Reader Rowan has asked for some direction in
building a tube microphone preamplifier. Two topologies are
shown.
In the last issue, reader Ian made a great
suggestion:  a tube amplifier that would mimic the mixed class
of operation of the Pass Labs Aleph amplifier (SE / push-pull Class
A). This month we have a brief follow up by presenting a current
source alternative to using a choke.
Remember, if
you have a request or suggestion of your own for either an article
topic or circuit, please e-mail:

Editor

This
Issue

We were hoping to let the Circular/Balanced/Bridge
amplifier rest and not make an appearance this issue, but it is here
in an article on tube buffers. Expect more on this topology next
month as well, for we are not nearly done excavating this vein. The
circuit from the July article, "Unbalancing Acts," is back in the
same buffer article. In this same article you find the secret to
optimizing the White Cathode Follower as a Class A output stage.
Headphone fans take note.
I have found that many
tube circuit neophytes and, unfortunately, far too many tube gurus
have only the Grounded Cathode amplifier under their belt, so to
speak. Good as this circuit is, a bigger repertoire is welcome. (I
am saddened by sights such as the earnest tube fancier wasting his
time trying different brands of the same valued plate resistor in an
attempt to make the 12AX7 based line stage he owns better drive the
15 feet of high capacitance interconnect to the amplifiers.) The aim
of this journal is to increase the vacuum tube circuit vocabulary of
the readers.

The
Cathode Follower

A
Quick Overview
Right after the Grounded Cathode amplifier,
the second most common tube circuit in use is the Cathode Follower.
The simplest buffer that can be made with tubes, it is used to match
a signal from a high impedance source to a low impedance load.

In This
Issue

1
4
8
9
11
14
18

Cathode Follower
White
Cathode Follower

Plate
Follower
Broskie
Cathode Follower
Circular/Balanced/Bridge
amplifier
Tube
Microphone Preamplifier
E-Mail
Publishing
Information
Glossary
of Audio Terms

The circuit is single-ended and Class
A by design, as
there is only one active device. The plate is, in AC terms, but not
in DC terms, grounded and thus the Cathode Follower other name: the
Grounded Plate amplifier.

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