class A sound

Ferres

reberly wrote: »

Just wondering how you know what class your amp is if the specs don't tell you. Is there something else in the ratngs that might give you a clue. For instance I have parasound HCA1500A and 1200 II amps. Could someone tell me what class that would be? I plan on going to my local high end dealer and asking to demo some amps that might be of different classes just to get an idea of what you all are talking about.

Thanks

You can tell it's a class A by your electric bill.:p

Yashu

I was talking about amp, not pre. The most common amp is class B. Class B is easy to make sound very good these days. Feedback loops easily overcome transistor crossing problems.

I have a class A pre, but my amp is all class B... it might be biased more towards A for the first watt or so, but it is definately a class B design. Most SS poweramps are class B. For reference, mine is a NAD, and it sounds damn good.

reeltrouble1

I am on the wagon with the other Class A polkies around this joint. That said the A/B amps fufill a need in audio. I suppose the class D will continue to gain ground for there applications.

RT1

Yashu

Yeah I would kill for a class A amp... I don't know a good budget class A amp, other than fleapower tubes.

Now, I can say that there is no reason not to have class A under the hood of your pre. It doesn't cost nearly as much but it still sounds so good. I try to use as much of the gain in my pre as I can to get the most out of it... that is until I can get a warm sounding class A poweramp, would probably have to be something vintage... not sure where to look for a good warm class A poweramp that I can afford.

heiney9

Yashu wrote: »

I was talking about amp, not pre. The most common amp is class B. Class B is easy to make sound very good these days. Feedback loops easily overcome transistor crossing problems.

I have a class A pre, but my amp is all class B... it might be biased more towards A for the first watt or so, but it is definately a class B design. Most SS poweramps are class B. For reference, mine is a NAD, and it sounds damn good.

Think what you want, class B amps are not ideal for audio and are far from the norm. The normal SS amp is A/B which is quite a different animal than class B. Class D, G, and H are making the rounds as well. Never heard of a pure class B amp and I wouldn't want to.

H9

heiney9

Yashu, I think I just found why we are having a bit of a mis-communication. Some places refer to class B and A/B as being the same. If in fact you mean class B to also mean A/B then yes I agree that it is the most common type of SS amp and when designed properly and using top components can actually sound quite good. For some designs I'd say 85-90% as a good class A.

H9

Systems

Zero wrote: »

Hate ta break it2ya.. but *pure* class B amplifiers are a rarity - for good reason.

Useful for driving subwoofers only, where high frequency distortion will not be an issue.I believe Vandersteen uses a class b amp to drive the bass section of their Model 5A .

disneyjoe7

Class A is always on most if not all pre amps are built this way. Most amps are A/B meaning that at a low level output they are indeed class A say 1 watt or so, as the volume gets louder the amp is forced in to class B. Class C is used in RF outputs stages so that's why we in Audio don't hear about this class often. Class D is a switching mode like full on full off (Think square wave) very efficient but need to operate at a frequency above the audio output desired. So if 20k output I would think 4 to 5+ times over is needed to get that 20k output "Clean"
These high frequency must be filtered out but 80k to 100k is pretty easy to filter out if you only need 20k output. But anything added can cause noise / distortion so I stand by my comment Class D amps called Class T now will never replace A or A/B amps.

heiney9

One very impt distinction between class B and Class A/B is that for strict class B is the following way the devices react to an input signal.

Class A/B amps do NOT infact run in class B, they run in class A/B which is different than running in class A up to a point and then switching to class B. They run in class A and then switch to A/B operation.

Amplifier circuits are classified as A, B, AB and C for analog designs, and class D and E for switching designs. For the analog classes, each class defines what proportion of the input signal cycle (called the angle of flow) is used to actually switch on the amplifying device:

Class A
100% of the input signal is used (conduction angle a = 360° or 2π)
Class AB
more than 50% but less than 100% is used. (181° to 359°, π < a < 2π)

* Class AB1 applies to tube or transistor amplifiers in class AB where the grid or base is more negatively biased than it is in class A.

