In reading the post about Runoffgroove and Jake Nagy’s Blue Magic and seeing that no less than 8 people wanting a schematic that was taken down, I feel an opportunity to issue a challenge. Before going further, I want to say that I in no way mean to diminish or demean the great work that Jake (whose designs you should always check out, Jake has a golden ear and a remarkable sense for designing good tone) and Runoffgroove have done and I feel that you should ALWAYS credit those who helped or inspired you to create something (you want people to do that to you don't you? 8) ) . But my challenge stems from the fact that we know something good can come from a MOSFET driving a JFET with filtering in there. So, I challenge those willing to try their hand at going beyond building and getting into the whole DIY FX “roll your own†experience.
When I first got into this hobby I guess five years ago on Aron’s original site, there were a ton of new designs coming out. Jack released the minibooster, Aron’s released the Shaka stuff, Doug and Ed built on the Mini-Tubes and Aron’s work, Gus was slamming out simple home runs constantly, R.G., GFR. Ed. R. etc. There was a lot of work going on, everyone bouncing ideas off each other; the emphasis seemed to be more on creating than building old designs. Sure, everyone started out modding something, building a FF or cloning something else, but eventually most went to designing, and nearly all of what came out was better than what you could buy commercially.
So, I am using this post to try to help those who want to try to get into designing their own by using the Blue Magic and PepperMill’s basic topology as a base. Again, without belittling what Jake and Runoff have done.
Well where do we start? First off, we know that a MOSFET into a JFET with some filtering can sound good, so we will use that. Now of course this leaves a TON of information we need out but if we do a little work we can get something drawn up that will at least work well enough to form a base on a breadboard that we can experiment with to build a great effect.
So, we start with a blank sheet of paper and start drawing up a rough schematic of the circuit. First thing to do is the housekeeping. All effects need some common things to work but the most basic are: a power supply and click prevention. So, we know to put pull down resistors on caps on the input and output and we have to create a power supply.
We start with our “Vinâ€, put it over or through a reverse polarity protection diode (everything here is a choice, from resistor values to cap types, here we choose whether we sacrifice a little bit of safety or voltage with our choice of diode arrangement), then through a small resistor say 100 ohm, then over a large cap, 10uf to 470uf will do, to filter and clean the voltage and then we have a “V+â€. Now we know we won’t need a specific bias voltage as would be the case with an op amp in the circuit, but if we did, put V+ through two 10ks, take the voltage from the junction of the resistors, filter it with another cap and then we would have a “Vbiasâ€.
OK, we have a power supply and reverse polarity protection so we are ready to start with the actual circuit. We start with a high value resistor, say 1 Meg, to pull down excess voltage, into a DC blocking/AC coupling cap to bring our guitar signal into our circuit without it’s own DC bias voltage there to mess up all of our soon to be hard work. We do not know the value of this cap specifically yet so we will pick one before we go to the breadboard. But that is later.
The next step is to figure out how we are going to bias our first MOSFET stage. Glancing through any EE textbook should get you at least three different ways to bias any transistor, looking at the internal schematics of commercial opamps will blow your mind as to how many ways there are to bias a transistor stage. What we need right now is to come up with something that works, is fairly easy, and allows for adjustment of the bias of the stage because we are experimenting and need control over bias.
I would choose what is called constant voltage biasing to start with, then if later on I wanted to do work on tightening up the sound or changing specific characteristics of the circuit’s distortion, I can go back and mess with the bias arrangement of the stages. For now we will put a pot with one outside lug to V+ the other outside lug to ground and the wiper going to a high value bias resistor, 1 Meg ought to cut it, high enough to not load down the previous stage and not too high to induce noise. This resistor goes from the wiper of the bias trim pot to the junction of the input cap and the gate of the MOSFET. Also we will put a high value cap from the wiper to ground to further filter the bias voltage from any noise. The value of the pot can be arbitrary but with a little thought we can save ourselves some power. A MOSFETs base draws no current, so we can use a higher value trim pot as we only need voltage, not current, say 100k or 470k; the cap off the wiper should filter out any noise that the higher value trim pot induces.
Now we have some more questions to ask ourselves: Do we want high gain or a specific lower amount? It is a distortion so we will want high gain. Do we want to run in the high or low current section of the devices transfer curve? For now this is arbitrary but we need to choose one to get it to work off the bat so I will choose high current, which mean lower drain and resistor values (opposite for low current). Next, do we want the gain to be stable or a little unstable using the devices internal inconsistencies to add character to the distortion? If we want it stable we use a source resistor for its negative feedback and a cap to bypass it to jump up the gain. If we want a little unstable we leave resistor off the source and go straight to ground. For this experiment I will pick stable high gain using high current. So we pick some values that fall into this range. I would say 20k for the drain resistor, 1k for the source resistor and a 10uF cap to bypass the source resistor and allow the whole frequency range to be boosted. In may be worth noting that in modifying the frequency shaping of your circuit, you are most likely better off starting out experimenting with the values of the caps and then fine tuning with the resistor values.
