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Old 4th June 2008, 08:52 PM   #1
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Default Outside the box - Low Gain High current Amp

This is thinking out of the box and bringing it to reality.

I'd like to design an amplifier that doesn't follow the typical device values or currents used when building an amplifier. Something simple and works well. Something that doesn't follow the rules

The idea is simply for three things in mind.
1. Stability
2. Ease of building
3. Power - 4, 2 or 1 ohm drive capable depending on rail voltage you use. so there's NO issue about what speakers work with the amp. It will play them all.

SQ is good too, but super-wide high frequency response 3x higher than human hearing and insane slew rates and all isn't the object of the design.

Instead of trying to get a high gain power amp, I want a really low gain, and low input impedance, and have the amp input driven by a strong paralleled opamp to provide the input drive needed for full power.

Here's why.
We get a .lot of requests here for a simple amp to build for high power, and many folks here get oscillation, so I'm aiming for a simple DIY solution for that. I figure low impedances and higher currents won't pick up as much noise. Also it may make layout less dependent since not everyone can etch their own boards, or some prefer veroboard.

Some brain storms:
1. 10K or 4.7K ohm input and feedback resistors
2. 10mA Input differential stage
3. 30-40mA VAS
4. Base Stopper resistors on all outputs and drivers
5. 2-4 pairs of outputs
6. sufficient RF filtering

I'm designing a few schematics for one now, if you folks have any ideas, feel free to post.
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Old 4th June 2008, 09:33 PM   #2
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Location: SiliconValley
A good starting point might be to search for Leach and Krell KSA100-clone schematics that have been changed to use On-Semi ThermalTrak bipolar outputs. Both can be biased to different levels of Class-A bias.

You can lower just the output power supply voltages to deliver safe operation into low impedance loads.

You can change the input impedance and feedback circuits to meet your goals.

Both are proven designs with PCBs.

If you want to drive extremely low impedances below 0.5 ohms, a super-symm or bridged topology where the output is not connected to ground seems more dynamic to my ears.

Naturally, you could also build a Class-D amp with large MOSFET outputs that can efficiently drive your 1-4 ohm loads.
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