Class A, Class D amps ?

[xgsjx]

The Mrs just got a hairdryer that says "Turbo HD" on it. Does that make it modern retro?

[flyfisher]

[quote name='Phil Starr' timestamp='1335512976' post='1632300']
It's all a bit like modern cars, better cheaper, more reliable but buggers to work on when they do break down.
[/quote]

Not a bad analogy. A modern, hi-tech, fuel-injected, turbo, multi-valve, computer-controlled marvel of engineering design or just a large capacity V8 full of 'grunt'.

[danhkr]

[quote name='Phil Starr' timestamp='1335512976' post='1632300']
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.
[/quote]

Good post, but do you think switch mode supplies [i]are[/i] more reliable? I'm not so sure they're as robust as a 'good' old-fashioned transformer, and in the case of stuff like Mark Bass, maybe cheaper for the manufacturer, but certainly not the consumer.

Edited April 27, 2012 by danhkr

[flyfisher]

Well, increased complexity can mean less reliability although the PC I'm using for this post contains hundreds of millions of transistors.

I reckon reliability is more to do with the design approach rather than the design itself. For example, if a transistor is required to handle 10A then an over-specified part that is actually rated to handle 20A is likely to last longer. A crude example, but you get the idea.

Using a car engine analogy again, It's quite possible to get 1000bhp from a 1500cc engine (as F1 used to allow) but it's going to be more reliable churning out 90bhp in a family car.

[danhkr]

[quote name='flyfisher' timestamp='1335530682' post='1632718']
Well, increased complexity can mean less reliability although the PC I'm using for this post contains hundreds of millions of transistors.

I reckon reliability is more to do with the design approach rather than the design itself. For example, if a transistor is required to handle 10A then an over-specified part that is actually rated to handle 20A is likely to last longer. A crude example, but you get the idea.

Using a car engine analogy again, It's quite possible to get 1000bhp from a 1500cc engine (as F1 used to allow) but it's going to be more reliable churning out 90bhp in a family car.
[/quote]

Aye, although I wouldn't fancy my PC going through the transportation, heat, and speaker vibrations that my bass amp does. I guess the rule of thumb for any amplifier is try not to push it too hard however it's made.

[flyfisher]

Interesting point about speaker vibration. My Ampeg combo developed an intermittent problem a couple of years ago. I opened it up and discovered that a high wattage (i.e. big and relatively heavy) resistor had become disconected from its PCB track. The resistor was only held in place by the legs and I'm pretty sure that years of vibration of these heavy components resulted in the PCD track fracture. Good practice is to mechanically fix large/heavy components in place before soldering the connections. Anyway, it was a simple fix but it did make me wonder.

Years ago I was involved in a project to install LCD screens in railway carriages. The electronics we built had to comply with various international standards for railways (not surprisingly) and a big part of this was resilience to vibration. In practice this requirement was quite easy to meet by applying a transparent conformal coating to the PCB, which also has the additional advantage of protecting the circuitry from dust, moisture etc.

So it's quite possible to easily protect against bass-induced vibration, if the manufacturers deem it worthwhile and customer are prepared to pay another couple of pounds.

[4 Strings]

[quote name='danhkr' timestamp='1335607714' post='1633613']
Aye, although I wouldn't fancy my PC going through the transportation, heat, and speaker vibrations that my bass amp does. I guess the rule of thumb for any amplifier is try not to push it too hard however it's made.
[/quote]

Or take it off the speaker. Pushing its output is fine, why wouldn't it be? Its not made like your pc.

[4 Strings]

[quote name='flyfisher' timestamp='1335619564' post='1633794']
...by applying a transparent conformal coating to the PCB, which also has the additional advantage of protecting the circuitry from dust, moisture etc.
[/quote]

This stuff is great and should encase[u] everything [/u]in an amp to protect from vibrations etc, except you can't get to replace anything afterwards...

I must say I get a little cross when I see weighty electronic components hanging from their own legs, much worse controls fixed only by the contacts with the pcb.

[Count Bassy]

At the risk of being kippered, I'd say that a class D amp [b]is[/b] digital, in that the output devices are either 'On' of 'Off' (apart from brief transients) In the same way that digital computers works with "ons" and "offs".
Not digital in the sense of a CD or MP3 where a digital value represents an instantaneous volume level, but digital in the sense of Pulse Width Modulation.
Unlike analogue computers which used to work with, well, analogue signals.


