Archive for the ‘General’ Category

Colorless writings, part 16 – The Transistor

Monday, October 13th, 2014

A transistor? As in electronics 101?

Yes. A transistor. A rather simple device that we’ll find in almost any stompbox, in form or another. Transistor is usually a triode. Meaning that there are three terminals and all those three terminals have their own purpose. You know, a tri-ode. Three terminals. As opposite to diode – di-ode, which has two. Simple analogy forward to tubes that may be pentodes and so on. Transistors can be used for a few different purposes, most notably as switches and signal amplifiers. The latter one is is the one i’ll be focusing on. And we usually can find two distinct types of transistors – NPN and PNP. I’ll be focusing on NPN type, but i’ll talk more about this later. Just a second ago i said that transistors have three terminals. These are called a collector, a base and an emitter. The base is where you apply your signal. Collector collects and emitter emits. Can’t get much simpler than this. When i was introducing myself to the magical little devices, the obvious thing to assume was that the emitter emits the amplified signal and collector collects the juice for this amplification. This is not true. Emitter emits the juice to inside the device. Collector collects the amplified signal and this is the output we can get out if it. Somehow i don’t think i’m the only person who’s had this misconception when getting to know his/her transistors.

Let’s take a look at the subject in even simpler terms. Semiconductors in general work in a very simple way. The voltage and/or current is passed through the semi-conducting material in one direction, but the other. are you familiar with a diode? For a diode, we have anode and cathode as the terminals. Cathode is the end with a stripe on it.. If we apply 9V DC voltage to the anode, we’ll end up having a voltage that’s close to 9V DC on the diode’s cathode, as this is the direction the diode passes voltage and current. But if we apply the same voltage to the cathode, the anode won’t have any voltage, because the diode doesn’t pass the voltage or current in this direction. This is the fundamental, basic idea for all semiconductors. That’s what they do. Once you get this, everything will start looking a lot simpler.

How does a diode get us closer to a transistor?

I just explained how a diode works. There’s not a lot of options how that third terminal is connected inside this device called a transistor. Since i’m talking about NPN type transistors, think of the transistor as two diodes. Both anodes tied together as a base, one cathode is your collector and the other is your emitter. NPN stands for negative, positive, negative. Now, if we apply that 9VDC voltage to the base, or two anodes tied together, we’ll have near 9V on both, emitter and collector. This doesn’t amplify anything, but it shows us the idea behind the transistor. Let’s play with a thought of it doing some amplification without going into mathematics. To begin with, transistors amplify current, so we’ll need to give it some. Our guitar output is good source of low voltage AC signal and it’ll have hot and cold leads. For this example, cold is the same we have as DC ground, so  we can use just a single signal path. As we’ll need to apply some voltages to get the device doing the work, we’ll need to place a capacitor in series with the base and apply the signal to the free end of that cap. This cap will pass the signal to the base, but block the DC voltage from the base from getting to your guitar. Now it all comes down to bias. I know. It’s a concept that isn’t as clear as pancakes for most people. To get the amplification going, we’ll need to have a voltage on the base, which has to be smaller than the voltage on collector. If we take 1M resistor from the 9V supply to the base and another one with 100k value from base to ground, we’ll end up with something like 0,8V DC voltage on the base. That’ll work. For the emitter, we’ll take a small resistor from it to ground. Let’s say 470 ohm. Finally, we’ll need something like 10-12k resistor from supply to the collector and an output cap to block the near supply voltage from our real output.

What happened?

We applied low bias voltage to the base with our signal. Ground potential at the emitter and the bias, or reference voltage pushed the signal towards the collector. Which collected it and made it to pushed the signal out with way higher current than what we applied to the base. That’s the amplification of  a small signal in the simplest possible way. Four resistors, two capacitors and a single transistor. This is the configuration we’ll find inside EHX LPB-1 Linear Power Booster.Sure. This information doesn’t take you very far. But i’m hoping it’ll offer enough snack for thought, so that digging deeper may become slightly easier. There are tons and tons of good articles and videos around the internet if you feel like going further.

Colorless writings, part 15 – Fuzz vs. Overdrive vs. Distrtion

Saturday, September 13th, 2014

I found myself in very weird situation. Today, i simply had nothing to say. But i can’t pass on a colorless writing, as that would mess up my OCD. I did start on one more demanding subject, but i realised i won’t be able to finish it without messing up my schedule. So i just needed to drop that topic (it’ll be featured as part 16)  and write something else instead. I needed a subject that would be easier to cover. So why not bring up this age old question about how to categorise the effects that produce distorted tones.

Fuzz versus Overdrive versus Distortion?

Exactly. How do we tell which one is which? How can we be certain that a Tubescreamer is in fact a overdrive effect rather than a distortion? We can’t. It’s more likely all in the marketing speak than in real world electronic designs. Let’s start with the early days of distorted tone. Legend has it that certain guitarist for a group called The Kinks used a razor blade to slash a cheap combo amp’s speaker cone to get that distorted sound for one 60’s hit recording. Later in the sixties we were blessed with a ton of fuzz effects that were designed to mimic that broken speaker cone. The most basic fuzz design was (and still is) called a shunt-series feedback amplifier. The circuit was well known before any fuzz pedal was  ever produced. The fact that a guitar’s output is enough to push this circuit to sweet distortion wasn’t exactly mentioned on the text book the circuit was originally from. But there you have it. A very first electronic guitar effect that gives out a distorted tone.

