PRO-3 Answers

["JHF" <John.Fisher@m.cc.utah.edu>]

your unit on our nickle. Call first for arrangements.  A large amount 
of the  147/122 low rotor richness comes from the spacial 
distribution of the sound. A stereo low rotor amp on your PRO-3 goes 
a long way in providing that. Someone on the list posted  an idea 
that I regularly use-- send  the the PRO-3 left out to the amp in back 
of you and send the right out to your PA system, helps a lot. If you 
want more AM mod lower resistor R41 (see owners guide) 22k to 10k.
This also effects the left right seperation. (You will have to 
re-adjust the balance control pot P2). Place a 10k trimmer with a 1k 
resistor in series between the left and right output jacks- use that 
to set the AM you desire.
                   The ramp up-down time of the horn can be 
increased by changing or adding to capacitor  C26  (1ufd 35v 
non-polar). Doubleling the value  (2ufd will double the times ect.) 
Trimmer P7 will still give variable control. The low rotor times can 
also be changed by changing resistor R38=ramp-up R35 ramp-down. 
Capacitor C17 (1ufd 35v non-polar) can be changed as in the horn 
description above and effects both up and down times.
             Mods ? here are the  most significant:
     
       1.    SN 1864    Pre-amp gain reduced from 50 to 40 - 
original gain was for (gasp) guitar player.  Reduced to lower 
distortion and provide better trasient response.
       2. Crossover changed to 800 hz, Diaphragm problems at the 
original 700 Hz.
       3. Bandwidth lowered from 10 to 7 Khz.
       4. Crossover changed from 18 to 12 db on horn.
       5. Horn septum devider added, lowers resonant point.
       6. Ground wires placed between motor, horn driver and chassis, 
eliminates static "pops" in dry climates.
       SN 2106  Change silicone "red" belt to black buna. Silicone 
belts are great unless you get a bad batch (they are a compound) .
 We now use Black Buna belts Parker  #  2-158N70, These are much more
consistant in quality and the projected life is the same. They are 
available at most O-ring suppliers or from us.
        Some hardwood parts were added to stregthen the cabinet and 
stop screw stripping.

                                 Enough tech for now, lets rotate !


                                      John Fisher.