Class D – The beginning of a new Era

Why Class D amplifiers are the way to go

As a young (or old) student it takes some time to get one’s head around the design idiosyncrasies of solid state amplifiers. Truth be told many of us found tube nomenclature and circuit design easier to comprehend than anything that followed “hole” theory.  Big bad things come to an end and eventually we found it easier to crib other designs.

Class D insides
Behringer 6000 4 channel Class D

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Tripath Amplifiers – are they analogue?

Lepai Class T 20W per channel

Tripath amplifiers – analogue switching amplifier TA2020

Note: As of 2007 Cirrus Logic currently own the original Tripath intellectual capital and as a result the companyTripath is no longer in existence. The Lepai and the legendary TA2020 are still available. Lepai and Tripath were not the same company. Lepai, Lvpin is now sold as Lepy. There are three chip ranges that you should be aware of:  2020A (Yamaha) 2020+ (Tripath) 2020TI (Texas Instruments).

Class D / Tripath class T

Class D – super efficient, mobile friendly to head stomping 12kW power amplifiers.

Lepai Class T 20W per channel
Lepai Class T (registered Trademark) 20W per channel – eBay or Aliexpress

Going back a few steps we need to look at the original class-D designs. The first attempt at a commercial “working” Class D amplifier came through Sinclair Radionics, brainchild of Sir Clive Sinclair, genius inventor and entrepreneur.  The commercial failure of this amplifier, the 10W ‘X10’ was more due to the piss poor frequency response and switching characteristics of the Germanium transistors to be had at the time.

Although on paper the class D amplifier looks nothing more than a high frequency switch modulated by audio with a Pulse Width Modulated output there were some technological hiccups.  Although tubes are linear devices and operate well in class A, AB, C configurations they are also very inefficient as switches. There are devices which were designed for this purpose such as the thyratron but they only offer a modest switching speed.

It was only in the 90s that the work from some companies forking out on a Class D solution started paying off.  One such company was ICEpower,  a combination of resources from team Karsten Nielsen and the Bang & Olufsen audio group. ICEpower remains one of the top end suppliers of class D audio. Tact or later,Lyngdorf was another company specialising in high end class D and this as a result of their variable supply and digitally controlled PWM amp, the TacT Millennium.

The TA2020

Specification sheet for the Tripath TA2020

Tripath, named after Adya Tripathi the CEO,  was the first company to mass manufacture a class-D chip, the TA1101. It was only when the TA2020 was released did the audio fraternity sit up and take notice – 20W into 4 Ohms at a fraction of the price of equivalent chipamps of class-AB design. After the demise of Tripath the market became flooded with the 2020. The TA2020 is rated as one of the top 20 IC breakthroughs ever, in line with 555 timers, ARM1 and Intel’s 8088.  A fabulous testament to the short lived Tripath name.

Tripath Schematic 20W+20W into 4 Ohms
Tripath Schematic 20W+20W into 4 Ohms

There are lots of add-on circuits for these amplifiers on the web but mostly one would be looking at pre-amps etc. The circuit itself may not lend itself to much better output quality due to the self-contained 2020 (ever tried to open a chip) but there is a definite improvement by using a higher current PSU and according to DIY audio (the site), recapping and resoldering should make a difference. These amplifiers were sold in South Africa for about R250.00 and to date the cheapest is about R350.00 on Bid or Buy. For that price don’t expect a Premier 5, do expect the best value for money, especially if driving from a PC.

One day the original chip will become a collector’s item – so box and stash away.

Oh yes, I believe the Texas Instruments chip has the best figures. More about this later.

Class D is here to stay.