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What's more important, watts or capacitance?

I'm confused about what makes an amp able to reproduce musical transients realistically. Some articles I've read state that one needs lots of power, measured in watts, to handle dynamics, especially when pushing moderately sensitive speakers. Other articles refer to capacitance as the key. Currently, I use an amp with 600W / 900W into 8/4 ohms, and if I read the specs correctly, it has 60,000 microfarrads of capacitance. An alternative I'm considering puts out 'only' about 220W / 400W but claims capacitance of 200,000 microfarrads. So which amp will sound more dynamic? FWIW, my speakers have a sensitivity of 87.5 db, avg. impedence of 4 ohms and a minimum impedence of 3 ohms. I don't listen at real high volumes, but I do like classical music at close to live levels.

Thanks for any insight!
slanski62
stanwal's avatar
stanwal
3,147 posts
 
Watts are the amount of power that can be delivered, capacitance the amount of current stored for immediate delivery. It is possible to add outboard cap banks IF you know what you are doing, possible to generate an interesting epitaph if you don't. If you have an amp that really delivers 900 watts into 4 ohms and has 60K of capacitance you should have enough, but specs don't always tell the whole story on sound quality. Current storage is far less important for Class D amps and similar which can draw current very quickly. A complicated question with no simple answer; remember again specs aren't sound quality. Some think very large storage is critical, others think small caps give a more agile sound, Classe use to take this route, may still.
hifihvn
943 posts
 
Like Stan said,large caps aren't a guarantee of a better amp.A company may have a smaller power transformer,with bigger caps,and give good short time needed power.An amp with a big power transformer,and smaller caps,can give you that same power on a continuous basis.If a lot of power is needed,that one may have better overall power.With that said,it's still the overall design of everything that make an amp sound good.Not just big caps.Those booming car stereos use extra big caps to store up power,to give those short big booms.In between each big boom,the caps charge up quickly,for the next big boom.Definitely,not high end.Overall good design is whats important.I hope this gives you an idea of what big caps alone do.
almarg's avatar
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almarg
9,670 posts
 
Stanwal: A complicated question with no simple answer; remember again specs aren't sound quality.

Hifihvn: Overall good design is whats important.
I second these comments. At best those specs will tell you how much maximum volume can be generated without clipping the amp. However, the subjective perception of dynamics involves a lot more than watts or energy storage, including a lot of things that can only be assessed by listening.

In particular, the subjective perception of dynamics will depend on how well the system reproduces the leading edges of rapidly changing transients. Things like risetime, ringing, overshoot, etc. Those things in turn can be affected by a whole lot of things, including the use of feedback in the design, transient intermodulation distortion, harmonic distortion, bandwidth, phase response, etc.

Regards,
-- Al
kijanki's avatar
kijanki
4,428 posts
 
I agree - It is much more complicated than amount of caps and the size of transformer. Power supply capacitors are in the signal path (circuit closes thru them) and their inductance and ESR have direct effect on transients and therefore perceived loudness. Good capacitors are expensive.
blkadr
739 posts
 
This is similar to a recent thread about choosing speakers by specs. You might get a general idea about how an amp will drive a specific speaker, but in real world use you can not choose components by numbers. And even if you can predict an amp's ability to drive a load, you cant predict if it will sound worth a darn. I have seen (heard) little amps outclass amps that were much bigger by the numbers. I have also seen speakers with similar specs give completely different results from the same amp.
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