Lets talk Amps

[Audiophile Mancave]

 

Why haven't the manu's dropped Class A/B  for the G and D setups?  I know Rotel did for a while, but I noticed they have started offering the A/B topos again in their integrated amps.

 

Both class "G" and "D" have been making really good progress.

I think most of NAD's top end is Class "D" at this point?  Well at least some of them ... ;-)

Class "G" I think involves a modulating the rail voltage - which is really hard to do and not lose transient response and dynamic range.  Dunno.

[djk]

"Class "G" I think involves a modulating the rail voltage - which is really hard to do and not lose transient response and dynamic range.  Dunno."

 

 

.As we can see it is an ordinary class AB amplifier until the voltage exceeds the lower rail voltage. As it needs more output voltage it cascodes itself and runs from the higher voltage rail. D2 and D4 are the only difference between this and a normal cascode amplifier (like a Threshold), they must be of a schottky type to avoid noise.

[AllenTacey]

wdecho what happens to the sound if you sit two meters back from the wall instead of only one? My speakers manufacturer advise us to sit 1.5 times the distance speaker to speaker.I use two very high powered solid stat amplifiers. The reason is easy when you become aware that to raise the volume to where you can hear the change in volume from your speakers specifications. To hear a 3dBs rise in sound (where you actually here it get louder) you need a hundred fold more power.

What I am saying is to hear an extra 3dBs over 1 watt you will need 100 watts. This is why I recommend buying the most power you can afford and one that has as high as possible dynamic range. I do not turn up the volume recklessly I use what it takes to reproduce the sound stage intended. Listen to a full Orchestra 30 watts does not cut it.

[djk]

3dB is double the power, doubling the distance is 6dB less, or 4x the power.

[AllenTacey]

wdecho small World I listened to a pair of those Crowns might have been a 200 or 2000 series (know it started with two) last Saturday and was impressed. It was outside in a small shell used for live music and we had a four piece band entertaining us. The pair was slim drove four monitors. My system far outweighs that setup. I am medically retired and since 1991 had everything but the speakers and after making a speaker purchase in May I also bought a circa 1980 solid state amplifier. HiFi back then and sonically still silent adding nothing in the way of notice. I am pleased at the beautiful sound stage which playing classical music needs horsepower but I do not want, well maybe I do need to respect neighbors. The levels I listen to today could not be possible with my first amplifier a 35 watts per channel thd .05 in 1977. Guess I have not been convinced tubes or convinced the most really powerful wattages we can afford is not the ticket. I like 98dBs output really would not mind a couple of klipschorns falling into my hands 114 dBs?? Well two powerful amps will have to suffice...

[AllenTacey]

My amp has a 22 pound transformer and 4, two per channel, 40,000 microfarad capacitators. My first speakers fainted when they caught sight of it. Then I bought a ten pound ten inch square amplifier and my speakers giggled like school girls until they got broke in. Now that they are all properly introduced they spend the day making beautiful music together...

[Blvdre]

What I am saying is to hear an extra 3dBs over 1 watt you will need 100 watts. 

 

What djk said. To increase the level 3dB from 1 Watt, double the power to 2W.

[Max2]

It's not just me

http://www.pooraudiophile.com/2015/07/benchmark-ahb2-power-amplifier-review.html

 

 

You should start a thread on that amp Josh. I would love to hear more about it and the loads of amps you have owned to compare it to.

[joshnich]

Hi Max

I probably should. So far I feel I have been pissing up a rope. I am getting lectures on the benefits of class A , SET, Nelson Pass etc. this amp has replaced them all and in my mind outperformed them all by a wide margin. When I get a little time I'll gather the thoughts and put them down with a history of the amps that I'm comparing this incredible game changer to.

J

[Ski Bum]

It's not falling on deaf ears, J.  On paper, those appear to be ideal for extra revealing, high sensitivity speakers, and it's nice to get some feedback from an actual user whose tried just about everything with speakers we can relate to.  I would have one if I had two thousand bucks burning a hole in my pocket.

[Bubo]

There are plenty of good Class A/B amplifiers that sound exceptional with Klipsch speakers. This is an entertainment hobby and if it pleases you be buy one and be happy. But that being said it is a fact that the most linear of all classes is Class A. All A/B amplifiers have crossover distortion that has to be dealt with in some manner to sound decent. Single ended Class A does not have this to begin with. Some designers throw many components and circuits to cancel this crossover distortion others bias the A/B amplifier higher. Class A amplifiers whether tube or transistor are not for every speaker because of their limited wattage without getting very expensive. Klipsch speakers are made for Class A because of their efficiency. A well designed Class A/B amplifier will sound better than a poorly designed A. I personally would not buy an expensive A/B amplifier with a highly efficient speaker when I could buy a good quality Class A for the same price. If I had speakers that needed 100 watts I would definitely buy an quality Class A/B amplifier. I have owned many, many amplifiers and nothing has sound as good with my speakers as the worst Class A amplifier I have owned. Do your research on amplifier designs and they will substantiate my comments of the most linear of all designs, Class A.

