Roto-tone Deluxe & Pathfinder 15 Diode clipping mods

[Anonymous]

Hi all,

I did some optimizations on this small Vox Pathfinder 15 V9158 (like a lot of people ;-):
Volume Boost, mid pot, op-amps, diodes and condos changed, 10″ Emincence Speaker.
The best improvements I did were Volume Boost and a wider speaker.

I did the famous led mod… very cool, the amp is warmer, louder… But I would like to do something better with Roto-tone and i need your help to understand how to have a bigger forward voltage by assembling leds.

These two asymmetric red LEDs are used to clip and limit the signal when we send a certain amount of energy into it and this limits the volume by distorting the signal.
I would like to have different clipping thresholds with different leds.

I liked using red led and blue leds, but i would like a bigger forward voltage than with two unbalanced blue leds. But I don’t understand how to calculate it…. Does anybody have links or an idea to do it?

How can I add another led to make this fwd bigger?

I know it’s not to do the best amp, but it’s a way for me to learn 😀

Have a good day, see you

Franck

[Anonymous]

If you add LEDs in series the Vf of each LED is added together.  So if you have a LED with a Vf of 0.6 mV and you add another 0.6mV, together in series the Vf will be 1.2 mV.

Try using the smaller 3mm LEDs.  You can also Teepee 3 LEDs together in a string.  That would use 6 LEDs for one position on the Roto-Tone board.

You have noticed that the clippng LEDs reduce the volume.  You can adjust for different volume levels as you switch between positions on the Roto-tone by changing the value of the CLR resistors or other resistors in the signal path.  Try using a pot with lugs 1 and 2 shorted to substitute for the CLR/resistor.  Adjust the pot to achieve the desired level.  Then measure the resistance between lug 2 and 3.  Substitute a fixed resistor that is close to that value. Viola!

[Anonymous]

Consult the Roto-Tone build document for information on how to use the Roto-Tone.  Look at the picture that shows you which pads belong to each letter. I believe you have the LEDs in your picture installed incorrectly.

[Cybercow]

Alternatively, for space considerations, you can use 3mm LEDs. They exhibit the same Fvd as their 5mm versions.

And note please, water clear colors will always exhibit their respective color-related Fvd values. Many times, manufacturers will us the same ‘white’ LED doping material and wrap them in transparent colored plastic housings to achieve the different colors – for those, the Fvd will be the same across the different colors. I took my bag of cheap assorted plastic colored LEDs and measured the Fvd on all the different colors – the Fvd measurements on each of colored plastic ones was identical. YMMV

For the water-clear colored LEDs, each different color does exhibit a different Vfd for their respective colors.

[Author]

Posts