The Steel Guitar Forum

Does anyone know if any manufacturers are working on ultra-high efficiency topologies such as class D for combo or rack-mounted amps?

I think some manufacturers are working on professional sound reinforcement class G power amps with switch-mode power supplies (SMPS) and power factor correction (PFC) in the 1 to 3 kW range that way only about 30 lbs.!

Seems to me that a class D amp in combination with an SMPS might be the wave of the future as far as efficiency and weight are concerned.

Keep on pickin'!
Glenn<FONT SIZE=1 COLOR="#8e236b"><p align=CENTER>[This message was edited by Glenn Suchan on 28 April 2004 at 06:49 AM.]</p></FONT>

Glen, I may be mistaken, but I believe that the Peavey Nashville 1000 uses a class D power section. It's 300 watts clean and very lightweight.

Brad Sarno
Blue Jade Audio Mastering
St. Louis, MO

Glenn, another thought on SMPS. They are lightweight since they don't need transformers to create the proper supply voltage, but there are side effects. It may be less of an issue for guitar amps, but in the audiophile and hi-end pro audio world, switchmode power supplies are often avoided. It dependes on at what frequency the power supply is doing its switching, but often times it's just above the audio band, like 32kHz or so. This power supply switching frequency can interact and intermodulate with the audio with adverse results. There is a guy who's name I wont mention who sells refurbished and rebuilt hi-end mic preamps, API, Neve, and the like. He had been using switching power supplies on earlier products until I and a friend noticed this switching frequency quite clearly on a scope in the audio signal of one of his API mic preamps. There were also visible yet more subtle subharmonics or "undertones" in the audible band as well. We gave him a heads-up on this issue. He quit using the switching supplies from there on out. If power supply designers can successfully filter out the oscillation, SMPS will probably be quite successful in the future of hi-end audio applications. For big, high power PA applications, I can see it really taking off. Gravity is such a menace sometimes.

Brad

Brad,

Thanks for the insight on SMPS's. I see where they might be a problem for design engineers.

Here's a URL I just discovered on a class G power amp from Gibson: http://labs.gibson.com/amplifiers.html

Keep on pickin'!
Glenn

are there better power to weight ratio transformers out there then?

Toroidal transformers are lighter but also more expensive.

I'm not sure why the harmonics produced by switching power supplies are such a disadvantage. Conventional power supplies also produce a harmonic of 60 or 120 hz (depending on the type of rectification). Furthermore, the higher frequencies generated by switching power supplies should be much easier to filter out than the low freqs of a conventional power supply.

A standard transformer can usually be replaced with a well designed toroidal transformer.The basic design of a toroidal transformer gives it more surface area per unit VA than a conventional transformer, so it dissipate more heat per unit temperature rise. They are very efficient overall and about half the size and weight of standard transformers for the same voltage/ power level. For example The power transformer in my Evans FET 500 Custom LV amp could possibly be replaced with a toroidal transformer 1/2 the size, weight and back pain.

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I used to work for a firm that makes class-D amplifiers. The amplifiers sound very good, too, because of the choice of modulation scheme (not pulse width modulation). Their products have found their way into a lot of compact 10W-100W designs (TVs, boom boxes, compact surround sound DVD players, car stereos). But for whatever reason, the technology has been adopted by few OEMs in the high power sound reinforcement area. It may be because above the 100W level, the OEM amplifier makers had to manage the design of output stages themselves (though this company I speak of would do reference designs and a lot of hand-holding along the way). Bear in mind that it's a big paradigm shift going from conventional class-AB to class-D, and the OEM guys are often not willing to make that leap despite the advantages. There may be some NIH factor involved since the OEM amplifier engineer has to relinquish most of the design to the ready-made class-D circuitry. Also, class-D at high power levels can also be quite squirrely and even downright scary. It's easy to fry output FETs with voltage overshoot, current overload protection is very tricky, and electromagnetic interference (EMI) can be difficult to manage. But if you can jump those hurdles, you can get a great product. I can't remember the names of all the OEMs who did make class-D amplifiers with my former employer's products, but Carvin (at least) comes to mind. I don't know which model(s).

A few examples of non-PA type amplifiers with my former employer's technology inside:

http://www.belcantodesign.com/prod_evo2.html http://www.audioresearch.com/150.2.html http://www.audio-n-more.com/maaudio/ma_audio_amplifiers.shtml#CLASS%20T%20AMPLIFIER http://incolor.inebraska.com/weisinator/components/amplifiers/blaupunkt/pa2100.htm

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