Ok, so we have a MOSFET stage with a tune-able bias with high current and high gain, good enough for rock and roll right now, remember we just want to get this thing up and running, we can dicker with the tone to our heart’s content after that.
Next we need to put in another DC blocking/AC coupling cap at the drain of the MOSFET and then from there to the drive stage which will allow us to adjust how hard we hit the JFET stage with our now amplified signal. For now we will want the whole range, so we can find a sweet spot if there is one, and add tapering and scaling resistors later to limit the Drive pot’s influence to that range if we want to. Again, getting it going is paramount right now, so we will leave any filtering networks out for now and go back to that once it is on the breadboard. From the coupling cap, we send the signal to an outer lug of the Drive pot, the other outer lug to ground and the wiper to another DC blocking/AC coupling cap to ensure that the Drive pot doesn’t interfere with the biasing of the next stage. As for values for these parts, again, the coupling caps will be changed later almost assuredly so their value we will wait on, the pot however is a bit tricky. We do not want to load down the previous stage and rob ourselves of the gain we worked so hard to get and we do not want it TOO high so that it makes for a hard source and is loaded down by the next stage. I would pick 100k for now, the 20k output impedance of the MOSFET stage won’t be loaded down too much and it won’t be too high for what will most likely be a high, 1 Meg, input impedance of the following JFET stage.
Ok so now we are at the JFET stage. All of the questions I put forth earlier about the MOSFET stage apply here too, but the biasing is a little different as the JFET functions different than the MOSFET. A JFET needs its gate to be LOWER than the source where as a MOSFET needs it to be HIGHER. This pretty much ensures that I will be using a source resistor (as I am using a single supply V+) on the JFET stage. No biggie really. In fact I am going to use the same set up to be able to control HOW MUCH lower the gate is than the source, as well as being able to adjust the bias voltage at the drain without messing with the gain structure by using a trim as a resistor on the drain (though there is no reason you can’t do both).
So I pick a stable, high gain, high current stage, keeping in mind that JFETs have significantly less gain available than MOSFETs, so I pick a 5k drain resistor, 470 ohm source resistor and the same 10uF source bypass cap. Again, these values are arbitrary mostly, I just want to get the thing up and running, I can come back and mess with them later and almost certainly, I will. Add another DC blocking/AC coupling cap at the drain and that stage is finished.
Now we come to an important point, the tone control, not that we couldn’t have put one earlier, and when it is on the breadboard whose to say we wont? No one. The question lies in the fact that if we put one in now we will not hear the distortion from the basic circuit itself unadulterated, it will always be filtered through the tone control. So, for now I would skip it and come back later once I like the overall sound the distortion is giving me.
SO to finish the circuit on paper, I put in a simple Level pot (audio taper of course), again 100k for the same reasons, take the output from the wiper, no need for a pull down resistor in this case and BINGO! We can go to the breadboard.
So we start by putting the circuit on the breadboard, power supply first, using our multimeter to test to ensure we are getting the right voltage out. Next, we put in the circuit, all we do not know are the coupling cap values but we do know the input impedances of the stages and knowing that we can figure that anything in the range of .001uF to .1uF will work. Once we complete the circuit, we twiddle the bias trims until we get the drains to read ½ V+ (and checking and fixing things if we can’t), then we plug in our guitar, turn the level pot all the way down, plug into our amp, increase the level pot and check out our initial creation!
Now I have no idea what the above circuit I sketched out will sound like but I am 99% sure you will get something out of it worth messing with. The important thing here is to start taking notes and going through the range of all of the pots and trims noting what sounds good overall and also under specific conditions, what don’t you like about the tone? The distortion? Etc.
Once we have our notes, we have a base to start messing with parts. Is the sound woofy and bassy? Try lowering the coupling cap values and the source bypass cap values. Is there too mush high-end hash? Try putting in small caps in different places; across drain resistors, at the gates, off the drive pot wiper. Does the sound get muddy as you turn down the drive? Try putting a small cap from the “hot†lug of the Drive pot to the wiper to keep highs strong as the pot is turned down. Now is the time to start trying filter networks in places, noting “sweet spots†if any in the Drive pot’s travel, the effect of different bias points on the tone etc. Then you can decide if you want to add a tone control, if you want to buffer the tone control or buffer the tone control’s output, or maybe even the Level pots output (I like this myself, tend to lose less highs as the level is turned down). If you want to try and tighten up the over all distortion you can mess with the drain and source resistor values, you can try adding negative feedback or crack open that textbook and find a different way to bias the stages. Not to be trite but the possibilities are literally endless.
