Fender optoisolator tremolo ticking/clicking

[ribo1989]

Hi everybody,

I tried a couple of ways to eliminate the ticking caused by the neon bulb in Fender tremolo circuits with optoisolator. Here are the results.

1. Added a .01uF or .022uF mylar cap from bulb to ground. Ticking was reduced, but it was still audible. No success. Removed it.

2. Added a .01uF or .022uF mylar cap from R43 to ground. No avail. Removed it.

3. Replaced the 12AX7 with a 12AY7. Ticking went away, but the tremolo could not be turned off. Same with a 12AT7. Permanent tremolo. Who needs this? No one. Back to 12AX7.

4. Replaced the grid wires to V5 pin 2 and pin 7 wit shielded wires grounded at one end. This helped a lot, but a barely audible ticking remained.

5. Removed the optoisolator, replaced the neon bulb with a white LED and reinstalled it. Ticking stopped, but a thumping sound was audible for ca. 1 second after hitting the footswitch to start the tremolo. The thumping sound was also there when I played single notes on the upper register of the low E and A string. No thumping or ticking when playing chords in general or single notes on D, G, B and E strings.

Removed the cathode bypass capacitor C24 from the neon driver triode of the tremolo tube. The thumping noise was completely eliminated. The tremolo intensity is not affected and it sounds a bit smoother. I think this is due to the reduced gain of the tremolo tube without the bypass cap.

I hope this mod will be useful for everybody trying to get rid of the ticking/thumping noise of the Fender LDR tremolo. Any thoughts, additions and recommendations would be highly appreciated.

[jpfamps]

I've found the cap from bulb to ground if anything makes the problem worse!

Most of the time I've found that the ticking can be eliminated by changing the either the whole optocoupler or the neon bulb in the optocoupler.

I think the ticking is caused by noise from the neon bulb striking. As the bulb ages material from the electrodes in the bulb gets deposited on the inner surface of the bulb, and my guess is that this causes the bulb to progressively noisier, possibly due to current leakage.

I would value opinions on this.

[g1]

According to Fender, the primary cause is lead dress: Fender Tech Notes - Vibrato Ticking Fix.pdf

[Enzo]

I have found that to be the case in my experience. Usually repositioning the wires solves it.

[nosaj]

According to Fender, the primary cause is lead dress: [ATTACH]23775[/ATTACH]

Where do you find Fender tech notes at?

nosaj

[g1]

Where do you find Fender tech notes at?

See the 3 black circles for a 3 ring binder? That's one I had photocopied out of a binder of Fender schematics. Back in the nineteen hundreds...before the turn of the century...when the interwebz were for gopher's and most tech documentation was still on sheets of paper!
But seriously, the shop I worked at had binders full of schematics. I don't recall seeing many tech bulletins from Fender, so it had to be a very common problem for them to issue one. I imagine they would have provided them to warranty stations along with schematics.

[Enzo]

They are available to authorized service centers. As far as I know, they don't distribute them to civilians. You pretty much have to ask someone to share them. There are not all that many. They issue a handful a year.

[ribo1989]

According to Fender, the primary cause is lead dress: [ATTACH]23775[/ATTACH]

Unfortunately the Fender reissue amps do not allow an effective lead dress as the wires are very short and go directly from the PCB to the tube pins. All I could do was moving the wires of the tremolo tube away from each other; but sometimes I had to bunch them together to reduce ticking. Replacing the grid wires of tremolo tube with shielded ones helps a lot, too. But all this helps only reduce the ticking but never eliminates it.

Regards