* Class AB2 applies to tube or transistor amplifiers in class AB where the grid or base is often more negatively biased than in AB1, and the input signal is often larger. When the drive is high enough to make the grid or the base more positive, the grid or base current will increase. It is possible depending on the level of the signal input for the amplifier to move from class AB1 to AB2.

Class B
50% of the input signal is used (a = 180° or π)
Class C
less than 50% is used (0° to 179°, a < π)

disneyjoe7

heiney9 wrote: »

Class A/B amps do NOT infact run in class B, they run in class A/B which is different than running in class A up to a point and then switching to class B. They run in class A and then switch to A/B operation.

No Class A/B amps run class B when pushed it's just a marketing tool IMHO as all class B amps need to run in the A mode at low levels. Some amps run warmer then others just meaning they are biased more on then a cooler amp, they can sound better also as amps in the mode are cleaner less distortion.

Now take a 200w amp running in your A/B mode say under 5w they run in A mode as they are biased high. Push that amp during a bass note and you're in B Class / mode.

heiney9

disneyjoe7 wrote: »

Now take a 200w amp running in your A/B mode say under 5w they run in A mode as they are biased high. Push that amp during a bass note and you're in B Class / mode.

You will always be in A/B mode when not running in A. The output devices must have more than 180 degree conduction angle to avoid the worst part of switching distortion. B runs at exactly 180 degrees which is not ideal, A/B runs 181-359 degrees conduction which reduces (moves the nastiest switching distortion to a different point in the signal). An amp running in class B (defined as having the output devices exactly 180 degrees conduction) will not sound good over then entire audio spectrum. They are best used for low freq reproduction like subs.

so it's, A--->A/B not A--->B

H9

heiney9

When someone describes an amp as A/B is does NOT mean it's biased to run in Class A to a point then switches to B.

It means it runs in class A to a point then switches to class A/B. A, A/B and B are all different. A well designed A/B amp should never run in class B at any time.

H9

disneyjoe7

How can I understand 98% what you say but............




Can I ask your this

Age.

Education in electronics / jobs in electronics.

Where you went to school.

Where you grow up.

Yashu

I think we were getting mixed up in words then...

I was considering the definition of B class, that is, push pull operation, which is the most common audio amplifier type. I understand that many B amps use a feedback loop to minimize crossover distortion, and that also for about the first watt or so, operate in near class A.

I was always taught that class AB was beyond this, where they operate in class A for much more than the first watt or so, generally, and only crossover under much more stress.

I guess we can say we were both right. First watt or not, if one side is biased totally on for any period, that makes it an AB. I guess I always looked at the distinction being in the degree at which the amp runs as A before moving towards a push pull type operation.

I re-read some reviews that call my amp (and other way more expensive ones) a class B, but I know it to run A-like for about a watt or two, that is probably why, over the years, I thought there was that distinction.

EDIT: Heh, while I typed mine, you typed yours.

disneyjoe7

Well I can agree with all, and yes feel its more of mixed words.

Different age in which we where taught, where we where taught, and who taught it.

disneyjoe7

Like when I was in school early 80's there was A, B, C, D nothing else. Now we have A, A/B, C, D, T what ever. In my mind they are some up to A, B, C, D class some how.

heiney9

disneyjoe7 wrote: »

How can I understand 98% what you say but............




Can I ask your this

Age.

Education in electronics / jobs in electronics.

Where you went to school.

Where you grow up.

Not sure what you are getting at or what's not to understand it's audio 101.

Age 41
No formal electronics degree, but an avid hobbiest and avid electronics reader
Illinois State University-Bachelors in Bus. Admin.
Illinois

Joe, I know you have a background in electrical. Everything I've stated is pretty basic and straight forward about output devices in an audio amplifier.

Not trying to start a pissing match.

Systems

heiney9 wrote: »

When someone describes an amp as A/B is does NOT mean it's biased to run in Class A to a point then switches to B.

correct

It means it runs in class A to a point then switches to class A/B. A, A/B and B are all different.

correct

A well designed A/B amp should never run in class B at any time.

