Strange new vibrato circuit in DR Reissue

[Steve Conner]

If it were me I'd junk the whole section and replace it with the state-variable filter circuit from the LM13700 datasheet. Do it quick before the LM13700 goes obsolete too.

Actually that's probably a bit drastic: any LDR that would work as a trem bug would probably do something in this circuit. The H11F1/3 are totally different things to LDRs, I have no idea why RG recommended them.

[emaxxx]

Tremolo optocoupler

I bought the optocoupler from Tube-Town and its looks like a Fender but I am not sure. I ordered two genuine Fender optocouplers and I will try them one after the other.

Meanwhile I replaced the stock V5 with a Tungsol 12AX7 and the tremolo intensity increased a little, but still too shallow. I checked the voltages around the circuit and they are OK.

Regards.

Hi,
I recently bought a deluxe reverb and found the same digital pcb. Pulled out the 7 10k grid resistors and put in the optocoupler but same as you the tremolo intensity is a bit low. The effect doesn't kick in until 4 or 5 on the pot.
Is it normal?
I bought mine locally and think isn't oem... maybe I should order the original fender part.
Are there different optocoupler/optoisolators around and the intensity of the effect depends on this?

[Chuck H]

Does your circuit use the proper 3M reverse log pot? If not then I would expect the same level of intensity at the pots extreme settings, but very different in the controls middle ranges. Because the effect is variable it's unfair to deem it's "intensity is a bit low" based solely on the intensity at one pot setting. It may be that the intensity is low at that setting, but not overall. And all that is needed it the right potentiometer to make the setting sound more intuitive.

EDIT: Just realized I was chasing the "speed" pot and not the "intensity" pot. OOPS!

[emaxxx]

The pot are good, I never touched them and I think they're right. The problem is that with the intensity pot on 10 the effect isn't a strong on/off like I've heard on other deluxe reverbs, it's more subtle making the intensity lower through the whole range of the pot. I think it's more of an optocoupler problem. Are optocoupler replacement sold by shops differents from the oem fender part and could this be the problem?
Thanks for the reply

[Chuck H]

Your observation is accurate then. Unfortunately there are many things it could be other than the optocoupler. In fact, for low intensity I might suspect either the tube, a circuit difference or a miswire all before the optocoupler. Unless you verify that all the components in the new trem module are identical in value to those used in a stock Deluxe Reverb and that the in circuit connections are the same too there is no way to know.

What is the measured value of your intensity pot?

[Tom Phillips]

As Chuck H points out there are many things that can cause low tremolo intensity. In my experience,however, I have found that the characteristics and performance of replacement light bugs are all over the place. When you open them up you find many different LDR parts and different build techniques. One way to characterize / test them is to measure the resistance of the LDR under light and dark conditions. It's best to have dark resistance well over 1 Meg Ohm and light resistance well under 1 k Ohm. There is also more to consider. The response time of the LDR is important too. I received a whole batch one that responded so slowly that they produced weak tremolo even though the static range of light and dark resistance measured good. There is more technical information but the bottom line is that it's easiest to substitute parts from other sources or obtain a fender replacement part as you suggested.

[adnanb]

The pot are good, I never touched them and I think they're right. The problem is that with the intensity pot on 10 the effect isn't a strong on/off like I've heard on other deluxe reverbs, it's more subtle making the intensity lower through the whole range of the pot. I think it's more of an optocoupler problem. Are optocoupler replacement sold by shops differents from the oem fender part and could this be the problem?
Thanks for the reply

I would say, it is normal that the tremolo kicks in at 4 or 5. My original Fender optoisolator kicks in at 4 and gives the on-off effect at 10.

I tried a few optoisolators (Weber, TAD, Tube Town, eBay) with different results. The trem depth were not equal, of course. The original Fender optoisolator is the best so far. I made a few myself too. They are as deep as Fender's. It depends on the photocell you use. And, I used LEDs instead of neon bulbs. This eliminated the tremolo tick-tick caused by the neon bulb. If you would like to increase the trem depth even more, you can lift the ground leg of the Intensity pot and solder a 56K resistor between the ground leg of the Intensity pot and ground. The trem effect kicks in at 1 then.

