NEWBIE: Designing a Simple Audio Amp

[N. Thornton]

Fwom:Ricky Romaya (something@somewhere.com)
NoSpam@daqarta.com (Bob Masta) wrote in
news:41d80947.1263957@news.itd.umich.edu:

On 01 Jan 2005 17:04:46 GMT, Ricky Romaya <something@somewhere.com
wrote:

Power amp gains are typically set so a "line level" of about 1 VRMS
will drive them to their maximum output, which depends mostly upon
the power supply rails... you size your devices to handle the
rails.

Care to elaborate on this? I've noticed that the power amp op-amps
have
their gain preset. Do you mean that to drive them to max output, you
need
1 VRMS input? Take TBA820M for example, it's gain is preset to 20 (if
not
mistaken), then a 1 VRMS input will give 20 VRMS output,

right, but the amp can only give that if its supplied with enough V to
deliver that, which it wont be in practice. What the amp does is take
the power supply V and limit it to whatevers needed for the speaker at
any moment.

and the power on
the 8 ohm speaker is then (20^2)/8 = 50W? But it says that TBA820M is
a
2W power amp (on 8 ohm load and 12V rails).

Hence under those circumstances it would have a life maesured in
seconds, maybe less.

NT