[a1rocketpilot]

Just a random late night musing while looking at stuff for my circuits class, is there any way to bias a PINT into Class A? It is possible with the PIMETA and the PPA and many other amps out there, so why can't we attach a resistor connecting the output of the opamps and V-? And if it is possible, has anyone done it?

Aditya

 

[majkel]

You can only bias into class A the output of the first op-amp in the virtual ground circuit. Single JFET transistor + resistor works better than a resistor alone. All other need huge current to stay in class A regime which makes no sense and spills up the batteries very quick.

 

[a1rocketpilot]

Quote:

Originally Posted by majkel /img/forum/go_quote.gif You can only bias into class A the output of the first op-amp in the virtual ground circuit.

Why is that? Why can't the other opamps, namely the L/R channels be biased?

Quote:

All other need huge current to stay in class A regime which makes no sense and spills up the batteries very quick.

Assuming a wall power supply with the ability to output several amps was used, then would this make any sense?

Aditya

 

[perfectturmoil]

Quote:

Originally Posted by a1rocketpilot /img/forum/go_quote.gif ...Assuming a wall power supply with the ability to output several amps was used, then would this make any sense?...

Well, I would say it doesn't make a whole lot of sense only because the pint was very much designed to be a portable amp... You'd probably be better off building a PPA or other amp meant to be class A biased (or just building a class A amp) rather than try to fudge this one..

 

[jcx]

if you learned anything in that circuits class how about running some #s?

12 V split supply 32 Ohm cans => 1.125 W dissapation per channel

active ground ground channel has to handle 2X the current (both channels in phase as is the case at low freq) =>2.25 W in the ground channel op amp

I don't think any existing Pint will be designed for the heat extraction, at least you have a chance with AD8397

see my (jcx) posts in AD8397-Class A thread:

http://www.head-fi.org/forums/showthread.php?t=190991

 

[a1rocketpilot]

Yes, I am well aware of Ohm's Law and Joule's Law. I know the kind of power dissipation we are talking about. However, the graph I looked at was the EPAD version, which won't really make much difference on a PINT board. I also was not considering biasing it into full Class A, as I am aware what that will do to the chip. This was purely a theoretical "what if" scenario.

Aditya