Print PDF
Favorite
Email
Here'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!
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!
Remove these ads by
Signing UpStep 1Let'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.
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.
| « Previous Step | Download PDFView All Steps | Next Step » |
Find a point along the signal path after a coupling capacitor and before an amplifying component (transistor, opamp, tube, etc.)
Look at step five for ideas to control the amount of clipping.
It should be reiterated that the total voltage drop for the diodes should be calculated for the peak voltage of the signal path, and not just taken verbatim from my project...
http://folkurban.com/Site/SimpleSquareWaveShaperMadeSimpler-712.html.
Check It out
Incidentally, diode-clipping distortion is MUCH older than any of Tim Escobedo's circuits. TONS of guitar effects use it.
Tim E. made some cool (and some oddball) FX...
The other two tabs are identical for linear POTs, other than effecting the direction (whether resistance changes up or down, right or left.)
Log or audio POTs also have a taper, so greater "change" is bunched up on either side. They'll have to be tested in the circuit.
Check out those AMZ links (Step 5) on saturation and warp controls for more options...
also would it matter what color the leds are and can i use leds for all of the designs or would it sound beter with real diodes ?
this does work with transistor amps right?
Each diode type--LED, silicon or germanium--has a "forward voltage drop," and that determines when clipping starts.
General purpose silicon diodes have the smallest voltage drop, So they will clip at a lower voltage (MORE clipping.) LEDs have a larger voltage drop (less clipping), and different color LEDs have different voltage drop.
Transistors amps will work too. Just place the diodes after a coupling cap.
silicon diodes are the plastic ones that are usually black or grey in color right?
do 3mm leds have lower voltage drop than 5mm
what is a coupling cap
The color of the LED is more important than it's size. Check the diode specs., it will indicate Si or Ger.
Capacitive coupling -- amplifier stages are separated by a coupling cap. Stages amplify DC voltages as well as the AC signal voltage. The cap blocks that additional DC.
A clipping diode must be placed after that cap, because the clipping won't work with the DC offset voltage present. The diode would remove the AC signal entirely.
but it wil still sound as good right?
so is this stuff sold in radio shack or do i need to buy online
ok none of this matters if it is inside the guitar right?
But at that point, you might just start thinking about building a "real" stompbox from one of the many plans online. That would get you more predicable results, since it will take some experimentation with the diodes, etc., to come up with a workable sound.
The diode setup I used was "custom fitted" to the amp. I hope that's clear from the 'ible--that every amp is a little different.
i ve thought of bulding one but i dont have any way of powering them (no 9V or AC adapters) also i like to make things as easy as possible
so if yours was custom how do you think i should do mine (just useing signal then wtih the booster)
Surely you can get your hands on a 9V battery or two?
Customizing the effect--
-- Find a likely spot in the signal path; EARLY in the signal path. Not at the very input, but definitely not in the power amp section.
-- Test it for DC voltage with a voltmeter. Should be zero (it's after a coupling cap.)
-- Ideally, you would then use an oscilloscope to find the AC peak voltage (help to chose the diodes.)
You probably don't have a 'scope. So try this instead--
-- Find a likely spot in the signal path; EARLY in the signal path. Not at the very input, but definitely not in the power amp section.
-- Test it for DC voltage with a voltmeter. Should be zero (it's after a coupling cap.)
-- Breadboard the diode clipper. Connect one side to the GND. Then very carefully jumper the other end to the signal path. You might have to solder a test lead in place, to prevent shorting the amp with your jumper connection.
DISCLAIMER: Hey--even a running solid state amp COULD have enough voltage to kill you. YOU PROBABLY SHOULDN'T BE DOING THIS WITH THE AMP ON--OR OFF, FOR THAT MATTER. These instructions are for educational use only. THIS IS POTENTIALLY DANGEROUS.
i dont have a voltmeter either so would i just use some diodes htat you have used here?
I didnt know that solid state amps are potentially dangerous because ive disassembled my amps 4 times i think so that concerns me
but doesnt the guitar have a very low (if any) stored electricity when unplugged?
so could i damage my pickups by putting a 9v in its path because they are passive pickups
i was also wondering what would happin if this low volume circuit was turned to a high volume?
the overall question is it this possible to put this in the actual guitar with a booster curcuit with no damage to my equipment?
There's more to it than just the battery...but a boost circuit doesn't need to be very complicated. Here's the Fetzer valve circuit (which itself gives some overdrive, too.) It's just a single transistor and some discrete components. You could add diode clipping to that very easily.
You could try the circuit as-is, but like I said: silicon diodes will clip the most, LEDs the least... Play with different combinations. There will be no danger if working with a low-voltage boost.
Using a correctly-wired boost will not harm your guitar. But you shouldn't try wiring a battery in there by itself--it won't do anything, anyway. I was merely asking if you had access to batteries, since originally it seemed to be a problem...
And the guitar itself poses no danger if unplugged.
i can try that
and the best way is to have asymetrical on both sides
i can get 1 or 2 batteries yes
\i didnt think it did i just needed to double check from someone more experianced
what about if it is plugged in and the amp is running
And just to drive the point home, here's Tim's 'ible on DC welding using batteries. It's a 36V setup. You wanna take a chance with that? Even if it doesn't kill you, it could do major damage...
The coupling cap will remove any DC bias.
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.