History of SMPS in audio ??

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PM2.0 was a switcher? I don;t recall that. Then again I don't recall a lot anymore. Carver used multiple power supply voltages and switched them in and out as needed, but that is not SMPS. And they have that whole "magnetic resonance" triac controlled power transformer, but that too is not SMPS.

The QSC Powerlite was their first SMPS amplifier that I can think of. Then the PLX series. Again, the earlier amps with multiple power supplies switching in and out are not SMPS designs.

Switched Mode Power Supply refers to the power supply itself, not what the amplifier circuit does with the power.
Technics used SMPS in 1979

Technics built some compact stereo components around 1980. The SE-C01 power amp had a switching supply, and was probably introduced in 1979. It is listed in the Audio October 1981 Annual Equipment Directory (40 watts/channel, $400 list price). (Winter 1980 Consumer Guide "Stereo & Tape Equipment" says list was $360, low retail price was $270.)

(By the way, I have one, along with the matching preamp and tuner. The amp doesn't work. If someone happens to have a service manual or schematic, please let me know.)

Ben Duncan's "High Performance Audio Power Amplifiers" book doesn't say who used SMPS first, but mentions Sony using one in a Class D amp in the late '70s.

One could argue that vibrator power supplies in battery powered tube gear were switching supplies, although I don't think they ran at particularly high frequencies.
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I wouldn't own one personally.

I used to work at a sound shop. People would bring in Powerlites all blown up.
An output would short and take out the power supply with it. The IGBTs would blow up and vaporize traces on the board. It looks like a grenade went off inside the amp. The rebuild kit for just the power supply is $80. I can tell you after rebuilding the (smt) power supply that the circuit board would probably not take another rebuild. I thought it was the poorest built amp that I had ever seen.
If they are used by professionals they might be all right. I know of a gogo bar that uses them and they have never failed. But I know of churches that have bad wiring for their speaker system and they blow them up all the time.
Infinity had their switch-mode amp with switch-mode powers upply in the mid-70's. It was 200W/channel if I remember correctly. I recall hearing about it when I was still in school. A few years later, I encountered an engineer that worked on the project. He said that the amp used a pair of Solitron high speed BJTs in the output stage, and the power supply had a big problem with bass "pumping", where the energy stored in the woofer got fed back to the power supply through the output commutation diodes and pumped up the power supply rails. This amp (or the rumor of it, as I never saw one) was one of the inspirations that that led me into a career in SMPS design. Now i design and build linear amps for a hobby - go figure.
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