BRZZLER - Transistor Variable Bias Heavy Distortion Guitar Effect




Introduction: BRZZLER - Transistor Variable Bias Heavy Distortion Guitar Effect

About: Hi, I'm Roland, allround hobby techie, musician, metal head, blues enjoyer, audio engineering and process engineering enthusiast. Im all about the functionality of things. I do care about their looks only in e…

Hi there, this is my first try on an instructable!

Maybe you are a guitar player and always wanted to create your very own 100% personal distortion sound, or you want to see how good a self-built distortion sound can get with not spending more than a few bucks, or you're just keen on gathering knowledge about distortion sounds and how they work, or even all of the mentioned? In either case you might want to give this thing here a try!

However, please be aware it is a few components circuit, it wont compete with a high price commercial product, even after all the polishing, but personally i really was astonished what actually can be done in such a basic way. (you can listen to the test sample with increasing guitar volume pot setting I recorded)

Also be aware that this thing is a kind of high-gain-channel only, you probably won't get a clean sound out of it (unless you remove the transistor and listen to the output of the LM386, however even then you might need to turn down your guitar to be really clean).

Step 1: Working Principle & Theory...

Well i did develop the details of the circuit myself, but the vital spirit beyond, the one that actually does the magic has been brought to me by an epic guy called Rob Robinette. He seems to be a much devoted hobbyist building and modding cars, guns and tube based guitar amps. He really does both the research and the testing and also brings everything into entertaining as educating pictured online texts.

However the great thing that powers my project is that fact that if you drive an amplifying unit (such as a transistor or tube) with bias way off center (meaning: the signal comes not in the middle between the accepted minimum (cutoff) and maximum (saturation) limits of the tube/Transistor, but somewhere off-center), then you get by the asymmetrical clipping a heavy, but still way more harmonic and pleasurable distortion sound than with centered bias (both side clipping). While "Mr. Robrob" was writing almost exclusively about tubes, I'm using a transistor for the trick, i still found it could do something that sounds way different and better than just over-stressing an op-amp.

OK, heres the deal:

> Guitar's signal is fed into an LM386 for pre-amplification (red highlighted path in the schematic). A little less than the minimum 20x gain of the LM386 might had been better (centered clipping occurs to a small extent already here when the guitar's volume pot is set to max, but more on that later).

> Via a coupling cap C1 and a little resistor, The boosted signal (blue highlight) is put on a variable voltage divider that lets you vary the bias from completely connected to ground to completely connected to vdd, depending on the mood and play style, or simply for the experience of what it sounds like in each position. To avoid transistor damage, either use additional resistors or low enough overall voltage to ensure maximum rated base-emitter voltage is not exceeded! An NPN transistor is used here, of course, if you know how to switch polarity you can also build this circuit with a PNP.

> After another decoupling cap from the transistor's collector, The now freshly baked sound can be tasted.

> The switchable bypass cap C3 at the transistor's collector is said to remove nasty distortion bits and boost the signal, however it also depends on my mood whether i like its sound at the Moment or not.

Step 2: Picking the Components

I varied all the passive components in the schematic until i was sure to have the one that sounded best for my needs. In the end, these were:

1x LM386

1x BC547B NPN general purpose transistor*

1x 4.7 kOhm Poti

1x >100 kOhm Poti (optional, for volume control)

2x On/Off-switch, (both optional)

1x 37 Ohm resistor

1x 68 nF cap**

1x 25 µF cap***

1x min 250 µF cap***

- Jacks and cables for signal in & output

- Headphones/sound system


And of course a board to solder or stick it on, together with some connection wires, and if you prefer a nice look, feel free to design what ever kind of housing you like.

Be warned off blindly varying components too much! Under-sized caps and exceeding the first resistor's 37 Ohm might lead to ugly cross-over-distortion (trust me, i love extreme metal, so when I say ugly, i mean its not useable)

I also tried a few transistors and some really gave trashy results. Again, not in a thrash metal "in your face"-sense, but in a "just don't do it, its garbage"-sense.

*I will test my way through a list of >10 kinds of transistors and document their sound characteristics right here:

- BC548C: BAD (cross-over-distortion problem gets worse)

- …to be continued soon!

** If anyone here knows why they always favor foil caps over other types, i would really like to know, because i cannot make out an audible difference...

*** Be aware of the polarity of electrolyte caps! always connect the (+) end to the source/"prior component" and the (-) end to the component that comes subsequently in the signal path. Possible exception: When using PNP-transistors, use your mind or a multimeter to check which potential will be higher and orient the cap accordingly!

Step 3: Putting It Together

Well... Im afraid i have to keep it rather unspecific about how to get the components into a working circuit. All i can say by now is sorry, I have neither a detailed explanation, nor really good pictures, so i hope you can read the schematics and find a good layout yourselves, and I'm sure you will soon have one that is better than mine.

And you will notice a few things from the schematic are missing here, namely: the volume pot and switches (i already told you they are optional) However I am especially sorry about the volume pot, I'm still waiting for a shipment with larger pots, so there might be updates soon. I just guess 500k might be sized too big.

I tried to highlight the signal path also on the breadboard, so you get a better idea what this layout actually does and how it is related to the schematic.

