[HAM] Vibrato Problem

[RBROWN8962 at AOL.COM]

Short of a Trek replacement, can the ao28 be retrofitted with any solid state parts?


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-----Original Message-----
From: Rick Prevallet <rickp at tonewheelgeneral.com>

Date: Wed, 14 May 2008 10:11:54 
To:The Hammond Forum <hammond at zeni.net>
Subject: Re: [HAM] Vibrato Problem


Scott sez...

 >
OK, I'm now officially lost.
<

Can't have that now.


Then Jim sez...

 >
Also as per Rick Prevallet's (Tonewheel General Hospital) suggestion, I 
jumped the C and D terminals together.
<

This is just a way to eliminate the scanner and vibrato line from the 
equation.  Terminal C is the preamp output to the vibrato line, and 
terminal D is the output from the scanner back to the preamp.

If you open your service manual to the AO-28 schematic you can see how 
this works, but you certainly wouldn't want to play with this 
"modification".

I've completely forgotten what I might have typed/said otherwise, but 
low volume is almost always (maybe always) due to low voltage.  A preamp 
with out of whack voltages won't sound good, ever.

==
Rick Prevallet
Hammond Age List Administrator
rickp at tonewheelgeneral.com
www.tonewheelgeneral.com
Skype:  Leslie_Hammond



Scott Hawthorn wrote:
> At 09:42 PM 5/13/2008, Jim Shanks wrote:
>   
>> OK, checked the resistors.  They're OK.  Also checked for AC voltage
>> coming off of the "C" terminal on the AO-28.  Got about 1.8V AC at about
>> half expression on middle C with the vibrato on (get zero with vibrato
>> off).  It varies with expression and notes played.  Sound reasonable?
>> Also as per Rick Prevallet's (Tonewheel General Hospital) suggestion, I
>> jumped the C and D terminals together.  Got a real obnoxious distorted
>> sound, but it seems the preamp is putting out signal on the C terminal.
>> And it scared the hell out of me.
>>     
>
> OK, I'm now officially lost. If Rick is helping you privately, go with 
> that, 'cuz I have no idea what the above is about. He's certainly capable 
> of fixing this. If you're trying to find out if there's a problem in the 
> delay/scanner circuits as opposed to the vibrato amplification channel, the 
> common test would be to switch the wires at 'A' and 'B,' the respective 
> inputs to the two channels.
>
>   
>> So . . . on to the line box and scanner?  Again, I do have sound through
>> the vibrato, and it sounds right (vibrato and everything), just VERY quiet.
>>     
>
> No. The line box and scanner would have nothing to do with low signal in 
> the vibrato circuit, as far as I can figure.
>
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