DC coupling without capacitors?

[Gnome]

Hi!

I've just read about the new Z.Vex hi-fi amp named iMPAMP, and they say that there's not a single capacitor in the signal path.

How do they do that? Wouldn't that be ideal in f.eks. buffers etc?

http://www.impamp.com/impvideo.html

[Paul Perry (Frostwave)]

Well, 'no caps' was standard back in the days of the analog computers. Because, amplifier response had to go down to DC.
In that case, tubes were used throughout, and you had a (typically) -150v rail as well as the normal + 150 or whatever.
And from the anode resistor, you had a voltage divider chain down to the -150, and you picked off the amplified signal at a point where the voltage was (in absence of a signal) 0 volts.
It is easy to make a no-cap circuit from solid state, of course.

[Gnome]

Hi!

Thanks, I think I have a small sense of how it goes.

Do you have any examples on such circuits? Or even better, a schem on some unt that uses it?

[Paul Perry (Frostwave)]

http://www.national.com/rap/images/AAA.gif

A 1950's tube op amp :shock:

And a tragic story about one of the tube op amp developers:
http://www.eetimes.com/anniversary/designclassics/opamp.html

Note a familiar name at the bottom of the article.. Alan Pearlman.  Yep, the guy who used some of his patents in the Arp synthesisers! and lost the lot when the company got in a hotshot management guy who voted to make a GUITAR synth :cry:
Perelman had his five minutes of fame though, I think he's in the synth scene in Close Encounters of the Third Kind.

[Gnome]

I still have some problems understanding excactly what's going on, but this has definately helped me!

I might get a friend of mine to explain it


Emil