From: META <META@UNB.CA>
Subject: Re: Stupid Marshall/Bassman tricks???
Organization: The University of New Brunswick
Date: Tue, 22 Dec 1992 14:53:05 GMT

META (that's me) wrote:
>> Actually, the two channels on the Bassman appear to have exactly the
>> same amount of gain.  What differs between them is that one has a
>> bypass capacitor hard-wired to the volume control to give a "bright"
>> channel instead of a a normalchannel with a bright switch, while the
>> other one has no such capacitor - a normal channel with the bright
>> switch "off".  The two channels are mixed together at the next stage
>> before going to the tone controls.
>>
>> I stumbled onto the patching trick about 20 years ago with another
>> amp that shall remain nameless, butalso had 4 jacks.  The net effect
>> is to get a beefier sound since there is some high end loss
>> resulting from "passive y-ing" of the signal.  If one used an active
>> splitter box and fed each channel separately, you could get the
>> overdrive benefits without the high end loss. In the case of the
>> Bassman, depending on which channel, bright or normal, is treated as
>> theprimary channel, this high end lossmay be offset to some degree.
>>
>> A more elegant solution is to use an active splitter (e.g., the Spluffer
>> from Craig Anderton's EPFM book, available from PAiA, is a decent
>> littleunit). I built one for a friend using an early 60's Strat and
>> late 60's Super Reverb, so that he could select one orthe other
>> channel remotely. The splitter also buffered the highimpedance
>> output ofthe guitar so thathe got a much crisper single-coil sound
>> than he had gotten before.  Highly recommended!
>>
>> Some players do "the Bassman trick" across amps as well.  If memory
>> serves, before wehad Bob Bradshaws in the world, people like Jimi
>> and Pete would simply run guitar cords from the extra input jack to
>> the next Marshall head over, and daisy chain 'em.  A little voice
>> inside of me,however, says this is not likely the safest, or most
>> hum free arrangement, although it will do in a pinch.  Bear in mind,
>> though,that theBassman trick results in two input channels bearing
>> down on the same mixer while the Jimi trick sends the same inputto
>> another head.  A quick glance at the schematic indicates that the
>> signal available at the extra jack is attenuated, relative to the
>> primary one.  Maybe this is where Steve gets the 6db difference
>> from. The gain structure of each channel is identical, but the signal
>> each is receiving, using the patch cord trick, is not.
>>
>> Mark Hammer
>>
>
> The 6db came from the manual included with the amp. Input 1
> of both the Normal and Bright channel have 6db more gain than
> input 2. The 6db is also mentioned in "Fender Frontier" Magazine.
> The Fender Frontier is kinda like the Peavey Monitor. The Fender
> mag answers questions from us pee-ons. Back in the summer they
> ran a little "tips" section for Bassman owners.
>
> The Bassman manual supply's a schematic. It also describes that
> as shipped the amp is over 60watts. The manual also tells you
> what to do to get down into the 50watt and 40watt range. It explains
> the diff between the sound of a solid state and a tube rectifier.
>
> Steve
> Doin That Blues ThAng!
>.
>.
Thanks for the clarrification Steve.  It would seem that "vintage"
remakes are not so vintage after all.  Looking at the schematic for
the *real* 1959 Bassman (which the remake purports to be a remake
of), thereis simply NO difference between the channels all the way
from the input jacks to the mixing stage OTHER than the presnce of a
"bright" capacitoron the volume control of the "bright" channel.
Again, while this may add more perceivable loudness at the same
volume setting, I wouldn't exactly term it a 6db difference in gain.
I also took a peak at the Fender article, and it strikes me that
what Fender may have done is stuck in a 12AX7 in place of the 12AY7
in the first pre-amp stage, and perhaps stuck an attenuating circuit
ahead of that to give differential signal levels from each channel.
I'm guessing here, but it strikes me as a likely change, since it
would not result in a drastic overhaul of the original design, and
plays up to the market pressures for at least one higher gain
channel for overdriven sounds.

Incidentally, if the 4 inputs are of no use to you, you can always
take one out and wire in a switch to turn the bright off and on.  On
theother hand, I suppose that 1meg push-pull switching pots must be
available from somewhere, and would let you keep your 4 inputs while
being able to switch the brightness in or out.

(Incidentally, for an inhouse publication, the Fender mag isn't that
bad actually.  I find it reasonably informative, and amazingly
common sense in orientation.)

Mark Hammer (Doing that thesis thang)

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