Add Diode-Clipping Distortion to your Guitar Amp


Step 3: The design

Picture of The design
diodeclip_circuitdrawing copy.jpg
As mentioned, using a combination of diodes, including LEDs, is a great way to begin. I've included a schematic, a wiring diagram and a photo (showing just how simple this circuit is.)

After much swapping in-and-out, I choose a combination of one germanium diode, one silicon diode and one LED.

-- a 1N4148 (D1) and a 1N60 (D2) for a combined forward voltage of ~1.05V
-- a red LED (D3) with a forward voltage of ~1.7V

The diode pairings are connected to SW1, an on-off-on double-pole switch. The center setting is "off," or no diode clipping at all. The other two settings are:

-- the diodes connected directly to the signal path.
-- the diodes connected through a pair of resistors (R1: 47K, R2: 100K)

The resistance softens the clipping, which shapes the effect. When the resistors are connected, more of the natural tube signal leaks through. There are many ways to accomplish this, and this is merely a simple example (See the "Other options" step for more info.)

To help you choose your components, here are the forward voltages for some common diodes:

~790mV -- 1N4148 (Silicon)
~265mV -- 1N60 (Germanium)
~1700mV -- LED (red)
~205mV -- Schottky 1N5819
~740mV -- 1n4001 (Silicon)

Germanium diodes tend to have softer transitions which give a non-linear, more "tubey" sound. But silicon diodes can give a sharper "square wave" metallic distortion, if that's your thing.

Before you build it:

It's important to understand that the peak signal voltages will differ greatly, amp-to-amp. No one combination of diodes will give the same effect in different amps.

And no one combination of diodes sounds good to everyone, either. Experiment! Try 2, 3, 4 or more diodes in series. Keep the sides unbalanced, or use switches to tap the signal in different ways.

(Note: on some amps, the LED(s) will actually light up--they don't in my amp, the peak voltages aren't high enough.)
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indrekhaav4 years ago
You mention that you chose, quote, "a combination of two germanium diodes and one LED", yet immediately afterwards you specify a 1N4148 which is a silicon diode. Was it a typo?
gmoon (author)  indrekhaav4 years ago
Nope, just me assuming that all glass-envelope diodes are germanium...which were the most common type when I was growing up...

Obviously I was confused about this myself when I wrote it--I list 1N4148's as either Germanium and Silicon.

Definitely has a forward voltage appropriate for SI, though.

I'll need to fix this soon, thanks.
No problem, and thanks for the clarification.
Mandela5 years ago
I'm still confused at here (im beginner) If guitar voltage output is beetween .1V and 1V, arent the voltage never been cut because the forward voltage is more than 1V ?
gmoon (author)  Mandela5 years ago
Good question. The diodes follow a preamp stage, which boosts the signal peak voltage. But yes, if the voltages don't exceed the forward voltage drop there won't be any clipping.
Mandela gmoon5 years ago
thanks oh yes! i almost forget that you made this effect to the amp ! :D But if i want to make guitar effect (not at the amp) i just have too buy lower(under 1V) forward voltage ? thanks again !
pyrohaz Mandela5 years ago
If you got 0.5v P-P output on your guitar, (Ultra mega hot humbuckers can produce this, or active guitars) You MIGHT be able to get away with this effect using either Signal diodes (Germanium) Or schkotty diodes