Class A solid state amplifiers.

[Zaphod Beeblebrox]

Just now, 125dBmonster said:

I think Zaph is suggesting that a real class A Amplifier is single ended only  

 

Nope. The designation of Class A is well defined. It can be push pull, single ended, or even, like the mighty Sumo Nine - bridged single ended Class A. 

[Wimbo]

1 minute ago, 125dBmonster said:

Correct

 

Thanks mate.

[Guest]

On 3/3/2017 at 8:43 PM, Wimbo said:

Thanks mate.

Thank Zaph  he has the 100 years experience (in a 50yo body) 

 

[Wimbo]

2 minutes ago, Zaphod Beeblebrox said:

 

Nope. The designation of Class A is well defined. It can be push pull, single ended, or even, like the mighty Sumo Nine - bridged single ended Class A. 

I use to own a Sumo Nine back in the day.

[Wimbo]

1 minute ago, 125dBmonster said:

Thank Zaph  he has the 100 years experience (in a 50yo body) 

 

Hes not 50. Thanks Zaph btw.

I could,nt get that out of Dave Astley decades ago. Or maybe I just wasnt listening, I don't know.

[Zaphod Beeblebrox]

Just now, 125dBmonster said:

Thank Zaph  he has the 100 years experience (in a 50yo body) 

 

 

Make that a 63 year old body.

[Wimbo]

1 minute ago, Zaphod Beeblebrox said:

 

Make that a 63 year old body.

Like me mate hehe.

[Zaphod Beeblebrox]

Just now, Wimbo said:

I use to own a Sumo Nine back in the day.

 

Great amp. I still have one lurking about the place. I must re-build it. Excellent sounding old amp. 75 Watts Class A per channel. 1,400VA power transformer. The late, lamented Jim Bongiorno knew exactly what he was doing way back then.

[Guest]

On 3/3/2017 at 8:50 PM, Zaphod Beeblebrox said:

 

Make that a 63 year old body.

and sharp as a thumb tack 

[Wimbo]

1 minute ago, Zaphod Beeblebrox said:

 

Great amp. I still have one lurking about the place. I must re-build it. Excellent sounding old amp. 75 Watts Class A per channel. 1,400VA power transformer. The late, lamented Jim Bongiorno knew exactly what he was doing way back then.

Yeah mate. He did the GAS and the Marantz Esotec series as well I think.

[Boris Karlof]

LOL love it. Speaking of Single ended transformer coupled Class A

Say hello to my little friend. Big Red.

23 kg of battery powered flea watt transformer OP madness. 1.5 wrms ch of siliconey goodness. Mmmmmm.

BTW I spun the image upside down because the right way up it loads upside down. Loaded from upside down it loads guess what that's right upside down. lf stereonet doesn't care about this issue well then neither do I.

Just adds more madness to an already sanity challenged world. Put that fire out with gasoline WooHoo!

[Guest]

On 3/4/2017 at 6:32 PM, Boris Karlof said:

LOL love it. Speaking of Single ended transformer coupled Class A

Say hello to my little friend. Big Red.

23 kg of battery powered flea watt transformer OP madness. 1.5 wrms ch of siliconey goodness. Mmmmmm.

BTW I spun the image upside down because the right way up it loads upside down. Loaded from upside down it loads guess what that's right upside down. lf stereonet doesn't care about this issue well then neither do I.

Just adds more madness to an already sanity challenged world. Put that fire out with gasoline WooHoo!

Battery powered Class A, really, do tell  very interested how this is accomplished  

 

Proof or it's BS Mate 

Edited March 5, 2017 by Guest

[Boris Karlof]

5 Mobile Phone relay station backup Batteries in parallel. The 12V-13 rating does limit OP to the fleawatt level.

1.5 wrms but boy does it sound good.

