Class A, Class D amps ?

[jonunders]

Hi,

Would someone please explain (in simple terms) the difference between Class A / D and any other class of amp on the market. I see these terms often used in the market place but have never understood their meanings.
Also if you have time the type of cab and the different settings which would suit each one.

Thank you for your time

Jonathan

[eddiehoffmann]

http://en.m.wikipedia.org/w/index.php?title=Electronic_amplifier

[Mr. Foxen]

You won't see class A for bass very often, unless it is just the preamp, it will usually be class A/B, and B alone is never suitable for music purposes. Even stuff like the Vox AC30 that lots of people call class A is class A/B.

Simplest explanation (oversimplified) of class A/B is that half the valves/transistors push an half pull, slightly better is picture a graph of a wave, the top half and the bottom half are each drawn by different halves of the power amp, with a little overlap so there isn't a kink between them (the overlap is the class A part, the different halves is class B, the kink is what makes class B not suited to music).

Class D over simplified is imagine that line is pixellated if you look real close, but if you look at a sensible distance, you can't see the pixels.

[Dood]

If anyone dare use the word 'digital' in reference to D Class, I'll come round and slap them with a kipper!! There's no Analogue to Digital conversion and thus they're not digital. I.e. the D doesn't mean 'digital' it's just the class.

[Dood]

Oh cool, that wiki link is pretty detailed!

[jonunders]

I'm sooooo glad i read the wiki article, everything is now as clear as mud!

[charic]

[quote name='dood' timestamp='1330296658' post='1555474']
If anyone dare use the word 'digital' in reference to D Class, I'll come round and slap them with a kipper!! There's no Analogue to Digital conversion and thus they're not digital. I.e. the D doesn't mean 'digital' it's just the class.
[/quote]

You better hope no-one with a kipper fetish sees this!

[Dood]

Hahaha! You guys!! I should post the monty python sketch video really shouldn't I?

[flyfisher]

[quote name='dood' timestamp='1330296658' post='1555474']
If anyone dare use the word 'digital' in reference to D Class, I'll come round and slap them with a kipper!! There's no Analogue to Digital conversion and thus they're not digital. I.e. the D doesn't mean 'digital' it's just the class.
[/quote]
The 'D' may not mean 'digital' but, at the risk of being slapped with a kipper, it's an understandable popular description. Another way of looking at things is that class D is not an analogue amplifier but operates by switching fully-on or fully-off, which is certainly reminiscent of a 'digital' mechanism.

I guess it's mainly marketing guff really - a bit like the craze to add 'turbo' to loads of product names.

Funny how switch-mode power supplies are not generally regarded as 'digital' power supplies though.

[charic]

[quote name='flyfisher' timestamp='1330336694' post='1555717']
The 'D' may not mean 'digital' but, at the risk of being slapped with a kipper, it's an understandable popular description. Another way of looking at things is that class D is not an analogue amplifier but operates by switching fully-on or fully-off, which is certainly reminiscent of a 'digital' mechanism.

I guess it's mainly marketing guff really - a bit like the craze to add 'turbo' to loads of product names.

Funny how switch-mode power supplies are not generally regarded as 'digital' power supplies though.
[/quote]

Watched top gear last night didn't you

I think the current fad is to add HD to product names tbh!

[flyfisher]

No, didn't see Top Gear, though I can imagine the sort of thing they'd make of such things.

'turbo' is a bit old-hat these days, though vacuum cleaners still seem to use it a fair bit.

[RandomBass]

[quote name='charic' timestamp='1330332328' post='1555649']


You better hope no-one with a kipper fetish sees this!
[/quote]

Do I have to supply my own kipper?

[Mr. Foxen]

[quote name='flyfisher' timestamp='1330336694' post='1555717']
Funny how switch-mode power supplies are not generally regarded as 'digital' power supplies though.
[/quote]

I've seen them described thus.