Basically, you are now ready to create your own distortion EXACTLY how you like it, you may get lucky, you may stumble on your tone quickly, or it may take you forever with complicated filter networks and biasing arrangements. It is usually when you are perfecting something that you come up with a new “building block†that other people can grab and use in their designs. Then when you are done, perf it up, throw it in a box, make sure it works, and then draw up the schematic, give credit to those you helped or inspired you to create what you did and post it if you want. Hopefully you will teach someone else and maybe even get paid the ultimate compliment by having someone use your design on stage in front of people somewhere.
I hope that this little write up will help some of you make the jump into creating new stuff on your own and keep this hobby growing and to maintain our communities ability to come up with circuits that are miles ahead of what is available commercially.
Respectfully,
Jay Doyle
Nice work Jay!
Just to add a little to what you've said, with the MOSFET bias method you mentioned you can replace the resistor from the trim's wiper to FET's gate with a 1Mpot. One outer lug connects to the trim's wiper, the pot's wiper connects to the FET's gate and the input signal is coupled via a cap to the remaining outer lug. It functions as a 'drive' control and simplifies things slightly.
This is very exciting Jay!
I'm in! I was looking for an excuse to make a MOSFET driven circuit. Jake's circuit is one of the best for low drive... so I might make mine high drive :twisted:
amen jay,Should be interestimg I love working with fets.
mike.
Quote from: aronI'm in! I was looking for an excuse to make a MOSFET driven circuit. Jake's circuit is one of the best for low drive... so I might make mine high drive :twisted:
I wouldn't expect any less Aron.
Got Gain?
:D
Cool, thanks for this great text. I will give a try when I got a little time.
FWIW, because of this forum I went from "designing" this:
http://www.joefus.com/oldstuff/images/4trans.gif
to this:
http://www.joefus.com/pedals/images/bf2beta.gif
(shameless plug)
Back then I just wanted a distortion pedal that was "mine". I really don't play a whole lot of guitar, but I'm more interested in the electronics "challenge" anyway. (I always need something for my brain to chew on...) I do like the sound of high-gain distortion so that's what I've focused on, constantly trying to improve the sound.
I think trying to build your own stuff is a "funner" way to get into electronics, since there are so many possibilities, and you learn stuff along the way.
This forum is great because you can get answers pretty fast when you're stuck, as well as the vast amount of information on this and other related websites. Just knowing someone might try out (or even package) my circuits gave me an excuse to do more and more.
Now I feel I understand electronics in a different way than the typical engineer, who may understand the physics and math -- but perhaps not the fine-line between what sounds good and bad, and the magic of making something that's "yours".
hi,
thanks for the inspiration guys.
I would love to be able to design my own effects- but how can I begin the design process? I mean, I can follow a schematic like a 'recipe', but in terms of 'why' and 'how' I just dont have a clue. Well, thats not ENTIRELY true, but I would still love some advice as to going about designing my own pedal.
Thanks, and hope the New year is great for us all,
Cheers,
Luke
This is how I look at electronics knowledge:
I have many compartments in my memory, and on each one there is a sticker saying what it does. Say "clip signal" and I open the compartment and see two back-to-back diodes, get what I mean. If I want amplification, I see an opamp, etc. If I want a tone control I see a big muff tone control :twisted:
So think of what you want your design to do, and think of how you're going to accomplish that. You don't have to pull it out of your brains, the internet is here to provide you with all the info you need! ;) Just don't forget to put pulldown resistors and DC blocking caps in ;)
But i'm tired of making fuzz pedals. I fancy something a little more different that still sounds cool. It's time to invent a new effect! :D
I'm doing this as we speak(with Runoff Groove helping). I'm personalizing a Peppermill/Blue Magicish thing for my own selfish needs & I think everyone here should also!
Regards
RDV
Jay,
That was awesome! You've just armed me with the knowhow to not only create a great distortion, but to modify just about any other pedal to suit my tastes!
Quote from: javacodyJay,
That was awesome! You've just armed me with the knowhow to not only create a great distortion, but to modify just about any other pedal to suit my tastes!
Not to take anything away from Jay's excellent post, but coupling caps, input caps, filters etc.... were in the simple mods for
years!Please check out the page if you haven't. In fact, please view my homepage:
http://www.diystompboxes.com/pedals/index2.html
In the simple mods, check out secrets of stacked stages.
Quote from: Lukehi,
thanks for the inspiration guys.