PS: Has anyone put a switch mode PSU into a "conventional" (solid state) Amp? -would preserve the original sound (if you believe that there's a difference), but save a ton of weight.

Edited April 30, 2012 by Count Bassy

[guildbass]

As a sort of aside to this. years ago I acquired a pair of similar amps. One had been modified to be a superfi reference amp for a speaker manufacturer (IAS in Southampton) the other hadn't. Both were Mosfet (that's simply the name for the type of amplifier devices used inside...normal transistors amplify current, valves amplify voltage and Mosfets also amplify voltage...Sonically and in terms of the circuit architecture there are differences but ultimately they are all used to make things louder).
These amps were made by Ambit and were originally class B...90 watts into 4 ohms per channel.

Anyway, the modified one had been made to run a little 'on' during the resting stage either when the input signal was in the middle of it's swing, or when there was no signal. This meant that it was technically AB instead of pure class B and meant it got warm at the heatsink even when doing nothing...Not hot, just...warm. The unmodified pure class B heatsink stayed chilly cold if no signal was going in.
Sonically, they were VERY similar with the modded one sounding just a little smoother. less brittle ...More sophisticated if you like...But to one's ears the differences were slight.

In fact, thinking about it, I think perhaps the unmodded one was also class AB, but less 'A'...if you follow...

Anyway, the other little point is that almost EVERY HiFi amp apart from a few super sexy nutter amps are class AB...Which is really class B with a little bit of 'A' thrown in during the quiet bits to get them over that 'twitch'

First here's a picture of a class 'B' curve...you can see the bit in the middle at '0' volts which causes distortion. Next pic is a straight single transistor or valve class 'A' curve and you can see the curved bit at the bottom which you don't normally use...That's the bit which when joined to an inverted mirror image curve in class 'B' (to 'do' the negative half of the waveform) goes to make up the earlier image's distortion causing wibble in the middle.

a lot of valve HiFi stuff was class 'A' because the things were already so hot and drank so much juice cuz of the heaters and so on that it hardly mattered incidentally.
As regards Bass.....Could one tell the differenve between class B (which is almost always really AB), and class A without much HF signal...Hmm...Not sure...

[attachment=106535:Clipboard01.jpg][attachment=106536:Clipboard02.jpg]

[Mr. Foxen]

[quote name='Count Bassy' timestamp='1335743787' post='1635445']
PS: Has anyone put a switch mode PSU into a "conventional" (solid state) Amp? -would preserve the original sound (if you believe that there's a difference), but save a ton of weight.
[/quote]

Little Mark has SMPS in a class A/B output amp. Peavey made a valve amp with SMPS. It tookk a while to figure coupling SMPS and class D output so they did other things with it in the meantime.

[flyfisher]

[quote name='Count Bassy' timestamp='1335743787' post='1635445']
At the risk of being kippered, I'd say that a class D amp [b]is[/b] digital, in that the output devices are either 'On' of 'Off' (apart from brief transients) In the same way that digital computers works with "ons" and "offs".
Not digital in the sense of a CD or MP3 where a digital value represents an instantaneous volume level, but digital in the sense of Pulse Width Modulation.
Unlike analogue computers which used to work with, well, analogue signals.
[/quote]

No risk of being kippered by me - that's a very fair description.

[Phil Starr]

[quote name='guildbass' timestamp='1335784330' post='1635866']


a lot of valve HiFi stuff was class 'A' because the things were already so hot and drank so much juice cuz of the heaters and so on that it hardly mattered incidentally.
As regards Bass.....Could one tell the differenve between class B (which is almost always really AB), and class A without much HF signal...Hmm...Not sure...


[/quote]

Originally a lot of valve amps were class A because of simpler circuit design and lower component count. Essentially every radio, just about, had a 5W classA amp built in. Usually coupled to a highly efficient but bass limited speaker. I think the hi-fi thing of the 90's for classA /zero feedback amps was a bit of nostalgia combined with a kind of reaction to the introduction of digital sources. Undoubtedly some of them sounded good though.