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All other settings being equal, for output volume, based on my audio interface meters: Germanium, Silicon, LED !!!!! (twice as loud as the others, signal-wise) The switch should be laid out in that order (Ge, Si, LED) but that is probably an easy tweak. How can I beat the LED output down: a simple swap of a higher resistor value? Audibly, the germaniums are "round", the silicon "square" and the LEDs "spikey" (or "smooth", "crunchy" and "bright") but volume-wise they are 1, 1.2, 2 in terms of level. My goal is to be able to flick the switch and retain the output volume at a nearly constant level, but the LED circuit blows out my interface.

Unfortunately:

1. ...the greater loudness of the LED clippers reflects their intrinsic electrical properties, and...
2. ...there isn't a simple/uncomplicated modification to get around this.

The volume difference is a manifestation of how diode clipping works. When the amplitude of the audio signal exceeds the forward voltage threshold of the clipping diode, the signal above that threshold gets "clipped", that is it's shunted out of the audio signal path. Because audio signals are AC in nature and are a waveform, they have both a positive and a negative side. This is why clipping diodes are paired in opposite polarities, to be able to clip each of the sides of the waveform. The lower the forward voltage threshold (FVT), the more of the audio signal that will be clipped off. Germanium diodes typically have a FVT of ~0.3V and silicon diodes are ~0.6V. LED's on the other hand, have an FVT ~2V, so they clip significantly less of the signal. Less signal clipped = more signal output = greater volume. Since the diode pairs are all located in the same part of the circuit, any modification you make to the clipping stage as a whole will affect ALL of the diode pairs, so you would change the clipping character of all three settings.

Alternatively, you could add a resistor in series to the other diode pairs to increase their FVTs to that of the LEDs, but this would drastically alter their clipping character. To be able to affect just the output volume for the LEDs, you would need to get into some much more complicated switching scheme that kicked in ONLY when the LED clippers were selected and affected the output downstream from them--perhaps adding a switch that simultaneously selected the LEDs and added a resistor in series with the pedal's level pot. Possible, but pretty complicated and would necessitate adding hardware to what is already a fairly cramped space. Personally, I would think it would be much easier just to determine how much of a reduction of your volume pot setting is necessary to approximate the volume for the other clipping settings and roll it down accordingly when you switch to the LED clippers.

Incidentally, this change in volume is considered a useful feature by many players who use the LED setting as a quasi-boost for soloing.

_________________
“My favorite programming language is SOLDER” - Bob Pease (RIP)

My Website * My Musical Gear * My DIY Pedals: Pg.1 - Pg.2

One other thing I should mention:


Umm, actually, not at all. This on-off-on SPDT clipping switch must be laid out with the diodes with the highest FVT in the middle (off) position. When the toggle is in the middle, the LEDs are the only diodes in the clipping circuit. When you switch to either of the outer "on" positions, it puts one or the other of the lower FVT diode pairs in parallel with the LEDs. Since electrical current will follow the path of least resistance, the signal will then clip through the lower FVT pair and bypass the LEDs. Think of the diodes as analogous to water dams--if a river splits and goes between two channels to dams of different heights, the water will spill over the lower one and never rise to the level of the higher one. It's a pretty clever switching scheme, when you think about it, but not a flexible one.

_________________
“My favorite programming language is SOLDER” - Bob Pease (RIP)

My Website * My Musical Gear * My DIY Pedals: Pg.1 - Pg.2

Great info, thank you for taking the time to explain that, and thanks for the link to your page.