🚀 go-pugleaf

adams@pdv2.fmr.maschinenbau.th-darmstadt.de (Adams) writes:

> In article <4764@umriscc.isc.umr.edu> dshipley@cs.umr.edu (Dan Shipley) write
> 
> >   I just got a car audio amplifier from Coustic.  In the manual, it says it
> >   uses hex-FET's and NOT to turn the amplifier on if there is no load on th
> >   outputs.
> 
> >   I don't know anything about hex-FET's, but it seems unusual that an infin
> >   output impedance would cause damage to a transistor.  However, I'm always
> >   learning just how much I don't know, so if someone could enlighten me in 
> >   ways of hex-FET's or why this might cause damage, I'd be grateful.
> 
> first guess (using hexfets as a linear voltage controlled current source):
> How about oscillating? It is not so uncommon, that amplifiers may not 
> be operated without specified burden. It is not uncommon, that 
> infinite impedance (e.q. no burden) fries an output stage. Ask an RF engineer
> 
> second guess (hexfets used as current switches): As you can use it as a
> voltage controlled current source, and switch it very easily, you can use
> it as driver stage in a a low resolution (down to 1bit) D/A converter.
> To obtain your signal, you need a reconstruction filter. This may be 
> the impedance of your speaker set / earphone. As much as I know, some
> walkmans by Sony use this strategy.
> 
> Just guesses... adams.
> 
> If I am wrong, please tell me so --- but no flames.

It may be that the audio circuit is unstable in this mode.
Most Audio amps have a tnedancy to oscillate (100KHZ typ) unless there is 
a HF load try using a RC load that applies say 8 ohms above 
|>LnI(XXw*e~
tG[myow3
20KHz..choose the appropriate series cap.

dino@inqmind.bison.mb.ca
The Inquiring Mind BBS, Winnipeg, Manitoba  204 488-1607