[Phil Starr]

[quote name='jonunders' timestamp='1330297222' post='1555489']
I'm sooooo glad i read the wiki article, everything is now as clear as mud!
[/quote]It is pretty hard to explain something as technical as this in simple terms. One day I'll have a proper go. Mr Foxens analogy is as good as anything. I'll attempt something in between this and the wiki article.

You need to understand the way the amp works just a little The sound from a speaker is made as the speaker moves forward and back in time with your strings vibration. To make it do this the amp increases the voltage to push speaker cone forward and reduces it to let it back, at some point the voltage then reverses and the speaker moves further backwards behind its starting/resting position.

The simplest way to do this is to have a single output transistor or valve doing the whole process. This is class A. The problem with this is that when the speaker is in the halfway position the voltage and current in the amp are also halfway so the amp is working pretty hard when the speaker is in the resting position doing nothing. This means class A amps get very hot even with low signals as all that energy has to go somewhere. As a result class A amps tend to be low powered and inefficient as it is the heat that kills transistors and valves.

The next trick is to split the signal so one device does the positive side of the cycle and another does the negative side. This is class B. Now when the speaker isn't moving neither transistor or valve needs to do anything and there is no energy to disperse as heat. This makes class B amps more efficient and more reliable. The problem now is the point where you switch from one transistor/valve to another. The output devices aren't very linear at the bottom end of their range, there's always a bit of a gap and you end up with distortion when they change over, This is really noticeable in the quiet bits of music or whatever.

The solution which worked for years was to have both output devices working at the crossover point, meaning you had a class A amp at this point filling in the gap and class B for the loud stuff. This is class AB. This is still the most common way of doing things though it is changing rapidly.

The next way is to control the sound by switching the output devices on and off very quickly. This is class D. By switching them on more than off you get more current and therefore more power and less by having them off more than on. Because transistors make really efficient switches this means less energy and so the manufacturer saves on expensive heatsinking and supermassive transformers. this means class D is cheaper for really powerful amps. so your PA amp or anything over 200W is likely to be class D.

Class H (orG) is using a different trick of varying the power supply voltage in the amp to make it more efficient again saving on heat problems and expensive power supplies.

The reality is that you don't need to know any of this. You won't find a class B amp. Guitarists might have a class A amp or even one they can switch from A to AB. Some people think a class A amp sounds sweeter. Typically switching from class A to AB means the amp will go from 7W to 15-20W.

Bass amps won't be class A unless they are nutty 'boutique amps'. (discuss). You'll get class AB, D or H. It won't matter because you'll be playing and not designing the thing. They do have different distortion characteristics but you aren't intending to distort by overloading the amp anyway. It is more important that they are well engineered rather than what class they are.

Hope this helps

[Marvin]

[quote name='Phil Starr' timestamp='1330365800' post='1556311']
It is pretty hard to explain something as technical as this in simple terms. One day I'll have a proper go. Mr Foxens analogy is as good as anything. I'll attempt something in between this and the wiki article.

You need to understand the way the amp works just a little The sound from a speaker is made as the speaker moves forward and back in time with your strings vibration. To make it do this the amp increases the voltage to push speaker cone forward and reduces it to let it back, at some point the voltage then reverses and the speaker moves further backwards behind its starting/resting position.

The simplest way to do this is to have a single output transistor or valve doing the whole process. This is class A. The problem with this is that when the speaker is in the halfway position the voltage and current in the amp are also halfway so the amp is working pretty hard when the speaker is in the resting position doing nothing. This means class A amps get very hot even with low signals as all that energy has to go somewhere. As a result class A amps tend to be low powered and inefficient as it is the heat that kills transistors and valves.

The next trick is to split the signal so one device does the positive side of the cycle and another does the negative side. This is class B. Now when the speaker isn't moving neither transistor or valve needs to do anything and there is no energy to disperse as heat. This makes class B amps more efficient and more reliable. The problem now is the point where you switch from one transistor/valve to another. The output devices aren't very linear at the bottom end of their range, there's always a bit of a gap and you end up with distortion when they change over, This is really noticeable in the quiet bits of music or whatever.

