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Add Diode-Clipping Distortion to your Guitar Ampby gmoon on March 2, 2008 Table of Contents Add Diode-Clipping Distortion to your Guitar Amp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Intro: Add Diode-Clipping Distortion to your Guitar Amp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Step 1: Let's examine diode clipping... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Step 2: Types of diode clipping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Step 3: The design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Step 4: Inserting the circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Step 5: Other options... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Step 6: But how does it sound? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Related Instructables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Comments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 2 2 3 4 5 6 7 7 8

http://www.instructables.com/id/Add-Diode-Clipping-Distortion-to-your-Guitar-Amp/

Intro: Add Diode-Clipping Distortion to your Guitar AmpHere's a relatively simple way to add some "bite" to your old guitar amplifier. Amplifier overdrive and distortion is usually achieved by signal clipping--pushing the gain until the signal peaks are chopped off. "Real" tube overdrive isn't possible without major changes (adding additional preamp stages, etc.), but here's another option: Preamp clipping can be simulated by installing a diode-clipping circuit . In fact, some big-name amp manufacturers (Marshall and Fender, for instance) have used diode clipping for a more ballsy sound (especially at low volumes.) In fact, it's made a bit of a resurgence in boutique amps... The danger of converting a tube sound into a harsh "solid state" sound exists. Tubes clip with a softer "shoulder" and have a more pleasant, warm sound....of course, it's a matter of taste, after all. But a carefully designed diode-clipper circuit can mimic those tube characteristics. "Peak clipping" more closely approximates tubes than "crossover clipping," which is common to transistor design. Plus we can utilize asymmetrical clipping to emphasize the "correct" harmonics. And since our new sound is contained within a tube amp, it will help to soften the effect. Of course, diode-clipping can be used (and is) for solid state amps, too. Video clip shows the three switch-selected settings: 1) clean; 2) medium clipping; 3) max clipping:

Warning : This is a "mod," and does require a bit of rewiring. All the usually cautions about discharging power supply filter capacitors apply here. To restate them: Don't touch the internal components of a guitar amp without first draining the filter capacitors. Please. You could really harm yourself. Here's a link to my older amp project, and the section Discharge those Caps!

Step 1: Let's examine diode clipping...Wow--at first glance, a diode connecting the the signal path to the ground looks like a short circuit! How can this work? In theory, diodes conduct current in only one direction. But they don't operate "perfectly." All diodes have a "forward voltage" -- they won't conduct until that voltage is reached. If a diode is connected between the signal path and the ground, the signal won't be channeled (shunted) to ground until it exceeds the forward voltage. And even then, the whole signal isn't dissipated, only the portion of the signal above that forward voltage. So it's peaks are simply "chopped off." But it also results in more attenuation, as some of the signal is lost. That isn't all bad! Clipping the loudest parts is also a form of "limiting" -- you loose some dynamics, but accentuate the lower-volume sounds. Plus, many amps don't begin to distort until turned up too loud for many venues. Like a stomp-box, diode-clipping lends a killer sound at a lower volume. Your family, roommates and neighbors will thank you.

http://www.instructables.com/id/Add-Diode-Clipping-Distortion-to-your-Guitar-Amp/

Image Notes 1. The simplest diode clipping circuit. 2. Similar to a square wave, and that equals distortion.

Image Notes 1. An unclipped, unmodified signal

Step 2: Types of diode clippingThe clipping effect works in both directions relative to ground--so a circuit that clips both the positive and negative signal peaks is two diodes connected in opposing directions. The diodes can be chosen to pass as much of the signal as necessary. More clipping equals more distortion. The first illustration shows: 1) An unclipped signal 2) Asymmetrical clipping, one side of the signal (not limited to a single diode.) 3) Symmetrical clipping, where both the + and - signal is clipped equally. 4) Asymmetrical clipping, both sides. Variation #4, asymmetrical clipping , offers the most natural and "tube-like" sound. Plus, it's the most flexible--any number of diodes in series can be used to shape the effect. Picture #2 shows just a few variations of asymmetrical clipping. Notice that LEDs are used as diodes in examples B and C! LEDs have a much higher forward voltage than typical diodes, so the clipping can be softer and more subtle.

Image Notes 1. This is usually the best choice...

Image Notes 1. One diode + two diode combination 2. One diode + one LED combination 3. One LED + two diodes combination 4. Different clipping voltage peaks.... equal asymmetrical clipping.

http://www.instructables.com/id/Add-Diode-Clipping-Distortion-to-your-Guitar-Amp/

Step 3: The designAs 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.)

Image Notes 1. Ignore the color bands, and use the values in the table. 2. Drawing shows the correct polarities, for all three diodes. The diode bands and the flat LED end represent the cathodes. 3. The picture has the order of D1 and D2 switched--but this doesn't effect the overall voltage drop.

http://www.instructables.com/id/Add-Diode-Clipping-Distortion-to-your-Guitar-Amp/

Image Notes 1. Different wattage resistors...what I had handy... 1/4 watt is fine. 2.