The amazing secrets of Krank Distortus Maximus

This distortion pedal has a fascinating history, an unusual circuit design, and great sound. It's hard to believe that just one LM386N3 chip plus two bipolar transistors at the input and output can sound like this, even without clamping diodes!

Yes, that's not a typo. We are used to the fact that the LM386 is a power amplifier chip for headphones or a tiny speaker. But in essence, it is an operational amplifier. It can do a decent job as a part of the overload effect.

Krank Amplifiers is a boutique brand for expensive and rare tube guitar amps that are no longer in production and, therefore, are very desirable and collectible.

Tony Krank started his career as a guitar technician. He has collaborated with star guitarists like Slayer's Kerry King and Metallica's James Hetfield. From repairing amplifiers, Tony naturally moved on to modifying them and then making his own ones.

In 2003, brothers Tony and Kent founded Krank Amps in Tempe, Arizona. Their amplifiers came out as very innovative and unique. Of course, they were intended for the extreme metal and hard rock genres.

The amplifiers had two channels: clean (KLEEN) and cranked (KRANK). If your last name is Krank and you make amps for metal bands, these are the most appropriate names for amp channels!

In fact, the last name of brothers Tony and Kent is Dow. But Tony played for a long time in The Kranks and became known as Tony Krank. So, he passed this surname to the amplifiers.

The Krank channel provides very high gain and a compelling growl sound, mandatory for killer thrash metal riffs.

And the Kleen channel of these amplifiers has no extremes: not too sweet or sparkling. Just what you need for clean-sounding losses in modern progressive metal.

Not all guitarists liked the high-gain sound. Krank amps, like any other, take some getting used to. In particular, it takes some time to achieve such a balance of treble and presence settings to sound musically pleasing both on stage and in recording.

Ten years ago, Krank amps and cabinets were a common sight on stage, but now almost all of them have gone for good. There are several reasons for this.

Firstly, the amplifier design wasn't durable enough to survive a concert tour, and breakdowns occurred quite often.

Secondly, many touring guitarists have started to favor three- and four-channel amps, not to mention those who switched to digital.

Thirdly, and most importantly, many copies of Krank cabinets, heads, and amps have been bought by music producers. These devices were successfully used in studios when there's enough time to set up the best sound; structural strength is low on the priority list, and the quality of recording for thousands of pairs of headphones and speakers is a top goal.

In 2007, Krank introduced two new pedals at NAMM. The first was fine, yet unremarkable, Krankshaft Overdrive. The circuit was just a rip-off from the Ibanez Tube Screamer TS808.

We have a separate post about Tube Screamers and their numerous variations. I think that every guitarist absolutely needs at least one Tube Screamer. It could also be Krankshaft Overdrive: a great-sounding, well-designed, and well-made pedal, just like your average Tube Screamer.

Much more exciting and unique was the second pedal—the Distortus Maximus. With a full three-way tone stack and an authentic Krank high-gain channel sound, this is indeed a pedal everyone should at least try!

Building your own copy is not difficult; the pedal circuit can be called very simple. The guitar signal path begins with the amplifier stage on transistor Q1. This seems to be the most common cascade with a common emitter, but it has a few features affecting the sound.

The BC550C is a low-noise transistor with a high current gain of 420 to 800. Look closer at the resistor values that set its base bias.

Typically, in preamp stages, these ratings are made equal or almost equal so that half the supply voltage is at the base of the transistor, and the stage operates in class A mode with minimal distortion.

There are also circuits with no lower resistor, and the resistance of the upper one is selected so that it provides the desired quiescent currents of the collector and base.

This was often done on battery-powered radios to save battery life. DIY superheterodyne from the post on Regency TR-1 is no exception. All high-, intermediate-, and audio-frequency pre-amplifier stages in the circuit of this receiver are designed exactly like this.

And in the Krank Distortus Maximus circuit, the resistance values in the base circuit are designed to ensure the minimum quiescent current of the cascade. For this reason, they differ tenfold! This results in AB mode, which is very close to pure class B.

In this mode, the imperfections of the already low-noise transistor will be completely minimal, which is crucial for a high-gain amplifier. And also, significant nonlinear distortions will occur, which in this case will give the sound asymmetrical compression, even to the point of slight limitation. And these distortions have a pleasant "tube" tint.

One day, I will try to rebuild the Q2 preamp stage of the BOSS DS-1 according to the design of the first stage of the Distortus Maximus. This should respond more pleasantly to the powerful signal of classic hot-rodded and modern humbuckers.

The LM386 chip in the Distortus Maximus is configured to have maximum gain; pins 1 and 8 are connected. They are also connected to a tone-correcting chain consisting of a 100-ohm resistor and a 47-uF capacitor to ground.

Next, we see a complete three-way tone stack and a seemingly ordinary output buffer made according to an emitter-follower circuit. But this buffer is also unusual.

No lower resistor would set the base voltage of transistor Q2 along with the upper 100 kilo-ohm resistor. Therefore, we have not just a voltage follower but a circuit stage that introduces distortion with a "tube" character into the output signal!

This pedal is, to put it mildly, a circuitry masterpiece. Behind its apparent simplicity lies a deep feel for guitar sound; the design utilizes the nuances of transistors and LM386 operation. The video below captures its actual sound.

This is probably my best homemade distortion pedal to date. It is practically an entire single-channel amplifier in a box. I never cease to be amazed by the sound obtained from such a small pile of simple parts!