Re: PRO-3 mods

[Mark Longo <longo@swanky.zk3.dec.com>]

> I have seen passing references in this list to changes in the
> PRO-3's drivers and components since it first was released.
> Can anyone enumerate what they were, and the reasons for
> the changes?

        I can't remember exactly all the changes.  They should be listed in the 
list digests as they were posted and described by John Fisher, the PRO-3 
designer from Motion Sound.  If you search the digests beginning with June '95 
or so, (available through the FAQ) for "Fisher" you'll find them.  I believe 
the 
last modification John described was posted in 1995.
        
        There were a few circuit board modifications (add wire jumpeer, remore 
cap or resisitor sorts of changes) that improved the tonality somewhat and I 
was 
glad I made them.  

> My unit is numbered 1200-something - how do
> I figure out if these changes are in my unit?  Are the mods on
> my nickel or Motion Sound's?  Is there any adjustment to
> increase the depth of the modulation on the bass simulator?
> I can get enough volume, but it sounds sterile next to a 122
> (yeah, I know, I know..., but more mod depth would definitely
> help!)  

        Most of the modifications happened early on, though I don't know the 
exact serial numbers where the changes were made, I believe you will find those 
numbers in John Fishers postings from the digests.  I think your unit has 
probably had most of them done.  One of the mods increased the boost of the 
bass 
simulator and I think there may have been another that would reduce the depth 
of 
the simulation (not increase it).  There's a little more depth if you use the 
bass rotor simulator in mono mode, rather than stereo.
        
        Back when the modifications were announced Motion Sound was offering to 
send a modification kit free of charge that included a small trim pot that 
could 
be added to the early units to control the accel/decel times.
        
        The most major modification was done to the driver diaphram.  Early on 
Motion Sound had the diaphrams of many customer units blow.  They were 
replacing 
those old diaphrams (free in exchange for the old one) with a newer unit that 
had "MS" stamped on it.  You can tell if you have the newer one by removing the 
port door on the bottom of your PRO-3 and looking for the letters "MS" stamped 
on the diaphram cover.  I don't know if the Motion Sound offer for free 
exchange 
is still in effect.

        There have been some later mods that change the cutoff frequency 
between 
the rotor and bass rotor simulation from 700Hz to 800Hz but there may not be a 
way to field-modify your PRO-3 to do this, or at least a modification has not 
been announced.  In any case, if the simulation is not deep enough to suit your 
taste, you would probably prefer to keep the lower cutoff frequency anyway.

        Mark