The solution which worked for years was to have both output devices working at the crossover point, meaning you had a class A amp at this point filling in the gap and class B for the loud stuff. This is class AB. This is still the most common way of doing things though it is changing rapidly.

The next way is to control the sound by switching the output devices on and off very quickly. This is class D. By switching them on more than off you get more current and therefore more power and less by having them off more than on. Because transistors make really efficient switches this means less energy and so the manufacturer saves on expensive heatsinking and supermassive transformers. this means class D is cheaper for really powerful amps. so your PA amp or anything over 200W is likely to be class D.

Class H (orG) is using a different trick of varying the power supply voltage in the amp to make it more efficient again saving on heat problems and expensive power supplies.

The reality is that you don't need to know any of this. You won't find a class B amp. Guitarists might have a class A amp or even one they can switch from A to AB. Some people think a class A amp sounds sweeter. Typically switching from class A to AB means the amp will go from 7W to 15-20W.

Bass amps won't be class A unless they are nutty 'boutique amps'. (discuss). You'll get class AB, D or H. It won't matter because you'll be playing and not designing the thing. They do have different distortion characteristics but you aren't intending to distort by overloading the amp anyway. It is more important that they are well engineered rather than what class they are.

Hope this helps
[/quote]

WICKED! I understood that. A HUGE thanks.

[charic]

[quote name='Phil Starr' timestamp='1330365800' post='1556311']
It is pretty hard to explain something as technical as this in simple terms. One day I'll have a proper go. Mr Foxens analogy is as good as anything. I'll attempt something in between this and the wiki article.

You need to understand the way the amp works just a little The sound from a speaker is made as the speaker moves forward and back in time with your strings vibration. To make it do this the amp increases the voltage to push speaker cone forward and reduces it to let it back, at some point the voltage then reverses and the speaker moves further backwards behind its starting/resting position.

The simplest way to do this is to have a single output transistor or valve doing the whole process. This is class A. The problem with this is that when the speaker is in the halfway position the voltage and current in the amp are also halfway so the amp is working pretty hard when the speaker is in the resting position doing nothing. This means class A amps get very hot even with low signals as all that energy has to go somewhere. As a result class A amps tend to be low powered and inefficient as it is the heat that kills transistors and valves.

The next trick is to split the signal so one device does the positive side of the cycle and another does the negative side. This is class B. Now when the speaker isn't moving neither transistor or valve needs to do anything and there is no energy to disperse as heat. This makes class B amps more efficient and more reliable. The problem now is the point where you switch from one transistor/valve to another. The output devices aren't very linear at the bottom end of their range, there's always a bit of a gap and you end up with distortion when they change over, This is really noticeable in the quiet bits of music or whatever.

The solution which worked for years was to have both output devices working at the crossover point, meaning you had a class A amp at this point filling in the gap and class B for the loud stuff. This is class AB. This is still the most common way of doing things though it is changing rapidly.

The next way is to control the sound by switching the output devices on and off very quickly. This is class D. By switching them on more than off you get more current and therefore more power and less by having them off more than on. Because transistors make really efficient switches this means less energy and so the manufacturer saves on expensive heatsinking and supermassive transformers. this means class D is cheaper for really powerful amps. so your PA amp or anything over 200W is likely to be class D.

Class H (orG) is using a different trick of varying the power supply voltage in the amp to make it more efficient again saving on heat problems and expensive power supplies.

The reality is that you don't need to know any of this. You won't find a class B amp. Guitarists might have a class A amp or even one they can switch from A to AB. Some people think a class A amp sounds sweeter. Typically switching from class A to AB means the amp will go from 7W to 15-20W.

Bass amps won't be class A unless they are nutty 'boutique amps'. (discuss). You'll get class AB, D or H. It won't matter because you'll be playing and not designing the thing. They do have different distortion characteristics but you aren't intending to distort by overloading the amp anyway. It is more important that they are well engineered rather than what class they are.

