Electrical engineering for morons...

[extrejec]

So, you guys are probably going to hate me for asking this, as I'm sure it's been asked a gazillocrunkton of times, but can anyone explain how signal actually flows through the circuitry of a pedal and what the components are doing to it as it passes through? I have this grand plan for building all kinds of crazy effect pedals, but I want to understand what is doing what to what so I can play around a bit as I build... modulating clean tones with distorted versions of itself, feedback loops using only wet reverb signals, delayed pre-delays, &tc.

I know what each component is and what it does, but I don't understand how the subtleties of their effects on audio signals. I've even spent the last few days staring at schematics and can now recognize the general shapes of tone and gain circuits, but I feel like for all I know I'd be better off just buying a kit and assembling something that way. But that's no fun. I'm not building a model airplane. I want to be able to creatively alter a circuit to make it do all kinds of weird sh!t.

This one in particular intruiges me: http://www.schematicheaven.com/effec..._modulator.pdf. It's a ring-modulator. I think my eyes are bleeding from staring at it so long. If it's not too much to ask, a brief description of what's happening in the circuit would go a long way to helping me understand how the rest of the pedals I want to play with work.

Come to think of it what I'm really looking for is a noob's-eye-view of an electrical engineering degree. This seems like a good place to get it. Most of what you guys talk about goes a rather long way over my head.

Any help would be greatly appreciated.

Thanks in advance.

[52 Bill]

This one in particular intruiges me: http://www.schematicheaven.com/effec..._modulator.pdf. It's a ring-modulator.

It looks more like a tremolo type pedal to me.

The first stage is a gainstage with a tone circuit. Then there is a phase shift oscillator that feeds a transistor that is used as a variable shunt to ground out the signal in time with the oscillator.

[Steve Conner]

There is no noob's eye view. If any noob could do electronic engineering, we wouldn't get paid as well as we do. Well, that's what my union told me to say at least.

I agree that this is a tremolo circuit as described by 52 Bill, and a pretty ghetto one at that. If you turn the LFO frequency up into the audible range, it will make an effect similar to a ring modulator. Though to be pedantic, this is an amplitude modulator, while a true ring modulator is a balanced modulator, giving better carrier suppression, which means more weirdness and less of the original guitar tone.

[extrejec]

I don't want your job. I just want to mod my pedals and have some idea of what I'm doing. Trial and error is a great way to learn some things, but I don't have the money to go buying all new pedals 'cause I fucked mine up.

Case in point, the fact that you guys can just look at the schematic and know that it's a tremolo and not a ring modulator. I don't even know how the circuitry of an lfo creates low frequency oscillation. I'm only interested in my own muckings about anyway, so your careers are safe. Maybe...

[Mark Hammer]

The Jen HF Modulator IS a tremolo. But as is the case with virtually all modulation pedals - tremolo, vibrato, chorus, flanger, phaser, et al - when the rate of modulation moves from the sub-audio (<20hz) to audio range, you start to produce what sound like, and probably are, sideband products. In other words, it sounds like a ring modulator to one's ears, even though it technically isn't one.

You can take the most plain vanilla 4-stage phaser, swap out the LFO range-setting capacitor for one around 1/5 the original value, and yu'll get something that sounds just like a "rubber band" when the speed is maxed.

My old blue rackmount MXR Digital Delay has a x100 multiplier on the modulation circuit. This allows you to set the modulation speed well into the audio range (as fast as 1khz) and get all those boingy sounds.

[extrejec]

I see. That makes sense. Thanks.

[Enzo]

I don;t think Steve is worried you will take his job. I think he is more worried you will keep the imprssion we can describe electronics in a couple posts and have you then understand it. ANy more than a 20 minute video can teach you to play guitar.

There is knowing what each part is, then understanding what each component does. I mean by themselves, not as a circuit... yet. What does a resistor do, what does a capacitor do, what does a diode do. Then there is the concept of circuits, various types of those. Then circuits get combined to form more complex circuits. For example, at the heart of an oscillator is an amplifier. it becomes an oscillator when you feed its output back to its input with positive phase. Then within oscillators you need to understand how it works so you can have an idea what frequencies it operates at - that 3 Hertz oscillator might be useful as a trem driver, but your ear can;t hear 3Hz. On the other hand a 3000Hz oscillator would be a piercing high note. Not useful in a guitar amp, that 3000Hz oscillator, but in a keyboard it might be the basis of a great tone patch.

We can direct you to electronics basics, then to circuit descriptions, and so on, but since one builds upon the other, there is no short cut. I have been learning electronics now for about 55 years, and have come a long way since that first crystal radio kit, but I am still learning things every day. You never "finish" learning. And that's the truth, not some cornball pep talk slogan. You won't need anywhere near that long to gain useful levels of knowledge, or course. But you will need to invest some time and effort.

