Chainsaw

Brutal high-gain distortion

 

 

The Chainsaw distortion rack effect module compares to the original MIJ Boss Heavy Metal HM-2 and the DOD FM56 American Metal pedals.  The HM-2 is at the core of the Swedish death metal tone.  Just add humbuckers and a solid state amp, turn the knobs all the way up, and you're there.  But if you turn it down a bit you might find some of your favorite British metal tones from Iron Maiden and Judas Priest.

 

Description

The Boss HM-2 was manufactured from 1983 to 1991, first in Japan and later in Taiwan.  The two versions of the circuit are nearly identical, with just some minor part changes.  The earlier MIJ model is the most popular, although it is doubtful most could tell the difference between the ones made in Japan and Taiwan.  The HM-2 wasn't really all that popular, but you may remember that the heavy metal bands were just beginning to emerge around that time.  Somehow it caught on in Sweden, and suddenly the price of the older units jumped as players began buying them up for the heaviest of heavy metal tones.

In 1984, US pedal company DOD released the FX56.  The FX56 circuit is basically the same as the HM-2, but some different part values were used and the Low and High controls were combined into a single Presence control.  It continued to use the unique tonestack design of the HM-2, but with slightly tweaked frequency ranges.  The FX56 goes from overdrive to distortion, although perhaps the level of distortion is a bit lower.  The Presence control goes from a subdued, compressed tone to bright and cutting.  With the controls turned up, you'll likely get out-of-control feedback and squealing.

There is a lot going on for a distortion circuit - output buffer, FET input buffer, multiple gain stages, three different clipping sections, and a unique tone stack design that tries to maintain some note clarity in all the sonic mayhem.  We offer some options, but chances are you're looking at this module for that certain high-gain tone.  If so, the options are not needed.  But if you'd like to change it up a bit, no problem. 

This is a very high gain circuit.  Gain multiplies noise.  High gain multiplies noise a lot.  You'll probably want some sort of noise reduction unit to keep the noise manageable.  Humbuckers will also help.  Feedback and squealing will likely be encountered on the highest settings.  If so, just back it down a bit - you have hit maximum gain for your setup when that happens.

 

Configurations

  • HM-2 - compares to MIJ Boss Heavy Metal HM-2

  • FX56 - compares to the DOD FX56 American Metal

 

Options

Some have looked at the tone stack in the circuit and noted that it is divided into three sections, each controlling a different range.  In the FX56 configuration, the Low section has no control.  The middle and High section are tied together and controlled with the Presence control.  In the HM2 config, the Low section is controlled by the Low control and the middle and High section are tied together and controlled by the High control.

About the only popular mod for this circuit is to add a Mid control, separating control of the middle and High sections.  This can be done, but it doesn't really give you Lo/Med/High tonestack controls, as the ranges weren't really designed that way.  Of course, the ranges can also be tweaked.  But part of the unique sound of this circuit is achieved by controlling the middle and high sections together to create sort of an adjustable band control.  It works in the frequency ranges that often make high-gain muddy and less clear.  For that reason, we don't really recommend any of our tone stack options, unless you are familiar with the circuit and know you would like to specifically change up the tone stack.  If you want that Swedish Death Metal sound from the HM-2, then consider it carefully.  You can still get pretty close to the original controls by adjusting the new Mid and original High controls together to the same setting.

  • Mids Control - Separate the middle and high sections of the tone stack and add a new control for Mids.  Can be done to HM2 and FX56 configs.
  • Low Control - Add a Low control for the low section in the FX56 tone stack.
  • HM-2 Tone Control - Change the values in the FM56 tonestack to be the same as the HM2, and add the Low control.  This does not make the FX56 the same as the HM2, as there are several other part differences in other parts of the circuit.  Most of those other part differences are minor, but they do add up.
  • Custom Clipping Diodes - You can change up the clipping diodes in any or all of the 3 clipping sections - soft clipping, inline clipping, and hard clipping.  For each section, you can choose single symmetric (2 diodes total), asymmetric (3 diodes total), or symmetric pairs (4 diodes total), in addition to your diode type(s). 
  • Switchable Clipping Diodes - If you wish, you can switch between two different configurations for any or all of the 3 clipping stages.  You can decide if you want the 3 sections switchable separately or together. 
  • Original Components - For the HM2, by default we will use 2N5087 and 2N5089 BJT transistors, a 2N5457 JFET, 4558D op amps, 1N4148 silicon clipping diodes, and BAT46 silicon diodes in place of the original Ge diodes (similar clipping voltages).  The original used 2SA970 and 2SC732 BJT transistors, an SK30A JFET, M518L or 4558S op amps, 1S2473 silicon diodes, and 1S188FM Ge diodes.  For the FX56, by default we will use the same parts as the default HM2 config.  Some of those parts are the same as the original parts, except the original Ge diodes were 1N34, BJTs were sometimes 2N3906 and/or 2N5088, JFET was J113, and the op amps were TL022 and/or LM1458.  
  • Custom Op Amps - A wide variety of op amps can be used in this circuit - any that are pin-compatible with 4558 style op amps.  Due to all the gain, it's generally a good idea to use some quiet op amps so that you aren't applying all that gain to any more noise than you must.  But you may want to try some other op amps, if you like the tubey sound of FET op amps or something.  You could even move up into some high-end audio op amps for even lower noise and higher clarity.  With all that gain, other than the noise level, other tonal differences you might hear between different types of op amps in a lower gain circuit may be less apparent, though.

 

Front Panel

  • On/Off indicator LED
  • Volume
  • Distortion
  • Presence (FX56)
  • Lo (HM-2, optional for FX56)
  • (optional) Mid
  • Hi (HM-2, optional for FX56)
  • (optional) Clipping switch(es)

 

Rear Panel

  • Audio In
  • Audio Out
  • On/Off Footswitch
  • On/Off Override
  • DC Power
  • DC Power LED

 

Module Width

  • 1.5" standard
  • 2.0" with options
  • 2" left wing available for standard 4-control configuration
  • 1.5" right wing available for standard 4-control configuration

 

Power Consumption (aprox)

20 - 25mA

 

Base Configurations

Part # Description List Price
MOD-CHAINSAW-HM2 Chainsaw Module, HM-2 configuration $219
MOD-CHAINSAW-FX56 Chainsaw Module, FX56 configuration $214

 

Options

Part # Description List Price
MOPT-CHAINSAW-MID  Add Mid Control $19
MOPT-CHAINSAW-LOW Add Low Control to FX56 $19
MOPT-CHAINSAW-HM2TONE Change FX56 tone stack to HM-2 tone stack $19
MOPT-CHAINSAW-DIODES Custom Clipping Diodes $0-TBD
MOPT-CHAINSAW-SWDIODES Custom Switched Clipping Diodes  $19-TBD
MOPT-CHAINSAW-COMPONENTS Custom Components $0-TBD