[HAM] Al Goff on V-21 and development of replacement

[Kon Zissis]

Hi Mark and everyone.
Thank you for the link to Al Goff's 1996 Hamtech post.
I have tried out the following treble drivers in a Leslie 122  :
Original Jensen V-21,
1981 Rola Jensen V21 with ceramic magnet, 
JBL 2482 ,
JBL 2420 , 
Two Atlas PD-60's , 
Hammond Suzuki ( Eden ) 100 watt ferro fluid driver ,
BT-75 ( P-Audio PA-D 50 ), 
Two slightly different sized Kustom brand drivers with no model number
on them,
TOA 650 
 
The Rola Jensen V21 with the ceramic magnet sounds similar to the V-21
except that it has more midrange content whilst the V-21 has the more
characteristic hollow sound in  the midrange .
 
The 16 ohms 120 watt RMS / 120 decibel SPL  rated JBL 2482 which weighs
a massive 11 kilograms has a fatter sound and less  treble edginess than
the V-21 and it is my favourite of the replacement  treble driver
because it works very well in the Leslie. The JBL 2482 was the stock
treble driver in the Leslie 925 and also in Bill Beer's high power solid
state Leslies.
 
I have a JBL 2482 in my Leslie 122 and I have an L-pad  wired before the
JBL 2482 so that I can bring down it's volume level so that it is
properly matched with the bass speaker. 
The JBL 2482 has a smooth sound without the excessive upper midrange
honkiness of the other more modern treble drivers  so therefore apart
from the L-pad volume control it does not need extra filtering to make
it sound acceptable in the Leslie 122.  
 
If the JBL 2482 is driven to distortion by an excessively  high power
solid state amplifier it can then get nasty and unpleasantly brittle
sounding as can be heard with Jon Lord's solid state high power Leslie
on some of the tracks on the 1974 "Deep Purple California Jam" concert
DVD. Jon Lord's high power Leslie had Crown DC300 solid state amplifiers
, a Gauss 15 inch bass speaker and a JBL 2482 treble driver.  This
brittle sound was quite different to that of my own set up where I have
properly matched the volume level of the JBL 2482 with the bass speaker
and I don't overload the speakers with excessively loud levels so
therefore I get a very nice warm natural sound out if my JBL 2482. I use
my overdrive unit to get a nice warm dirty sounding distortion at any
volume levels.
 
The JBL 2420 sounds OK , kind of like a V21 with extended high  treble
response.
 
To my ears the Atlas PD-60 , the 100 watt ferro fluid driver and the
BT-75 treble drivers  have a sterile plasticky sound with excessive
upper midrange honkiness. Some kind of filtering is needed to help tame
down the plasticky sound and to make them sound more acceptable. 
 
I have been told that the 100 watt Ferro fluid driver is supposed to
have been designed to have  a similar frequency response curve as the
old Jensen V-21  but in the Leslie there is an obvious difference in the
sound . My friend only kept his BT-75  driver and his  Ferro fluid
driver for a short while so therefore I did not get a chance to
experiment with filtering them  and bringing their  volume level down to
V-21 levels so that I can hear how closely they can be made to sound
like a V-21.
I have experimented with my own two Atlas PD-60 drivers and the
filtering did improve the sound but I could never get it to sound as
good as the JBL 2482 or the V-21. 
 
The two Kustom drivers and the TOA 650 sounded awful in my Leslie 122 (
especially when using the overdrive effect ) and no amount of filtering
that I tried out  could make them sound acceptable.   
 
Al Goff mentioned in that Hamtech post that he measured and plotted
graphs of the V-21 and the ferro fluid driver whilst they were connected
to a Leslie horn , but to my knowledge he has not yet released these
frequency response  graphs. I am very interested to see these graphs.
All the best.
Kon
 
William Mark Bristow wrote:
Guys,  
Here's the info on the Jensen original speakers from www.goffprof.com
 
Al Goff helped design the previous Leslie Treble driver after the V-21
went
out of production and before the Ferro-Fluid.
 -- Mark
--- from www.goffprof.com website ---
http://www.goffprof.com/shopping.jsp?p=5