Home OTL Asylum

OTL, Output Transformerless Amplifier User Group.

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

RE: A tricky issue

By installing a resistance between the cathodes of the input tubes, the coupling between them is reduced. There is a price paid for this: reduced differential effect, which results in lower gain and higher distortion. There is also the need for some means to adjust the resulting plate voltages- a big mismatch in them means distortion.

A variable resistance installed in the cathode circuit, with the wiper tied to the CCS can be used to solve this problem, but it will be immediately seen that other problems are introduced, leaving the distortion issue nearly untouched.

Also, to be truly effective, a 2-stage CCS is highly recommended any time a differential amplifier is executed, along with a B- voltage of sufficient value such that a true high impedance effect can be realized in the CCS.

It is possible to mix the feedback signal with the incoming signal with a resistive divider network, thus eliminating the cathode coupling problem in the first stage. The increased gain can then be used to assist with additional feedback, if desired.

However, it should be noted that while feedback **seems** to decrease output impedance, that if that were really the case, the output power at lower impedances would increase, and it doesn't. What it *does* do is push the amplifier design towards behaving more like a voltage source, but unlike a transistor amp which might double power as load impedance is halved, in this case the total output power into higher impedances will be limited by the power that the amplifier is capable of into lower impedances.

IOW, a set of ZEROs will still be a good idea on lower impedance speakers.

This post is made possible by the generous support of people like you and our sponsors:
  Amplified Parts  

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 ]