aion QUARK User manual

QUARK VINTAGE OVERDRIVE 1
PROJECT NAME
QUARK
BASED ON
EFFECT TYPE
PROJECT SUMMARY
DOCUMENT VERSION
Maxon®OD-880 Overdrive
An early overdrive circuit inspired by the MXR Distortion+, but incorporating a few changes that would
later evolve into the Tube Screamer a few years later.
Overdrive 1.0.0 (2021-03-19)
BUILD DIFFICULTY
Easy
Actual size is 2.3” x 1.86” (main board) and 1.78” x 0.86” (bypass board).

QUARK VINTAGE OVERDRIVE 2
TABLE OF CONTENTS
1Project Overview 7Drill Template
2Introduction & Usage 8Enclosure Layout
3-4 Parts List 9Wiring Diagram
5Build Notes 10 Licensing
6Schematic 10 Document Revisions
INTRODUCTION
The Quark Vintage Overdrive is a clone of the Maxon OD-880 Overdrive / Soft Distortion, originally
released in 1976.
This pedal was huge in Japan, being the favored overdrive pedal of Char, one of the country’s most
popular guitarists, who—like the pedal—never really got noticed out of Japan. It was reissued a few
times, notably in the mid-90’s as well as more recently.
It’s an interesting circuit from a historical perspective, being sort of a “transitional species” between
the Distortion+ and the Boss OD-1 OverDrive. It added the input and output buffers and changed the
Drive potentiometer to a flat op-amp boost instead of a gain modifier that also affected the bass tone,
as in the Dist+. The Boss OD-1 is essentially an OD-880 with feedback clipping diodes instead of diode-
to-ground clipping. This diode arrangement turned out to be a very big deal and made way for the Tube
Screamer a couple of years later.
The Quark is a direct clone of the OD-880, but with a few additions. A clipping toggle allows switching
between three different sets of diodes. An EQ switch engages a second mode with increased gain and
more bass. And since the OD-880 lacks a tone control, a Treble switch selects between three different
post-clipping hi-cut modes.
The updated version of the Quark is the same as the original 1590B version, but with the addition of the
Treble switch which the original Quark did not have.
USAGE
The Quark has the following controls:
• Drive controls the amount of gain in the op-amp feedback diode clipping stage.
• Volume controls the overall output of the effect.
• Clip (toggle switch) selects between three sets of diodes: 1x silicon (stock), 2x silicon, and LEDs.
• EQ (toggle switch) selects between two different tones: stock mode (similar to the Tube Screamer)
and another mode with slightly higher gain and less bass cut.
• Treble (toggle switch) selects between three different treble-cut modes. Stock mode has the
highest treble cut.

QUARK VINTAGE OVERDRIVE 3
PARTS LIST
This parts list is also available in a spreadsheet format which can be imported directly into Mouser for
easy parts ordering. Mouser doesn’t carry all the parts (most notably potentiometers) so the second tab
lists all the non-Mouser parts as well as sources for each.
View parts list spreadsheet →
PART VALUE TYPE NOTES
R1 10k Metal film resistor, 1/4W
R2 470k Metal film resistor, 1/4W
R3 10k Metal film resistor, 1/4W
R4 10k Metal film resistor, 1/4W
R5 470k Metal film resistor, 1/4W
R6 100R Metal film resistor, 1/4W
R7 100k Metal film resistor, 1/4W
R8 4k7 Metal film resistor, 1/4W
R9 3k3 Metal film resistor, 1/4W Part of EQ mod. See build notes.
R10 10k Metal film resistor, 1/4W
R11 10k Metal film resistor, 1/4W
R12 9k1 Metal film resistor, 1/4W
R13 100k Metal film resistor, 1/4W
R14 68k Metal film resistor, 1/4W
R15 10k Metal film resistor, 1/4W
R16 10k Metal film resistor, 1/4W
R17 100R Metal film resistor, 1/4W Power supply filter resistor.
RPD 2M2 Metal film resistor, 1/4W Input pulldown resistor.
LEDR 4k7 Metal film resistor, 1/4W LED current-limiting resistor. Adjust value to change LED brightness.
C1 47n Film capacitor, 7.2 x 2.5mm
C2 47n Film capacitor, 7.2 x 2.5mm
C3 47n Film capacitor, 7.2 x 2.5mm
C4 330n Film capacitor, 7.2 x 2.5mm Part of EQ mod. See build notes.
C5 47pF MLCC capacitor, NP0/C0G Not present in original. See build notes.
C6 100n Film capacitor, 7.2 x 2.5mm
C7 100n Film capacitor, 7.2 x 2.5mm
C8 820pF MLCC capacitor, NP0/C0G Part of treble mod. See build notes.
C9 3n9 Film capacitor, 7.2 x 2.5mm Part of treble mod. See build notes.
C10 1n2 Film capacitor, 7.2 x 2.5mm Part of treble mod. See build notes.
C11 100n Film capacitor, 7.2 x 2.5mm Power supply filter capacitor.

