Ageing Amplifier: Concerned about Damaging Speakers?

[davedotco]

Blocking capacitors are routinely used in professional applications particularly if the speakers are actively driven. The switch on thump from some power amplifiers can, in particular, over extend high frequency units with low frequencies they are not designed to handle causing both overheating of the coils and over extension of the suspension.

It is occasionally used on bass drivers too though not so much these days. Some famous pro amplifiers of yesteryear could, when overdriven, produce transient DC offset sufficient to push (part of) the voicecoil out of the gap and it's cooling effect causing coil burnout. A DC blocking capacitor could prevent this, as could a suitably large inductor used in parallel, seen that done to.

This is much less likely to happen with hi-fi amplifiers, which tend to be bandwidth limited and will only produce DC following a catastrophic failure.

Which reminds me of the old pro definition of an amplifier output fuse as a device carefully selected and placed in a speaker output such that it is 100% protected by the speaker that will off course blow first, thus saving the fuse.

 

[TrevC]

Current flows from positive to negative,

With an AC signal ?

so connect the positive lead of the cap to the output of the amp, and the negative side to the speaker.

Since the audio signal is AC it doesn't matter. If your protecting against amplifier failure and a massive DC offset it would be wiser to use a bipolar cap since you don't know if it will be a + or - DC offset. After all you don't want exploded cap everywhere too........

But overall it is totally unnecessary, anyone who is running vintage gear worth any value would have it serviced unless they are stupid, in that case they deserve to have their speaker coils fry ;-)

Don't question standard procedure. AC is the hardest part of electronics. Very complex. Hard enough to digest it let alone question it.

Back to the textbook, Madhouse. Eggontoast is quite right, assuming you want to put a DC block in place then an electrolytic cap is very bad idea. The plus and minus (or red and black) markings on an amp's speaker outputs are primarily to help you get speaker phase correct. The output signal is AC and the plus and minus outputs will swing both positive and negative realtive to each other every AC cycle.

Which is why (if you care) you should theoretically use two in series back to back. In reality, it works perfectly well, because an electrolytic will tolerate a small negative voltage swing.

 

[proffski]

I give up! So, what we are saying on this “Hi-Fi” forum is that some of us can tell the difference between a couple of metres of loudspeaker cable but a great non-linear chemical factory like an electrolytic capacitor in series with the loudspeaker will have no influence on the sound quality over the usable audio banwidth at any normal listening levels?

 

[Anonymous]

From a pratical point of view, YOU ARE correct. Either way around it will work.
I'd imagine that you also see AC mains wiring active and netural either way round as OK too.
You go against a system.

 

[davedotco]

I give up! So, what we are saying on this “Hi-Fi” forum is that some of us can tell the difference between a couple of metres of loudspeaker cable but a great non-linear chemical factory like an electrolytic capacitor in series with the loudspeaker will have no influence on the sound quality over the usable audio banwidth at any normal listening levels?

Exactly.

You are beginning to understand the realities of dealing with the hi-fi fraternity!

That said, I do not think anyone has suggested that such devices do not make a difference, just that properly implemented, the effect is negligible.

Electrolitics though are a different matter, non electrolitics are used on higher frequency units but for full range and bass drivers they are prohibitively expensive, electrolitics are used, often back to back sometimes not. Protection and reliability is the issue here, ultimate sound quality less so.

 

[Anonymous]

Current flows from positive to negative,

With an AC signal ?

so connect the positive lead of the cap to the output of the amp, and the negative side to the speaker.

Since the audio signal is AC it doesn't matter. If your protecting against amplifier failure and a massive DC offset it would be wiser to use a bipolar cap since you don't know if it will be a + or - DC offset. After all you don't want exploded cap everywhere too........

But overall it is totally unnecessary, anyone who is running vintage gear worth any value would have it serviced unless they are stupid, in that case they deserve to have their speaker coils fry ;-)

Don't question standard procedure. AC is the hardest part of electronics. Very complex. Hard enough to digest it let alone question it.

Back to the textbook, Madhouse. Eggontoast is quite right, assuming you want to put a DC block in place then an electrolytic cap is very bad idea. The plus and minus (or red and black) markings on an amp's speaker outputs are primarily to help you get speaker phase correct. The output signal is AC and the plus and minus outputs will swing both positive and negative realtive to each other every AC cycle.

