#1
I'm going to be making some effects pedals. Any suggestions?

So far this is what I have:

1. Distortion/Overdrive
2. Chorus
3. Phaser

I am probably going to be making my own circuits here. It sorta fits in cause I have to make a project this year (I'm studying electrical engineering), and as such, I won't be using the standard circuits available online.

From what I know, distortion is just clipping of the guitar input signal. Depending on what circuit elements you use to cause the clipping, the quality changes. As I will have to design the circuits from scratch, I'm going to keep it simple. I suppose I'll update this thread as I go along and post up what I have as soon as I figure out an over all circuit diagram.

For the chorus, though traditionally variable frequency delays are used, I'm going to add harmonics to the guitar signal to give it that saturated, 'fuller' sound.

The phaser will probably be the last one I get down to cause it seems to be the most complicated one right now. The idea here is to use some sort of oscillator circuit wrt which I'll modulate the signal to get phase variations. Finally, adding the original guitar signal to the phased signal should get me something close to what a phasor should sound like.

If there are any EE's here or anyone else who has experience with pedals and can tell me something about what I need to do to the signal to reproduce the sounds, it'll make my life a lot easier.

Another thing I wanted to know is that all these circuits will be put together on one single pcb, so should I use one power supply or separate power supplies for the various circuits. I havent looked into the device ratings yet (stupid, I know), so once I do that I will know if one supply will suffice, but other than the device ratings, is there any reason to have different supplies for the different circuits?

EDIT: I'll probably be using Tl 082/84 op amps with 7809 voltage regulators. I dont know which manufacturers regulator will be easily available or the power ratings, but it seems like 9v/1A for the regulator should be enough to power all three circuits. The op amps use something like 35mA/9-14V, so it should all be under the max power rating of the 7809.
Quote by jpnyc
You are what they call a “rhythm guitarist”. While it's not as glamorous as playing lead you can still get laid. Especially if you can sing and play.




Beer is the solutions to the world's problems.

Last edited by hitman_47 at Sep 10, 2010,
#2
1A is will most likely work for all 3 effects. i doubt youd even have to heatsink it.

distortion is definitely the easiest. chorus and phaser...i've never seen a simple chorus or phaser. they are big and very complicated circuits.

so are you building all 3 of these or what?
#3
Distortion/Overdrive is simple, but its a bit of a work out to get one that sounds really nice. The op-amp you chose will work well for that. I personally like the AD712 when I need a dual op amp, or the CA3140 when I only need a single op amp.

A chrous is basically a delay that adds something a bit above the note, or a bit below the note, or both to the signal. You therefore have the option of using a digital chip, PT2399, or an analog chip. If you go the digital route you will need to have a 5V regulator to provide the correct voltage to the delay chip.

The problem in this case, is that with the PT2399 you have to do any sort of modulation at the Vref pin. This isn't a huge issue, provided you make sure your modulation doesn't exceed the voltage limitation of the pin. Modulation at pin 6, which sets the delay frequency, is very difficult due to the fact that you have to use a very low resistance to set delay short enough. I don't have any experience with the analog versions, but I know you have to have both a timer IC and then the delay IC as well.

I can't say much about a phaser as I have never worked with them.

Feel free to ask any other questions and I'll do my best to try to help out.
#4
A chorus and phaser isn't something you want to tangle with to start IMO. Most phaser builds are advanced, as are choruses.

Distortion isn't just clipping, it's a changed output, if the input waveform isn't exactly the sam as the output(with the exception of size), the signal is distorted. Clipping is just a term we use for the change in waveform resulting with part of the waveform being chopped or clipped off. Special care needs to b done when designing a dirt box, just slapping clipping diodes in there doesn't cut it. frequency response before and after the clipping needs to be considered carefully and tested.

A phaser basically goes,
buffer>phase shift>phase shift>phase shift> phase shift> mix
-------->dry signal is mixed with wet at output
that's a rough idea of a 4 stage phaser, 4 and 6 are common.
http://www.geofex.com/article_folders/phasers/phase.html

A chorus combines a phase shifted delayed signal back with the dry signal. The PT does this okay, but is limited in what it can do. Analog BBDs are common and are what I'm using when I design a chorus. Another thing is that I'll be running my LFO IC off of 5 volts to ensure that the waveform isn't too big. Since it's a Low Frequency Oscillator the frequency response of the IC at such a low voltage isn't of much concern. The delay shouldn't be too short nor too long, play with the timing components, find what you like.

