Audiophile Class D – Part Two – Practical Examples
Just before we get started, Kenneth, a reader wants to know why if we claim to be “Analogians” why we keep on harping on Class D? I think an explanation by way of clarification is necessary.
Kenneth, although the name of the website is a play on words, my name is Ian, we do understand the importance of digital electronics. Actually just as important and in many cases more so than analogue. I do not think that a switching amplifier is indeed a digital device even if the PWM and switcher itself are controlled by DSP. The raw class D amplifier has a triangle waveform generator, a comparator and PWM. If digital is all around bit-rate and 0s and 1s at a predefined 5V level then this is surely not digital. Just as if a rail shifting amplifier can be made to switch to various voltage levels through a digitally controlled switch it does not necessarily make the amplifier a digital one. What does seem to be the tendency is that switching amplifiers are being termed more “digital” now than ever and this is going to stick. Possibly we do need to have a more inventive description however.
Practical examples of Class D
It wasn’t that long ago that I needed to build a Class D kit. I needed to find out what it sounded like. I needed to know that this topology was a flash in the pan. It was just a gadget. And then move on to better things.
ICEpower and then the Pro NU6000
Firstly there were no kits available. ICEpower seemed to dominate the market and in South Africa an amplifier would set you back about R4k for 2 x 200W modules. And I had to wait two months unless I paid R1 500.00 express shipping. A short while after, pro audio company Sound Select were offering the new Behringer NU4-6000 for a little bit more than this and it was available. It was also a usable 1200W RMS into a 2 Ohm load. DJs and Musos were queuing up for this amplifier in the USA so I took a gamble.
For the price it is hard to beat. Sure, users complained of the fan noise. If you are using it for home theatre then be my guest and change the fans. This is not a home theatre amplifier although it lends itself perfectly to drive your ears to Mars and beyond. The SNR is fantastic, it has incredible bass response and driving two 18″ bins with Piezo tops pushes my other audio amps into the junk pile. (not really). It was all about raw power. The only thing I don’t like is after a few years of ownership the fan guards became rusty. Durban weather?
The shopping mall
Nowadays one can pick up Class D amplifiers very cheaply.
The image above is also a reality checker. Specifications are:
Power supply: dual DC power supply 58- 70V, rated output power: 500W ( 65V power supply, 4 ohm load, distortion 10%) , efficiency:> = 90%, SNR: 90dB , THD 380W ( 65V power 4 ohm speaker, distortion <0.1%), 280W ( 65V power 8 ohm speaker, distortion <0.1%), frequency range: 20Hz-20KHz Output short circuit protection.
DC bias protection speaker protection.
Product Size: approx. 100*50*30mm / 3.93*1.96*1.18”
Net weight: approx. 100g (IRS2092 chip driver)
The two products above are typical examples of what can be purchased overseas (wish.com) for comparatively little outlay. Now it’s only up to the user with a bit of creativity to assemble into a classy enclosure and boast to his friends. With a SMPSU we are looking at a very tiny enclosure, heat is minimal and hopefully, it has huge sound.
I had to throw in the Behringer NU6000 amplifier of course.
Class D and the DIYer
Class D unfortunately does not lend itself easily to DIY construction although there are many that have done it. As can be seen by the prices listed above could you build it for cheaper even though one could boast of the “I Did It Factor”? With the spec and application details given out by the chip manufacturers it could very well be done but as mentioned elsewhere, our lovely country doesn’t lend itself easily to build something like this over a week-end unless you have all the parts and boards at your disposal already. Oh, and on the fly mods for better sound. Most probably highly unlikely.
Such is progress.
In closing it becomes apparent that for the home experimenter your old linear design topologies are still the way to go. For very low current, eco friendly audio for Granny’s radio, Class D cannot be beaten. And for vinyl…. tubes, inefficiency and a full wallet.
Plus ça change, plus c’est la même chose – Jean-Baptiste Alphonse Karr (24 November 1808 – 29 September 1890)
Previous: Part One