OT Amplifier problem

Odds on he' shorted the loudspeaker output terminals somewhere. Protection mode might mean over temperature, or too much DC in the signal, or a short.

Steve

Wot ee said.

Almost certainly a short across the output.

Best leave it like that - he'll thank you in late middle age when he can still hear and all his mates are deaf*. I suggest a judiciously-placed

2BA brass bolt is probably favourite - good for about 100A at least!

Regards,

Simonm.

*actually I'm not kidding. Impulse noise, such as digitally recorded uncompressed drum tracks, can cause a serious notch at 3kHz. That frequency is one of the most important for speech sibilance (consonant recognition), and that type of problem is replicated in classic industrial hearing damage.

There is empirical scientific evidence that the onset of deafness is caused by enviromentally-induced damage over a lifetime, not an inherent feature of growing old.

I assume youve checked things like the fuse(s) on the side of the amp?

I used to have an old amp in the car, which liked to melt fuses and when it had gone it still had a red light on the side.

I agree a 1000 W sub woofer - I'll lend him a disc with the brown noise frequency on it - that should be fun. I never understand why the young uns of today want music that loud in a very small space - I wonder the sound pressure level is ?? and how mangled their innards are !!!

Makes me laugh I used to do sound for concerts running much less than that wattage on the main front of house PA rig !!!

Dave

You'll find that (if the speaker is not shorted), one of the output power transistors (FETS more likely) has shorted and the amp has sensed this and shut down the final output stage. In rare instances, one of the power supply switching FETS could be leaky or shorted and the amp has shut down the power supply, however, most of them cannot report this as a fault - it's simply "dead-in-the-water" if that happens.

I'll bet pounds-to-pennys the music was as distorted as all hell just prior to it going "nighty-night".

There's a limit to the amount of current that amplifiers can supply - and when the sound starts distorting (clipping), that's a very good sign that very soon after you will have a melted output stage - usually the resultant DC to the speaker(s) also burns out or warps the voice coil as well if it's not already done so just before the amp died.

-Craig.

How would one tell?

Too late now, but perhaps it will be necessary to test the repaired system with a few suitable recordings.

First suggestion--The Queen of the Night from "Die Fliedermaus", just to de-wax the test apparatus. OK, it's not much good for the subwoofer test.

Digital cannons from the 1812 overture bugger the DC protection on my amplifier.

Steve

And that recording actually tore the base speaker cones suspension on my demonstration Bang & Olufsen speakers in the shop I worked at. Damn customer never showed me the warning on the cover untill after!

Alan C

|| First suggestion--The Queen of the Night from "Die Fliedermaus", || just to de-wax the test apparatus.

Die Zauberflöte, isn't it?

|| OK, it's not much good for the || subwoofer test.

But it'll push the rest of the kit to its limits.

and click on "Cristina" at the bottom of the page. Frightening. Brings a prickle to my eyes every time.

There's a wonderful (and I believe, true) story about the famous Telarc 'digital cannon' record of the 1980s so beloved of the late Angus McKenzie et al. The story was that your hi-fi was only acceptable if aforementioned cannon (digitally recorded and played into the direct-cut recording, IIRC) could track the noisy bit properly.

In frustration, someone applied a travelling microscope to their copy of the disc, only to discover that the groove wall angle was almost on a radius at the leading edge of the cannon envelope - in other words, it had been cut-able by a *driven* cutter head, but was totally un-trackable by a stylus deriving its output from movement against the groove wall.

Good game, while it lasted. I think the 'vinyl is best' adherents now advocate 'burning-in' gold-flashed power cables...

Regards,

Simonm.

On or around 4 Aug 2006 10:29:04 -0700, snipped-for-privacy@bbc.co.uk enlightened us thusly:

digital cannons? bah. proper 1812 is done with real genuine analogue cannons and gunpowder. Usually possible to detect this as it's almost impossible to get the timing perfect. Mind, I'd expect B&O speakers to cope with pretty much anything.

If you have the full version of "Master and Commander" on DVD, one of the extras shows them recording the sound of cannon fire. And some guns do ring. They also set up a wooden strcture, and put a 12-pound shot through it.

Digitally RECORDED cannons Austin, to get the sharpest possible rising edge on the shockwaves...

Steve

|| Austin Shackles wrote: || ||| digital cannons? bah. proper 1812 is done with real genuine ||| analogue cannons and gunpowder. || || Digitally RECORDED cannons Austin, to get the sharpest possible || rising edge on the shockwaves... || || Steve

I think he meant genuine cannons on stage and fired at the appropriate moment. You can always tell on a recording - if the cannons fire on the beat, there is NO WAY they are in "real time" with the music, as it were. I can just imagine the guy with the match and the big responsibility - well, we've timed the fuse to burn an average of 4.5 seconds, so that's six crotchets and a dotted quaver, so when the trumpet hits the sharp A flat, count to four-and-a-half and BURN, baby! Kadoof.

"Genuine" recordings I have heard seem to get the cannon within half a beat of where it should be, which I think is pretty good, and they must have burned a lot of powder to get it even that close.

On or around Sat, 05 Aug 2006 12:16:59 +0100, steve enlightened us thusly:

which just proves the point about digital recording... sound is analogue in nature. You can record sound digitally and use the digital record to re-create an analogue sound which, if you throw enough money at it, is extremely close to the original and to be honest, if I listen to a GOOD digital recording played on decent equipment I can't tell the difference.

however, the process of A-D and D-A can't, in the ultimate analysis, exactly reproduce an analogue signal. If it's done well you can produce a new signal which is indistinguishable to the average or even to the trained ear

- however, it's not always done well (and of course, neither is analogue recording) and especially in the case of music to which compression has been applied, you can easily spoil the sound.

The compression thing is amply demonstrated in a way that's appreciable to almost everyone by looking at heavily-compressed jpeg images, or mpeg movies. The picture is still recognisable, but the detail is lost or rendered fuzzy. Jpeg is an impressive system, in fact, and does better than many other compression systems in preserving detail while also making small file sizes, and I presume that mpeg does similar tricks to audio - jpeg seems to work by making large-ish areas of nearly-the-same colour actually the same, while preserving detail by having small areas where there are high-contrast colour changes. By this method you can get a recognisable picture in very small file space, but it's not a GOOD picture, and even quite high resolution uncompressed digital images struggle to approach the quality of high-definition film.

In the ulitmate analysis nothing can, and no analogue recording method can offer the dynamic range or SNR of a digital recording.

Steve

On or around Sat, 05 Aug 2006 16:48:50 +0100, steve enlightened us thusly:

I'd put it the other way around... in theory, you could get an analogue recording to exactly replicate the pressure waves that we interpret as sound. OK, in practice, you can't. However, digital recording can't manage it even in theory.

again, in practical terms, it might be that digital recording can produce better results on a limited budget. But there are flaws - there's been much talk of streaming audio and bitrate - the beeb reduced the bitrate on R3 'cos they wanted some of the bandwidth for something else. Proms listeners were unamused. This is I assume the equivalent of too much compression affecting sound quality.

Yes it could, if the signal resolution was below that of the theoretical SNR. In an analogue system, that SNR sets the miniumum possible - you can't recover the signal from below the noise floor, unless its encoded.

Steve