I would love to be able to design my own effects- but how can I begin the design process? I mean, I can follow a schematic like a 'recipe', but in terms of 'why' and 'how' I just dont have a clue. Well, thats not ENTIRELY true, but I would still love some advice as to going about designing my own pedal.
Thanks, and hope the New year is great for us all,
Cheers,
Luke
buy breadboard and parts to expirament with.
look at alot of shematics. like for instance lets say you like the low end of a metal zones eqing but you dont' like the actual distortion htat it is making. so like i believe it was mike burgundy made a eq section that is sperate. so now if you know you like that low sweep then you look at the freq response range of it. and other circuits that you like. now lets say you like the cascading sound of other pedals. or amplifiers then you konw you need mulitple stages at low gain to make your toenails smile.
so you piece all of htis together piece by piece. knowing what filters you need from each piece to get a particular sound wich adds to the variable equation that will be your design. now say you like the germanium cliping that happens in the feedback loop of a ts9 but yo also like the hard hitting crunchiness of a marshall guvnor . so you add in both at different stages. so now we have this design.
guitar>>>>>>preamp section 1 gain 20>>>>>>preamp section 2 gain of 20 one germ diode pointed one way in feedbackloop.>>>>>>premap section 3 gain of 20 germ diode facing opposite the first one.>>>>>>metal zone style eq.>>>>>>gain section 4 gain of 20>>>>>>gainsection 5 gain of 30>>>>>>redleds.>>>>>>load resistor>>>>>>preamp section six variable gain of 25 to bring up volume back to just above unity.
now there we have a 6 section gain stage. in my head using a cmos 4049 chip. with variable gain in section 1 with fixed gain in sections 2-5 with various germ diode clippingn from a ts9 mt2 eq and red led clipping ala the guvnor and other pedals. and a recovery stage.
so basically we have a hybrid fuzz distortion pedal here that is mulit staged has cmos and opamp boosting in here. and utilized three or more designs from pedals. but it is a unique design and each stage allows you to see how each section effects the signal and see what you like.
so now if you konw you like to distort your bottom end all the way down to 32hz. and that rocks your little world then you can make it a staple of what you like and incorporate it in your designs. whcih will give you a sound in your head of what it should sound like.
and you go from there.
Thanks for the reminder Aron. Most of those tips/mods didn't make sense to me a month or two ago. I suppose that Jay's post was right place/right time where things clicked for me, after hanging out here at the stompbox forum for the last couple of months. Obviously, it wouldn't have clicked without all the help everyone here has given me (especially Peter Snowberg).
Quote from: javacodyI suppose that Jay's post was right place/right time where things clicked for me,\
I had exactly the same deal with these circuits. I had Anderton's EPFM for YEARS! I even tried to build them (I GUESS since they were hilighted and have notes on them). The funny part is I don't even remebmer!!!!
Anyway, it wasn't until his 35 projects for guitarists that one day it all made sense. After that, reading a schematic was much easier.
Sometimes it just takes a phrase said in a way that makes sense.
When I learned to program in Pascal, there was this wonderful writer; I can't remember his name. For some reason, I understood things the way he explained them.
I learned a lot from his books, Pascal, Object-Pascal, C and C++.
After that, I always chose a book - not so much on the "promise of contents" but on the writer's style and approach.
I wish I could remember his name....???
Anway, hope you know what I mean.
Yeah, I gotcha. I had the same experience learning to program Perl.
Also, all the information in the world is useless, if your mind is unprepared for it. :D
I tried programming in Visual basic but even that gets me confuzzled :?
Quote from: smoguzbenjaminI tried programming in Visual basic but even that gets me confuzzled :?
Try realbasic! Very cool!
realbasic.com
Quote from: aronQuote from: javacodyI suppose that Jay's post was right place/right time where things clicked for me,\
When I learned to program in Pascal, there was this wonderful writer; I can't remember his name. For some reason, I understood things the way he explained them.
I learned a lot from his books, Pascal, Object-Pascal, C and C++.
After that, I always chose a book - not so much on the "promise of contents" but on the writer's style and approach.
I wish I could remember his name....???
I wish you could remember it too! Most times my eyes just glaze over when I start reading a programming book ....
Realbasic looks cool! I'm gonna try the demo :mrgreen:
QuoteI wish you could remember it too! Most times my eyes just glaze over when I start reading a programming book ..
Darn it... his name is Tom.....rrrrrrrr!!! All my programming books (old ones) are in storage......
He wrote a number of Turbo Pascal, Turbo C,
I think his name is Tom Swan! Anyone else have his books?
http://www.amazon.com/exec/obidos/tg/detail/-/0672484226/qid=1073189705/sr=1-1/ref=sr_1_1/103-1072879-8137464?v=glance&s=books
Quote from: smoguzbenjaminRealbasic looks cool! I'm gonna try the demo :mrgreen:
Realbasic is pretty cool.
