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-   -   does class A amp feel more powerful with same ratings compared to class AB? (http://www.diyaudio.com/forums/solid-state/225378-does-class-amp-feel-more-powerful-same-ratings-compared-class-ab.html)

rhythmsandy 10th December 2012 01:33 PM

does class A amp feel more powerful with same ratings compared to class AB?
 
example I spoke to one of my friend who build a hiraga 8w amplifier and he is using a 200Va for both stereo. He said that its driving 3 way speaker with 10 inch driver with ease and it even rattles the room once the volume is cranked up.

how come class A do that but a classAB of same power ratings cant do...
or the dynamics makes us feel that its powerful...

i initially thought to build Hiraga 30W but will be starting soon.

now the question is what is the multiplication factor which makes class A more powerful..

analog_sa 10th December 2012 02:14 PM

There is no "multiplication factor" and i really don't think class A amps sound more powerful than similarly rated class AB provided the power supplies are similar.

KatieandDad 10th December 2012 02:39 PM

There are too many variables in your initial statement.

A Class A amplifier will by its nature have a far more substantial power supply than its Class A/B brethren.

If a Class A/B amplifier is designed correctly and has a large enough power supply, it too will be able to deliver the transients that are generally the noticeable feature about Class A amps.

If you think about it - this is in general terms.

A 50W Class A amplifier may require a 300W power supply. A lot of that 300W is stored in huge capacitors and is able to deliver quite a current surge for a short period of time.

A 50W Class B amplifier may only require a 100W power supply.

Most Class B amplifiers are designed to be efficient, it is this which is limiting its ability to punch out the high currents. A poor Class A design will have similar attrbutes.

But, to answer your question. A good Class A against a good Class B, they will sound just as loud as each other - they will have different characteristics though.

KatieandDad 10th December 2012 03:59 PM

Shame this topic is being driven underground by the general drivel on this site.

forr 10th December 2012 04:42 PM

Why all the watts are not equal
 
The difference of "subjective power", as Hiraga called it, does not rely in the difference of classes but in the behaviour at clipping and the way power amps are rated.

If two amps are rated at the same voltage (converted in W/8 Ohm) for 1% of distorsion, the first one may suddenly clip just above that voltage as the other may have a much higher voltage amplitude without clipping but with a lot of distorsion.

This last behaviour is often called "soft clipping" but in fact, it's only a non-linearity effect as far as there is no plateau in the output signal. It is not as detectable as severe clipping.

The reason why the two amps may appear to be of different power is due to the standard practice of measuring power for 1% distorsion.

To have the same "subjective power", the first amp may need to be rated as much as 4 times the second one.
.

weinstro 10th December 2012 04:53 PM

Quote:

Originally Posted by rhythmsandy (Post 3278684)
example I spoke to one of my friend who build a hiraga 8w amplifier and he is using a 200Va for both stereo. He said that its driving 3 way speaker with 10 inch driver with ease and it even rattles the room once the volume is cranked up.

If the speakers are efficient enough, that could be true for any 8 watt amp.

Quote:

Originally Posted by rhythmsandy (Post 3278684)
how come class A do that but a classAB of same power ratings cant do...
or the dynamics makes us feel that its powerful...

It runs hotter. Class A amplifier power supply must put out rated power continuously. Class AB amplifier power supply must put out rated power only on peaks.

There is no crossover distortion in a Class A amplifier, and therefore less feedback may be required. Consequently, when a Class A amplifier clips, it won't sound nearly as bad as a clipping Class AB amp at the same output power rating. That's probably the phenomena you and your friend are observing - you can drive the Class A amp a bit harder before the distortion becomes objectionable than you can a Class AB amp.

I have an amp that is switchable. In Class A, it's rated for 30W. In Class (A)B, it's rated for 120W. Either mode sounds pretty good.

Regards,

Rob

AndrewT 10th December 2012 04:58 PM

Valve amps have enormous power when severely overdriven.
This effect is used in music creation.

This effect is rarely used in music reproduction.
We generally want linear amplification of what is in the recording so that we can hear what the music creator did with his/her severely overdriven value amplifier.

The same can be arranged to happen in solid state. Cordell's Klever Klipper is possibly a way of getting some distortion effect as maximum output is approached.

But all of that has nothing to do with peak SPL, nor average SPL available from a music reproduction system.

wahab 10th December 2012 05:21 PM

Quote:

Originally Posted by forr (Post 3278929)
If two amps are rated at the same voltage (converted in W/8 Ohm) for 1% of distorsion, the first one may suddenly clip just above that voltage as the other may have a much higher voltage amplitude without clipping but with a lot of distorsion.

This last behaviour is often called "soft clipping" but in fact, it's only a non-linearity effect as far as there is no plateau in the output signal. It is not as detectable as severe clipping.

The reason why the two amps may appear to be of different power is due to the standard practice of measuring power for 1% distorsion.

To have the same "subjective power", the first amp may need to be rated as much as 4 times the second one. .

So one clips completely once there s more than 1% THD while the other ,
more powerfull , continue to have its power increased past this ratio...

I guess that this definition of the "same watts" is , as expected ,
lengthily stretched.


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