[HAM] buzzy 122

[Kon Zissis]

Hi Carl.
With  stereo headphones you can connect one of the G outputs to the left
channel and the other G output to the right  channel and thus hear the
organ sound loud and clear. With this set up there is no need to connect
anything to the headphone common/ ground wire.
 
The Leslie 122 has a hum cancelling balanced line dual input stage which
uses the two out of phase signals coming from the two GG outputs of the
organ preamp.
With the 122 set up the balanced line in dual inputs are on the pins 1
and 6 which are for the two GG output signals,  and the pin 2 is the
ground. 
 
The Leslie 147 has an unbalanced line in single input stage which only
uses one of the G outputs and the ground. The pin 6 is the input and the
pin 1 is the ground. The connection will not work properly if you try to
connect one G output to the input pin 6 and the other G output to the
grounding pin 1 because the GG output transformer has a grounded centre
tap so therefore  connecting one of the G outputs to the grounding pin 6
will in effect short out one half of the secondary winding  of  the GG
transformer. This will cause a hum and a reduced sound quality. 
 
Another difference with the 122 and 147 is that the 122 uses a Leslie
connector kit such as the 428 kit and a second 12AU7 valve in order to
activate the fast and slow speed switching . The speed switching voltage
from the Leslie connector kit is superimposed on the audio signal lines
that go to the pins 1 and 6 and from there the voltage goes to the
second 12AU7.
The 147  uses a simpler  direct mains AC voltage speed switching set up
so therefore there is no need for the second 12AU7 valve and the
expensive Leslie 428 connector kit. 
Because the pin outs on the 122 and 147 are different , you cannot
connect a 122 and a 147 together in parallel.
All the best.
Kon
 
Carl Mal wrote:
As far as I know,  G1 and G2 are 180 out of phase, thereby balanced
(mutually cancelling) when sharing common ground.
 
I expect this was used because of the  rf and emf rejection properties,
still in use today with microphone cables for example.
 
Do you mean you tested with headphones G1 & gnd, then G2 & gnd, -or- you
clamped your headphones onto G and G?
 
When I 1st got my trek OBL-2, I tried clamping it onto G and G and got
nasty humm.  When I connected to ONE of the Gs and chassis ground, it
worked like it says on the box.
 
I don't expect the trek preamp would be any different than the old
preamp in this regard.
 
I'm still a newb but starting to get it I hope,
MC/SW/CC/Kon/JW/DW/KC/etc. will correct me if I'm wrong
 
I don't have a 122 but a 147 and am struggling to understand the
differences.  
 
One day I might just post, 122/147 what's the Diff?