In <31A7BD73.591--(at)--n.com> "Jack A. Zucker"
>I tried Torres's mods for "Heating up that normal channel"
>last night. Unfortunately, it sounded like shit.
>Bright, thin, (It reminded me of Ned Beatty in Deliverence)
>1) Seperating the shared cathode in the 2nd gain stage. (Formerly
>shared with the Vibrato channel's cathode)
Probably not audible, but I have no problem with this change.
>2) Converting the cathodes of the first 2 gain stages from
> 1500ohm/25uf to 2.2k/.68uf.
That's going the wrong direction. You'll get just a bit more gain
by going with a slightly LOWER cathode bias resistor, but at the
expense of headroom: the plate voltage will be thrown off-center.
That 100k plate/1.5k cathode circuit is by classic RCA formula.
If you do change the cathode resistor, consider leaving the 2nd
stage at the stock 1.5k value. Note that this comment relates to
use of 100k plate resistors.
The .68uf may be the culprit. Leave the 25u/25v cap.
>3) Changing the plate resistors to 220k
>4) Changing the tone stack slope resistor to 56k
This shows Mr T's lack of understanding of plate loading,
unfortunately. There is no point in going to higher plate
resistors if you AC-load the plate with a 56k 'slope' resistor.
You could get just a bit more gain with a 220k plate resistor
if there were no additional loading effects.
I'd leave the 100k slope resistor if you are going to experiment with
higher value plate resistors. If the plate resistors are changed
to 220k, then the cathode resistors should be raised as well. Again,
this keeps reasonable headroom.
>5) Changing the tone stack from 250pf, .047uf, .1uf to
>500pf, .022uf, .022uf
The .1 to .022 change is miniscule. Rolls of a tiny bit more bass.
The .047 to .022 change makes a bit more sense in that it will
give you a bit more low mid, at the expense of less Fender-
like mid-scoop. (I thought you *liked* the Fender mid-scoop!)
The 250p to 500p change does the equivalent to the top-mids, but
this doesn't make as much sense.
The latter two changes will give you a much less scooped, more
midrangey sound. This may appear as more gain also, due to the
slightly lower 'insertion loss'.
>I changed back to the dull/lifeless original circuit but I remember
>I seem to remember either Mark or R.G. talking about a simple FET
>which can boost the gain and maybe with only 2 gain stages to play
>around with, the normal channel would be a good place to put that.
>Any of you guys remember talking about this ?
It was probably RG. I've used FET followers for drivers when I have
to, but I am not a big fan of followers. They sound harsh and barky
to me when they overload, though many others like them for that same
reason. Are you looking for a more Marshal-like sound? Seems that
way, as that's where most of these mods are headed.
By the way, the 56k slope resistor could work if it's driven by
a follower. That's Marshall's usual topology. The 56k will move
the circuit further toward the Marshall sound: less separation
between control effects...more mids...less insertion loss...kind
of phasey sounding mid notch.
Check with Dave Cigna. I think he's got a tone control modelling
program on his web page. This should help you to visualize the
tone differences. I don't remember if it models any of the plate-
loading effects, though.
How about trying out an active preamp at the guitar side? This would
drive the guitar cable more effectively, and would afford a lot more
gain if you need it. The Torres mods described here will not give you
much more gain so much as just allowing more mids thru the tone controls.
There's only so much gain to be had with a couple 12ax7 stages.
I have absolutely no problem with raising mids, but I design my own
circuits for doing that. The Fender tone circuit is not suited to
true mid-boost, if that's what you're after.
Mark G.
micK pages
From ja--(at)--n.com Mon May 27 13:57:14 CDT 1996
Article: 10209 of rec.audio.tubes
From: Dee Zucker
Newsgroups: rec.audio.tubes,alt.guitar.amps
Subject: Re: Fender Normal Channel
Date: Sun, 26 May 1996 21:12:08 -0400
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Thanks once again Mark.
In terms of what I'm looking for, I've converted the phase inverter
and power section to blackface specs, including removing the .002uf
caps (all over the place), etc. I'm just looking to get something
usable out of the normal channel. The Vibrato channel sounds great
for jazz and country and pretty damn good for early 60's rock as
well. Unfortunately, the tremelo photo-resistor was bad and I bought
a new photo-resistor/neon pair from Mojo but it does not do that
great of a job. It seems that perhaps the resistance is not high
enough since the sound never goes completely off. I know blackface
amps were not the best for tremelo but my Showman sounds much better
for example. Maybe someone else makes a Optoisolator closer to the
vintage one ?
