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What does "fast" mean with regards to an amp?
- Thread starter Nozza
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MakeMineVinyl
Major Contributor
I like my amplifiers to be as slow as possible.
Sheesh. To me, fast amp is one that is actually powerful enough not to compress loud musical attacks so that they sound dull. A slow amp is one that lacks the power to complete that waveform when it appears. Lots of music has a sharp transient followed by a sustained pitch, and that compression depresses the sharp transient.
I can hear it when I play my 40-watt Kenwood amp from the 70's too loudly with really dynamic music that is recorded dry without a lot of reverberation or processing. Bigger amps have the headroom to keep up with those dynamics.
Call it sighted bias if you will, but the propensity of smaller amps to clip or compress when playing dynamic music loudly is not exactly controversial, or at least it shouldn't be.
Rick "wondering how many shibboleths trace their roots to underpowered amps and speakers that are overdriven" Denney
I can hear it when I play my 40-watt Kenwood amp from the 70's too loudly with really dynamic music that is recorded dry without a lot of reverberation or processing. Bigger amps have the headroom to keep up with those dynamics.
Call it sighted bias if you will, but the propensity of smaller amps to clip or compress when playing dynamic music loudly is not exactly controversial, or at least it shouldn't be.
Rick "wondering how many shibboleths trace their roots to underpowered amps and speakers that are overdriven" Denney
If the current isn't there, the voltage across the speaker leads won't be there either, so, it is already (indirectly) measured, and the usual voltage measures would reveal a problem, I should think.
Though, the above won't give you a value for current into the variable impedance, just indicate a lack.
If the speaker impedance is largely inductive, the inductance will place a limit on the rate of change of current. So a voltage source that turns on instantly, placed across this load, will not make the current change any faster than the inductance allows it to. Magnetic fields, responsible for inductive effects, don't suddenly appear and disappear. They build up & collapse and take time to do so.
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How quickly does this happen and is it audible? That would be interesting to test.
When a load is inductive, it simply means its impedance rises with frequency, and therefore draws less current with the same voltage amplitude as the signal frequency goes up.
The job of a speaker amplifier is to output a voltage that follows the voltage of the input, multiplied by the gain, while being able to supply whatever current the load draws at that output voltage. If the amplifier cannot provide the required current, the output voltage sags and we have clipping, just as what @RayDunzl said in post #86.
A "slow" current rise through an inductor has nothing to do with "speed" (of the supplied voltage). It is the result of the lower current draw by the high frequency components of the step versus its lower frequency components. If you look at the waveforms of the current, they are all going to look the same for any amplifiers with sufficient frequency bandwidth (and voltage and current capacity) to reproduce the step.
It probably is not a strong enough effect to seriously matter, otherwise all speakers with voice coils, tweeters and all, would have a serious problem, and speakers made with those sound just fine. Also Zobels can be employed in x-over networks to flatten the impedance over frequency. So basically, worrying about it is pointless. It's a nothingburger.
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