Class D Audio Amplifiers – the way forward

Class D audio - kit from eBay

Class D Audio Amplifiers – another form of class C without the Morse code.

Simply put a class D device is a fast acting switching circuit – either on or off. Think of class C RF equipment – Morse code transmissions were all more or less class C amplified – when there was no RF applied to the power amplifier the output devices were biased off. Morse code transmissions were only on or off – a dot one third the length of a dash.  Simple.

Class D audio - kit from eBay
TDA 8920 completed kit – eBay  (source hylbuy – this link may change)

Along came first generation audio amplifiers  – what was recorded had to be faithfully reproduced, analogously. Class A amplifiers do this remarkably but at a cost. Class A amplifiers are at maximum 50% efficient – the incoming signal goes through at worst various stages of phase inversion but the end result in a properly designed class A circuit is – sine wave in – sine wave out. A photocopy.  Class B amplifiers draw current as soon as there is a signal – not very good for distortion so through a simple modification the designer sets a small idle or quiescent current to the output devices – changing the class to AB. AB amplifiers are noted for their maximum 78% efficiency – they idle at a few milli-amperes (bias current of output devices) and as a signal is applied the amplifier draws more and more current depending on input amplitude and load resistance until the onset of distortion. Yes, there are lots of other criteria involved here – but the biggest drawback is the switchover between output devices in push pull configuration causing crossover distortion – most noticeable at lower output levels. Poorly designed amplifiers often sound very harsh at low outputs. Fuzzy. And no, they aren’t all like this – most amplifiers nowadays running in AB class are designed using perfectly matched output devices and idle current is optimized for low input/output signals. Class AB amplifiers are also categorized AB1, AB2 etc. Single Sideband transmission uses class AB power amplification – this is again all to do with the distortion produced and possibly in very poorly designed circuits – loss of intelligence. SSB transmitters are very expensive because they don’t normally get designed by monkeys. Likewise the first class D amplifiers and modern design.

Class D amplifiers and EMI

Class D amplifiers, if not designed and built properly will sound ghastly and more importantly will have the authorities tapping on your door because of the radio interference (EMI). But because they don’t draw current unless it’s really needed as defined by the audio signal are great for the Greenpeace Movement. How exactly do they work?

It’s all in the Abbs

 I thought as one gets older the arrogance disappears because as one goes through life’s travels it doesn’t take too long to realize that we are no more clever (or stupid) than the next guy.

I was in a computer store and I heard a salesman telling a would be buyer that the Logitech speakers the lady wanted weren’t rated in PMPO because they were made in Europe where they only use Real Mean Sound as the measurement. The lady asked him to repeat what she had just heard and then cracked up with laughter. This obviously made the guy quite irate because she didn’t tell him what was so funny. As they say, ‘you can bullshit some of the people some of the time but not all of them all of the time”.

I had heard the Real Mean Sound story a long time back and wonder if this guy misinterpreted the story and now thought that this was the proper terminology.

A friend of mine used to fix CB radios and one day he told a client that he had to replace the aerial because the Signal Warning Resistance light was on. Now that made me cry out, it embarrassed my friend as well because he didn’t know why I thought that this was so funny. In actual fact what had happened he wasn’t lying to the client – he just didn’t know what SWR meant. Now as it happens if you don’t know what it means then you can’t have much in depth knowledge on how aerials and radio waves work either.

A very technical customer one day gave me an in-depth recital on how PMPO was measured. ‘at 1uS the maximum power that can be blah blah blah’. Now where do people come with this shit? I do not know whether this is now a new term learnt when students of electronics are studying for their MSc but it was unheard of in the 80’s. I heard this term came about due to the promotion of ‘Ghettoblasters’ years back. This sounds more like it. The question that arises is that more and more people like throwing around abbreviations like there is no tomorrow.  I have, strangely enough for an uneducated idiot like myself, found that most of them are also uneducated idiots. I too have educated friends – they most probably find me comical to speak to, but in all essence I don’t hear them throwing around abbreviations in their high tech gizmo talk. I have therefore come to the conclusion that the more intelligent or educated you are the less likely you will have to study abbreviations to make your argument sound more intelligent.

Now let’s have a look at these abbreviations:

R.M.S. – Real Mean Sound
S.W.R. – Signal Warning Resistance
P.F. – Power Force
BIOS –  Basic Instruction Output System
RAM – Read Addressed Memory
FILO – File In Ledger Output
RAMBUS – Randomly Addressed Module with BIOS Updated Structure (a new term used for flash) LOL
UPS – Upgradeable Power System
FET – First Effective Transistor
FUBAR – strange that everyone gets that right!
PAL – Phase Adjusted Light
NTSC – New Television Startup Committee
LASER – Lighting Adjusted through a Scientific Enhanced Ruby
MIPS – Millions of Input Phases per Second

There’s only more I can remember…

RADAR – Radio Defence and Research

If anybody would like to add more to the list, please do so.  I’m sure I have heard many more but believe me when I tell you that most of these abbs. I have heard from people that should know better.