In early seventies other types of pedals started to emerge. Some were called boosters and some were called distortion boosters, but they were still mostly boxes with fuzz sounds coming out of them. Later in the seventies, the dawn for Tubescreamer, DOD OD250, MXR Distortion+, Boss OD-1, DS-1 and ProCo Rat widened the spectrum of distorted tones available. That may not be complete list of units that suit the bill, but it’ll get us going. It must have been in those days when the split happened.

Let’s look at the OD250 and Dist+ first. These two pedals share the circuit topology with each other. Main difference is the type of hard clipping diodes after the gain stage. OD250 uses Si diodes with lower voltage drop and more volume, while Dist+ has Ge diodes with higher voltage drop and less volume. This means that the sound of these is very close to each other. Nevertheless, the former was (and still is) marketed as Overdrive/Preamp and the latter as a Distortion. You guys must now be getting my point?

Boss DS-1 works in same principles as the two, but it has more driving stages. ProCo Rat has similarities too, although its gain control isn’t even close. I’d like to point out that some Rat versions had a text “fuzztones for connoisseur” printed on their circuit boards. So is the classic Rat a Distortion or a Fuzz?

The debate may still be going on which one was the first to take clipping diodes to the feedback loop of non-inverting amplifier and creating softer clipping. Usual answers to this 40 year old debate would be TS808 and OD-1. I have no idea which was the first, so i’m not going to waste my time in speculating about that. There are hundreds and hundreds forum posts about this subject to be found on the interwebs. In case you are interested. These pedals with soft clipping are usually referred as overdrives. Although, there are numerous distortion designs out there with similar clipping diode arrangement.

To sum it up?

A fuzz. This should the easiest one to point out. No clipping diodes and no opamps. Just a bunch of transistors driving the hell out of each other in order to create clipped or distorted signal. But is it that simple? As usual, no. Take a EHX Big Muff Pi for example. This design (and its hundreds of derivatives) is often referred to as a fuzz. Another nice examples would be Anderton’s tube Sound Fuzz and Colorsound Tonebender reissue from the 90’s. I’d call all of those distortions or overdrives rather than fuzzes.

Going forward with the Distortion. This one may be simpler. Hard clipping diodes. But even here, this may not always be the case. There are pedals like ZVex Distortron that is usually considered a distortion, but to my ears it sounds (without going any further on its electronics) a way more like an overdrive. As the earlier example with OD250/Dist+ shows, the design with hard clipping could also be called just about anything.

Overdrive? Now this leaves us with soft clipping and thus, these should be easier to identify. But no. If we take a look at good ol’ Way Huge Red Llama overdrive, we’ll see it’s way closer to Anderton’s Tube  Sound Fuzz than any other OD we’ve seen. There are a number of JFET-based overdrives too. These may not have clipping diodes in them at all, but they will still offer full soft clipping sounds.

Is that what you call a sum of the subject?

Well. Maybe not. But it does show us one thing. There isn’t one clear, or even fuzzy logic to when we call a  circuit a fuzz, overdrive or a distortion. It’s all in the head of designer at first – then in the heads of the people at the marketing department and after that – in our heads.

Sure it would be easy for me to think that these pedals are fuzzes, these  pedals are overdrives and these pedals are distortions. But that won’t do. We can’t define something that’s completely undefinable. And since there is not a way to define which is which, we all may face the situation where our newly bought a) fuzz sounds like a distortion, b) fuzz sounds like an overdrive, c) overdrive sounds like a fuzz, d) overdrive sounds like a distortion, e) distortion sounds like a fuzz, or f) distortion sounds like an overdrive.

I’m going to leave you with one summing thought – there is no way to define or categorise which is which, from electronic point of view. It’s all in the marketing and in our heads.

This does easily apply to all the other pedal genres as well.

Sometimes a redo should work.

Friday, July 19th, 2013

It’s been a while since i used this domain for something useful. Most of my old writings were completely obsolete. All that is gone for good. I still dig the simple, minimal layout of this page, so complete overhaul of the content should suffice. Instead of talking/whining about this f*d up world in general, i thought i should use this site for something that i, well.. love.

Couple years ago i started building pedals by accident. Since then i’ve become somewhat a freak when it comes to guitar effects. I’ve studied a lot designs and made even some of my own ( I do not know everything about electronics, nor do i think i ever will. However, i do know theory to some extent and i have this gut feeling which tells me what value component will do what in where and why.

Anyway. The point of this overhaul is quite simple. My collection of new(ish) and vintage pedals seems to be ever growing. So why not write about some of them. My goal is to write about a pedal once a week. We’ll see if can keep that up… That’s enough of this crap.