big audio amp as an inverter 120v/60Hz

[mikepecchio]

hello

I'm settting up a new mastering room and was thinking about doing something kindof crazy for the power conditioning. I want to generate a clean, balanced AC waveform. 120v, 60Hz. there's only about 600 watts to supply.

I think I could do this without a transformer by using 2 very large audio amps, bridged, and grounding the "center tap". I 'll feed an audio oscillator to the inputs and adjust the gain for 60V per side. seems like it would work, right?

what kind of amps would you guys recomend? class-D subwoofer amps are an ovbious choice cos they are relativly cheap and optimized for low frequency operation. But I wonder about the distortion and high frequency noise. I would probably have to add some output filtering. and most I've seen run on 12V (car audio).

Ive got a giant old UREI amp (maybe 1500W per side?) with a minor problem I could try to fix, but I wonder if it will swing 60v with some headroom. I also wonder what it will do with that kind of signal and no load... Any input is much appreciated!

mike p

[tlf9999]

it should work.

however, i would propose something different: if your purpose is to use the "amps" to power audio equipment, you might as well go the full length and generate DC rail voltages out of those boxes.

Two ways to do that:

a) generate DC of desired voltage. and hook them up to your amps directly.

b) generate high frequency A/C and rectify it using a full bridge and capacitors. for starters, how about 20khz 50v?. Because you are rectifying much higher frequencies, you don't have to use huge capacitors so your power supply will be very company. No need for transformers here.

[woody]

Mike, when you say 120v ac you are realy talking about 120v ac
RMS or 169.2 v ac peak so your project just got a lot harder. A good power conditioner like ebay # 7549850571 would probably
suite your needs a lot easier. Oh the ebay item does not belong to me or anyone I know.

Regards

[mikepecchio]

Thanks, some good ideas there!

"Run the whole thing on DC" is a solution to another problem. But Im using outboard that already has very well designed PSUs: GML, Lavry, Cello, etc. I want to use AC but make it very clean. and balanced.

mike p

[mikepecchio]

yes 120V RMS. But like I said, I'm going to use 2 amps in series. so that's 60V RMS per channel. not too bad, right? I don't know cause I haven't ever tested a big amp for voltage swing. Iv'e got a 75 watt hafler here that clips at 37V RMS. how much voltage can a 1500 watt (into 8 ohms) PA amp put out at 1/2 max power? Im going to find out saturday.

I just found this group and I'm loving it already. I'm an experienced tech and recording engineer. I like all the suggestions, but guys I am certain I want to try this. I have the big amp already (will fix it soon anyway), so this isn't going to cost much. I'm also going to hook up a distortion analyzer and scope in the rack. and maybe a chart recorder on the analyzer's residual output... Im serious! but can you imagine the look on people's faces when I show them the "power conditioner"?

mike p

[darkfenriz]

modern inverters use IGBTs for higher efficiency runnig at way lower frequencies than class D audio amplifiers. But the latter will surely work, maybe even too sophisticated, for 60Hz you don't really need 200kHz PWM and short dead times, rather maximum efficiecy. Another thing is signal source- for an inverter you could use a digital source with pulse width modulated sine without a need to modulate and drive and so on in analog domain. It makes tings easier a lot.

[ctardi]

I measured a 1400w (700/Channel) at 107V, clipping.

[fmw63]

You may want to try the pro audio forum - maybe some old-timers there. Something like this (or maybe exactly) was done in the past using Crown DC-300's - usually for outdoor use where there wasn't stable AC.

[quasi]

If you use class D then you can get efficiency too.

[darkfenriz]

...but 88% and 94% make two times difference in dissipation. For these powers it does matter.