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History of Class D Amplifiers and Smaller Speakers

History of Class D Amplifiers and Smaller Speakers

Moments in Bass History… Class D Amplifiers and Smaller Speakers – the Rise of Smaller, More Lightweight Bass Gear.

Bass amplification is heavy. To get a decent sound we need to use powerful amplifiers and huge speaker systems….or do we? Tim Fletcher looks into the rise of smaller, more lightweight bass gear. 

The first time I saw a Class D amplifier was about a decade ago, in a shop managed by one of my former students. It was by Yamaha, and I asked him if it was just a headphone amp: “No, it’s a proper amp – it’s just really small. It’s a Class D amp, and these are the future!” I was sceptical – how this could possibly compete with a big, powerful amplifier. He was right though… Fast forward to the present day, and these amplifiers have gradually become commonplace in the bass community, and manufacturers such as Mark Bass, Demeter and Quilter have developed high quality products that match, and sometimes surpass the quality and power of their more traditional predecessors.

Although we may think of Class D amplifiers as being something new, they have been around for over sixty years.

The originator of the concept was Alec Reeves, a brilliant British scientist whose work included helping set up the first transatlantic phone cable, developing digital delay lines and condenser microphones. He also designed the first PCM (Pulse Code Modulation) system, and during WW2 he helped develop electronic counter-measures and radio navigation aids for British Royal Air Force. He later led a team that produced the first fibre-optic cables. During the 1950s he developed the first Class D amplifier by dispensing with the heavy toroidal transformer (and therefore also meaning that the heat sink and fan used in traditional amplifiers was not needed) by using pairs of transistors as switches rather than as linear amplifiers.

Reeves’ new amplifier concept first found a commercial use in 1964, when Sinclair Radionics’ produced the X-10 amp, a home-build kit system that produced a whopping 2.5 watts.

This was followed by the more powerful X-20 in 1966, but the quality of the transistors on these early models made them very unreliable, and a commercial failure. However, this wasn’t the end of the Class D amplifier, and the development of the more advanced MOSFET transistors eventually enabled a more reliable product to be made. The first of these was the Sony TA-N88 studio power amp that was first produced in 1978, and the first commercially available bass amplifier using Class D technology was made by Peavey in 1984. These amplifiers was still quite bulky, but in 1996 the electronics component manufacture Tripath developed the Class D on a much smaller integrated circuit board. This allowed the size of bass amplifiers to shrink from the standard 19” rack mount size to around the size of a book. 

The bass world is generally quite conservative, and it was relatively slow to respond to the new technology.

The early Class D amps were very light and portable but lacked the ‘oomph’ of traditional tube amps (and even the older transistor amplifiers) and bass players were reluctant to let go of their big heavy gear. Gradually, the development of better-sounding and more sophisticated Class D amps in the last few years by newer manufacturers such as TC Electronic and MarkBass has encouraged more players to invest in the new technology (myself included), and this success has prompted the major brands to produce their own versions. Now almost all have at least one Class D model in their range, and some seem to be competing to make the smallest possible amplifier, with TC Electronics’ BAM 200 (920g) and Trace Elliot’s tiny Elf (730g) leading the field.

Trace Elliot ELF

As amplifier technology improved in the last decade, so did speaker technology – the paper in the cones has been replaced with more advanced materials such as Kevlar and carbon fibre, other components are stiffer and more able to cope with higher sound levels more efficiently, and voice coils are more effective in dissipating heat. Advancements in enclosure design have also made for more effective replication of the frequency range, especially the low end. All these advances mean that lower frequencies are produced effectively by smaller speakers, and the huge rigs of old are no longer needed – I used to use a rig that was taller than me, but now I use two 210 cabinets, and it’s probably about as loud. 

Are the days of huge bass rigs over?

Probably not, as they still have a specific sound that bass players still like, and they look cool onstage…

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