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Class A versus Class AB mode (Marantz PM7200)


MeloManiac

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https://www.marantz.com/nl-nl/shop/amplifier/pm7200?status=discontinue

I'm a little bit intrigued by the Marnantz PM7200, of which two used specimens are available at a reasonable price in my region. This amp came out around 2005 and has amazing looks.

It also has a feature that is, to my knowledge, pretty unique: it can be started in Class AB mode, and then has 95W at 8 ohm, or you hit the Class A button and reboot, and then has 25W at 8 ohm. According to 'professional reviews', in Class A mode, it loses a bit in the bass end, but has a lot more 'audiophile' clarity, a wider 3D-stage, and you'll hear a lot more detail because it is now 'distortion free'. It produces quite some heat in Class A mode, which is normal. In 2005, it cost around €500, so it's no high end  amp, though it has the looks of one (that's just my personal opinion). 

 

My heart says: "Go out and buy the thing, and you'll know if you like it. It is the perfect amp for a set of Heresy speakers" But I have little place left to put it and my kids and the wife will turn the evil eye to me signalling 'Another amp, dad???'.

So first, I'd like to ask your opnion here: Is this PM7200 going to sound any different than the amplifiers I already own (Marantz PM5500, Denon RCD41, TubeCube 7, Onkyo A05). After all, I mostly listen at modest levels, and I have read somewhere that most amplifiers start out as Class A amps and go into AB mode automatically when volume increases.

 

There are a lot of user reviews here: http://www.audioreview.com/product/amplification/integrated-amplifiers/marantz/pm7200.html 

 

 

 

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  • 2 weeks later...

I have 8 amps on the shelves behind me

One on my work bench, another I have to order the parts for to re-cap it

In the LR I have 5, 4 on my surround system Yamaha, and my McIntosh stack for the LaScalas

The Yamaha's have a slightly better sound than the Mac, two generations newer, but I like the blue lights

Upstairs, its' 3 more receivers and a killer Yamaha stereo separates stack with heresy's

 

Every Amp has it's own intricacies and design trade offs.

Each one has it's own sound, which yes you can sit and pick them apart

 

One of the best sounding is a Yamaha surround the DSP A -700

Mint used they sell for $100 or less, it was Yamaha's statement product the year they brought it out

New I think it might have been between $2-3000

Using it with no pre amp, the sound is awesome even with a cheap Sony CD player

 

The Yamaha MX 600, 800, 1000 Amps sound is awesome, and can be run with no pre amp

They run in Class A for the first few watts, with LaScalas .5 watts is screaming.

Maybe a passive volume control or a DAC with an integral volume control

 

If the money is not an issue on the Marantz, why not have a fling with it ?

Do some research and see if the Marantz is biased to run in Class A for the first few watts

Class A mode will generate lots of heat, I would get a silent USB fan and leave it on top of the unit plugged into the switched socket.

As long as you can sell it for what your paid, why not ?

 

My acid test for any of them, is female vocal with few if any instruments or just piano

is the voice clear, is it natural, easy to understand ?

Are the piano strikes realistic, from zero to wide open on the strike.

Piano covers almost the entire range of audible music

 

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14 hours ago, Bubo said:

Every Amp has it's own intricacies and design trade offs.

Each one has it's own sound, which yes you can sit and pick them apart

 

Thank you for your insights. I couldn't agree more.

Already I'm 'space challenged', so if I buy this Marantz amp, something else will have to go. And I 'm pretty sure the Marantz will sound different to me, but not necessarily better. That's why I'm hesitating...

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Class A is more linear and most serious audiophiles will prefer Class A. The problem is the heat. If you want 100 watts from one you will need air conditioning and a fork lift to lift the thing. That is the reason those that are sensible buy in the 25 watt range. More power generally means better bass whether A, A/B. or D. I have always favored Class A but that being said I am right now listening with a 150 watt Class A/B amplifier and loving the sound. All classes can sound outstanding when used by a good designer. The circuitry and designer is the determining factor on how an amplifier will sound. That and of course how much is spent.  In theory and on paper Class A is the best. In reality they all can sound outstanding 

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6 minutes ago, henry4841 said:

Class A is more linear and most serious audiophiles will prefer Class A. The problem is the heat. I have always favored Class A but that being said I am right now listening with a 150 watt Class A/B amplifier and loving the sound.  In theory and on paper Class A is the best. In reality they all can sound outstanding 

Yeah I really enjoyed my Adcom GFA-5800 it runs Class A for the first 10 or 15 watts cant remember off hand it sounded very good with my Chorus II's it sounded so good it replaced my Sunfire 300 for a few months until summer came along then it was just too hot raised the room temp a few degrees at least so it had to go.

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1 hour ago, jjptkd said:

Yeah I really enjoyed my Adcom GFA-5800 it runs Class A for the first 10 or 15 watts cant remember off hand it sounded very good with my Chorus II's it sounded so good it replaced my Sunfire 300 for a few months until summer came along then it was just too hot raised the room temp a few degrees at least so it had to go.

With our speakers many class A/B amplifiers never leave class A average signal. Maybe on peaks if you push it hard. That is essentially what class A/B means. Starts at class A then transitions to class B at some point depending on how the amp is bias'ed. Diy'ers can bias an A/B amplifier higher to stay in class A longer. To lesson the crossover distortion in B you have to use a relatively large amount of feedback compared to feedback in a class A if used at all. Just technical stuff that really does not mean how good an A/B amplifier will sound. The one I am listening with now is superb sounding and I have a lot of class A amplifiers. 