Which is why (if you care) you should theoretically use two in series back to back. In reality, it works perfectly well, because an electrolytic will tolerate a small negative voltage swing.

Problem is that these [EDITED YET AGAIN FOR OFFENSIVE TERMINOLOGY] are confusing a series circuit with a parrallel. ARE YOU feeling GREASY?

 

[TrevC]

I give up! So, what we are saying on this “Hi-Fi” forum is that some of us can tell the difference between a couple of metres of loudspeaker cable but a great non-linear chemical factory like an electrolytic capacitor in series with the loudspeaker will have no influence on the sound quality over the usable audio banwidth at any normal listening levels?

Nobody said anything about it not affecting sound quality. I certainly didn't. All I said was it's fine for eliminating the possibility of woofer destruction while testing an old amplifier. Which it is.

 

[andyjm]

Problem is that these [EDITED YET AGAIN FOR OFFENSIVE TERMINOLOGY] are confusing a series circuit with a parrallel. ARE YOU feeling GREASY?

Madhouse,

I am not sure where you picked up your AC theory, but I am afraid you are a bit adrift here. Consider a single sine wave. At the top of the wave the red terminal or (+) on the amp will be positive and the back terminal (or -) will be negative (relative to each other). At the bottom of the wave the opposite will be true, the red terminal will be negative relative to the black terminal.

The capacitor will be in series with the speaker but will still have current flow in both directions.

 

[Anonymous]

Problem is that these [EDITED YET AGAIN FOR OFFENSIVE TERMINOLOGY] are confusing a series circuit with a parrallel. ARE YOU feeling GREASY?

Madhouse,

I am not sure where you picked up your AC theory, but I am afraid you are a bit adrift here. Consider a single sine wave. At the top of the wave the red terminal or (+) on the amp will be positive and the back terminal (or -) will be negative (relative to each other). At the bottom of the wave the opposite will be true, the red terminal will be negative relative to the black terminal.

The capacitor will be in series with the speaker but will still have current flow in both directions.

Like I said, from a pratical point of view-- you are correct.
You go against a system though. Your high-end system has input coupling + to -.

Please do not try and preach basic AC principles to me. I studied it formally back in 98 with an 90% pass grade.

 

[Anonymous]

Problem is that these [EDITED YET AGAIN FOR OFFENSIVE TERMINOLOGY] are confusing a series circuit with a parrallel. ARE YOU feeling GREASY?

Madhouse,

I am not sure where you picked up your AC theory, but I am afraid you are a bit adrift here. Consider a single sine wave. At the top of the wave the red terminal or (+) on the amp will be positive and the back terminal (or -) will be negative (relative to each other). At the bottom of the wave the opposite will be true, the red terminal will be negative relative to the black terminal.

The capacitor will be in series with the speaker but will still have current flow in both directions.

Like I said, from a pratical point of view-- you are correct. You go against a system though. Your high-end system has input coupling + to -. Please do not try and preach basic AC principles to me. I studied it formally back in 98 with an 90% pass grade.

Go and formally study capacitors and PHASORS.
You have been reading too much google !

 

[Anonymous]

Fact of the matter is that unless you are a scientist, electronics is all about built building blocks with protocol (a set of rules) Why be a [DEEPLY OFFENSIVE TERM REMOVED and user banned] and try and confuse everyone with your insanity?

 

[BigH]

Fact of the matter is that unless you are a scientist, electronics is all about built building blocks with protocol (a set of rules) Why be a [DEEPLY OFFENSIVE TERM REMOVED and user banned][/b] and try and confuse everyone with your insanity?

You should know!

[UNPUBLISED AS REFERENCED POST MODERATED]

 

[BenLaw]

Mods have pruned this thread, but I don't understand why madhouse is still here. I've seen members permanently banned (hifilover1979) for such language, deliberately overcoming the swear filter.

Madhouse, maybe this was the 10% you got wrong in your unspecified qualification?

 

[Andrew Everard]

Mods have pruned this thread, but I don't understand why madhouse is still here. I've seen members permanently banned (hifilover1979) for such language, deliberately overcoming the swear filter.

As it says, [DEEPLY OFFENSIVE TERM REMOVED and user banned]