I own both the windows and macintosh versions. There ARE bugs, but they are trying to fix them.
Lots of 3rd party support! 8)
Quote from: aronNot to take anything away from Jay's excellent post, but coupling caps, input caps, filters etc.... were in the simple mods for years!...
...In the simple mods, check out secrets of stacked stages.
Yes, read everything on Aron's site, especially the FAQ. Read until the ideas become second nature. Remember a bunch of us learned this themselves, without EE classes, so you can too; just remember that it requires work on your part too, no one here has the inclination or time to teach you EE.
My point was to just outline the way to start rolling your own. Boscorelli has a great little section on how to start, you think of your idea and write down what it is an what you want it to do. From that description you then create a block diagram which incorporates your ideas and creates a system of "building blocks" that will fulfill the needs of your idea. From there you build it up on the breadboard and tweak until it sounds good. This last part is the important part, most ideas will work if solidly designed, the question is will it sound good? Tweaking out bad tone and creating good is hard. Then once you have it sounding good you can go onto the building stage.
Hopefully in my post I was able to make the process look easier than it sounds at first to those a little intimidated. It is possible to do this knowing a minimal amount of EE. I did not mean to imply that what I was saying was new, just write up a little bit on the
process of rolling your own. There are a lot of questions you need to answer from the beginning to end and knowing which are the important ones to answer first is the key.
Jay
Nice thread, Jay. There's one thing I'd like to add, though.
After awhile of doing this type of design, you will start to develop a sense for what the basic skeleton of the circuit needs to be to get the desired sound. Maybe a mosfet stage driving a jfet, maybe a pair of mosfets, etc. You'll develop an ear for what each component sounds like. Then you can use certain components for their favorable characterisitcs.
I think that was what I wanted to say. Hope it got through.
Quote from: GaryAfter awhile of doing this type of design, you will start to develop a sense for what the basic skeleton of the circuit needs to be to get the desired sound. Maybe a mosfet stage driving a jfet, maybe a pair of mosfets, etc. You'll develop an ear for what each component sounds like. Then you can use certain components for their favorable characterisitcs.
This is very true, just as doing an "opamp shootout" with a TS style circuit will give you a better idea for the differences between opamps, the more you use single stages or configurations the more intimate you get with the sound of those stages. You get a "feel" for the sound ingredients of a MOSFET stage, then a feel for it at high or low current, with a bypass cap and without, at different bias points or configurations etc.
As with any learning venture, the more you experiment the more you learn that is useful later on.
Jay
I haven't done enough work with MOSFETs. I kind of stayed away from them since they seemed to "blow up" so easily... (Static electricity) and this is in Hawaii (humid).
Quote from: aronQuoteI wish you could remember it too! Most times my eyes just glaze over when I start reading a programming book ..
Darn it... his name is Tom.....rrrrrrrr!!! All my programming books (old ones) are in storage......
He wrote a number of Turbo Pascal, Turbo C,
I think his name is Tom Swan! Anyone else have his books?
http://www.amazon.com/exec/obidos/tg/detail/-/0672484226/qid=1073189705/sr=1-1/ref=sr_1_1/103-1072879-8137464?v=glance&s=books
thanks Aron - I checked out Amazon, looks like Tom hasn't written a programming book for a while ...
What are (or were?) Peppermill and Black Magic? Sights? Pedals? If they can give me more input into designing my own pedals I'd love to know about them.
QuoteFor now we will put a pot with one outside lug to V+ the other outside lug to ground and the wiper going to a high value bias resistor, 1 Meg ought to cut it, high enough to not load down the previous stage and not too high to induce noise. This resistor goes from the wiper of the bias trim pot to the junction of the input cap and the gate of the MOSFET.
Jay,
Can you explain a little on what that 1MEG resistor does? How does it affect a previous stage when:
This is the first stage in the pedal. If so, does it matter?
If it's the 2nd of cascaded stages, do we need a pot for every stage and how does that 1M resistor affect a previous stage? What does it load down exactly? It is limiting current?
Thanks,
Aron
Aron
Been playing with MOSFETs for years, and never managed to blow one up yet.
A humid environment ought to be safer - less risk of static.
Quote from: aronQuoteFor now we will put a pot with one outside lug to V+ the other outside lug to ground and the wiper going to a high value bias resistor, 1 Meg ought to cut it, high enough to not load down the previous stage and not too high to induce noise. This resistor goes from the wiper of the bias trim pot to the junction of the input cap and the gate of the MOSFET.
