From rongo–(at)–way.net Tue Jun 11 21:47:35 CDT 1996
Article: 10729 of rec.audio.tubes
Path: geraldo.cc.utexas.edu!cs.utexas.edu!howland.reston.ans.net!math.ohio-state.edu!jussieu.fr!oleane!hole.news.pipex.net!pipex!tube.news.pipex.net!pipex!lade.news.pipex.net!pipex!news.be.innet.net!INbe.net!news.nl.innet.net!INnl.net!hunter.premier.net!newsfeed.internetmci.com!in2.uu.net!betty.bway.net!news
From: Ron Gonzalez
Newsgroups: rec.audio.tubes
Subject: Re: Fender Normal Channel
Date: Tue, 11 Jun 1996 20:03:21 -0400
Organization: Mannes / New School Jazz Program
Lines: 61
Message-ID: <31BE0949.7--(at)--way.net>
References: <31B5A4F6.3A2--(at)--n.com> <31B84118.305--(at)--way.net> <31B84AB1.199--(at)--n.com>
Reply-To: rongo–(at)–way.net
NNTP-Posting-Host: dial08.bway.net
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Transfer-Encoding: 7bit
X-Mailer: Mozilla 3.0b4 (Win95; I)
Jack A. Zucker wrote:
>
> Ron Gonzalez wrote:
> >
>
> > You’re on to somethin’ there. I re-wire my Fenders so that the two
> > channels are joined (via 220k resistors) right after the output cap of
> > the Vibrato channel preamp (.022 mF in most).
>
> Thanks Ron,
>
> What about the 220k grid load resistors at the phase invertor. Should those
> be lowered to compensate for the loss of gain when adding the 220k resistors
> earlier in the circuit ?
>
> -Jaz
________________________________________________________________________
Jack,
Sorry about the confusion… I meant to say that if you have two 220k
resistors in a similar config mixing the signals from the two preamp
sections *prior* to the reverb circuit, then the two 220k resistors
right before the grid blocking cap at pin 2 of the 12AT7 are no longer
necessary. The two 220k new resistors should meet right before the point
where there is a 10pF cap and a 3.3 Mohm resistor in parallel, but after
the .022 and .047 mF caps on the outputs of the two channels. Like this:
.022
—-||—– <220k 10pF
> |—||—|
|———–||———- to pin 7 of 12AX7 mixer
< |-^^^^^^-|
----||----- >220k | 3.3M |
.047||
>from outputs (pin 6) =500pF from 470k coming from “Reverb” pot
of preamp 12AX7’s|
|
to pins 2,7 of
12AT7
*please excuse my wretched ASCII art*
Now you can connect the output cap on pin 6 of the last 12AX7 (.01 mF)
to the input blocking cap leading to the input grid on the phase
inverter (pin 2 on 12AT7), thus doing away with the 220k resistors that
reside there. You can even dipense with the .01mF cap if you like,
as long as you retain the .001 mF cap on the input grid of the phase
inverter. Your two channels should now both have reverb and be
in-phase with eachother to boot! Try plugging an A-B box into the two
channels and switching one or the other channel in, or using both at
once. They won’t cancel eachother out any more.
_______________________________________________________________________This is pretty “trick” stuff, and one can seriously screw up a perfectly
good amp by mis-wiring it. If you feel I have not explained how to do
this adequately, I urge you to show this thread to a good amp tech and
have him/her do the mod for you.
Have fun,
Ron G.
