How to Use a JFET as a Buffer in a Guitar Distortion Pedal - DC To Daylight
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- เผยแพร่เมื่อ 19 มิ.ย. 2024
- In the previous episode of DC to Daylight, we worked with JFETS. In this application-based episode, we're making a prototype guitar distortion pedal, using JFETs as input and output buffers. We go over the basics of making a distortion pedal, some points of interest in typical topologies, and point out subcircuits that affect the tone of your guitar along the way. Let's get shredding!
Discuss the episode and ask Derek questions over on the element14 Community: bit.ly/3TtsP8a
Also, check out Clem's vacuum tube guitar distortion pedal project! bit.ly/3TrKlcE
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#0:00 Welcome to DC to Daylight
#0:58 Distortion Pedal
#2:06 Voltages
#3:20 Schematic
#9:25 Breadboard
#10:07 Shredding!
#11:19 Give Your Feedback
#jfet #distortionpedal #guitarpedal #guitarpedals #overdrivepedal #fuzzpedal #fuzzpedals - วิทยาศาสตร์และเทคโนโลยี
Straightforward, I must say.
I am interested in revisiting the flip-flop.
I am too. I will definitely add it to my to-do list! -Derek
Very nice circuit analysis. Thanks.
Thanks Anthony! -Derek
Nice and warm sounding distortion !!
Wish I still had my old strat to try on it. Thanks Donald. -Derek
Nice chops man.
Thank you. -Derek
When I built pedals back in the late 80s, I had a lot of success with using different diodes such as OA79s (Germanium) to induce softer clipping, which introduces more even order harmonics than silicon which is primarily odd order. So much fun was had for such a simple circuit. Crazy things ensued beyond that!
Hi Tristan. I wish I had some old germanium diodes to test.. later realized that I had some old Ge transistors that I could have used the base-emitter junction as diodes. Might have sounded better... Someone made a video recently comparing red/blue/green LEDs, Si, Ge, zeners, etc.. There were subtle differences, but my ear couldn't pull it out. Thanks for the info on harmonics. I'm going to have to try that part number on my own. =Derek
@@AmRadPodcast Good point on the BE junction. Germanium are probably way less common these days than they were "back then". I've got a big bunch of weird old diodes that I picked up on a whim for some low wattage "terrible as possible blues" valve amp idea I had. I've never tried LEDs, however I'd imagine that there's SO many things that are possible with the availability of different clipping options. I'd better not talk myself into projects, because I'm sure you know how that might get....! Oh no...here it comes...
@@jim9930 There's all sorts of weird and wonderful combinations that can be achieved, definitely. Making them usable across a range is quite a trick, as they easily become very on-off. I recall RA Penfold publishing a nice dynamic distortion transposing input characteristics onto the distorted signal, that sounded great in principle.
That was cool. I love a nice jackson. I have 2 from when I was younger playing the technical death metal but now I'm a prog guy
This is actually my daughter's guitar. I donated all of my guitars during the pandemic - what was I thinking? Anyway, Jackson is my go to guitar for shreddy shred. -Derek
Oh now that is a project to give s try!
This would make a nice kit. -D
This video Rocks!!
Thanks Isan! -Derek
Nice!
This is great, it's not something I've looked at before but it's inspired me to look at making one for a friend who loves his guitars, thank you. Can you make the schematic available to download please, it would be easier to view than pausing the screen?
Awesome! Before electronics school (and the Internet) I tried to reverse-engineer the foot switch circuit from a cheap Boss pedal and got discouraged when I saw that it went to a bunch of transistors. The flip-flop transistor arrangement looked scary so I gave up. I never did revisit it after school. I was super happy to see you touched on it here.
The DS-1 has a little cap across the clipping diodes. Maybe to kill some of the over 20kHz harmonics so they don't cause intermodulation distortion?
Would a little demo of harmonics (say, of a proper overdriven pair of 6L6 tubes compared to a distortion pedal output) be something people would find interesting? That was another thing I really wanted to try if I ever got an audio-frequency spectrum analyzer.
Howdy Jim. Yesssss! I really liked the Boss bypass circuit with discrete components which is why I wanted to try that out here.. unfortunately, I had to abort, and finish the core of the video. I really wanted the flip flop to work!
I believe that the cap bypassing the clipping diodes was to attenuate higher harmonics as you mention. I've never tried it.