Jay,
Can you explain a little on what that 1MEG resistor does? How does it affect a previous stage when:
This is the first stage in the pedal. If so, does it matter?
If it's the 2nd of cascaded stages, do we need a pot for every stage and how does that 1M resistor affect a previous stage? What does it load down exactly? It is limiting current?
Thanks,
Aron
Aron,
That first one Meg resistor is just the biasing resistor. By previous stage I meant anything from another pedal to the raw guitar signal itself. It sets the input impedance of the stage.
No, you don't need a pot to do this you can figure it out with resistors, but I feel that using a pot allows you to dial in any bias point possible for the stage and therefore you can use it to tune the bias easier than switching out resistors. Once the effect is ready to come off the breadboard you can decide whether you want to keep it a trim or use resistors, either is just as good, though the trim allows you to adjust it. I use the same idea with the JFET but it is in fact less useful there with a small source resistor, but having it on the breadboard can't hurt I figure...
Sorry if what I wrote was confusing.
For MOSFETs here are a few things to keep in mind:
1. They have a SUPER high input impedance, literally a physical barrier of metal.
2. They are static sensitive.
3. They work like FETs but bias like BJTs meaning that they don't draw any current through their gate but their gate needs to be higher than the source by some amount.
The trim pot allows you to dial in the voltage needed in #3.
Let me know if you have any other questions.
Jay
Jay, I can just sum it all up by saying: "thank you"
I hope it's eanough...
Regards,
Dan.
:P :P :P :P :P :P :P :P :P :) :D :lol: :P
No Problem. Stay tuned, I am in the middle of putting the information down in a paper...
With some pretty pictures :D
Oh, well then please do E-Mail me when it's done... :)
Phorhas@Icqmail.com
Thanx once More... :)
When it comes to the "dry" parts of design - the electronic theory - I'm at a total loss. I couldn't bias a transistor if someone had a knife at my family's throat. What I DO have a good sense of though, is how it all fits together as a system.
For me, the challenge is not so much building something new in terms of what copyright law would acknowledge as different. Rather, the challenge is to design things that DO something different, which, in some respects can be a whole lot easier, OR a whole lot harder.
I've made stack of distortion units, and at a certain point it's bit like eating fries somewhere different every meal for a month or locking yourself away with a mountain of porn. It eventually all looks, feels, sounds, tastes, the same, or so minimally different that you can't justify the existence of most of it.
Once in a while, though, you get something that makes you think and play differently. For me, THAT is the challenge. I was playing through a Univibe-modded phaser last night, and the difference between how you play with a phaser and a Univibe is really quite remarkable. Where the obvious moving notches in a phaser get you to steer away from holding notes that might be suddenly obliterated by a notch, the more watery and less peaky sound of a Univibe encourages you to hang onto clean notes longer because there will be no sudden dips to erase them. Similarly, I can see why Adrian Belew is as fond of his Foxx Tone Machine as he is. The octave function begets a certain style of playing that doesn't occur to you normally, and the way octaves arise is something different than a mere fuzz.
So, the challenge is not to make the same thing over again with different parts and slightly different EQ-ing. A less fizzy Fuzz Face will not change how you use the pedal, merely how much or little you need to tinker with the amp's treble control or how pleasingly the sound records. The challenge is to think first about what would throw a curve into how you approach the effect. For me, this often turns into performance controls, rather than core design elements, but it can translate into core design elements too.
How much planning and intentionality is involved is another thing too. Ansil, for instance, tends to prefer "design by monkey wrench", tossing in obstructions to normal functioning, in the hopes that something new and different will emerge. At the other extreme, some of the Z-Vex effects are painstakingly planned out to be new and different. Both are valid.
Why have we generally drifted from "true" DIY and innovativeness to "clone-only"? Well, first, let me say that I don't think we have. There have been as many fascinating and innovative ideas here in the last few weeks as there were in the same time period in 1998. Hell, maybe even more. I'm reading a book now entitled "Enabling Knowledge Creation" about how large successful organizations bring people together informally to develop concepts that no single person could ever do on their own. Satisfyingly, this forum tends to illustrate many of the best practices outlined in the book.
Are there more "clone-only" people than in the past? Yeah, I think so. Partly that reflects an increasing technical competence on the part of musicians (or maybe an increasing musical interest on the part of electricians!). Partly that reflects an increasing awareness of the value of historical pedals and especially the virtues of analog and all its quirks. Partly that reflects a desire by current musicians to have as broad a tonal palette as possible, incorporating both the full range of the known in addition to a smattering of the unknown. And partly it reflects the fact that a forum like this is not such a well-kept secret anymore.
