F5 power amplifier

[Nelson Pass]

Originally posted by Zen Mod
talking about Profet ;
NFB is bloody different

Much of the difference is due to the high degeneration of their
input JFETs, the lower transconductance of Laterals and their relatively
high output gain. This means a lot less feedback, as seen by the
output impedance and distortion specs.

For Common Source topologies, damping factor = feedback.

[EUVL]

I guess you won't be showing us any measurements of distortion or bandwidth until the article is out ?


Patrick

[chinsettawong]

Wow! This F5 doesn't have any C!

Get well soon, Nelson.

Wachara C.

[Nelson Pass]

Originally posted by EUVL
I guess you won't be showing us any measurements of distortion or bandwidth until the article is out ?

You can look at posts #1740 and 1741 in DIY Progress Report, and
here earlier I posted a 2 ohm distortion curve. Here's an 8 ohm
curve, this with a regulated supply.

[Nelson Pass]

Hmmm... I see that I didn't post the 2 ohm curve. I guess that
was just the Vicodin talking.

Oh well, they're pretty good too.

[EUVL]

> And yes, "current feedback" is pretty fast.

I must be still asleep.

I am not sure which part of the circuit you are referring to is current feedback.

For global current feedback, e.g., I would expect the feedback signal be derived from a sensing resistor in series with the load. Since the output current does not go through the 2x 50R feedback resistors, at least the global loop is voltage feedback, be it with a twist.

Anyone care to explain to me, Tino ?


Patrick

[EUVL]

I think I got it now.

Thanks anyway,
Patrick

[stefanobilliani]

Originally posted by Nelson Pass


You can look at posts #1740 and 1741 in DIY Progress Report, and
here earlier I posted a 2 ohm distortion curve. Here's an 8 ohm
curve, this with a regulated supply.

Does the F5 have a regulator for each rail ?

[mpmarino]

Originally posted by Nelson Pass


...............

Now I've done it. The F5 isn't even out and some of you will
already be scrambling to build the two balanced versions.

...are you kidding me? The group buy started this morning

[Nelson Pass]

Originally posted by EUVL
> And yes, "current feedback" is pretty fast.

I am not sure which part of the circuit you are referring to is current feedback.

For global current feedback, e.g., I would expect the feedback signal be derived from a sensing resistor in series with the load. Since the output current does not go through the 2x 50R feedback resistors, at least the global loop is voltage feedback, be it with a twist.

You are quite right, and that's why "current feedback" is in quotes.

As I have previously pointed out elsewhere and in the F5 write-up,
this term probably came from the marketing departments at the
chip companies when they began selling high speed op amps using
this approach.