Exactly as it will still have some bias current.Class B has no bias current.

disneyjoe7

Sorry Heiney9 I meant no offense. You know thinking about it we all could go to a class on amps and come out with something else then someone else did.

I'm 43 for the record.

I have an ASEE which I never completed the BSEE thing more of a $ issue at the time. Was told by a teacher I should have gone to MIT, well I think $$ would be even a greater issue for me.

heiney9

As I understand it the very basics

Class A conducts a signal for the full 360 degree cycle of the output device. This leads to the best signal linearity and is also the least efficient

Class B conducts a signal for exactly 1/2 (180 degree) cycle of the output device. Up to 78.5 % efficient and has the least desirable linearity characteristics because of it switching to another cycle at exactly 180 degrees.

Class C conducts a signal for less than 180 degree cycle of the output device. Up to 90 % efficient with a high amount of distortion and even less linearity than class B

Class A/B conducts a signal for more than 180 degrees and less than 360 degrees of the output cycle. More efficient than class A but not as efficient as class B or C. By using feedback the x-over distortion and linearity can be controlled to make a very nice sounding output stage.

H9

heiney9

disneyjoe7 wrote: »

Sorry Heiney9 I meant no offense. You know thinking about it we all could go to a class on amps and come out with something else then someone else did.

I'm 43 for the record.

I have an ASEE which I never completed the BSEE thing more of a $ issue at the time. Was told by a teacher I should have gone to MIT, well I think $$ would be even a greater issue for me.

No problem and I agree 100% about refresher classes on amps and electronics in general. No offense taken at all. We all probably have the same basic idea's in out heads but putting them down in a way that makes sense to others is sometimes challenging.

H9

Yashu

heiney9, for what it's worth, I agree with your definitions. I should have been more clear in the beginning.

WagnerRC

ttt for good information here. I am still doing homework on the XA30.5 vs. X150.5 pass lab amp. The prices are just about the same on the used market.

txcoastal1

WagnerRC wrote: »

ttt for good information here. I am still doing homework on the XA30.5 vs. X150.5 pass lab amp. The prices are just about the same on the used market.

What speakers? My XA30.5 loves my Usher MD2's but not my Dynaudio C1's

WagnerRC

I will be using paradigm s8 and or s6. I have both. Thanks

txcoastal1

Those should pair up nicely
I would go with the XA30.5 IMHO

The XA does switch over to A/B upto 180watts

WagnerRC

Thank you very much.

FTGV

heiney9 wrote: »

When someone describes an amp as A/B is does NOT mean it's biased to run in Class A to a point then switches to B.

That is precisely what it means.

highway_chile

I recently picked up my first Class A amp, the Luxman M-300 because I, too, wanted to find out if they are really all they're purported to be. Prior to this I'd been running a Luxman M-02 or M-2000, with Luxman preamps CX-100 or C-1010. The M-300 has the ability to be switched from Class A to A/B without shutting it off. It does run hot, HOT in Class A; just HOT in A/B. To this point I've listened more in A/B; I'm in a small room and since the temps have been in the 90's and above since i got it I'm hesitant to pump that much heat into the room. I will say that as much as I prefer the cosmetics of the other 2 Luxmans, I do believe this one sounds better even in A/B mode.
I've used a few different options in cooling fans; recently bought a Cool Components CP-DF. I'm very disappointed in that. It's totally inadequate for this big of a job. I had a laptop fan that I bought for $3 at a garage sale and I am going to go back to that. It's noisy as can be, but it keeps the unit cool as a cucumber. Once again, the heat is pumped out into the room, so I may wait 'til this heat wave passes to give Class A more extended listening.
It is one beast of an amp; weighing around 70 lbs., but I got it for a steal ($395 + shipping).

WagnerRC

This amp will be used in my downstairs media room which stays very cool year round here in the Pacific NW. Thanks for your comments.