Any favorites on the class As that you can share?

[Bubo]

On my main system, my typical listening levels as measured on my McIntosh 2205 are typically at 200ths of 1 watt with my LaScalas peaking when I crank it up at around .2 watts. At 2 watts it's ear splitting and will drive you out of a 30 foot room.

 

The LaScalas are circa 1980 so the rating is either 102db or 104db at 1W1M. The Mc will push 200W per channel all day long, I have never been able to test it. From what I have read, even though it is an AB amplifier the first few watts may be class A.

 

If I understand it correctly, my Yamaha Amps which I love, also produce Class A for the first watts then switch into Class AB. On the MX-800 someone who has looked at it told me that the first 35 watts are class A.

 

For what its worth, both the Mc and the Yammys have massive transformers and filter caps.

 

Based on my observed power usage, I would think a really well made 20 watt class A amp would blow your socks off with the LaScallas.

 

The argument for tubes, simplicity, is appealing and they have other performance characteristics. The Mc 30s that I sampled sounded great to me, they do come at a high price if they are refurbished. On the MC30 spec sheet, the specs for .5 watt are published and they are spectacular compared to anything.

Edited August 11, 2015 by Bubo

[djk]

"the MX-800 someone who has looked at it told me that the first 35 watts are class A."

 

Had not a clue, did he?

 

http://www.hifiengine.com/hfe_downloads/index.php?yamaha/yamaha_mx-70_800_service_en.pdf

 

10mV across 0.22Ω is 45mA x 3 sets of outputs is 135mA of bias, about 292mW into 8Ω.

 

"Push-pull circuitry more or less doubles the efficiency of a class A output stage (Fig. 4c) because unlike the constant current sourced design, its idle current need be only one half the peak output current," (Nelson Pass)

 

The MC2205 has even less bias.

[juniper]

It doesn't have to be Class A, I heard some bridged monoblocks in my system the other  day that were made by Spectron. I have never heard transients it big orchestral pieces handled so effortlessly.  These amps are around 600 watts a channel and for peeks will jump to 3500 watts. Amazing sound...

[joshnich]

There are plenty of good Class A/B amplifiers that sound exceptional with Klipsch speakers. This is an entertainment hobby and if it pleases you be buy one and be happy. But that being said it is a fact that the most linear of all classes is Class A. All A/B amplifiers have crossover distortion that has to be dealt with in some manner to sound decent. Single ended Class A does not have this to begin with. Some designers throw many components and circuits to cancel this crossover distortion others bias the A/B amplifier higher. Class A amplifiers whether tube or transistor are not for every speaker because of their limited wattage without getting very expensive. Klipsch speakers are made for Class A because of their efficiency. A well designed Class A/B amplifier will sound better than a poorly designed A. I personally would not buy an expensive A/B amplifier with a highly efficient speaker when I could buy a good quality Class A for the same price. If I had speakers that needed 100 watts I would definitely buy an quality Class A/B amplifier. I have owned many, many amplifiers and nothing has sound as good with my speakers as the worst Class A amplifier I have owned. Do your research on amplifier designs and they will substantiate my comments of the most linear of all designs, Class A.

You make it sound as if folks here haven't done any research on amplification topology. I can assure you that is not the case. I admit that I am not nearly as technical as some on this forum but I have done a significant amount of research on amplifier topology. I in fact owned class A tube amps and class A solid state amps. I would encourage you to do some research on THX 's Achromatic Audio Amplification technology as well as Benchmarks feed forward error correction approach.

I know from professional experience that it is hard for people to change their minds, in fact it's virtually impossible regardless of the evidence and facts presented - so I dont have much confidence that I will change yours. I just hope that with a little research you might find a smaller horse

Edited August 11, 2015 by joshnich

[Guest thesloth]

All A/B amplifiers have crossover distortion that has to be dealt with in some manner to sound decent.

 

 

I disagree.

 

I have tested many A/B amplifiers to full rated output and there is ZERO crossover distortion in the output. In fact that is the whole point of biasing an amp properly.

 

Just becaue one device goes into cut off doesn't mean that the output will have a notch at the zero point.

 

I would go on and say that in an AB amplifier because of the bias point the tube is usually operated in it's most non linear region which would create distortion, which feedback then just fixes.