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3 hours ago, henry4841 said:

Class A is more linear and most serious audiophiles will prefer Class A. The problem is the heat. If you want 100 watts from one you will need air conditioning and a fork lift to lift the thing. That is the reason those that are sensible buy in the 25 watt range. More power generally means better bass whether A, A/B. or D. I have always favored Class A but that being said I am right now listening with a 150 watt Class A/B amplifier and loving the sound. All classes can sound outstanding when used by a good designer. The circuitry and designer is the determining factor on how an amplifier will sound. That and of course how much is spent.  In theory and on paper Class A is the best. In reality they all can sound outstanding 


More heat yes, forklift required not necessarily. You may be well familiar with Pass First Watt amps that all use Class A, all built in the same chassis for cost effect. Due to the same chassis for each circuit variation, power is relegated to the cooling capabilities of said chassis. The FW are hefty but certainly  not heavy when compared to his Pass Lab products in which you are correct - forklift worthy.

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3 hours ago, henry4841 said:

That is essentially what class A/B means. Starts at class A then transitions to class B at some point depending on how the amp is bias'ed.

Ah...no, that is not what class AB means. Only on special , and the manufacturer will surely let you know,  do amps run class A the first few watts and then change to AB or B.

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the , Marnantz PM7200, runs 25 watts as  Class A amp ,this is fantastic , plus it's only sold in Europe ,  we can't buy it in North America - and these amps are quite rare -

 

  I say buy it ,---since a 25 watts Class A amp for 500 Euros , it's more like 1500 Euros and upwards ,

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46 minutes ago, babadono said:
3 hours ago, henry4841 said:

That is essentially what class A/B means. Starts at class A then transitions to class B at some point depending on how the amp is bias'ed.

Ah...no, that is not what class AB means. Only on special , and the manufacturer will surely let you know,  do amps run class A the first few watts and then change to AB or B.

 

Even the old Dynaco ST-70 was class A to over 10 watts... maybe up to 15, before it went AB. I don't know that they advertised it.

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4 hours ago, richieb said:


More heat yes, forklift required not necessarily. You may be well familiar with Pass First Watt amps that all use Class A, all built in the same chassis for cost effect. Due to the same chassis for each circuit variation, power is relegated to the cooling capabilities of said chassis. The FW are hefty but certainly  not heavy when compared to his Pass Lab products in which you are correct - forklift worthy.

Thinking of building a kit FW

After I finish my other projects, which will be in ......

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3 hours ago, babadono said:

Ah...no, that is not what class AB means. 

?     At least that is my understanding for many years of what it means. If not explain your understanding of what A/B means. 

 

"Starts at class A then transitions to class B at some point depending on how the amp is bias'ed."  Yes, that is what I have been taught. 

 

 In A you do not have a transfer of the voltage swing from one transistor to another. In B one transistor handles the positive swing and the other transistor the negative swing. My understanding of what A/B means is both transistors in and A/B amplifier handles both the positive swing and negative swing at lower levels then being not biased high enough converts over to B at some point. A/B's run cool at low volumes and heat up at higher volumes. Class A is biased pretty much at the best working level (high)of a transistor all the time and handle both swings at the same time. Once a Class A amplifier reaches it operating temperature it does not change it's temperature no matter the input signal strength.  

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Class A means output devices are biased on even when there is no signal. This "wastes" power. Class B means output devices are biased off with no signal and depend on the signal to get them conducting. This causes a distortion called crossover distortion because as the signal is transitioning near zero potential neither device is conducting. Class AB tries to overcome this distortion and yet remain efficient(not wasting power like Class A) by biasing the output devices very close or even slightly into conducting with no signal.

I had to go to school back in the day to learn this stuff...now you can just google it:)

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15 minutes ago, babadono said:

 

I had to go to school back in the day to learn this stuff...now you can just google it:)

great education  , I think you explained it quite well ,  now with a class A amp  , you power it up , you use it right away , you stop listening to music , you shut it  down right  away -

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47 minutes ago, Bubo said:

Thinking of building a kit FW

After I finish my other projects, which will be in ......

best deal is to buy a used amp at low prices , as a non operative , and repair it --    the repairs can be  , in most cases , quite trivial and simpler than other amps  -

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I was not entirely correct about A/B after some thought. The best analogy I have ever heard was by Nelson Pass. He compares it to two runners in a baton race. In class A one runner takes the baton and runs as fast as he can and never passes the baton. In class B the runner runs as fast as he can then stops then passes the baton and the other runner then he takes off. In other words the transistors cut on and off depending on when they have to go to work. In class A/B the runner with the baton runs as fast as he can then slows down and passes the baton at say a trot to the other runner at a trot and he takes off. Both the positive working transistor and the negative working transistor are biased some from complete off before running as fast as possible, at least at the operating function built into the design. In other words they never completely cut off when transferring the current or voltage. The speed at transfer of the baton is what is called bias of a transistor at idle. Below that point both transistors are working in Class A below that point. I hope this clarifies my understanding of the difference between A/AB/ and B. There are better descriptions on the web from people that have a much better understanding of the classes then I do. Wonderful we have youtube with very knowledgeable people describing the operation of electronic circuits. Great teachers. 

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A B AB D T

The world of trade offs on any engineering design

With the Heritage - retro Klipsch the efficiency makes the A decision

more affordable and a reasonable weight

.5 watts on the LaScallas is screaming, 2 watts is unbearable in my space

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