Is there a virtue to attempting to accomplish the same goals in other ways? Sure. I was looking through a huge stack of distortion schems in bed last night (I can only take so much of the Golden Globes) and stumbled across Jay's assorted boosters that are essentially discrete op-amps. Do we need something as simple as an op-amp made more complicated? Sure. Experimentation with effects ideas is good but experimentation with making the familiar behave more predictably (or unpredictably as the case may be) is also good.
Ultimately, the challenge to pedal freaks and DIY-ers is the same as the challenge to musicians: How much do you want to play "the classics" the way they deserve to be played, and how much of an obligation do you have to do something entirely different?
Happy Australia day!
:shock: Wow. Well after all that, my words are going to sound infantile :mrgreen: Ahem.
It's time to bodge some wierd and cool circuits together! :P
Mark,
My point wasn't to help to design yet another distortion. It was to show those who may be intimidated with starting to design with a blank piece of paper and an idea how to take that idea and turn it into an effect. The process you use to design a new distortion, if done thoroughly and thoughtfully, should be the same process as designing a new phaser, or a combination tremolo/phaser that can have LFOs synched together or seperate for each effect.
I was merely using Jake's idea of a "MOSFET into a JFET" as the basis for showing the process. And my paper will address that process more specifically.
I do understand your point though.
Jay
Thanks a lot for an unbelievable piece of information. Of course i'd love to see that paper when it's finished!!
Jay,
Sorry, I am still confused. OK, here's our 1MEG pull down resistor to avoid pops right?
>OK, we have a power supply and reverse polarity protection so we are ready to start with the actual circuit. We start with a high value resistor, say 1 Meg, to pull down excess voltage, into a DC blocking/AC coupling cap...
Ok, here is where I am confused...
>...with the bias arrangement of the stages. For now we will put a pot with one outside lug to V+ the other outside lug to ground and the wiper going to a high value bias resistor, 1 Meg ought to cut it, high enough to not load down the previous stage and not too high to induce noise. This resistor goes from the wiper of the bias trim pot to the junction of the input cap and the gate of the MOSFET.
So we have a 100K pot with outer lug to V+, other lug to ground (Voltage divider) then wiper to a 1M resistor which goes directly to gate right? OK, so this gives the signal a DC offset/bias.
Assuming the above is correct, what does the 1M resistor do? I assume if we adjust the 100K pot to middle on a 9V source, we get 4.5V out of the wiper. Now, what does the 1M resistor in series do when connecting to the gate?
I'm so used to seeing voltage dividers on the gates. On subsequent stages, do you need a gate resistor to ground or does this 1M suffice?
I hope you understand what I am asking.
Aron, take a look at the EA trem at runoff. The input stage is along the lines of what Jay is describing.
Because different MOSFETs have different thresholds a trim is used to set the bias. The down side to this is that input impedance will vary according to whatever resistance is on the pot - it’s not consistent from circuit to circuit - so a resistor is tied from wiper to gate and the input coupled directly to the gate. The 1M sets the input impedance (the pot being decoupled by a large value cap) and you can make it whatever value you desire.
Hope this helps.
Yes it does. OK, it is what I was thinking.
Thanks!
Exactly what gez said. Exactly. If you don't have a cap bypassing the source resistor, you can put a cap from the source to the junction of the wiper of the trim (where it joins the 1 Meg resistor) and that bootstraps the stage raising the input impedance. What is happening in that case is because the same input signal is on the source as is on the gate; the same signal appears at both ends of the 1 Meg resistor, so no voltage drops across it and it appears bigger than it is.
Anyway, what gez said... :D
Quote from: Mark HammerI've made stack of distortion units, and at a certain point it's bit like eating fries somewhere different every meal for a month or locking yourself away with a mountain of porn. It eventually all looks, feels, sounds, tastes, the same, or so minimally different that you can't justify the existence of most of it.
Guilty as charged. I have a stack-o-distortions that seem to get less interesting as time goes on. The pursuit of clipping and eq in and of itself can get dry and tedious after you have built a few of them.
However, I keep discovering new aspects of it, things that as you mentioned, come more under the "changing the way you play" category. For instance, I'm not too interested in any clipping effect that won't clean up reasonably well or radically change your tone in some useful way with the guitar volume. Anymore I'm more interested in the "organic" remote control style of playing.
At this point I'm pursuing more of the "feel" and "dynamic responsiveness" aspects too, those wonderful intangibles that are difficult to describe, yet we all know what they mean. If I could control harmonic blooms, compression, and clipping with picking strength and pick angle alone (and maybe guitar volume too), I would be well on my way to my "holy grail" setup. I'm looking for the ultimate "expressiveness" in the sound because that is what inspires me to play differently and breaks me out of ruts in my lead playing.