Oh yes, one more – I was laughing at a company that had the abbreviation of STD and a colleague asked what was so funny. Thinking that she possibly didn’t know what an STD was I asked her and her reply:   “Saving Time Daily, it’s used in the UK you idiot”.

Good grief, what is this world coming to?

Batteries and Alternative Power

 Strange thing this. Being in the distribution chain myself it’s quite unbelievable to see just what that mark-up is once it hits the retailer’s shelves. And consistency is not the key.

Over the next year we are going to be powering along with all things green and one thing we seriously need to look at is the price of batteries. I reside in sunny South Africa with climate that is perfectly matched to solar panels. Readers should check the different avenues to source deep cell batteries. Also manufacturers should now start setting a precedent – are you selling deep cell or hybrid? I look at pages and pages of waffle – pricing for deep cell batteries vary from 200U$ to 400U$ for 12V 80 to 120A/Hr. Why the vast price difference?

Coming from a technical background I am not going to get into a debate here. Manufacturers and resellers owe it to their customers to be open with their specifications and give the exact composite of their batteries. Likewise the manufacturers of audio spec’cing their amplifiers to the PMPO format is rubbish, our battery manufacturers need to tow the line with their standards. Many life dependent electrical circuits use deep cycle batteries and to buy one battery because it is cheaper over the other only to have disastrous consequences later is tantamount to a despicable crime.

There are numerous well known and very reliable battery manufacturers on the market – Willard, Delco and Yuasa to name a few. If you are looking for good second hand batteries (and sometimes free) you should be looking at electric stackers (fork-lifts). I doubt you will get by with this idea in sunny RSA though – they get recycled as soon as they are written off – and then resold. They have good value because they last for ever. I was in the merchant navy and in those good old days your emergency batteries were always NiFe (Nickel Iron or Nickel Alkaline). They cost a mint but they had a life span of anything between 10 to 20 years. And why was this – because by law a log had to be kept. Specific Gravity had to be drawn on each cell AND voltages and discharge ratings logged. This was once per month. There was no quick solution to this – these batteries could save the life of the crew in an emergency and if you did take a short cut you were in for the high jump. Safety surveyors could pick up short cuts a mile off and could stop a vessel from sailing if they weren’t happy. This obviously applies just as much today as thirty years ago.

What batteries to go for? Well if you are feeling slightly green go for the deep cycle variety – your charging current is not as high as regular (porous lead plates) lead acid cells which makes them ideal for solar panels. Solar panels obviously can be stacked for higher outputs but remember they are expensive. In south Africa a solar energy system – panels, regulator, inverter and deep cycle batteries for a three bed roomed home would cost anything upwards from R40 000 (6 000U$) if installed by a contractor. For the technically minded this can be done for far cheaper. Also look at where your main loads are – your geyser and stove if they are electrically run.  If both are on, your stove running with four plates and griller you would be drawing anything between 40 and 60 amperes at 220V and 250A from your 48V setup.  It’s not an economical solution – go with a solar heating system and a gas hybrid for a cooker. I have read quite a few articles on solar energy and wind turbines and they all rely on one thing – the user has to start looking at conservation. All things considered I can’t see us coming up with an instant efficient system to beat our local electrical grids in pricing and efficiency but you sure can run most of your appliances off a simple solar / charger / battery setup. Unless you build your own pebble reactor of course.

These huge current delivery batteries are also not without their own set of problems, all financially related. The cost saving over lifespan of the battery compared to your grid – have you checked the hybrid car battery replacement interval and pricing?  The wiring, thick copper cabling is extremely expensive. Living in Southern Africa one would think that copper would be a giveaway. Sadly the exact opposite is true – people trade in copper and with Chile being the world’s largest exporter, their life-blood is not going to be a freebie.

At present, in South Africa, we are stuck in the middle of the biggest electrical supply fiasco ever – our main (and only) supplier, Escom, is planning to push our electrical tariffs up by 60%  over the next three years. We do have cheap power here but this is fast going to become the most expensive in the world thanks to their ineptitude and bungling.  But let’s be realistic – this has been on the cards for some time. Not the salary increases the executors gave themselves but our power was just too cheap. Koeberg, our only reactor is coming to the end of its lifespan. The only viable cheap form of power right now is the commissioning of new reactors and there’s no money to pay for it without hiking prices.  So we get back to our solar, wind and other green alternatives to our current problem. You need money to save money – but is it an economical and viable solution?

I don’t think so.