[Troy81]

when trying to make a high power subwoofer amp for example. what would be your most important factor? high current or high voltage? why are there so many mosfets in a large amp? they create more amperage correct? they dont create any voltage, are they just part of the power supply circuit? if thats the case, where does the voltage come from in a large power amplifier?

 

[guzzler]

You need both voltage gain and current gain. If you look at most schematics, they'll be split into 3 obvious sections:

Input (often a differential amplifier)
Voltage gain
Current gain

For example, look at the schematic for amb's b22 amplifier (The β22 Stereo Amplifier). He has explained it all very nicely below.

In short, you can parallel output MOSFETs to reduce the power through each device, therefore giving you a higher maximum power than a single device itself would allow.

 

[Troy81]

so the output mosfets whould be parralelled at the very end of the entire circuit?

 

[guzzler]

Yes. Sticking with amb's stuff, look at the s22 power supply. Notice Q13 and Q14 are parallel - less heat dissipation per MOSFET. Note though that simply adding an extra MOSFET doesn't give you double the power output; the rest of the circuit has to be changed to drive it to its full potential.