If I had the time, I would totally use my DSA to compare the harmonics for a list of non-linear components. Tubes, Si, Ge, Zeners, different colored diodes. I had watched a video years ago, where someone did a sound comparison, but I'd like to SEE the spectral components on a screen for fun. That'd be pretty a pretty niche topic, but you never know! Later! -Derek
Epic! Few days ago I did clone of Electro Harmonics OD GLOVE which is totally outstanding. In this instead cliiping diodes used N-MOSFET 2N7002. The sounds of this is simply amazing. I had never guess it could be so difference and so fantastic.
So you removed the clipping diodes and Used N Mosfet 2N7002, and what did it do differently?
@@waynegram8907 Probably its a main difference. I can't put link and image here yt immediatelly delete post. You can check in Derek thread on the element14, which hi shared in describe. So yes I guess 90% work is done by Mosfets. Be precise I did little clone of GLOVE, now I inspired in the other distortion I'll try change 4148 diodes on to this mosfets :D Difference is total, pleasse check any GLOVE test on the YT. It got a very low self noices level, very wide distortion set from normal guitar by little overdrive/overdrive/distortion/hard distortion to fuzz at the end. And all of this have very warm(rich) TUBE AMPLIFIER SOUNDS.
Could I ask which software you use to draw the schematics?? Thanks! Amazing video
AND you can shredd as well 😁
I think you got the explanation of the tone control backwards. When you increase the value of the potmeter the cutoff frequency goes down.
Darn it. I went back and watched it.. sure enough, I got turned around backwards when explaining it on the bode plot. Thanks for pointing that out! -Derek
One modification to the hard clipping circuit that we rarely see is a tail resistor on the diodes. Considering how simple the mod is, I'm surprised that I still haven't tried it myself, but I've thought about using something like a 100 ohm pot in that position to vary the "hardness" of the clipping, from full-on clipping to something more akin to the plate saturation of an overdriven Class AB valve output stage. I've also considered experimenting with separate tail resistors to get asymmetrical distortion similar to those small Class A valve amps that many of the earlier rock guitarists used in the recording studio.
Hi Peter, this would be an interesting mod - I'll have to try this. The other thing I wanted to try, to soften the clipping, is play with the slew rate of the op amp... "over amplifying" the signal to the point where the op amp can't keep up, and limited slew rate comes into play.. maybe rounding off the signal, then it's attenuated before sending down the chain. I'll try it one of these days. -Derek
@@AmRadPodcast Thanks for the nice reply! I actually came up with the idea when I was looking for ways to simulate germanium diodes, and the results were all tail resistors...but not actually implemented in hardware, just simulated in SPICE.
Neat
Did you ever figure out why your fet analog switch setup was squealing? Would love to see what all happened with that.
Talking about Jfets, a few days ago I've build a simple buffer using a jfet and another using a opamp. Using any of them, the pedal before the buffers makes a big pop noise when I switch on the pedal. I can not find a real solution on it, does somebody has an answer to solve it?. I have build a three jfet stages overdrive and the sound is really good.
What does capacitor C10 do?
Why didn't you hook the switch to the VDD? I assuming VDD is a external power supply, like a battery. You're still using energy even if it off.
Hi Mike. In a real product a switch would be connected to the external supply.. this was mostly for a demo (how to build a pedal with a JFET). Good point though! -Derek
Maybe I'm mixed up, but this looks more like a fuzz box with its clipping diodes.
A distortion pedal overdrives an amplifier. It's hard to tell with the 1000s of different types on the market.
Hi A3Kr0n. I believe that a fuzz pedal drives the clipping diodes with a higher amplitude, making a very harsh square wave, and is indiscriminate when it comes to frequencies which are clipped. To me, a regular ol' distortion pedal, clips the signal at a "gentler level", so almost rounds off the input waveform instead of sharply clipping it. When you look at the waveform on a scope, this is pretty much what is seen. I don't think fuzz pedals make use of frequency selective distortion (adding poles in the feedback loop).
The overdrive pedal, to my knowledge, for example Boss' ancient OD-1, used asymmetric diode configurations in the op amp feedback loop to simulate asymmetric clipping of tube amplifiers (search for the schematic to see). The goal was to get get the gritty distorted tube sound at lower volume levels - back in the early days of tube amps without master volume OD circuits, when you didn't want to crank it up to 11 just to sound like AC/DC! If you've ever heard a 70's era 100w marshall stack at full blast, it's a world of pain.