Hope this helps
[/quote]

Nice explanation

[Mr. Foxen]

[quote name='Phil Starr' timestamp='1330365800' post='1556311']
the manufacturer saves on expensive heatsinking and supermassive transformers.
[/quote]

Transformers are power supply, an that is a separate thing, you could run an amp in class D with a transformer, but a switch mode power supply is more appropriate to weight saving. The problem with coupling the two is why class D wasn't in use till relatively recently, because you could get a beat tone (like when you play two notes out of tune slightly and get a slow oscillation effect) from the two switching frequencies that was low enough to be audible.

SMPS is actually the weight saving thing, and can power amps that are class A/B. like some of the Markbass stuff, but class D gives some saving on heatsinking and fans.

Edited February 28, 2012 by Mr. Foxen

[jonunders]

Thank you Phil for your explanation. I now understand a little more without having to source a turbo charged, HD Kipper.

Jonathan

[flyfisher]

SMPS also use transformers, but because they operate at relatively high frequencies instead of the 50/60Hz mains, they are far more efficient and can thus be much smaller and lighter.

[charic]

[quote name='jonunders' timestamp='1330432965' post='1557314']
Thank you Phil for your explanation. I now understand a little more without having to source a turbo charged, HD Kipper Transformer

Jonathan
[/quote]

Slight adjustment

[RandomBass]

[quote name='jonunders' timestamp='1330432965' post='1557314']
Thank you Phil for your explanation. I now understand a little more without having to source a turbo charged, HD Kipper.

Jonathan
[/quote]

actually a turbo charged HD Kipper is just an old fishwives tale

will get me coat (and kipper)

sorry....

[4 Strings]

Yes, thanks Phil. I recommend reading both Phil's response AND the wiki explanation to try to make it sink in. I hate it when people brag about their Class A amp being better than a mere B, let alone a crappy Class D - but my skin deep understanding won't allow be to explain why that's wrong!

[Salt on your Bass?]

I dont understand a lot of this stuff, but feel more informed by the previous posts. Thanks for the explanantions and education.

So is there any difference in the delivery of the sound in the real world between Class A/B and Class D amps? Assuming everything else is equal.

I've been looking around recently and considering a 'rig of doom' of sorts. I thought that a larger amp was necessary and been looking at Mesa M Pulse, Fender, ampeg etc all the usual stuff. What I dont understand is whether there really is any benefit to lugging round a hybrid double or triple the weight of, say, an OTB or Genz which is hybrid and class D......

Is there more 'ooomph' or 'grunt' to a class A/B head or is the weight merely a placebo and theres no difference at all? In which case, why fork out these days for something heavy and more expensive, for perhaps a 'nominal' improvement in tone? Or is it that tone your paying for? Or is it nothing at all tone related?

Not meaning to de-rail the thread, but thought it sat ok in here rather than a new'en.

[Phil Starr]

With the risk of being shot down in flames I'd say no difference in sound. At least not in relation to the class of the amp and with the proviso that you don't overload it. The design, construction and quality control do differ between designs and manufacturers, as ever. A lot in any difference in sound will be down to the adequacy or otherwise of the power supply. For example the designer of the Peavey IPR1600 has confirmed that it won't deliver its full power into 2ohms for more than a fraction of a second. Not everyone is so honest so don't think I'm being critical of Peavey, actually I went out and bought one of these for my PA and I'm delighted with it. AB amps almost always have under spec supplies anyway, always have had.

Class AB amps are generally made from bog standard components and are well known territory for most competent engineers and repair men. Even the bargain basement stuff is generally well made and reliable.

Class D and H usually have more exotic components in places and replacement parts might be more difficult to source especially in ten years time when the technology has moved on again. Switch mode power supplies are pretty well worked out technology now as they are almost universal for mobile phones and computers. Nonetheless they are intrinsically more difficult to repair than good old fashioned power supplies. Long term the new technology should be much more reliable though.

It's all a bit like modern cars, better cheaper, more reliable but buggers to work on when they do break down.

[rOB]

[quote name='Phil Starr' timestamp='1330365800' post='1556311']
Hope this helps
[/quote]

Thanks for this explanation. At a level I can just about understand