Edited August 11, 2015 by thesloth

[Bubo]

"the MX-800 someone who has looked at it told me that the first 35 watts are class A."

 

Had not a clue, did he?

 

http://www.hifiengine.com/hfe_downloads/index.php?yamaha/yamaha_mx-70_800_service_en.pdf

 

10mV across 0.22Ω is 45mA x 3 sets of outputs is 135mA of bias, about 292mW into 8Ω.

 

"Push-pull circuitry more or less doubles the efficiency of a class A output stage (Fig. 4c) because unlike the constant current sourced design, its idle current need be only one half the peak output current," (Nelson Pass)

 

The MC2205 has even less bias.

 

I understand that Pass has an article on biasing on his web site with formula for determining class A output.

 

This is a different discussion, about a different design(er) that Yamaha and apparently others used the "Hyperbolic circuit". I'm not feeling particularly good, so I'm going to pass on reading the 11+ pages, which would normally be interesting if nothing else. I think the gist of it is how to get Class A without a lot of heat in a solid state design, if you don't generate a lot of heat that may mean that you don't have a lot of surplus energy to dissipate.

 

Again I'm under the weather, but what I got from your comment is that you think the design(s) given the biasing are unlikely to generate much if any Class A operation. This is one of the many research projects and discussions that is on my list, but I never get to. Mostly I'm ramping up to rebuild my racks of sweet sounding gear, then figure out what else I can do with an iron and a scope....if I don't die from flux poising.

 

http://www.diyaudio.com/forums/solid-state/152734-yamahas-hyperbolic-conversion-amplification-hca-circuit.html

 

This may be a better thread

 

http://forums.phxaudiotape.com/showthread.php/535-Hyperbolic-Conversion-Amplification-Curcuit

Edited August 11, 2015 by Bubo

[Bubo]

 

 

All A/B amplifiers have crossover distortion that has to be dealt with in some manner to sound decent.

 

 

I disagree.

 

I have tested many A/B amplifiers to full rated output and there is ZERO crossover distortion in the output. In fact that is the whole point of biasing an amp properly.

 

Just becaue one device goes into cut off doesn't mean that the output will have a notch at the zero point.

 

I would go on and say that in an AB amplifier because of the bias point the tube is usually operated in it's most non linear region which would create distortion, which feedback then just fixes.

 

So you are saying that Class A/B amplifiers do not have crossover distortion to be dealt with in some way? There are lots of tube amplifiers that do not have any feedback whatsoever because none is needed. Most, if not all A/B amplifiers have tons of feedback correction. 

 

 

EL Paso Tube has lots of great videos on Youtube, former NASA and MIL tech, probably an engineer. Anyway, he always seems to be able to zoom his scope to make the crossover visible, since it must be there. I think the argument is, how inaudible does it have to be before it's a non issue.

Edited August 11, 2015 by Bubo

[derrickdj1]

If I understand it correctly, my Yamaha Amps which I love, also produce Class A for the first watts then switch into Class AB. On the MX-800 someone who has looked at it told me that the first 35 watts are class A.

 

I recall correctly, most of the Yamaha Legnedary amps do up to 20 watts class A and then switch to Class A/B.  Twenty watts is way more than you need for those LaScala's.    

[Guest thesloth]

 

 

All A/B amplifiers have crossover distortion that has to be dealt with in some manner to sound decent.

 

 

I disagree.

 

I have tested many A/B amplifiers to full rated output and there is ZERO crossover distortion in the output. In fact that is the whole point of biasing an amp properly.

 

Just becaue one device goes into cut off doesn't mean that the output will have a notch at the zero point.

 

I would go on and say that in an AB amplifier because of the bias point the tube is usually operated in it's most non linear region which would create distortion, which feedback then just fixes.

 

So you are saying that Class A/B amplifiers do not have crossover distortion to be dealt with in some way? There are lots of tube amplifiers that do not have any feedback whatsoever because none is needed. Most, if not all A/B amplifiers have tons of feedback correction. 

 

 

 

This might help clarify the subject of "feedback" for those who still don't understand it: http://ken-gilbert.com/images/pdf/Inherent_FB_inTriodes.pdf

 

 

I think you meant to say there are lots of tube amplifiers that do not have feedback which includes the output transformer in the loop, i.e. "global feedback".

 

 

I agree that most AB amps use the most common form of feedback which is tapped from the secondary of the output transformer and fed back to the input. This usually lowers distortion to lower levels then most SET without global feedback, if distortion isn't a problem in a SET which usually has up to 5% THD at full output why would less distortion in a PP class AB amp be an issue?