Class A , tube amp??

[jmstpierre]

Hi all,
Please excuse my ignorance in this subject. I don t even know how to describe what I want to ask you guys but I ll give it a go.
My question is about class A amps and tubes/valves amps. Are valves/tubes amps class A? If so what is the difference between a tube amp ( where the valves are visible)to a class A amp ( no tubes)slolid state. Not even sure if m describing it correctly but hopefully you understand what I mean.
I am wondering what a class A and a valve amp will bring to Martin Logan speakers? Pros and con...
Regards
John

 

[dmusoke]

Hi all,
Please excuse my ignorance in this subject. I don t even know how to describe what I want to ask you guys but I ll give it a go.
My question is about class A amps and tubes/valves amps. Are valves/tubes amps class A? If so what is the difference between a tube amp ( where the valves are visible)to a class A amp ( no tubes)slolid state. Not even sure if m describing it correctly but hopefully you understand what I mean.
I am wondering what a class A and a valve amp will bring to Martin Logan speakers? Pros and con...
Regards
John

John ... here's my take:

Class A refers to how a transistor or a tube is biased. In this mode, the tube/transitor always has current flowing all the time for both positive and negative cycles of the musical waveform producing minmal levels of distortion. The minus side is the Class A is very inefficient and class A amps produce lots of heat so that's why their power ratings are under 50 Watts per channel, if that!

Class B biasing allows conduction for most of the cycle, except when the signal is close to zero volts(actually 0.6V or a diode drop). This produces high levels of distortion (called cross-over distortion) which is musically unpleasant at normal listening levels.The amps are more efficient than Class A amps.

Class AB is the compromise between the two amplifier classes. The amp works in Class A at low power levels for minimal distortion but switches to class B at high music power levels where the increased distortion is easily masked by the music.

A tube or transistor amplifer can be biased as Class A or AB depending on the goals the designed intends for it(let's not deal with class D switching technology for the ultimate in efficiency of 80% or more).

ML speakers work well with Transistor amps as their output impedance is extremely low, usually less than 0.01 ohms. Tube amps have to use a transformer with selectabletaps for 8, 6 or even 2 ohms depending on the design but work well with ML's as well.

Hope this helps ...

David

 

[jmstpierre]

HI DAVID
thanks for the explanation. i ve done a lot of web browsing about class A amps and seems that they range in price and power. some have ridiculous low wattage and seem to have the higher price too. almost does not make sense, but i guess a good argument of quality over quantity..
as a general rule, what will a tube set up bring to ( irrespective of the amp brand) martin logan speakers and what will a pure class A add to the speakers.?
i think i read somewhere that with some of the martin logan that are biwirable, one could use a tube for panel and solid state for woofer.Am I right? i don t think i d be game to mix and match too much..i am one of those guys that sticks with the same brand if i can.
regards
john

 

[Northy]

As long as the gain on the two amplifiers are fairly similar, you should do fine. If you really want to get the best of the two worlds (ie. muscle of transistor and warmth of tubes), you should check out class AB designs from Pass Labs. I have been reading up very impressive reviews on their X series amps. They are pricey but seem to compliment ML stats very well. Furthermore, they employ Mosfet transistors as opposed to bi-ploar devices which have tube-like qualities with the muscle of a transistor.

I am saving up for a X150.5 model which retails new for $4,500.

 

[dmusoke]

HI DAVID
thanks for the explanation. i ve done a lot of web browsing about class A amps and seems that they range in price and power. some have ridiculous low wattage and seem to have the higher price too. almost does not make sense, but i guess a good argument of quality over quantity..
as a general rule, what will a tube set up bring to ( irrespective of the amp brand) martin logan speakers and what will a pure class A add to the speakers.?
i think i read somewhere that with some of the martin logan that are biwirable, one could use a tube for panel and solid state for woofer.Am I right? i don t think i d be game to mix and match too much..i am one of those guys that sticks with the same brand if i can.
regards
john

ML's ESL's are Bi-Wirable but the configuration you are talking about is Bi-Amping where you use two different amps, one for the ESL panel and a separate one for the woofer. ML's can obviously be bi-amped...

Tubes are known most for their 'glowing' midrange so that would fit the ESL panel perfectly. The Class A amp will handle the woofer just fine, tho the amp doesn't need to be Class A. It can also be the more Class AB amplifier.


BUT check to make sure the ML speaker version you have allows bi-amping. Those with powered woofers, like mine, aren't recommended for bi-amping.

 

[gmartan]

John ... here's my take:

ML speakers work well with Transistor amps as their output impedance is extremely low, usually less than 0.01 ohms. Tube amps have to use a transformer with selectabletaps for 8, 6 or even 2 ohms depending on the design but work well with ML's as well.

Hope this helps ...

David

I can't say that I've ever been able to tolerate an amp with output transformers powering my Summits. There is simply no way to get sufficient output at .06 ohms and therefore no "air" due to lack of high frequency extension. You need a quality direct-coupled transistor amp to really make them sing. Since the MLs are very revealing speakers a modern (neutral) tube preamp is highly recommended for it's ability to take the edge off poorly mastered popular music.

 

[Gordon Gray]

Much insight to be gained using the "search" function.

Doesn't mean it will be applicable to "your" system.

GG