I think I blew my amp??!!

I just got some new dual 6.5" speakers for the back. when i got them in they really sounded nice but when i turned it up with the bass they stoped working properly. they warrant as loud as the frunt ones. what is the power rating for the amp in my 1990 saab 9000 cd and where is it located. If i get a new cd player like a alpine or something will that fix the problem.

Reply to
es
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You could have blown the amp, or it may have just failed, but more often when you overdrive an amp it's the speaker that blows from distortion than the amp itself.

Reply to
James Sweet

Assuming you took the old speakers out and didn't just connect the new speakers across them, then it's unlikely that you damaged the amp. It sounds like the speakers have crapped out to me. Can you try the old ones back in as a test?

Cheers,

Colin.

Reply to
Colin Stamp

yes i will do that today and does that mean i need to get i higher watt speacker becuse these are 140 w max i really didnt thing the saab amp can do that much. So what is the watt specs on the amp and where is i located

Reply to
es

No you more likely need a higher wattage amp. If you drive an underpowered amp too hard it clips, and clipping is very hard on speakers.

Reply to
James Sweet

underpowered

What is clipping?

i looked at it today and i was just a loos wire and all is good but i need to knowe where the amp is so i can bypass it when i get a cd player. i also need to knowe the same thing for a 1992 saab 900 4dr.

Reply to
es

formatting link

Reply to
James Sweet

Yeak all that limited voltage and current wreaks havoc on the speakers... NOT.

Where do you people get this stuff?

-Fred W

Reply to
Malt_Hound

It can happen in theory. i.e. driving an amp hard into clipping can cause it to put out spikes in excess of it's rated output. If the speakers could only just cope with the amp's rated output then they could *theoretically* be damaged.

Virtually never happens in practice of course...

Cheers,

Colin.

Reply to
Colin Stamp

If that was true, the only thing I could see is possibly blowing out a tweeter, since the woofer would have plenty of power handling capability and the spikes would be very high frequency and so the crossover network would shunt it away from the woofer and midrange and send only to the tweeter.

But I don't see why driving a linear amplifier into its limits (that's what clipping is) would cause spikes...

-Fred W

Reply to
Malt_Hound

I think you would be surprised just how unlinear your linear amplifier becomes when cranked up. That being said there are a lot of factors involved, if your speakers are not very efficient or provide a difficult load for your amplifier, which may be poorly designed, it does not take very long for it to start having problems.

Hi-end hifi is my second hobby after Saab's

Mike

Reply to
<twopinkblobs

Yep. That's about right.

I don't make a study of it or anything, but I could take a couple of guesses...

  1. The amp's power rating will be at a certain, reasonable, distortion level - say 5%. That 5% distortion doesn't happen *at* the clipping point but some way before it. So you can drive the amp harder and get more power than it's rating, but it sounds crap so the manufacturer can't make any claims about this higher rating.

  1. If you then continue to drive the amp harder still, and into real clipping, the resulting sharp edges on the output waveform mean the amp is generating much more power at high frequencies than it would normally. The tweeters in the speaker system would normally only expect to see a small fraction of the amp's output, so when the amp starts producing serious power in the tweeter's range, safety margins can get eaten into.

Cheers,

Colin.

Reply to
Colin Stamp

underpowered

Happens all the time, obviously you've never worked in the consumer electronics service field.

Reply to
James Sweet

Actually it's more the rating of the *speaker* that's the issue. A 140W speaker will not handle 140W anywhere near continuously, that rating is music power, which assumes that the average RMS power is much lower. When an amplifier clips hard the output is much closer to DC at the *peak* power of the amplifier which is substantially higher than the RMS.

If you don't believe me, take a speaker rated at 140W, assuming it's 4 ohm, connect it to a 24V DC source (which will cause it to draw about 140W) and see how long it takes the voice coil to smoke. You probably won't get more than 10-15 seconds out of it. Tweeters usually go first, but I've seen

*many* speakers damaged by an underpowered amp clipping, if you open one up the voice coil is blackened.
Reply to
James Sweet

Actually, it would not surprise me as I am an EE. I only mentioned linear amplifier to distinguish it from a switching amp or Class C amp.

-Fred W

Reply to
Malt_Hound

Yes, you are absolutely correct. Clipping is one (very extreme) form of distortion.

Yup, and to clarify further, the amount of power in the distortion, while higher than normally seen at those high frequencies would be far less than the nominal power. So the end result may be that the tweeters would blow. But unlike the OPs situation, there would still be some sound from the remaining other drivers (speakers).

-Fred W

Reply to
Malt_Hound

No it's not. When an amplifier clips hard it produces a multitude of odd harmonic frequencies of the original. It doesn't produce DC. Other failures of amps can cause DC, but not clipping.

You are comparing apples and oranges. The power rating of a speaker is based on its impedance, not its DC resistance. They are very different things. When using a DC coupled amplifier, it is quite common for the amp to fail and produce a DC voltage. As you noted, this is very bad for the speakers' voice coil, which is a pretty fine piece of wire, and they burn out almost instantly.

-Fred W

Reply to
Malt_Hound

No, you're right. I've only worked in the military and medical electronics service fields for the past 30 years...

I know you can overdrive speakers and blow them. What I'm saying is that it is not due to the clipping (unless we are talking specifically about tweeters). It's due to the fact that amplifiers can put out more than their "rated" power. Most people assume a 50 watt amp can only put out 50 watts, so it's safe to hook up speakers that are rated at 50 watts. That's wrong.

As Colin pointed out, the amp's rating is at a particular usable distortion level. If you overdrive the amp, you are capable of putting out more power than the "rating" but at higher distortion levels. It's the power, not that distortion that takes out the speaker(s).

It might appear to be "chicken and the egg" I suppose... but significant in this case.

-Fred W

Reply to
Malt_Hound

This is all very interesting and highly technical. But to lighten the mood a little, has anyone else ever taken a tiny speaker out of a broken transistor radio, and wired it up to a 100w amp to see how much it would take? I have, and it went pop quite spectacularly. Not that I'm condoning wanton destruction, you understand, I was just bored. That was after making an industrial spud gun with a compressor and a gas pipe. Boredom is a terrible thing...

D ;-)

Reply to
1

The kids around here use PVC pipe and deodorant to make their spud cannons. They use a long piece of PVC with a cap glued on one end. Drill two holes in the cap and thread a piezo spark-gap device from a gas grille in one. The other is used to squirt the aerosol deodorant spray into.

Tamp a spud part way down the pipe, charge it with hairspray, aim, spark, Thwooob! It hucks those spuds a couple of blocks.

Quite ingenious actually! And relatively safe as explosive fun goes. I've never heard of anyone being killed by a potato missile. So long as they don't start spraying gasoline in their instead of hairspray...

Boredom? Oh, yeah. I have an older teen-age boy...

-Fred W

Reply to
Malt_Hound

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