[HAM] Making Vib/chorus and normal channel equally bright

[Kon Zissis]

Hi Dominik and everyone.
I have experimented with the AO28 wiring.
The R9 820 K resistor is wired in series with the output of the normal
channel and the high resistance causes the treble to roll off whilst
allowing the rest of the signal to pass through.

Totally shorting out the R9 820 K resistor makes the normal channel more
or less as bright as the Vib/Chorus channel. There is no loss of bass
with this mod regardless of whether you bypass the R9 with a capacitor
or whether you completely short out the resistor so therefore shorting
out the R9  forms an ''all pass filter'' instead of a high pass filter.
If you want the normal channel and the chorus channel to sound more or
less identical , then shorting out the R9 is the easiest way to do this.

The feedback circuit of the Vib/chorus channel V2 6AU6  produces a
brighter sound than the feedback circuit of the normal channel V1 6AU6
in order to compensate for the losses  created by the vibrato line box
and the vibrato scanner.

By the way , you can get a bass boost  in the normal channel and the Vib
/ chorus channel by inserting a 39 pf capacitor in series with the R5 10
M resistor on the feedback  circuit of the V1 6AU6 of the normal channel
and a 39 pf capacitor in series with the R14 10 M resistor on the
feedback circuit of the V2 6Au6 Vib/ chorus channel. 
If you want an even stronger bass boost and a lower midrange boost , you
can achieve this by completely removing  the R5 and the R10  feedback
resistors. 
I have put switches in my C3 to select these settings. 
All the best.
Kon 


there is a chap out there selling an e-book on ebay concerning mods and
maintenance of console organs (see link to homepage of this guy). He
states, that there is a mod to make the normal channel equally as bright
sounding, as the Vib/Chorus channel. 

I took a look at the schematic and the only way I figured this could be
done is by bypassing the 820k series-resistor (R9) after V1 of the
normal channel with a small capacitor. This would form a high pass
filter, thus one could get a brighter sound (with the loss of bass
though).

The other difference between the circuit of the pentodes of the normal
and chorus-channel (V1 and V2) is the amount of local negative feedback
(R4,R5 and C2 in case of V1 and R13, R14, C7, R15 on V2). 

Has anybody done the mod as per the mentioned e-book
http://www.hammondb3andleslietips.com/
and if so, what is involved with it, does it work?