So the fun for me is the pursuit of the "handles" that control these aspects. So although it seems like I'm in the "build another distortion" rut, I'm really working on some fine and subtle details well below the surface that make something "feel" much more "expressive" IMO.
But I still intend to build that EZ Vibe someday. I -swear- it...
Doug
Doug,
In research, the first step to making advances is to describe something, then figure out how to predict it, and finally how to control it. With natural science, you start by describing phenomena in the real world, and then move on to studying it closely enough to predict how it will act/behave. In the realm of technological research, you start out by describing either a set of operational goals/objectives that you want the technology to accomplish, or by describing a particular problem you want to solve.
With a domain as overworked as distortion pedals (just ponder for a moment the sheer number of commercial designs and prototypes that have existed over the years, and then add in all the protoypes and experiments that this community has contributed over the past 10 years), the challenge seems to be thinking up something more for the *act* of distortion to do.
As you rightly point out, "perfecting" a distortion turns quickly into rather banal EQ/gain parameter-chasing. So what is it that we want distortion to be able DO for us that it doesn't do at the moment? If you can adequately describe those goals/objectives, then you're halfway home to developing a new device.
You mention expressiveness, and this touches on a perennial problem of distortion devices. It gets called dynamics, touch, feel, and a host of other names. Ultimately, the gist of it is this, however. Distortion devices generally function by running out of headroom. It is the lack of headroom that results in the change in harmonic balance or addition of harmonic content. At the same time, distortion is used by musicians, whether tenor sax players, flute players, or guitarists, as a way of conveying additional emotion. I've gone on ad nauseum on Ampage about the biologically evolved connection between vocal raspiness, perception of emotion in others, and instrument distortion. We *use* distortion as a means of conveying emotion (because nature predisposes us to and the instrument permits it), but where conveying *more* emotional information requires the option to inject greater contrasts in both harmonic content and volume level, distortion boxes require us to sacrifice volume contrasts for distortion. I have a feeling this is why many players prefer creating distortion at the amp rather than with a pedal, because doing it at the amp permits both types of contrasts to be exploited (I submit Jeff Beck as my evidence), but enough said about that.
In sum, I'd say that what many players want from their distortion-enabling aspects of their rig is the capacity to:
a) maximize contrast possibilities in both volume level and distortion amount (i.e., broader range of each)
b) disconnect the one dimension from the other so that it would be possible to growl quietly and scream cleanly, in addition to being able to purr and roar.
An important qualification of these two principles is that the transition across the spectrum of distortion degrees needs to be smooth and seamless, the way it is with the human voice. One of the more common complaints about fuzzes of the 60's was that if you didn't play loud enough, they sounded bad or crapped out. So it is not just range of possible contrasts in volume/distortion, but how one moves across that range, leading to...
c) smooth gradual transition in amount of distortion as a function of playing/picking.
Again, I emphasize that the next step is successfully begun by asking yourself "What is it I need this technology to DO for me?". Armed with fully articulated goals, THEN one can start figuring out what circuit tweaks or core technologies will lead most effectively to attaining those goals.
To put a fine point to the last couple of posts, I was in the studio all day Sat. & Sun. making a Demo/E.P. and I took every box I have(& I have a bunch), and other than using my version of the Stupid Box(thanks again Brian Marshall) for a Stevie Ray-ish tone into my clean channel, nothing sounded better than my Marshall's lead channel into a 412 with my Les Paul cranked. Nothing came close distortion-wise for a heavy sound. Nothing. I was shocked and amazed because that's certainly not usually the case onstage. I did however use my Dr. Quacky on a screaming outro which was killer.
Regards
RDV
Hi. This discussion of the place and types of distortion is excellent.
Recently, I was feeling depressed about everything, including the lack of "magic" in any of my distortion pedals. None was offering anything special. Sure, the Ge fuzzface(FF) was dirtier, and the CMOS fuzz was "tubier", and the Distorion+ was "rockier", but I'd reverted to using my TS9 most of the time, and could find little joy in any of my distortion pedals.
Then, about a month ago, I was building one of Aron's "Rockets" (for someone else). I tried a trick that RG had recommended - piggybacking 2 transistors to get low gain. The sound was amazing. Not since I built a Blackfire or a Bazz Fuss had I heard such a unique distortion. The thread about it on this forum extended for days, involved dozens of replies, and much experimentation and theorising. The new sound was described as "organic", "amazing" etc. My much-loved Ge FF has now been replaced by a better sounding piggybacked Si FF.
The moral of this story is that there ARE new sounds out there. You never know when changing a resistor or adding a transistor will bring about an amazing change in a circuit. That's what's great about this hobby. Even better - someone like me, with no electronics training, can stumble on something significant. That's fun.