In short, they all use some kind of non-linear semiconductor device to make the clipping occur - at what amplitude, how "hard" that clipping occurs, and what frequencies are affected, determine what kind of distortion pedal you have... that's my opinion anyway! -Derek
What about a pedal series, showing how other guitar effects are done?
I would love to do that. I'll put that on the radar. Thanks! -Derek
ELEMENT14, How do the SLEWRATE of the op amp add more distortion and it also alters changes the frequency response? The slewrate is just the time interval it takes for the op amp to take the input signal to the output signal its just a timing issue in nanoseconds. I don't know why slewrate will add more distortion and change the frequency response of the input signal on the input pin to the op amp, can you explain more in a video lesson ?
When you have low slew rate it take longer time to change the output voltage. So as the volumes increases the bandwidth drops.
The slew rate is the maximum speed that the voltage can change at the output (not the stage delay of the opamp). For the 741, it's about 0.5V/μs. It has the effect of turning large signal outputs of any shape into triangle waves because the output simply cannot change any faster than a ramp going up or down at 0.5V/μs. The higher the frequency and the larger the signal, the more attenuated the triangle wave becomes.
@@RexxSchneider Distortion meaning taking a sinewave input the op amps slewrate will cause the sinewave input to be a triangle waveform on the output, but this is called waveshaping not distortion this is a misinformation term. I think he meant to say waveshaping not distortion. Slewrate is the speed/time interval it takes for the op amps output voltage to change. If you look the the op amps input pin and output pin using a 2 channel Oscope there won't Delay in time but there will be a shift of the instantaneous voltage point won't be at the same point as the input voltage to the output voltage because they will be at different points in the instantaneous voltages
@@waynegram8907 The definition of distortion is simply altering a signal. You are mistaken to think of it as waveshaping. We reserve the term "waveshaping" for signal processing that we deliberately introduce to produce a desired effect, and normally we control the extent and type of the distortion that we add. In the case of slew-rate limiting, distortion occurs in an uncontrolled manner, which really doesn't fit the concept of waveshaping. So, no, he _did_ mean to say distortion, because we have no control over the distortion introduced by an opamp that is slew-rate limited.
I've already told you what slew rate means, and it *does not* mean a "time interval". The clue is in the word "rate". It represents the maximum rate of change of the output signal, and I've already told you what the typical slew rate for a 741 is.
Slew rate has *nothing* to do with the time it takes for a signal to propagate from the input to the output of an opamp. Please try to get that through your head. If I use a scope to compare input and output signals of a non-inverting audio opamp, the only difference will be the amplitude of the signals, depending on the gain. The phase shift is completely negligible at audio frequencies. There will *not* be _"a shift of the instantaneous voltage point won't be at the same point as the input voltage to the output voltage because they will be at different points in the instantaneous voltages"._ Wherever you've got that nonsense from, please stop reading it before you embarrass yourself any further.
Next make an analog delay pedal
This sounds like a good challenge. -Derek
The 741 typically requires 80nA of dc bias current into its non-inverting input. Where is that coming from? Are you relying on leakage current from C5 to supply that, lol?
It's a sad comment on how much the art of designing with discrete transistors has declined, but it's just not cost-effective to use JFETs like the 2N5458 any more. The part itself is close to obsolete, and each one costs about £1 from Mouser. In contrast the TL074, a quad JFET-input opamp, costs about £0.60 which would replace the input and output buffers as well as the 741 with a spare opamp to play with. The TL074 needs 6mA from ±5V supplies, while the 741 needs ±10V at 3mA to stay within spec (it will work on lower supplies like a 9V battery, but it's not guaranteed). A CD4016 quad switch (£0.50) could replace the routing switches (2N5458) for dry/wet and have two spare switches to play with.
It's fun to see folks still designing around discrete transistors, but for JFETs, their days are probably numbered. Some time, you might like to try the effects you can get when you have 4 high impedance opamps and 4 solid-state switches to design with, for little more than the cost of a single 2N5458. Thanks for the video, it was trip down memory lane.
I came to ask the same for the input bias current.
Yes, the schematic has to be wrong. In fact you can see from the video at 9:37 there is a blue lead from pin 3 to a resistor that goes to the rail, which is different from the schematic.
how long did you figure this out?😂 It's quite complicated.
About 30 years 😉 I've been playing with pedal designs about as long as I've been playing guitar. -Derek
Frantone. Just saying.
Frantone. legit.