a particular sort of multiplexer because there are socially accepted conventions on what you need in a particular circuit, you use something that will work in that circuit.

It may seem obvious to you now, but you didn't bother making this less- than-helpful distinction when you originally corrected Panfilero. The analog/digital distinction captures more of the idea you were trying - rather ineptly - to get across. Of course, there are internally buffered analog multiplexers, which aren't bidirectional either, and "multiplexer/demultipler" does exclude these parts but you need to prime an unsophisticated audience fairly carefully (as I've done here) to make the title meaningful.

-- Bill Sloman, Nijmegen

Enough DC bias on the right loudspeaker could persuade the loudspeaker to generate acoustic side-bands of the AC content of the electrical input to the speaker. Guy Macon discusses the mechanism in more detail.

-- Bill Sloman, Nijmegen

Unless the speaker/amplifier was designed by cretins, there will be a 'DC blocking' capacitor at the input so it won't make any difference at all.

What you think is totally wrong. Apply a significant DC offset *directly* to the speaker and you'll get a very nasty effect.

Graham

He said a "speaker/amplifier".

Read the damn post FFS !

Graham

You can run a 4066 off +/- 7.5V and offset the logic inputs vial level translators. NO DC added.

Graham

The 4053 ? is also very popular in this kind of task. But you can make a 4016 or

Graham

Is this an ultra low cost design ? If not use something designed for the job like DG308s and DG211s.

Or even use a jfet (suitably driven). That's what I do. The J107-111 and thier complements J174 etc are very good for this and typically used in pro-audio.

Graham

Yes.

There is also a danger of 'bottoming' the voice coil or driving it out of the gap under conditions of extreme DC offset. Either may result in terminal damage.

Graham

Most speakers these days are not sealed cabinet designs anyway but ported.

Graham

In the early days of high power PA rigs such failures would often set the speaker cone alight !

Graham

Latch up ? Do you mean FAIL ?

I still have 4 H-H TPAs from those days and none ever 'latched up'. But I also didn't drive them into 4 ohms. Any fool could see they had inadequate heatsinking (as was often if not the norm back then). Phase Linears used for PAs became known as Flame Linears !

Graham

Not *THAT* again ! ;~)

Graham

Seen that done . With exteme care you might get the coil back in the gap.

Graham

Actually, it's a linear motor coupled to a cardboard cone (usually). Sometimes more exotic materials will be used.

Graham

Too true.

Graham