Amps for dummies

[TheMoose]

Originally Posted by deacongreg

TheMoose,

kenny gave you some real excellent advice on those Proceed amps. I would say, and this depends a whole on who your dealer is, but if he is a professional, and into good customer service, let him know you are considering a switch from a receiver to an amp, he should allow you a trial, then you could see for yourself in your OWN system at home.

Because, though kenny said some really great things, you will not really know until you hear it for yourself. With your speakers, your music, in your house, in your dedicated room.

Yea that's what I'll try try do when the time comes, I've got a good dealer that'll work with me. I'm still a ways off as I won't be upgrading until I build my standalone theater.

[kloneman]

Originally Posted by kennyt

Class A use full power all the time, so they are always ready to output it. They run hot and eat up electricity.

For Class A output, the transistors are biased so that they are conducting for both halves of AC waveforms, The highest "positive-going" output rides above a midpoint value, while the most "negative-going" output rides below the midpoint value but still out of the non-linear portion of the curve close to zero, rather than running at full power.

Originally Posted by kennyt

Class B switches on and off as needed, saves power and heat

Class B output is biased so that the transistors are off during almost one half of AC waveform. A second transistor is used to carry the opposite portion of the waveform during the time that the first one is off. This allows both transistors a chance to recover (each one has an average 50% duty cycle, and also allows for greater total signal swings, since the peak to peak signal is summed. Class B is non-linear because there is a period near the positive and negative region near zero, where neither transistor conducts.

Originally Posted by kennyt

Class A/B works like class A to a point, then uses class B type switching for the higher outputs.

In Class AB, a small bias is placed on the transistors to keep them conducting a little earlier than they normally would, to keep them out of that non-linear part of their curves close to zero.

Class C is where the transistors are biased to conduct less than 50% of the time, but they still linearly track a portion of the input signal that is higher than some threshold volue. One variation (Class G, I think) uses multiple sets of power supplies that are switched in as the signal swings toward the normal power supply limit, to extend the output signal beyond it. Another variation (Class H, I think) actually had separate transistors and power supplies that were turned on to follow the peaks.

Originally Posted by kennyt

D are digital or switching amps, they've been around a while but people are really just getting them accepted by the high end. No, all solid state amps are not digital amps.

This is obviously only a brief overview, but will give you the idea.

Class D is where the transistors are biased to conduct as switches - when they are on, they are driven to the supply rails - A variation on the pulse amplifier technique actually uses a form of modulation such as pulse width modulation, combined with summing up the pulses (integration) through the load and a capacitor to reconstruct an analog signal.

[rlpiii]

Originally Posted by kloneman

One variation (Class G, I think) uses multiple sets of power supplies that are switched in as the signal swings toward the normal power supply limit, to extend the output signal beyond it.

Class G is being used by Fosgate for their multi-channel amps. They are one of very few companies building HT amps with Class G design.

Below is what they have to say about it.
http://www.fosgateaudionics.com/products/FAA_1000_5.asp

"The new FAA 1000.5, incorporating the acclaimed Trans•ana circuit topology in a new Class-G version, delivers a level of audio performance previously available only in much more expensive and exotic products.

JFET input stages dramatically reduce noise modulation and cross-products which can cloud amplifier detail and clarity on complex musical material.

MOSFET power output devices assure high output current, fast transient response, reliability and transparent sound quality.

Trans•ana output topology is configured for “voltage gain,” allowing a simple signal path.

Output topology is dual-voltage-rail type, with soft transition between levels (Class-G), allowing cooler operation at typical 1/8 to 1/3 power levels. 4:1 power headroom (average) allows sustained high output levels -- a highly desirable characteristic for reproduction of movies or music. The FAA 1000.5 is virtually immune to thermal shutdown and meets UL and other regulatory requirements.

A real-time protection system continuously computes MOSFET power dissipation. Combined with the unique load-impedance selector switches, optimum operation is attainable with any type of loudspeakers."

Kloneman, I knew you could not resist this discussion. . .

[kloneman]

Originally Posted by rlpiii

Class G is being used by Fosgate for their multi-channel amps. They are one of very few companies building HT amps with Class G design.

Below is what they have to say about it.
http://www.fosgateaudionics.com/products/FAA_1000_5.asp

"The new FAA 1000.5, incorporating the acclaimed Trans•ana circuit topology in a new Class-G version, delivers a level of audio performance previously available only in much more expensive and exotic products.

JFET input stages dramatically reduce noise modulation and cross-products which can cloud amplifier detail and clarity on complex musical material.

MOSFET power output devices assure high output current, fast transient response, reliability and transparent sound quality.

Trans•ana output topology is configured for “voltage gain,” allowing a simple signal path.

Output topology is dual-voltage-rail type, with soft transition between levels (Class-G), allowing cooler operation at typical 1/8 to 1/3 power levels. 4:1 power headroom (average) allows sustained high output levels -- a highly desirable characteristic for reproduction of movies or music. The FAA 1000.5 is virtually immune to thermal shutdown and meets UL and other regulatory requirements.

A real-time protection system continuously computes MOSFET power dissipation. Combined with the unique load-impedance selector switches, optimum operation is attainable with any type of loudspeakers."

Kloneman, I knew you could not resist this discussion. . .

Cool. I was wondering if I got it right. The amplifiers I first saw that used Class G or H techniques were built by Hitachi over 20 years ago. I recalled both techniques but was unsure if I got the class of operation matched correctly with the technique. You know me (AKA frustrated "hardware guy" in a software-driven world) too well, grin.

[deacongreg]

Originally Posted by TheMoose

Yea that's what I'll try try do when the time comes, I've got a good dealer that'll work with me. I'm still a ways off as I won't be upgrading until I build my standalone theater.

Okay, that sounds really good. Good Luck on building your Home Theater.

[jsound]

Hi, Guys:
I'm just getting back into the audio thing after a long while. At first, I was looking at mini-systems, but then the old sound jones woke up.....well, you know... So, I just bought a Cambridge Audio 640C v2 CD player, & now I need either a receiver or an integrated amp. As a receiver, I'm looking at the HK3390 (80wpc). In integrateds, the Cambridge 640A v2, or the
NAD C326BEE. The speakers will most likely be the Polk Audio RtiA1's. Crazy thing is, I've only got 1/3 of the system, & I'm
already pushing the budget....I did start out with the idea of a mini, after all.
Anyhoo, I want something that I won't want to upgrade in 6 months. I'm also looking on Audiogon, & checking out the hifi stores for decent used equipment, figuring I could probably get better gear for about the same price. So far, it's looking like the NAD or Cambridge, new, will be the choice.
Any comments/suggestions?