amp 'Class' question

[Dave Blount]

I have a Parasound A23 and it's Class A for the first few Watts, like many amplifiers. I don't know of anything that runs Class A up to 30W, but someone probably makes them.

I believe the Parasound JC-1's get pretty close to the 30 watt number as do others...Pass Labs comes to mind

More accurately, Class AB means it operates in Class A for the first few Watts and then goes to Class B.

not quite........ Class A/B actually takes a bit of both classes so as to optimize the waveform efficiently. Whereas both devices operate slightly beyond the waveforms crossover point so as to mitigate any notch / crossover distortion

 

[Verdinut]

IMO, Class AB amplifiers are to be preferred for a stationary installation and also for musicians who are not too concerned about the weight of the equipment they have to carry around.

As a matter of fact, Class AB amps usually have better specs than Class D amps and there's a possibility also that they may be more reliable in the long run. Don't hesitate to correct me if I am out of the track.

I have been a Class AB adept since the advent of the solid state amp. It would take something better than a current Class D amp to change my opinion.

 

[lovinthehd]

IMO, Class AB amplifiers are to be preferred for a stationary installation and also for musicians who are not too concerned about the weight of the equipment they have to carry around.

As a matter of fact, Class AB amps usually have better specs than Class D amps and there's a possibility also that they may be more reliable in the long run. Don't hesitate to correct me if I am out of the track.

I have been a Class AB adept since the advent of the solid state amp. It would take something better than a current Class D amp to change my opinion.

Which class d amps have you used that brought you to this conclusion?

 

[Verdinut]

To date, I only have used a cheap subwoofer amp which was driving a Dayton Quatro subwoofer that I sold. But I read several comments on amp modules which failed like the ones used on some Pioneer receivers for instance.
Also, are there really some Class D amps that have as good or better specs than Class A/B amps?

 

[lovinthehd]

Don't think you're giving them much of a fair shake then. Reading comments doesn't tell you much. I've used a couple Crown XLS amps over the last few years and they're very nice units. I've heard of some Pioneer problems a few years ago but believe those problems have been resolved. I imagine there are some very nicely spec'd class d amps if you go looking; someone mentioned a Bel Canto amp the other day and I looked it up and it had very nice specs (and at $5000 for a two channel setup more expensive than I'd consider).

 

[Verdinut]

I agree with you. The Bel Canto has very nice specs, but a sum $5000 would also be outside of my spending budget for a two channel unit.
I would be more inclined to put a more important outlay on loudspeakers, the usual weakest link in any sound system.

 

[Dave Blount]

to date I have not listened to a lot of Class D amps but Mark Obrien (Rogue Audio) let me have one of these (Medusa) for a couple of weeks to drive my Martin Logan Spires and I was very pleased ......

http://www.rogueaudio.com/PDFs/Hydra Medusa.pdf

 

[PENG]

I believe many, but not all class AB amps operate in class A for the first few watts to maybe as high as 20 watts; and biased AB at higher output levels. Class AB does not automatically means that the bias will be switched to 0, i.e. class B. In class AB, there should always be a dc bias, albeit a small one. It is possible that some amps might in fact kick into class B at higher output level, but I would stay away from those.

 

[slipperybidness]

What does "Class A is always waiting for the signal." mean? All amps are waiting fr the signal until it arrives. Does this mean they're "faster" than other amps?

What do you do with the wasted energy from your Class A amp(s)?

What he means but doesn't quite capture and may not quite understand, is that "Class A is biased at the mid-point of the load line"

Also, I dunno where he got that "other classes need giant cap" idea

The irony is that I suspect that you understand this technical aspect.

 

[slipperybidness]

I believe many, but not all class AB amps operate in class A for the first few watts to maybe as high as 20 watts; and biased AB at higher output levels. Class AB does not automatically means that the bias will be switched to 0, i.e. class B. In class AB, there should always be a dc bias, albeit a small one. It is possible that some amps might in fact kick into class B at higher output level, but I would stay away from those.

Pure class B is no good for audio applications, the IMD is silly high for class B.

Thus, audio uses class AB

 

[Dave Blount]

I believe many, but not all class AB amps operate in class A for the first few watts to maybe as high as 20 watts; and biased AB at higher output levels.

....... and for those that do they are so classified as A A/B

 

[PENG]

....... and for those that do they are so classified as A A/B

Not always, for example, a 300/500W Bryston amp may remain in class A bias up to 20W, but they don't use the term A/AB in their literature. Parasound Halo, such as the A21, are specified as A/AB, but only biased in A for up to about 8 to 10 watts.

 

[Dave Blount]

Not always, for example, a 300/500W Bryston amp may remain in class A bias up to 20W, but they don't use the term A/AB in their literature. Parasound Halo, such as the A21, are specified as A/AB, but only biased in A for up to about 8 to 10 watts.

understood, I was merely stating what 'actually' happens if said amp is configured as such.

 

[Irvrobinson]

Not always, for example, a 300/500W Bryston amp may remain in class A bias up to 20W, but they don't use the term A/AB in their literature. Parasound Halo, such as the A21, are specified as A/AB, but only biased in A for up to about 8 to 10 watts.

These numbers sound really high. 20W at class A, which probably has a conversion efficiency of about 25%, means there's a standing output stage dissipation at idle of something like 160 watts (assuming two channels). Throw in the other amplifier stages and you'd be at nearly 200 watts at idle (admittedly a very rough guesstimate). That would be one hot amp, and the Bryston's I've seen run pretty cool. I think most amps without dynamic bias levels (like the old Levinsons and Krells) are probably tuned for class A operation for five watts or less. That's where I'm guessing my ATI is.

 

[PENG]

These numbers sound really high. 20W at class A, which probably has a conversion efficiency of about 25%, means there's a standing output stage dissipation at idle of something like 160 watts (assuming two channels). Throw in the other amplifier stages and you'd be at nearly 200 watts at idle (admittedly a very rough guesstimate). That would be one hot amp, and the Bryston's I've seen run pretty cool. I think most amps without dynamic bias levels (like the old Levinsons and Krells) are probably tuned for class A operation for five watts or less. That's where I'm guessing my ATI is.

I understand your point, and I just PM you about my source. My 4B SST runs quite warm idling, much warmer than the less powerful A21, but then the A21 has an over sized enclosure.

 

[PENG]

understood, I was merely stating what 'actually' happens if said amp is configured as such.

Okay I see your point. A/AB could actually be confusing for the hard core class A group. To them class A means class A full time, like those by Luxman, Audio Research and Pass Lab etc.

 

[Dave Blount]

These numbers sound really high. 20W at class A, which probably has a conversion efficiency of about 25%, means there's a standing output stage dissipation at idle of something like 160 watts (assuming two channels). Throw in the other amplifier stages and you'd be at nearly 200 watts at idle (admittedly a very rough guesstimate). That would be one hot amp, and the Bryston's I've seen run pretty cool. I think most amps without dynamic bias levels (like the old Levinsons and Krells) are probably tuned for class A operation for five watts or less. That's where I'm guessing my ATI is.

not high at all, I believe some of Pass Labs A A/B amps bias almost 30 watts or so before operating in A/B.

as for the Parasound JC1's (that I love BTW) they go to 25 watts, here's the link .......

http://www.parasound.com/jc1.php#