Also don't get confused about the input/output connectors, I'm using a few converters and took those connectors that already had useable cables on them

So.. sorry again for the poor presentation, still - good luck with sticking/soldering!

Step 4: Troubleshooting and Sound Improvement

Wanting to get a heavy distortion effect to work might run you into a variety of Problems (mistakes at component-sticking not counted, which I had plenty of ;)

1. insufficient gain

I will not cover this topic here, because the circuit provided indeed has plenty of gain to feed enormous amounts of distortion.

2. ugly portions of distortion (cross-over, center-bias)

You will face these over a wide range of the bias pot. actually i detected a really really narrow bias range (somewhat close to the 'cold' (GND) end of the pot), where the sound was really good, but i still left the circuit the way it was, because i find it very interesting to listen to different sounds from the whole range of bias temperatures! For those who just want a good circuit i will post my "optimal" pot values (hopefuly) soon.

The point is: all we can do against it is proper & precise component sizing.

3. self-oscillation of the circuit

This is really annoying. high gain amplification plus some combination of resistors and caps can easily lead to self oscillation, which basically takes over the sound system, either completely ignoring the input, so you can even rape that guitar and all you hear is still that ugly buzz, or you hear that buzz whenever your not playing hard enough or all you do with your playing is determine the frequency of that buzz (loud=high frequenzy buzz, silence=low frequenzy buzz, at least had that once - fun for a moment, but not the thing we want)

The solution is - once more - proper component sizing, but it seemed to me like the hi-cut cap C4 reduced the risk of self oscillation by a lot.

4. amplification of radio waves and other noise

noise is all around, so naturally high gain amps will output a lot of it. Let's break that point into 3 major sources of noise:

4.1 Power Supply - more obvious when using power from AC-origin; Any Amp even the high-end expensive professional guitar amps have that little portion of AC-buzz. However, even a battery gives you loud strange noises when not 'capped

The so-called smoothing cap C5 stores temporal excess electrons and feeds them back when the potential temporarily drops. 68 nF is good for battery or usb-power, but you might need to increase the capacity when running it from a wall socket transformator

4.2 noise introduced by (low quality) active parts. Any Amplifier will add some noise. And - hey, I really love the LM386 as an audio amp - its super cheap and has very good noise input, however it might not be so suitable as pre-amp, because any noise introduced there will be even amplified in the following stage(s), so for a really clear sounding amp we might want to spend some dollars on a higher quality, lower noise pre-amp.

4.3 noise from outside: of course, acoustic noise won't bother an amp (unless you have loud enough ear phones ;) however when testing the circuit you might suddenly hear radio stations, even in foreign languages through your amp. that's electromagnetic noise which are a topic in high gain amps!

the solutions here are: proper space management (it might matter if that cap is placed just next to the other one or somewhere on the other side of the board), as well as the absence of metal parts shaped in a way that favors their functionality as an antenna, but even more importantly proper shielding! yeah thats right!

in practice this means:

> use a metal casing

> use shielded cables (most prone to antenna-effect, especially true for the guitar cable)

> when soldering cables yourself, try to cover the soldering connections of the plug with the shielding all around of where you can see the wire(s)

OK, I would consider 4.2 & 4.3 as a "polish" already, but we can still do other things to improve the sound:

> vary the components; and I don't mean vary the value by much, but just a little. some parts are even so sensitive, you might hear a difference when replacing them with another one from the same package with the exact same rating. I guess that's why they sell handpicked paired tubes for the big amps.

> turn down the volume pot on the guitar. don't stop reading here, because this trick does real magic! Although that thought might not seem too heavy metal to you, but the moment i tried to turn down the guitar with good bias and component setting, i really was like "OMG, whats that?!" I mean seriously, when the excess clipping that cuts off the second-or-so harmonics was down, suddenly the sound became incredibly creamy and sweet and i couldn't stop playing because it was so wonderful!

Important to say I'm using a passive guitar, don't think the actives behave the like. But maybe you could use an active pickup instead of the LM386, so only a transistor is needed for the asymmetrical clipping fun, which would make that little circuit even smaller.

Step 5: JAM! Have Fun! Comment!

Whether you just got your circuit to work and want nothing other than grind down the electrics with your guitar, or you are a perfectionist having spent hours and days on the previous step, in which case you probably could teach me a lot of further things to take care of...

I wish anyone who built this thing a lot of fun with playing with a self-built custom distortion sound, as well as insights to how distortion can sound and what makes it sound like it does!

Please leave comments on whatever comes to your mind after reading or building this!

So once more - have fun playing and keep supporting music!

See you around, folks!

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    5 years ago

    Well, one thing has to be honestly mentioned about the sound of this thing: the intonation (plec picking noise) really is crap with max distortion settings, especially when palm muting. Maybe i get to record some evidence of this as well.

    However I'm looking forward to developing a new circuit without an LM386, and I will try to fix this issue there.


    5 years ago

    That's a neat setup, I'd like to see a video of how it sounds when played :)


    Reply 5 years ago

    Glad you like it, thx for the comment! You should be able to download the sound sample (link should be also on the intro page): brzzler_guit_lvl_increase.mp3

    I'm afraid I can't do a video at the moment, still, hope it helps!