I wouldn't worry about the amperage of the regulator unless it's under 300-500mA, most small PS won't put out near 1A of current. A phaser can run off of 9, 12, 15, or 18 volts if your chips can handle it. I suggest running everything but the delay chips and possibly its LFO off of the full voltage. Then including the regulator as needed on the board.
#5
^ Whats an analog BBD? I dont know how true this is exactly, but I was thinking of reproducing the chorusey effect by adding a lot of harmonics to the existing signal. It wouldnt be a classical chorus, but it would give you a similar effect.

The idea that I had here was to use several balanced modulators to obtain the harmonics and then to add them to the original signal. It would give me a richer sound, something close to what I would get from a chorus. It would be simpler than going down the modulation route.

It's also why I want to leave the phasor for last because ther I have no choice but to go for modulation in some form.

Also, as I will have to analyze what ever circuits I use, I'm going to try and keep them as simple as I can and still get the best quality possible.

Is there a particular reason why 4,6,8 stage phasers are used (even no of stages), like constructive/destructive interference or something like that? I'm also thinking of doing an unusual pedal. Maybe add an inductor or something just before the distortion, which should act like a filter of some sort (impedence varies for different signal frequencies before clipping which would give a different coloration to each note as the fundamental frequencies are different). Perhaps an odd stage phaser mixed with the dry signal and a wet stage signal would give a novel sound?
Quote by jpnyc
You are what they call a “rhythm guitarist”. While it's not as glamorous as playing lead you can still get laid. Especially if you can sing and play.




Beer is the solutions to the world's problems.

Last edited by hitman_47 at Sep 11, 2010,
#6
An Analog BBD refers to a Bucket Bridage Delay chip. Its basically series of FETs and capacitors. The FETs are controlled by two clock pulses. This allows the signal to be delayed. Its one way to have delay modulation, but It requires multiple chips

The idea behind the chorus effect is to give the feeling that multiple people are playing at once. This is why you have delay in the effect. If you have an ensemble of people playing the same thing none of them will play the note at the exact same time, or have the note tuned exactly the same. Without the delay you won't get the full chorus effect.
#7
^ It sound like the BBD is something like a set of serial registers looped. I need to check this out, I didnt know you could do something like this in the analog domain!
Quote by jpnyc
You are what they call a “rhythm guitarist”. While it's not as glamorous as playing lead you can still get laid. Especially if you can sing and play.




Beer is the solutions to the world's problems.

#8
Quote by R.G. Keen
The human ear does a huge amount of pre-processing before you get things bubbled up to your conscious mind. It separates thing by frequency, frequency change, and filtering and then pre-identifies a crude number of sources and perhaps direction to the source. Choruses fool the ear by slightly frequency shifted sounds that the ear thinks are multiple sources. This only happens if the time delay is in a highly specific range. Below that you hear flanging (comb filter effects) and above that echo. The simplest explanation of this I've seen is in Panasonic's old BBD data IIRC.


Simply adding harmonics would just make the signal sound more trebly.

Using multiple chips to add modulation is probably more complicated than just using the PT chip or a BBD.

A phaser works off of the phase shift that capacitors cause, the LFO in their design modulates the signal on the device, LDR/LED combos are used, as well as FETs set as variable resistors in addition to the LFO. If you look up a few designs you could probably figure out how they work. Optical phasers are controlled by an LDR/LED combo.

Simple is easy, good is a little harder, but doable, I hope you've got a decent sized breadboard, mine's a bit small for phasers and choruses, I'd suggest investing 20 bucks in a cheap-ish big one.

Analyzing them is relatively simple, you just have to do it step by step, and love trig if you're analyzing a phaser.

Different number of phase stages will give a different tone, some people include a switch to add 2 stages to the phase shift, I've only seen even number of stages in phasers, never odd. This has to do with the feedback if I had to guess without looking at a schematic. Try an odd stage, but be careful of where you stick the feedback, you only want negative feedback with the exception of the LFO.

http://www.smallbearelec.com/Projects/WMouse/WMouse.html
That's a distortion design from smallbear, iirc, he was going for a wah design at first. I'd suggest learning the basics of active filter design, active filters allow you to not need inductors. Which are big, hum susceptible, and possibly expensive, almost guaranteed to be costly compared to a capacitor.

Edit, analog was the original way to do it, tape recorders, oil can delays, and then BBDs. Digital came long after.
Last edited by blandguitar at Sep 11, 2010,
#9
^yeah, lol. Just checked out the BBD chips. Something like that just seems easier to do in the digital domain. Using the BBD seems a little complicated. I'll look into the active filter design. There was a circuit that I'd looked up to do a wah with using an op amp and a capaciter because I'd tried to find a decent inductor at that time and couldnt come up with anything. It was just an idea, I wont be able to use an inductor for sure.

