diode gain increases, question...

[nicox86x]

in this artical it says you can increase gain by increasing the number of diodes from 2 to 4. and that the later the diodes clip the wider the range is. that being said, what would happen with 6 or 8 diodes? more range?

they also say you could use an led and that would clip later.. would the led light up? and if it does, would it glow brighter the high the pot is turned?

Increasing gain using diodes




If you have a circuit like the Jordan Bosstone or MXR Distortion+ or DOD overdrive 250 and others that have a diode pair creating the distortion at the end of a circuit, you can increase the output level of the circuit with the expense of a little distortion by putting two diodes where there were one. So instead of 2 diodes, you now have four.

This mod will increase the output level with the expense of a little distortion.

More diodes in series will also give you a wider range of clean to distorted sound but less distortion when the circuit is maxxed. Something to note is that a germanium diode "clips"at around .3V and a silicon diode "clips" around .6V so you need roughly 2 germanium diodes to equal one silicon diode. A good multimeter will allow you to measure the diode and find out what the forward voltage is. LEDs will clip even later and give you more range of clean to distortion.

[Sir H C]

You do not increase the gain this way, you increase the signal swing before clipping. 

[Peter Snowberg]

Welcome to the forum.

Diodes have a parameter called V_f which is short for Forward Voltage. Below this voltage, the diode acts like it's not there. Above that voltage, the diode will start to conduct.

The way you put the question out, "more range?", is correct. Not more gain, but more range before clipping.

If you have diodes in a shunt clipper arrangement (between a signal line and ground like a Dist+), the signal will be able to vary between -V_f and +V_f. If V_f for your diodes is 0.6V you will have a signal swing of about 1.2 volts. If you substitute a pair of series diodes for each single diode (so that you now have 4 of them) the signal can vary between -1.2 and +1.2 for a swing of about 2.4 volts. While there isn't any additional gain, the output will have twice the signal swing and be much louder.

Feedback clippers (like the TubeScreamer) are a little different. Below V_f, a feedback clipper will have a high gain which is usually set by the drive control. Above V_f, the gain switches from a big number to 1. As with the shunt configuration, you will have more signal in the end if the V_f is raised.

LEDs have a much higher V_f. The actual V_f value depends on the chemistry of the semiconductor (and thus light color) but think in general terms about plain red LEDs being around 1.3V and green LEDs being more like 2.3V.

LEDs may light depending on the circuit around them. 

I like the tone from having different V_f for each direction. Try two in series in parallel with a single diode for the other direction.

If you use more diodes to raise the V_f, the tone will move from fuzzy to a more distorted sound to cleaner and crunchy. If the V_f gets high enough, you will only exceed that voltage during the attack of the note and the rest of the time it will sound clean.

Grab some Ge diodes like 1N34A, some Si diodes like 1N4001 or 1N4148, and a couple colors of LED. Run your guitar into a clean booster (set for moderate boost) and to your amp (at low volume). Try adding diodes to the output of the booster and see what you like. Playing with this setup will give you a "feel" for what's happening that will help you later on.

[aron]

Thank you for correcting my simple mods page Peter. It has been corrected.