ampere vs wattage

[murali]

In case people have not forgotten the basics, an amplifier never really "amplifies" the incoming signal. As arj has explained, all the amplifier does is to "create" an output signal from the power supply and the role of the input signal is only to trigger that. Hence for any amplifier, the most critical aspect is its power supply and that is what makes significant differences in its design, construction and performance. Look at any high-end amplifier and you will see that its power supply related components will be massive with a huge reserve to cater to transients.
The other issue is global feedback employed. That too makes a big difference. I belong to that category of people who hates global feedback. Listen to a high-end amplifier without global feedback and others with global feedback, and you will notice significant differences.

Just my 2 cents, please.
murali

 

[docjoe]

I am no expert yet wish to contribute my understanding. So, elec engrs, please do correct me when I am wrong. Some basic issues are covered here:

http://en.wikipedia.org/wiki/Watt

http://en.wikipedia.org/wiki/Electrical_impedance

https://en.wikipedia.org/wiki/Ampere

http://en.wikipedia.org/wiki/Voltage

A simple analogy here:

HowStuffWorks "What are amps, watts, volts and ohms?"

And here:

HowStuffWorks "Electrical Efficiency"

Amplifier A
80watts @ 8ohms, 120watts @ 4ohms

Amplifier B
50watts @ 8ohms, 100watt @ 4ohms, 200watts @ 2ohms

Prima facie, it seems to be more of an issue of flexibility. Amp B seems more accommodating of different speaker combos (which is what the query is all about, I suppose). Like, one has a small room? Fine, connect a low demand set of 50W speakers. Medium sized room would need a 100W set while a large room would require a 200W set.

This is the reason that most high end amps have the option for multiple impedance connections, I suppose. The quality of the output would depend on the quality of the amp as a whole.

I do not wish to speak about THD etc as I am not very conversant with deep audio terms.

 

[captrajesh]

I was told by a AV service engineer that SMPS based systems tend to weigh less when compared to the systems having isolation transformer.

I'm not an expert and there could be exceptions but barring Class D amplifiers which typically have efficiency figures hovering around 90% mark, all conventional (mainstream) Class A and AB amps have linear power supplies.

an amplifier never really "amplifies" the incoming signal. As arj has explained, all the amplifier does is to "create" an output signal from the power supply and the role of the input signal is only to trigger that.

If I may add, the low voltage input signal at line stage is a template which is used by the power amp to produce the music signal strong enough to flow through the voice coil and create the to and fro movements of the speaker cone. Thus the overall SQ would depend not only on how faithful the template is but also how faithful the output signal is to the original signal.

 

[shanmune]

I'm not an expert and there could be exceptions but barring Class D amplifiers which typically have efficiency figures hovering around 90% mark, all conventional (mainstream) Class A and AB amps have linear power supplies.

.

An year back, I took my brother's AV receiver (Yamaha RX-V671) to a service engineer. I was very curious to see inside the AV receiver when the engineer opened the top cover of the receiver (RX-V671 has Class AB amp). The service engineer said that it had an SMPS system, but the previous equivalent model (RX-V667) had the isolation transformer. He said that most of the new models (some time from 2010/2011) from various brands had started using SMPS (at least in the AV receivers). So is it true that most of the AV receivers use non-linear power supply systems ??? (I am not quite sure about dedicated amps)

I have also seen (from spec sheets) that most of the AV receiver models from Marantz, Denon, Onkyo, etc., have their weight getting reduced year over year. Is this some thing related to moving towards SMPS systems ?