Akashic Guitar effects circuit lookup
HIGH VOLUMEMID VOLUMELOW VOLUMEHIGH FREQMID FREQLOW FREQGAINLEVELDRIVE ON/OFF

125B · 9 knobs

Dead Air Studios

Sawzall HM-2 EQ & Overdrive

Based on the Boss HM-2 / MXR Distortion+

Category
Distortion
Controls
High Volume · Mid Volume · Low Volume · High Freq · Mid Freq · Low Freq · Gain · Level · Drive On/Off
Price
$11.00in stock

From the vendor

Included is the Sawzall DIY PCB and the 3PDT (footswitch) PCB.

There’s a certain school of thought about the HM2 - that the secret to its trademark sound is more about the EQ and less about its distortion. The SAWZALL provides two ways to experiment with this concept:

(1) Set the switch to CLEAN mode (Toggle Left) and run whatever effect you’d like through the EQ, or even just run the EQ by itself into a dirty amp.

(2) Set the switch to DRIVE mode (Toggle Right) and engage a modified take on the Distortion+/DOD 250 circuit. The idea here being that if the distortion on the original HM2 was perhaps a little overbearing, or essentially just ‘on’ or ‘off’, maybe using a classic overdrive circuit instead would provide more flexible results.

* Please note that the GAIN knob is only functional in DRIVE mode.

All three EQ bands are at their stock frequencies when the Frequency knobs are set at noon. For the classic chainsaw approach: Dial all Frequencies at noon and all EQ Volumes all the way up. Experiment to taste.

In regards to the EQ - with the Mid EQ separated out from the Treble (on the original HM2 they were controlled simultaneously by the HIGH knob), and giving the Mid Frequency range a wider sweep - this EQ is actually capable of a good bit more than just the Chainsaw sound. You could simply choose to view it as an overdrive with an interesting EQ. And thus we arrive at the SAWZALL - dangerous yet flexible.

For a final note - in CLEAN mode the EQ is more or less at unity volume with the LEVEL knob all the way up. If you’re using the EQ to boost frequencies, this is a non-issue, but if you’re primarily cutting frequencies with the EQ, you may experience a slight decrease in volume in CLEAN mode.

Schematic

The schematic is in the vendor's build document. Open the build document. No KiCad fragment has been drawn for this circuit yet.

Parts list 51 rows

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RefValueNormalizedTypeNotes
Resistors 19
R11M1M
R24.7k4.7k
R310k10k
R41M1M
R533k33k
R63.3k3.3k
R73.3k3.3k
R868k68k
R910k10k
R101M1M
R1151k51k
R1251k51k
R13330R330
R1443k43k
R15330R330
R1647k47k
R1747k47k
R18330R330
CLR4.7k4.7k
Capacitors 16
C268n68nFILM
C347n47nFILM
C4100uf100uELECTROLYTIC
C5470pf470pCERAMIC
C61n1nFILM
C71uf1uFILM
C810uf10uELECTROLYTIC
C91uf1uELECTROLYTIC
C1068n68nFILM
C114.7n4.7nFILM
C12100n100nFILM
C136.8n6.8nFILM
C14150n150nFILM
C1547uf47uELECTROLYTIC
C16470n470nFILM
C171uf1uFILM
Diodes 3
D11N9141N914
D21N9141N914
D31N58181N5818
ICs 4
IC1TL071TL071
IC2TL072TL072
IC3TL072TL072
IC4TL072TL072
Potentiometers 8
High VolumeB10KB10kPotentiometer
Mid VolumeB10KB10kPotentiometer
Low VolumeB10KB10kPotentiometer
High FreqB100KB100kPotentiometer
Mid FreqC250KC250kPotentiometer
Low FreqB100KB100kPotentiometer
GainC500KC500kPotentiometer
LevelB10KB10kPotentiometer
Switches 1
Drive On/OffDPDTDPDTSwitchON / ON