Mosfet Amp [Simple

[petemoore]

Hi pete... very cool and we are waiting for news now... and a schematic soon!!!
  The 'schematic' I used is a [far right most circuit section] fragment of the link at the top of the thread, I didn't draw up anything. My Amp is just the mosfet and source resistor, and a bias network from GEO...works right up.
  I skipped the whole CMOS thing he had going there, I didn't necessarily want clean preamp anyway.
  Just the left most 'column', the Mosfet..source gets a HUGE cap, to couple it to the speaker, drain goes..right to V+ (seemed 'fairly' forgiving, I got goods using a 15v 500ma...and a 14v 750ma....WW's I found, one is from a printer supply].
  Then it's just a matter of biasing the gate, with some big resistance.
  Any pot will do really, say 20k...outside lugs to V+ and Gnd. grab a largish to huge resistor and connect the wiper to the gate [1meg 2 meg...or use a HUGE pot and wiper directly to gate], this bias that mosfet, see GEO for mosfet boosters, RG's provided a resistor network that'll make the pot more 'fine tuning' and still accomodate all mosfets...{simple pot across the rails..big resistor between wiper and gate [gate is input]
  Add a source to the input capacitor, input cap to gate...done !
  That'll just barely noticably get a speaker moving, you'll need preamp section to get more volume/better sound. 9V gets a good ways there, 18v booster should increase headroom, I find 2 transistors work pretty good [like whatever 9v booster driving a 'preampish' booster running at 12v or 15v, I just tapped the supply of the amp to power the booster I used.
  I used a 2n7000 [right side] and a power mosfet irf510 for the right side boosters...anything'll do something pretty good, a matter of taste.
  so the 'amp' is a powermosfet source follower, and just drives the speaker [barely by itself].
  The source resistors gotta be a BIG wattage, see Aren's article [10ohm...I used 12ohm and 20ohm source to ground resistances with N/P's, but didn't calc anything [just threw them in there because I had 'em], using two R's parallel or series to get the resistance you want doubles the surface area and heat dissipation.
  You will need a substantial heatsink, use your thumb to test the heat, I burnt my finger once on it feeling the transistor and source resistor temps.
  Right now the amp is getting Loud enough [driving 1x8'' speaker per amp] and doesn't even get warm...

[brett]

Hi Pete
RE: those 12 and 20 ohm resistors
I've found that smaller values are good (and give more power), but the power supply must be able to handle the high current draw.
If I recall correctly, I was using 4.7 ohms 10 W with a 24 V suppy. 
As you say, a big heat sink (4 x 1 x 1 inches or a half pound of aluminium) is needed.

[petemoore]

but the power supply must be able to handle the high current draw.
  Yupp I'm kinda cheatin' with the WW power supplies, you can probably find a 15vdc 1000ma.
  Anything bigger' and the power supply would be the first thing would need 'more beef'.