The thing is, that most of the components that I will be able to get my hands on will be extremely cheap. The breadboards, pcbs, op amps etc wont be expensive at all, but they will probably not be the best available. This whole build will set my back by less than $20, so I'm willing to experiment.
Quote by jpnyc
You are what they call a “rhythm guitarist”. While it's not as glamorous as playing lead you can still get laid. Especially if you can sing and play.




Beer is the solutions to the world's problems.

#10
I've been a little busy with exams so I havent had much time to devote to this build. Just finished some preliminary research and I've got some basic ideas I'd like to sound out, let me know if they're good/bad/stupid/workable.

1. Dont want the guitar signal to degenerate, so first I'll be putting it through a differential amplifier. Additionally, it should help remove noise from the guitar signal. Op amps are cheap, and two or three TL 074 should be more than enough for the whole build.

Instead of this, I'm also thinking of just using a 2M resistor in parallel as a buffer so that the circuit doesnt load the signal.

Should I use both, i.e. a 2M resistor before a DA or just one of the two?

2. For the time based effects, Ill need an oscillator circuit to generate my own sine wave. I'm thinking of using a colpitt's oscillator for this. Additionally, I'm also thinking of using a gyrator circuit and a variable capacitor to simulate the inductor required. One question I have here is that will such an 'inductor' work in the circuit?

The advantage with this arrangement is that with the variable capacitor, I can change the modulation frequency thus keeping my effects 'in time'.

3. The power conversion circuit is fairly simple and doesnt need much thought atm. From my experiences with the 7809 so far, I've never had power frequency leakage, but should I think of employing a notch filter to be on the safe side?

4. I was also thinking of splitting the signal in before it goes into any of the effects blocks so that I can use all these effects in parallel if I want to. At the end, a summing amplifier should be sufficient to bring the signal back together, however I'm not too sure of this and any insights would be very helpful.

Off the top of my head, one thing I can think of is that if I use all effects in parallel and then sum them, the final amplitude of the signal might be more than what the op amps are capable of which would result in clipping. Granted, for that to happen it would have to be a 9v pp signal, but could it happen?

5. On the experimental side of things, I was thinking of using phase and amplitude modulation of some sort, but cant really think of anything concrete just yet.

Sorry for the dense post. Hopefully it makes some sense. I'll probably go and buy the components sometime during the week, but right now it looks like I'll need at least a day or two to figure out the circuit diagram. I'm hoping some of you who have more experience with these circuits can point me in the right direction.
Quote by jpnyc
You are what they call a “rhythm guitarist”. While it's not as glamorous as playing lead you can still get laid. Especially if you can sing and play.




Beer is the solutions to the world's problems.

#11
Anybody?
Quote by jpnyc
You are what they call a “rhythm guitarist”. While it's not as glamorous as playing lead you can still get laid. Especially if you can sing and play.




Beer is the solutions to the world's problems.

#12
Long time since I last posted. Thought maybe I'd give a progress report (lol).

I've just finished designing the circuit and bought most of the parts. Need a couple of more thngs to round off but I guess I'll start putting it together soon. In any case, I've procrastinated enough and I have to submit this in 2-3 weeks.

In the end I only ended up doing 2 effects: the distortion and the phaser. Ironically, the way I was apporaching the phaser design, it would have been more of a flanger than a phaser (I was thinking of going the LFO/VCO route which was getting a little too complicated to figure out all at once).

Then I thought of using unity gain low pass filters to get the phase shift only to realize that thats the way it has always been done. So far I havent been able to figure out an easier way to implement the phaser so I'm going to do it that way. I'm implementing a 6 stage phaser. Incidentally, you dont really have odd staged phasers because when you add the wet and the dry signals together, you get notches in the frequency spectrum. For an 'n' stage phaser, you'd get n/2 notches. Which is why doing an extra stage would be a waste because you'd get (n-1)/2 notches with a slightly wetter signal.

The distortion is the interesting part though. After scouring the internet for how distortion works, one thing that came up was that 'full', 'warm' distortion has a lot of even harmonics as compared to cold, 'digital' sounding distortion. I've figured out a novel way to get these even harmonics into the signal that I'm quite proud of. At the very least, I havent seen this particular method of getting even harmonics in all the circuits I've seen so far.

Another thing was the parallel effects chain. At first I thought I'd have to think of a complicated mechanical switching arrangement to mix in the various effects etc, but analog electronics is a vast ocean of knowledge and a simple modification to a summing amplifier is all that was required to change the mix levels, and the series/parallel effects chain.