[emaxxx]

Thanks much for the info. I bought a TAD optocoupler to try...can't find the fender one here in europe. I hope this will work fine. I also bought some preamp tubes...maybe these will help too.
Thanks much for the info.
I think the amp sound better without the grid resisors and the digital pcb tremolo so I'm really happy to have done the mod.

[Zouto]

Hi Pedro, I just got the same model with the same weird circuit in it, which I'd like re-mod to the normal neon/ldr optocoupler.
Do you remember what exactly has to be removed and how to connect the optocoupler?
Thanks for help,
Zouto

[Pedro Vecino]

- Remove new pcb´s from chassis.
- Desolder the shielded cables on the cell points.
- Install a new cell on them
- Disconnect from the general pcb the two yellow wires coming out from the new pcb.
- Desolder the two red wires in the new pcb coming from the power transformer.
- Connect the red wires (in the general pcb) in place where they were originally connected the yellows. Observe the color code (is marked on the board) RED/BLU and RED/YEL.
- Remove added grid resistors (10K) in each triode (I can not remember if there were six or eight). They are encapsulated in shrink tube connected to sockets pins 2 and 7.

* For safety it´s convenient to measure before and after the negative voltage on pin 5 of the 6V6´s.

[Zouto]

Pedro, THANKS A LOT for your detailed instructions and the pic.
Meanwhile I've removed the cables on the cell points and the seven 10K grid resistors, put in a new (homebrew) cell and the Vibrato works great now. The weird boards will stay in the amp, the red/blue and red/vellow cables are still soldered to that green-cap-pcb on the side of the chassis, I'll change them next.
All the best,
Zouto

[Zouto]

Pedro, THANKS A LOT for your detailed instructions and the pic.
Meanwhile I've removed the cables on the cell points and the seven 10K grid resistors, put in a new (homebrew) cell and the Vibrato works great now. The weird boards will stay in the amp, the red/blue and red/vellow cables are still soldered to that green-cap-pcb on the side of the chassis, I'll change them next.
All the best,
Zouto

Correction: There were only 6 GRID RESISTORS to be removed

[überfuzz]

Off topic: Every time I see a pcb board in a guitar amp I get an itch...

[J M Fahey]

Why didn't they just use a plain Fet?

If signal level at the classic "bug" position is too high for comfort, apply "tremodulation" to some other point where it can handle it.

Once tremodulated, always tremodulated.

The exact point where it's applied is not that important.

Yea, I know, I'll be rebuffed with the "one size fits all" standard Forum/Believer answer: "if it could be applied somewhere else Leo would have done that ... and he did not" .... to which I should remind that sometimes there's more than a solution to a problem and even some times one of them may be chosen by flipping a coin.

FWIW early Marshall amps with tremolo did use a Fet

[Steve A.]

- Remove new pcb´s from chassis.
- Desolder the shielded cables on the cell points.
- Install a new cell on them
- Disconnect from the general pcb the two yellow wires coming out from the new pcb.
- Desolder the two red wires in the new pcb coming from the power transformer.
- Connect the red wires (in the general pcb) in place where they were originally connected the yellows. Observe the color code (is marked on the board) RED/BLU and RED/YEL.
- Remove added grid resistors (10K) in each triode (I can not remember if there were six or eight). They are encapsulated in shrink tube connected to sockets pins 2 and 7.

* For safety it´s convenient to measure before and after the negative voltage on pin 5 of the 6V6´s.

I took the liberty of converting your post into a PDF file that I attached here so that people here can download it. Let me know if there are any edits that you would like.

Steve Ahola

P.S. This is an old thread so I was wondering if these PCB monstrosities are being sold in the US or is it just in the EU? Thanks for your detailed instructions with annotated photograph!

Here is the attached PDF file to download...
Replacing Fender tremolo PCB on Deluxe Reverb Reissue with optoisolator.pdf

And here is a JPG version of that file...