[HAM] E-112 percussion....long post...corrections welcomed

[Michael Fulk]

-----Original Message-----
From: Robert Hayton <x77dude at bigplanet.com>
To: The Hammond Forum <hamster at ns2.zeni.net>
Date: Wednesday, December 13, 2000 6:15 PM
Subject: Re: [HAM] E-112 percussion


>There's something in the archives about modifying the E-xxx percussion.  As
I
>recall (and I very well could be very wrong here), the mod requires that
certain
>resistors on a matrix circuit board be clipped.  The post detailing the
procedure
>is archived on my computer at home... and I'm at work.
>
>good luck!
>Robert Hayton
>San Jose, CA
><http://www.myplanet.net/x77dude>

The answer to this problem, IMHO, is basically simple.

Skip to last paragraph for mods, if the descriptions bore you.


Descriptions below are accuate, but for the sake pf brevity, and the desire
of my being as little complicated as possible....much detail is omitted

On the B-3 et. al. the drawbar signal is diverted from a drawbar, (2nd or
3rd hamonic), to a
"percusiion input transformer", and then on to the percussion
circuitry........that is, the primary of this transformer has a small extra
winding
which returns the drawbar harmonic to the the drawbar.  The secondary, which
contains the percussion signal,  goes to an amplifying tube and then to
another transformer primary, the secondary of which, along with a 12AU7 tube
constitutes the the percussion "gate" and then goes through still a *third*
transformer, the secondary of which contains the signal which goes to the
preamp, is amplified along with the vibrato scanner signal, and non-vibnrato
signal which all meet at one point, and so on through the preamp to output.
Without going into the intricacies of Hammond's "gate" on these models,
suffice to say that +24 volts needs to be grounded to make the the "gate"
start closing and then finally close, smoothly to give the characteristic
percussion decay, either slowly or fast.

Hammond could have added an extra contact to accomplish this grounding, but
instead chose to sacrfice one harmonic to do it....even this drawbar could
be left hooked up, and the percussion would work but then the DC would
engender a *very* large click every
time one played a percussion note(s).

On the E-100, things are done *very* differently.

The percussion input[or "rmatching"] transformer has several input
primaries, one for every two harmonics which are used, and but one
secondary.  When any percussive effect
is turned on the harmonic connected to the primary[also always remains
connected to drawbar], plus one other which maybe connected also to any one
primary, i.e. each primary may conduct as ,many as two harmonics.  The
secondary is connected push-pull style to the grids of of a dual triode
whose cathodes are set by means of a pot so that the tube does not
ordinarily conduct, (pot is "percussion cut-off" control").

Now when the percussion is turned "on" then a voltage, (source voltage 25
VDC run across 15k ohms and 6800 ohms to ground from end of 15k ohm resistor
opposite to supply voltage), is run to 61contacts devoted solely to this
purpose. Whenever a key is depressed with this voltage "on" then it is
applied to an internal busbar[similiar to all other internal busbars, except
that it carries DC instead of a signal].  This DC busbar voltage is applied
to a pulse
generator and shaper and capacitor whose pulse is fed to the  grids of a
double triode, (the "gate"),  making it conduct as long as the pulse lasts
and decays; that triode's signal is the amplified by another double triode ,
one of whose plates either goes to the non-vibrato preampmifier or the
vibrato preamplifier, (Add-Vibrato Tab).

The length of the pulse, and thus the decay time is controlled  by the
pulse's duration, which is in turn controlled by the discharge of a 1mfd
capacitor's charge being dissipated to ground through either an 18k ohm
resistor in parallel with a 330k ohm resistor....short decay, or an 18k ohm
resistor.[not relevant here but the 18k ohm resistor will be found to be in
series to ground with a 100k ohm po in circuit only whent when
reiterarion is used.]  As is the B-3, et. al. , all keys must be lifted for
percussion to sound again.

SOOOOoooooo..........find the percussion transfromer and feed to its
windings the 2nd harmonics and into another winding the third harmonic and
Voila!...B-3 percussion.... or any old combination you may choose, e.g. 3rd
and second together, or 2nd and 5th together...this latter, I have found to
be a favorite of people.

Experiment with the below values and have some fun......for cheap, cheap,
cheap......all components or variations thereof can be purchased at radion
shack.

All above components are located in, on or near the percussion chassis.
1 mfd capaciror is C204, 50 volts
15k ohm resistor isR207 1/2 watt
330k ohm resistor is R411.1/2watt

URGENT WARNING........THE ABOVE MODS INVOLVE, WHETHER THE INSTRUMENT IS
TURNED ON OR OFF, OR UNPLUGGED, THE POSSIBLE EVEN LIKELY EXPOSURE TO
EXTREMELY DANGEROUS AND  LETHAL VOLTAGES !!!

 DO NOT ATTEMPT IF YOU DO NOT UNDERSTAND!  INSTEAD ACQUIRE A COMPETENT
SERVICE TECHNICIAN!!!


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