Home OTL Asylum

OTL, Output Transformerless Amplifier User Group.

[ Follow Ups ] [ Post Followup ] Thread: [ Display  All  Email ] [ OTL Asylum ]
[ Alert Moderator ]

RE: more on output impedance

That difference has a lot to do with the difference between the Voltage and Power paradigms.

I use the word 'paradigm' as such is defined as a platform of thought, outside of which nothing exists or else is blasphemy. IOW one schooled in the Voltage Paradigm will have trouble seeing how 'output impedance' can be expressed in any other terms- I have run into this a lot.

I like to use the black box approach similar to how one measures the impedance of a speaker. In this case, the amp has an unknown impedance but we can easily find out what it is by simply connecting it to a variable load. We then find out at what impedance it makes its maximum power and then continue to reduce the load until that value is cut in half. At that point, half of the power is being dissipated in the output circuit itself (causing it to heat up) and the other half in the load. At this point the load must be equal to that of the output circuit.

The interesting thing about this approach is that the value is predicted by formula and corresponds in practice.

Under the Voltage Paradigm, the output impedance is that where the circuit makes maximum power, which corresponds to the (Delta V)/(Delta I) method.

The Power technique is measuring the impedance of the output circuit, the Voltage method is measuring the dynamic response of the circuit. In the former, the measurement does not change regardless of feedback, in the latter, it does.

IOW, at this point we are simply talking semantics. I agree that most of the industry is using the Voltage Paradigm, and in lo- and mid-fi applications this is perfectly justified. In high end, it isn't so much on account of higher performance loudspeakers like ESLs, horns and others that don't conform to Voltage Paradigm rules.

In case you think I am making this up (some have in the past), Google the Fisher A-55 amplifier and one of the first hits you will see is a YouTube image of the damping control of the amp. It is marked 'Constant Voltage' at one extreme, 'Constant Current' at the other, and where they cancel (zero feedback) it reads 'Constant Power'.

This post is made possible by the generous support of people like you and our sponsors:
  The Cable Cooker  

Follow Ups Full Thread
Follow Ups
FAQ

Post a Message!

 Forgot Password?
Moniker (Username):
Password (Optional):
  Remember my Moniker & Password  (What's this?)    Eat Me
E-Mail (Optional):
Subject:
Message:   (Posts are subject to Content Rules)
Optional Link URL:
Optional Link Title:
Optional Image URL:
Upload Image:
E-mail Replies:  Automagically notify you when someone responds.

[ Top Top of Page ] [ Contact Us ] [ Support/Wish List ] [ Copyright © 2024, Audio Asylum, all rights reserved ]
[ General ] [ Speakers ] [ Tubes ] [ Vinyl ] [ Digital ] [ Hi-Rez ] [ Video Asylum ] [ Cables ] [ Tweaks/DIY ] [ Music ] [ Films ]