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More intensity for Tremolo

9/1/2003 2:31 PM
Dominik More intensity for Tremolo
Hi there,  
I have a SFSR where the owner wants more Tremolo than stock.  
I seem to remember that there was a thread about Mods to the Fender Tremolo circuti using the Optocoppler, but a search did not come up with anything.  
It seems to me the archive here is searchable only for a time span of two - three weeks all in all.  
I would appreciate it very much, if somebody can help me out on this!  
9/2/2003 7:13 AM
Dominik 56k from cw to ground helps some
Hi there,  
I tinkered with it yesterday and installed a 56k to ground in place of the bare wire going to ground on the50k Intensity pot as comes stock.  
The owner installed the equal-wheighing-of-the-channels-mod and maybe there is something wrong with that as well. I did not have a schemo on hand so I need to go back in there.  
Keep you informed,  
9/3/2003 7:37 PM
Rick Erickson

"I tinkered with it yesterday and installed a 56k to ground in place of the bare wire going to ground on the50k Intensity pot as comes stock."
That would decrease intensity.  
9/3/2003 11:32 PM
Bruce /Mission Amps

Right.. I just unmodded a SF Vibrolux with a 50Kpot/on off combo switch.....  
the switch lifts the 50K b pot with a 150K resistor.  
It verily kills the vibrato and boost the gain to near unuseable level.  
Well, not quite unuseable but not very nice sounding IMHO.  
Dumped it and the pot, installed a proper 50K RA pot and it sounds great blackfaced, with a little less negative feedback and gassing up the preamp stages slightly instead.  
9/4/2003 8:05 AM
Hi Rick,  
well that is odd, since the owner said the Tremolo sounded deeper with the resistor in place. (Psychoacoustics??)  
If the Intensity pot is on ten, the LDR will be connected directly to the junction of the 220k resistor and the 0.1 uF decoupling cap of the Mixer stage. The LDR can then modulate the signal with the most intensity, since it actually pulls the signal to ground. If the Intensity pot is turned to 0, the LDR will modulate the signal less and less.  
(The Intensity pot acts as a 50k series resistor to ground if it is . Another 56k resistor in series with it will indeed boost the signal level)  
This was the logic behind the installment of the 56k from the ground lug of the Intensity pot to ground. And I might be terribly wrong with that! :-)  
If I remember correctly, the owner had soldered the wire coming from the Intensity pot to the junction of the PI input cap and the 220k series resistor.  
Maybe this is the culprit?  
Thanks for your help guys!  
9/4/2003 3:54 PM
Bruce /Mission Amps

Ya know what, I think you might be right Dom.  
The LDR part of the vibrato bug is in parallel with the 50k RA pot.  
As far as the one I just unmoded, I'm putting a new speaker in it and after looking at the way he had that 50K b pot wired with the on-off switch to the lifitng resistor, I pulled the chassis back out and now realise that his vibrato mod was just screwed up.  
In his old original mod, he had accidentally reversed the wires from the top of the pot (.1uF/220k junction) to the wiper and the other problem was that, with his intensity pot turned down all the down (0 = no vibrato) the vibrato would not shut off if the pedal POPO switch was in the on position.  
Good call.  
9/4/2003 6:57 PM
Rick Erickson

"Ya know what, I think you might be right Dom."
That's what I get for not looking at the schematic!  
You are correct Dominik, adding the 56K will increase Vib. depth but may not allow the Vib. to shut off with the intensity pot at minimum, unless you use the footswitch. Thanks for verifying this Bruce.  

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