[HAM] AO-28 Sounds

[David Anderson]

Jordan,

Scott Hawthorn is right; there aren't huge differences between AO-28s  
from different eras.

Sonic differences among AO-28s are primarily a function of the aging  
and drift of various components. For example, the 470k and 2.2M  
resistors around the input 6AU6s are often way off. I've seen 2.2M  
resistors that were completely open. The 330k plate resistors of the  
12AX7 often drift. And both 6AU6s and the 12AX7 all share one cathode  
bypass capacitor.

Hammond did use various different 1uF capacitors at the output to the  
vibrato line box. These can affect the "flavor" of the vibrato  
channel. For example, I was rebuilding an AO-28 in one of my organs  
that had some half-assed repairs, including a cheap 1uf cap. I had  
some Russian military surplus paper in oils I was using as crossover  
caps in another project, and I tried one of them as an experiment. It  
was an instant: "Wow, I like that."

Also, some AO-28s simply had better wire-routing in them than others.  
For example, it's best to keep signal wiring as far as possible from  
filament supply wires.

David

On Jan 18, 2008, at 11:59 PM, Jordan Kersten wrote:

>
> Is there a big difference between a silver and black transformer  
> AO-28?  How about a '60's black transformer and a '70's black one?   
> Which one would best replicate the tone of a re-built AO-10?
>
>
> -Jordan-