[extrejec]

It's exactly that that attracts me to working with electronics. The emergent and variable complexity of systems as they expand. The only... well, to be truthful not the only, but the major... hindrance I've been running into is in troubleshooting. I've been building a distortion pedal for the last couple of days. See, that in itself should be evidence enough. As near as I can tell a pedal of the ilk that I am endeavouring to construct should not take more than a handful of hours to cobble together and test. Nevertheless, I've been at it for a couple of days, putting it together, plugging it in, tearing my hair out, pulling it apart and starting over again, again, again... I just have almost no idea how the little jiggery-bits interact with each other. I do know what they do by themselves, but not when they're hanging out with friends.

I guess what I was looking for was just a helping hand. I've looked at a couple of sites that gave brief and barely literate descriptions of how certain circuits work, but they've not really been all that much help. Into the bargain the fact that the sites are 5+ years old and their owners are on permanent vacation in Majorca. My big thing is really being able to ask all manner of irritatingly ignorant and ignominious questions. This was the initial appeal of this site. The fact that you guys are not only so massively experienced that you know what more than 7 electro-engineering terms actually mean, but also accessible, well it seemed a wonderful opportunity for me to annoy perfect strangers.

That said, if you know of any good instructional sites I will gladly stop pestering you... for a while.

[Steve Conner]

I've been at it for a couple of days, putting it together, plugging it in, tearing my hair out, pulling it apart and starting over again, again, again... I just have almost no idea how the little jiggery-bits interact with each other.

Well, this is how you learn how the little jiggery bits interact with each other. A schematic on a piece of paper, or a circuit description in a textbook, is NOT the same thing as the actual circuit on the table in front of you. There's a lot of mojo in between, and most of that you learn the hard way, by trial and error.

You use words like "emergent" and "complex system", and if you really know what these mean, you'll know that there aren't many analytic short cuts when dealing with these systems. Having said that, the textbook behaviour of electronics is completely analytic, Laplacean or whatever, simply because that's the only way human engineers can tame it, to make it roll off a production line and bring home the bacon. Emergent behaviour usually only happens when it breaks down. It takes a lot of guts to deliberately provoke it, you get into the realms of circuit-bending and so on. But by the same token, troubleshooting means wrestling with the emergent side. The circuit is always working, it's just not always doing what you think it's supposed to.

I had nightmare circuits like this when I was learning, possibly the worst was a 150 watt hi-fi amp I built from scratch, that just refused to work. I was stuck on it for a month, and I wanted to set it on fire, smash it, but I couldn't because I'd spent over 300 bucks on the parts!

The problem was that I'd used different output transistors to the ones specified in the original design, and I eventually figured out that they needed extra components to stop them oscillating like crazy. These components weren't shown in the schematic I was working from, but other amps had them, so I finally tried adding them out of desperation. And straight away it started working perfectly.

Some schematics are actually wrong and won't ever work. If you're unsure, you can always post the schematic here and ask for advice.

If you have an oscilloscope, it really helps to form that mental picture of what's going on inside your circuit. You can pick one up pretty cheap, and you can always hide it when you have visitors coming. I also strongly recommend you borrow a copy of Horowitz and Hill's "The Art Of Electronics".

And yeah Enzo, that's what I meant. I've been doing electronics and playing guitar since I was about 10 years old, and I still learn something every day in both cases.

[extrejec]

OK. I'm going to take you up on that. Here's what I'm trying, seemingly in vain, to build:



To me this looks like an offensively simple circuit that really should be no problem at all to assemble and get working. I've got all the right parts and even looked up the data sheet for the IC to make sure about power and whatnot. In spite of this, all I can get to run through the damned thing is either what sounds like ground hum or nothing at all.

I feel like I must have something backwards or upside down or burnt out, but it's driving me bloody crazy.

[Steve Conner]

This schematic is only simple because it's incomplete, there's no power supply or input bias network shown. If you're running off a single 9V battery with its - terminal connected to the "ground" node, there's your problem: the op-amp won't have the correct DC bias on its input. (I learned about op-amp common mode range the hard way, too.)

I suggest you go over to geofex.com and read up on virtual grounding, also look for a better Rat schematic:

http://www.muzique.com/schem/pcrat1.gif
(notice the divider generating 4.5V? Simply adding this to your circuit, and the 100k resistor from it to the LM308 input, and a DC block capacitor to the guitar, would probably make it work)

ProCo-Rat schematic. Is it correct? - AMPAGE Archive
(you're not the only one foxed by the Rat)