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| High voltage audio amp? |
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| ssashton:
Hi guys and gals, I designed the little speakers in Dave's latest video. I've always got ideas floating around and for a long time I have wanted to make my own co-axial electrostatic driver. Maybe slightly bigger than an A5 sheet of paper with two concentric areas that work down to about 500Hz. A digital delay could be used to produce a virtual point source effect. The problem is driving voltage, since good quality step-up transformers are expensive and rare as hens teeth. Ideally it would be great to design an amplifier that can directly output audio up to 2000V. Discrete amp design is beyond my experience though, so I wanted to see if anyone had thoughts on the best way that could be achieved? Could it be as easy as using an existing discrete push-pull design but choosing some special high voltage output transistors? The load would be capacitive of course. Just throwing it out there! Simon |
| Conrad Hoffman:
Define 2000V- rms, peak to peak? It's a problem because the needed slew rate at high frequencies is huge. Getting stability with a capacitive load is also an issue. Good HV outputs are a problem. Maybe an OTL tube amp? IMO, transformers look better and better. |
| ssashton:
Thanks for your answer. 2000V RMS I guess. I wouldn't know the required voltage until I build a panel but 200V is pretty conservative for ESLs (ElectroStatic Loudspeakers). Tubes would be out of the question IMO. Is 20KHz high enough frequency to be a problem for slew rate? |
| Benta:
Huh? Normally you'd supply the stator plates with a high DC voltage and simply drive the diaphragm with standard audio voltages. What's different in your design that makes high voltage drive necessary? |
| Kleinstein:
High voltage linear amplifiers are kind of tricky. There are very few transistors that go much beyond 1000 V. In addition the power handling capability at high voltage is often relatively poor (e.g. more like 10-20 W power handling capability for a TO3 / TO247 case BJT at 500 V). High voltage MOSFETS can be a little better. There are a few such designs out there. The usual trick is to have several high voltage transistors or MOSFETs in series. There are few plans from higher voltage SMUs around that at least show the principle for some 500 or 1000 V. I also remember some circuits for bootstrapped OPs to get a high output voltage. So this would be really about a discrete design and not that similar to a normal class AB amplifier. A capacitive load does not make things easier. Using vacuum tubes would be another alternative - not that exotic at high voltage. |
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