Dying amplifier

[babebambi]

a semi-related question, does clipping the SS power section damage the amp itself? given that the amp is not over-heating. It is certainly not good for the speakers, I know that much...

 

[SwamiRob]

That clipping SS amps damaging speakers thing is a myth, the only reason it was thought to damage speakers is because clipping an SS amp has a similar effect as clipping a valve amp, so it puts out more power then it is meant to just without the smoothness of valve distortion and it's not really that good for them as far as I know.

Anyway alot of SS amps have limiters, how effective they are varies massively though.

 

[SwamiRob]

Ah. I'm wondering now about your bass. If it's active, have you tried a new battery?

There's going to be distortion from the pups if you dig in hard, and there's also speaker distortion from loud volumes. Is it possible you're just noticing the distortion from two completely different sources at different times?

...my bass is passive...

Your quite right to suspect that though, the jazz pickup I have in my ATK at the moment isn't as open as I expected it to be so there is a little mud coming from it at the moment, thinking of perhaps getting a Dimarzio Super J or something to replace it perhaps, but nothing on the level of mud that I'm getting out my amp when I use my matching 4x10.

Gonna test it a bit more next time I have practise just so I know what exactly is going on cos all of my dicking about to see what the problem was was only done in the 10 minutes or so when we were setting up for sound check at a couple of gigs. To be honest I think the cab is probably just a write off and has had too much thermal damage in it's time, so I'm probably just gonna use my Trace 15till I can afford to get my Berg fixed.

 

[babebambi]

That clipping SS amps damaging speakers thing is a myth, the only reason it was thought to damage speakers is because clipping an SS amp has a similar effect as clipping a valve amp, so it puts out more power then it is meant to just without the smoothness of valve distortion and it's not really that good for them as far as I know.

Anyway alot of SS amps have limiters, how effective they are varies massively though.

why do you think they put that limiter in there ...

 

[SwamiRob]

Ooops, I didn't fully answer the question there did I? What I was getting round to saying was that square wave distortion adds to the high frequency content rather alot in a pretty nasty manner, and since the clipping means your amp is putting out more then it should be doing and creating alot of that extra power at higher frequencies it causes tweeters to burn out. So a couple of pro audio companies briefly put this down to square wave distortion that SS amps put out, and this turned into the huge myth that square waves themselves blow speakers.

As for damaging the amplifier itself I wouldn't be too sure, it would depend how well engineered the amp was and how much you were clipping it, I can imagine even the most solidly designed amplifier isn't operating comfortably when it is being clipped to any noticeable extent however. Your not clipping you thunderfunk are you?

 

[B-string]

Not all SS amps have limiters, G-K overbuilds the power supply section, no limiters just protection circuits for overloads.

 

[seamonkey]

...I was getting round to saying was that square wave distortion adds to the high frequency content rather alot in a pretty nasty manner, ...

It doesn't really.
Take a look at:
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Try a Sine wave, and a Square wave.
First I hope you hear a square wave doesn't sound that bad. On the same page it mentions clarinets and recorders being closed pipes produce square waves and they can sound pretty good. Second, you'll see that the odd harmonic series to get a square wave is actually very little.

But a bass waveform is not a sine wave. And it doesn't turn into a square wave when clipped.

Load up a copy of audacity and load in you favorite bass playing just one note. You'll see first of all it's a complex waveform and it's asymmetrical. If you were to lightly clip it, it would clip one one side of the waveform more than the other. This is going to add some even harmonics.

Audacity and other sound software will let you do a spectrum analysis of the waveform. Try it before light clipping and after light clipping. There will be hardly any spectral difference.

Try it with heavy clipping and you end up with the Rane paper effect of bass compression and high frequency content from the input overdriving the hf drivers:
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Also:
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Most all the HF content is coming from the input signal itself and not from the amplifier clipping.

Part of the confusion here too is "THD" rating. Total Harmonic Distortion is too vague of term. What kinds of distortion is the amplifier adding? There are many different types of amplifier circuits and classes, and many types of output devices, all can create different distortions.

Consider a class-ab. If you were to feed it a sine wave, and overdrive it into a square wave. And say the power supply doesn't have enough poop to keep the rail voltage pegged. You'll get sag that looks like a sawtooth. Also you're likely to get crossover distortion as the signal crosses zero since the power supply couldn't hold it steady.

Contrast this to a class-d amplifier to which it isn't possible to get crossover distortion.

These two topologies are going to have different types of distortion mixes in their "THD" ratings.

All I'm trying to point out is you can't generalize all SS amplifiers into behaving the same. You wouldn't be able to say they all sound bad when overdriven.

Also with SS amplifiers easily providing 1000w these days it's hard to say you'd ever need to overdrive them as much as just a few years ago.

 

[SwamiRob]

Ah ok, I'm only going on what I remember being told and I was generalising most combined pre/poweramp bass heads as being class D because I've very rarely seen anything else. One of my Laneys is Class T but that's merely a variant of class D design as far as I know.

You are kinda right about the overdrive thing though, there was a 70s peavey heads I used a while back which was one of their first bass heads which in essence was a modified PA amp and that sounded really good overdriven, so much so I was kinda convinced that it was a valve amp cos I didn't imagine SS poweramp distortion could sound that smooth, that and the thing weighed a ton. Stuff like that seems kinda rare though, and every SS amp I've heard clipped sounds horrific other then that one.

Your right about the square wave thing (I love the sound of clarinet too) but alot of people do seem to say "square wave distortion" is why a clipped poweramp sounds bad. I was under the impression that most SS amps can't put out more then their limits, and when their limit is reached it essentially begins to compress the wave but in a very harsh manner causing it to square off the top and bottom of the wavefroms while adding to the harmonic content in a usually displeasing way causing nasty upper end distortion. Obviously it seems to not be quite that straightforward.