Another thought was to couple the output from the 2nd gain stage of
the normal channel back into the reverb section to have 'verb in
both channels, and then to slightly revoice the normal channel.
-Jaz
From timtub--(at)--ol.com Mon May 27 13:57:54 CDT 1996
Article: 10211 of rec.audio.tubes
From: timtub--(at)--ol.com (TimTube)
Newsgroups: rec.audio.tubes
Subject: Re: Fender Normal Channel
Date: 27 May 1996 00:45:19 -0400
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In article <31A7BD73.591--(at)--n.com>, "Jack A. Zucker"
>I'm looking for a way to "hop-up" the normal channel in my
>(non master) Fender Twin without adversely effecting the vibrato
>channel.
>
>I tried Torres's mods for "Heating up that normal channel"
>last night. Unfortunately, it sounded like shit.
>Bright, thin, (It reminded me of Ned Beatty in Deliverence)
>
>The mod involved:
>
>1) Seperating the shared cathode in the 2nd gain stage. (Formerly
>shared with the Vibrato channel's cathode)
>2) Converting the cathodes of the first 2 gain stages from
>1500ohm/25uf to 2.2k/.68uf.
>3) Changing the plate resistors to 220k
>4) Changing the tone stack slope resistor to 56k
>5) Changing the tone stack from 250pf, .047uf, .1uf to
>500pf, .022uf, .022uf
>
>I changed back to the dull/lifeless original circuit but I remember
>
>I seem to remember either Mark or R.G. talking about a simple FET
>which can boost the gain and maybe with only 2 gain stages to play
>around with, the normal channel would be a good place to put that.
>
>Any of you guys remember talking about this ?
>
>
Gotta love that Torres, a Marshalll tone stack in a Fender. The problem is
that this configuration needs an extra gain stage and the tone stack needs
to be driven by the cathode. You could add a tube or a transistor to his
mod and it would probably sound OK.
Here is an easy no brainer way to "heat up the normal channel", or the
other one for that matter. You do lose the bright switch if you want this
to be a switchable mod. If you don't want it switchable or just want to
try it first, only do step 2. This mod will give a pretty dramatic gain
increase.
1. Disconnect all connections to the bright switch.
2. Disconnect the ground connection on the midrange control.
3. Reconnect the midrange control to the bright switch.
4. Connect the other side of the bright switch to ground.
With this mod signal normally filtered to ground goes through the amp, no
signal is lost at the tone stack. Of course there is no tone control
either. If you don't use the bright switch this is a way to get some use
out of the switch. If you do use the bright switch, you could add a switch
or a push-pull pot for the mod. If you have the bright switch on all the
time, you could just wire the bright cap to the volume pot and free up the
switch.
Tim
A great amp can make a lousy guitar sound great.
A lousy amp will make a great guitar sound lousy.
From jpric--(at)--tdcs2.intel.com Thu May 30 01:06:58 CDT 1996
Article: 10311 of rec.audio.tubes
From: Jack Price
Newsgroups: rec.audio.tubes,alt.guitar.amps
Subject: Re: Fender Normal Channel
Date: 30 May 1996 00:37:50 GMT
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Dee Zucker
>Another thought was to couple the output from the 2nd gain stage of
>the normal channel back into the reverb section to have 'verb in
>both channels, and then to slightly revoice the normal channel.
Bingo! This is what I would suggest if you want to juice up the
normal channel. What I do is couple the norm and vib channel at
the reverb input as you suggested, hop up the norm channel just a little
by using 120K loads and 820 cathodes. Stick with the 25uf, it's a Fender
remember. Oh, don't forget to separate the shared cathode. Which I
guess you did at one time?
Now that both channels are in phase and the normal is a little hotter,
I use a Morely AorB/AandB box to externally channel switch. Usually I
play thru the vib channel and then add, not switch, the norm channel.
Playing thru both channels, now in phase, produces some really fat tone.
But it's still sounds like a Fender. Just fatter!
jp
--
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Phone: (503) 613-8116 FAX: (503) 613-8261
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