Also I've added a basic eq to the whole system and an input buffer stage so that the signal from the guitar isn't loaded/sucked dry by the effects.

If anyone wants, I'll put up the circuit diagrams, but they're hand drawn. Maybe I'll also put up some pics/sound clips soon.
Quote by jpnyc
You are what they call a “rhythm guitarist”. While it's not as glamorous as playing lead you can still get laid. Especially if you can sing and play.




Beer is the solutions to the world's problems.

#13
well, in addition to those, a standard yet versatile array are wah, delay, boost/OD, and if you play live, a tuner.

octavers are fun too. if you have all those, you can play just about any form of music with a unique touch (if you use them right)
#14
I'm going to do the wah after I've got these working. The wah actually seems to be a lot simpler. One thing I wanted to experement with there was using a capacitor to emulate an inductor (there are op amp based circuits that can do this), but I dont know how that would really effect the sound. Some wah's get their characteristic sounds because the inductors are of poor quality and add their own brand of harmonic distortion to the over all sound.

As for the boost, the eq circuit I've decided on seems similar to a boost. Its only a 3 band eq (0-200, 200-8000, 8000-up), but maybe I'll do something else with it.

With the delay, it gets a little complicated. That will take some time to do, which I dont really have at the moment. Maybe something to look at in the future. I was thinking of experimenting with some effects, but I can't really think of a sound that I couldnt do with these effects if done right.
Quote by jpnyc
You are what they call a “rhythm guitarist”. While it's not as glamorous as playing lead you can still get laid. Especially if you can sing and play.




Beer is the solutions to the world's problems.

#15
I badly need some help in trouble shooting the circuit. I've built the distortion block so far but Im not getting the output.

When I plug in the input jack (from the guitar), all I get is this constant hum. I mean like, the 60 hz hum but significantly amplified. Also, I'm not getting any output from the guitar.

When ever I play a note, nothing happens; all I get is that annoying hum. I've looked over my circuit a couple of time but I cant figure out whats wrong. Can somebody help me out?
Quote by jpnyc
You are what they call a “rhythm guitarist”. While it's not as glamorous as playing lead you can still get laid. Especially if you can sing and play.




Beer is the solutions to the world's problems.

#17
Quote by CodeMonk
the simplest pedal to build is a fuzz.


Very helpful. Honestly. I couldnt expect a better, well rounded off reply. Thats pure universal truth. I mean, wtf, here I am; I've been building this simple pedal for the last 3 days, and in reply to a fairly technical query, I get absolute, brilliant universal truth. Thank you for wasting 5 minutes of my life. Brilliantly done.
Quote by jpnyc
You are what they call a “rhythm guitarist”. While it's not as glamorous as playing lead you can still get laid. Especially if you can sing and play.




Beer is the solutions to the world's problems.

#19
Now boys, behave.

If you want help, you'll need to post a schematic and pics of your build (both sides of the board).
#20
Quote by CodeMonk

Shit...I was just trying to help a little. **** off

Bad time for it. I blew two transformers trying to figure out what was wrong with the power supply when I read that comment. But seriously? Fuzz is the easiest pedal to build? What were you trying to achieve there?

I had wired the ground incorrectly. Now I have to wait until I can get another transformer to test the damned thing again. I hope it works this time around; I've spent way too much time on this build already.

As for the schematic, I'll put a picture up but it goes something like this:



Input-> Audio Distribution Amplifier-> (Distortion Block)

Distortion Block:
 -------------------------------------------------------------
|                                                             | (-) 
From audio amp -->Diode-> Low Pass Filter (fc=6500hz) -> Differential Amplifier -> 

Diode->LPF(fc=6500hz)-> Output to Summing amplifier.

Quote by jpnyc
You are what they call a “rhythm guitarist”. While it's not as glamorous as playing lead you can still get laid. Especially if you can sing and play.




Beer is the solutions to the world's problems.

Last edited by hitman_47 at Dec 4, 2010,
#21
Draw the schematic out on paper or in a Spice program and post that here and it will help us with future troubleshooting. Its always very helpful to have that as I can quickly derive some idle voltages to have you check. If they are off then we can trouble shoot from there.

Its kinda like a divide and conquer route. When I work on tube amps the first thing that gets checked is always all of the anode voltages. If one of those are off by a lot then I start branching out into that area to determine whats wrong. Spice simulations are also helpful because that eliminates the need for me to derive voltages for you, or for you to derive them. If spice says a voltage at idle should be something, then it usually is pretty spot on.