[HAM] B-3 pre amp

[Dave Bishop]

I agree that the tube amps are preferred.  The TrekII preamp is easy to 
install, relatively small and light, and it offers reverb and percussion 
tweaks, all fine for a gigging organ.  It sounds close, but not as good as 
an AO-28, and is three times as expensive:  I my opinion it devalues a B-3 
in studio use.

The first thing to do is figure out what is generating the hum, i.e, whether 
the B-3 or your tone cabinet and connecting apparatus is the source.  That 
requires some simple diagnostics.

Try reversing the power cord poles and see whether there is any difference 
in the hum.  Try plugging the organ into an outlet on a different circuit 
breaker from the one you are using.  If either of these change the hum, 
report back before going further.

Make sure there are no flourescent lights, motors, or clocks near the organ 
or the floor under it, or try moving the organ to a different location in 
the building, or 90 degrees from its present orientation.  The Leslie should 
not be on the near left side of the organ, as it radiates EMI that can be 
picked up by the matching transformer.

Find out whether the hum is constant in volume or varies when you move the 
expression pedal.  Try all the combinations of percussion, vibrato, pre-sets 
and manuals, and determine whether the hum varies in amount with particular 
combinations.  Is the hum present when the organ is cold or does it fade in 
after it warms up more than 3 minutes or so?  Is the 60 Hz hum (a low Bb) or 
some higher tone?

Take off the back of the organ and visually inspect the wires, looking for 
something that has broken off from its solder joint:  particularly the black 
wires on the far right side of the TWG soldering lug strip.  Touch the metal 
(only) on the expression capacitor housing on the top of the preamp, and see 
whether your body capacitance affects the tone of the hum.

On the right side of the back of the organ is a pre-set bar matrix that 
looks like rows of brass bars with lots of wires running to it.  There are a 
bunch of screws holding on wires.  As to each screw, back it off slightly 
and then re-tighten it, making sure the wire under it is properly seated. 
Be sure to get the screws on the very bottom row.  On the pre-amp itself the 
wire connections should be covered by three Faraday shields that look like 
little metal boxes held on by nuts.  If any are missing, you will get hum.

You can fashion a headset by obaining a female 1/4 inch headphone socket and 
soldering on two wires a couple feet long, one on the tip lug and one on the 
barrel lug.  Attach the tip lug wire to one of the two outputs embossed "G" 
on the pre-amp and the other wire to any screw on the pre-amp chassis 
itself. Disconnect your Leslie or tone cabinet. Plug in a headset and listen 
through one earpiece for the faint sound of the pre-amp alone.  If the hum 
is not present at the headset, then the organ (including the pre-amp) is not 
the problem.  The list can make other suggestions if your get to this point.

Regards,

Dave Bishop