Edited March 5, 2017 by Boris Karlof

[soundfan]

[Guest]

On 3/4/2017 at 6:55 PM, Boris Karlof said:

5 Mobile Phone relay station backup Batteries in parallel. The 12V-13 rating does limit OP to the fleawatt level.

1.5 wrms but boy does it sound good.

Nice

Obviously there is an inverter there somewhere.

Maintenance ? brown coal or solar ?  

 

Battery powered gear is grand, nice set up there.

[Boris Karlof]

Actually No runs in as is and is good for around 6-8 hours of listening before I break out the ctek charger. Its been shelved ATM for a later active horn system. Where I intend it to run a high efficiency tweeter.  I want to find the safe Voltage limit per rail and feed each with it's own battery bank. For a 116dB horn 2 watts is what I want to squeeze out of it. The cleanliness of this power supply is very evident in country SA as I unfortunately still rent and have no aux solar connection. Bizzare is measurement wise it didn't measure all that well but sure sounds cleaner than a lot that do measure well. Just like a good  SE valve triode amp.

Cheers

Oh and because if its SE design 8 ohms is pretty much it although it will do 6-10 without too much fuss.

Edited March 5, 2017 by Boris Karlof

[MusicOne]

@Zaphod Beeblebrox  So Zaph, would I be right in assuming that class A amps (because they don't operate well at low impedances), are not a good match for ESLs like the Quad 57s?

[Rob181]

On 3/4/2017 at 3:34 PM, Zaphod Beeblebrox said:

 

A 300 Watt Class A amplifier will be running very hot indeed. In fact, I doubt that any amp has been built, short of something using industrial fan cooling or water cooling, to deliver that much Class A power. That said, if the amp was rated at 300 Watts Class A, then, provided it's power supply and output stage was sufficiently robustly rated, there is no reason why it could not deliver 600 Watts into 4 Ohm loads. It would, of course, be operating in Class B at that power level. 

 

1 x 300 Watt Class A amp coming up...& it is a beast based on Pass Specs...

 

https://passlabs.com/amplifier/xs-300

 

Leaves class A @ 600 peak as stated in their specs...

 

Xs 300 Specifications Low Frequency (Hz) 1.5

High Frequency (kHz) 150

Power at 8 Ohms 300

Power at 4 Ohms 600

Leaves Class A at pk 600

Power Consumption 1000

Temperature (°C) 53

Dimensions each (W x H x D) 19 x 11.5 x 28

Unit Weight (lbs) 298

Shipping Weight (lbs) 346

Edited March 5, 2017 by Rob181

[Wimbo]

48 minutes ago, Rob181 said:

 

1 x 300 Watt Class A amp coming up...& it is a beast based on Pass Specs...

 

https://passlabs.com/amplifier/xs-300

 

Leaves class A @ 600 peak as stated in their specs...

 

Xs 300 Specifications Low Frequency (Hz) 1.5

High Frequency (kHz) 150

Power at 8 Ohms 300

Power at 4 Ohms 600

Leaves Class A at pk 600

Power Consumption 1000

Temperature (°C) 53

Dimensions each (W x H x D) 19 x 11.5 x 28

Unit Weight (lbs) 298

Shipping Weight (lbs) 346

Gees, their heavier then the Krell KAS.

[walker1000]

This class A thing is very confusing. I was looking at the schematic of an accuphase E550 the other day which is rated 30w into 8 ohms 60 w into 4 ohms class A.

 

The bias on the output stage was 0.4 amps and the supply was +- 35 volts. This gives an idle dissipation of only 28 watts surely not enough for class A but is there such a thing as sliding bias on amps that will increase the bias as the output power increases to keep the amp operating in class A?

