Fender Tremolo roach

[Govmnt_Lacky]

Has anyone done a "roll your own" Tremolo roach for a Fender repair? Looking to find out the LDR min and max resistance AND whether or not an LED can be used or does it have to be a neon lamp.

Thanks!

[glebert]

I do my own with LEDs. The DIY roaches helped with thumping on a couple amps. I don't know the specs of the LDRs I used though, I just got a bag of them off Ebay and they worked well.

[Tom Phillips]

I have done some research about rolling my own lightbugs. One additional parameter to consider is the rate of LDR resistance change with respect to light and dark. That was included in the specification sheets when cadmium sulfide LDRs were more common in the past. Currently, it seems that one needs to buy a selection of LDRs and sort through them to select those that will perform well. I.e. give you the sound that you like over the range of choppy vs. smooth tremolo.

Once I returned a batch of 10 because they used LDRs with very fast attack and very slow release resulting in weak choppy sounding tremolo. At this time I still just buy lightbugs from the usual suppliers.

[Jon Snell]

I make my own using one https://uk.rs-online.com/web/p/colou...s/9146710?gb=s and one https://uk.rs-online.com/web/p/indic...s/6559413?gb=s.
Wrap them up with black heat shrink and there you go.

[Govmnt_Lacky]

Appreciate the inputs. My main question was in regards to using the LED instead of the Neon lamp. I have LDRs of varying resistances to test with. I was just wondering if LEDs could be used in place of the Neon lamps.

[Jon Snell]

If the driver is the anode load, as many are, an LED would not work without design change due to the lack of voltage drop that a neon has; 90volts vs 3volts and current drive.

[Govmnt_Lacky]

If the driver is the anode load, as many are, an LED would not work without design change due to the lack of voltage drop that a neon has; 90volts vs 3volts and current drive.

Thanks! That is what I figured. The LEDs would not be able to handle the voltage drop. Not a game stopper, just need to roll my own with a Neon lamp

[glebert]

Unfortunately it seems like all the people who wrote up using LEDs in place of the neon did it on blogs or forums that have disappeared. I am quite sure that I did not redesign anything when I did it on AB763 type circuits and that the 100k resistor could ballast the voltage sufficiently. The only direction I really needed was "attach the positive LED lead, the long one, to the 10M resistor". I think the worst thing that could happen is you burn out an LED.

[g1]

I think Leo_Gnardo has posted about using LED's, perhaps he could comment on circuit changes for the Lamp side of the circuit.

[Helmholtz]

Actually I can't think of a reason why an LED shouldn't work.
Both a neon (actually being a low pressure gas discharge device based on plasma arc discharge) and an LED depend on current drive and that's exactly what the high impedance circuit provides.
Main difference is the voltage drop, being around 60V with the neon and around 1.7V with a red LED.
With the LED load max. current should be around 0.5mAp meaning a peak power of 0.85mW.
That's certainly safe.
Only question is if that minute LED power produces sufficient light for the roach, as light emission efficiency of LEDs varies a lot.

[J M Fahey]

Do not ADD problems to a problem, just use a generic Neon bulb and a generic LDR.

Why reinvent the wheel and make it square to boot?

[Jon Snell]

If you want to have fun, put the LED in the cathode side. That will reduce the voltage (that is of no use) and allow for more current.
Just theoretical. I wouldn't do it but if you have nothing else to do ... maybe worth a try. Use an LED optocoupler with a pulse width modulated driver from the cathode of the driver stage. PWM is required as the output or switch of the optocoupler is as it says, on or off. You need to change it to an FM based signal to adjust the load on the drive amplitude.
Round holes ... square pegs etc.

BTW, Striking Voltage: The voltage at which the neon lamp ignites is usually between 45 and 65VAC for standard brightness types and between 70 and 95VAC for high brightness types. This can be called the breakdown or ignition voltage.
Georges Claude ... what a clever man to mix neon, nitrogen and a few other inert gasses together.