[Ken]

On ?4?/?03?/?2017 at 0:21 PM, Zaphod Beeblebrox said:

 

Oh dear, can 'o worms time. Here's the dirty little secret about Class A amps:

 

A Class A amp rated at 20 Watts @ 8 Ohms, will deliver:

10 Watts Class A @ 4 Ohms

5 Watts Class A @ 2 Ohms

2.5 Watts Class A @ 1 Ohm

 

I fully agree with Zaph on the above, but one thing has always puzzled me;

 

If you have a Class A Amp as per the above figures, that is rated to go to 100 watts Class 'A/B' once it exceeds 20 watts Class 'A' into 8 Ohms, what happens when using a pair of 4 Ohm speakers? Assuming that the power supply is strong enough, once the amp exceeds 10 watts, what is the Class A/B rating?

 

@Zaphod Beeblebrox

 

Ken

    

[sir sanders zingmore]

On 3/5/2017 at 4:25 PM, MusicOne said:

@Zaphod Beeblebrox  So Zaph, would I be right in assuming that class A amps (because they don't operate well at low impedances), are not a good match for ESLs like the Quad 57s?

 

that's a good question.

I'm interested in the response

[Shanghai Wally]

Aloha

Class A  Amps  produce if use the right speakers my favoured Transistor Sound for example

Pioneer A-09, M-22, M-25, A-27,Classe DR-8+DR-5

Cheers

Wally

 

Edited March 6, 2017 by Shanghai Wally
photos Pioneer A-09, M-22, M-25,M-27,Classe DR-8+DR-5

[MusicOne]

On 05/03/2017 at 4:25 PM, MusicOne said:

@Zaphod Beeblebrox  So Zaph, would I be right in assuming that class A amps (because they don't operate well at low impedances), are not a good match for ESLs like the Quad 57s?

 

On 06/03/2017 at 7:24 PM, Sir Sanders Zingmore said:

 

that's a good question.

I'm interested in the response

@Zaphod Beeblebrox Zaph may well just have overlooked this, but equally, I may be persona non grata.

 

Apparently I'm on several members' ignore lists.

Edited March 9, 2017 by MusicOne

[Zaphod Beeblebrox]

On 3/5/2017 at 4:25 PM, MusicOne said:

@Zaphod Beeblebrox  So Zaph, would I be right in assuming that class A amps (because they don't operate well at low impedances), are not a good match for ESLs like the Quad 57s?

 

It's complicated.

 

Ain't everything?

 

First off, there are (at least) 2 different types of Class A amplifiers:

 

Single ended and push pull. The two types are fundamentally different. 

 

When I explained that the Class A output of an amplifier decreased by half, with each halving of load impedance, that was literally true. However, when examining SE and PP amps, the ramifications of halving the output impedance is very different indeed. 

 

An SE amplifier cannot deliver more current than it is biased for. Therefore, when the load impedance is halved, so is the output power. 

 

A PP amp, OTOH, may be able to continue to deliver more power as impedances fall. The reason is that the PP amp is able to move into Class B operation. How much power it can sustain under such conditions will depend on power supply capacity, output device capability, current limit points, etc. 

 

Now, to your specific question about the Quads. Here's where it gets murky. The Quads are a very tough load for most ordinary amplifiers. As a consequence, many SS amps may suffer with their VI limiters being triggered. This is why the Quads should be driven by an amplifier that can deliver very large amounts of current and/or by an amplifier which does not employ intrusive VI limiter systems. In the SS world, such amps are rare, but in the valve world, VI limit systems are not required, due the high internal impedances of valves. Thus, although valve amps may be incapable of delivering the current required by the Quads, the result may be acceptable, because there are no VI limiters to cause nasty problems. And VI limiters can be VERY nasty indeed. Back in the 1970s, when I was service manager at Marantz, I was presented with the then biggest Marantz receiver made - the 2325. Rated at 125 Watts @ 8 Ohms, but easily exceeding 180 Watts @ 8 Ohms, 240 Watts @ 4 Ohms. A beast. The client brought in his AR 11Pi speakers, complaining of distortion. Sure enough, the Marantz managed less than 20 Watts, before the VI limiters kicked in. The result was very unpleasant. 

 

Now, it gets more murky.