QUARK VINTAGE OVERDRIVE 4
PARTS LIST, CONT.
PART VALUE TYPE NOTES
C12 47uF Electrolytic capacitor, 5mm Reference voltage filter capacitor.
C13 100uF Electrolytic capacitor, 6.3mm Power supply filter capacitor.
C14 100n MLCC capacitor, X7R Power supply filter capacitor.
D1 1N5817 Schottky diode, DO-41
D2 1N914 Fast-switching diode, DO-35
D3 1N914 Fast-switching diode, DO-35
D4 1N914 Fast-switching diode, DO-35
D5 1N914 Fast-switching diode, DO-35
D6 1N914 Fast-switching diode, DO-35
D7 1N914 Fast-switching diode, DO-35
D8 3mm LED LED, 3mm, red diffused
D9 3mm LED LED, 3mm, red diffused
IC1 LM741 Operational amplifier, DIP-8
IC1-S DIP-8 socket IC socket, DIP-8
IC2 LM741 Operational amplifier, DIP-8
IC2-S DIP-8 socket IC socket, DIP-8
IC3 LM741 Operational amplifier, DIP-8
IC3-S DIP-8 socket IC socket, DIP-8
SENS. 500kB 16mm right-angle PCB mount pot
LEVEL 10kB 16mm right-angle PCB mount pot
CLIP SPDT cntr off Toggle switch, SPDT on-off-on
TREBLE SPDT cntr off Toggle switch, SPDT on-off-on
EQ SPDT on-on Toggle switch, SPDT on-on
LED 5mm LED, 5mm, red diffused
IN 1/4" stereo 1/4" phone jack, closed frame Switchcraft 112BX or equivalent.
OUT 1/4" mono 1/4" phone jack, closed frame Switchcraft 111X or equivalent.
DC 2.1mm DC jack, 2.1mm panel mount Mouser 163-4302-E or equivalent.
BATT Battery snap 9V battery snap Optional. Use the soft plastic type—the hard-shell type will not fit.
FSW 3PDT Stomp switch, 3PDT
ENC 125B Enclosure, die-cast aluminum Can also use a Hammond 1590N1.

QUARK VINTAGE OVERDRIVE 5
BUILD NOTES
EQ switch
The original OD-880 uses an op-amp low cut arrangement similar to the Tube Screamer. The EQ switch
changes the resistor (which sets the gain ratio) and capacitor (which sets the low-cut frequency) for
alternate values. The values in the parts list work well as a starting point, but you can tweak if you want.
• For more available gain in the modded EQ mode, reduce the value of R9 (e.g. 2k2).
• For more bass cut (i.e. less bass), reduce the value of C4 (e.g. 100n or 220n).
• For less bass cut (i.e. more bass), increase the value of C4 (e.g. 470n or 1uF).
Make sure to use an on-on toggle switch for this since there is no center-off mode as with the other two
toggles. The center position of a center-off switch would cut out the signal.
Treble switch
The original OD-880 has a steep treble cut after the clipping diodes and no discrete tone control. The
default treble cut works pretty well, but you may find you need more for certain guitar & amp combos.
Or, you may want more treble on tap so you can turn it up and down directly from the guitar.
The stock capacitor value is 4n7. This has been modified so that it has 1n2 and 3n9 capacitors in parallel
with an always-on 820pF capacitor, which creates 3 different settings: 4n7 (stock), 2n2 (less treble cut)
and 820pF (least treble cut).
By tweaking these three values, you can end up with different modes. For example, by using a 4n7
capacitor instead of 1n2, you can have one mode with more treble cut, meaning there is one setting
above and one setting below the stock mode.
C5 capacitor
The original OD-880 does not include a feedback capacitor in the op-amp gain stage. This capacitor is
found on nearly every similar drive circuit that came afterward and is seen as best practice to limit the
bandwidth of the op-amp for better stability. It’s extremely subtle and has nearly no impact on the audio
frequencies except at higher drive settings.

SCHEMATIC
QUARK VINTAGE OVERDRIVE 6
GND
2M2
1N5817
100uF
GND
+9V
100n
VA
500kB
10kB
10k
LM741
LM741
LM741
47n
470k
GND
47n
10k
10k
470k
100R
100k
47n
4k7
GND
100n
330n
3k3
GND
10k
GND
100n
10k
9k1
1n2
100k
100n
68k
GND
GND
1N914
1N914
1N9141N914
1N914 1N914
GND
VB
VB VB
VB
VB
VA
VA
VA
100pF
10k
10k
GND
47uF
GND
100R
3n9
820pF
IN
OUT
RPD
D1
C13
C14
1
2
3
SENSITIVITY
LEVEL
1
2
3
R1 5
1
2
3
6
8
74
IC1
5
1
2
3
6
8
74
IC2
5
1
2
3
6
8
74
IC3
C1
R2
C2
R3
R4
R5
R6
R7
C3
R8
C6
C4
R9
R10
C7
R11
R12
C10
R13
C11
R14
D2 D3
CLIP
2
3 1
D4D5
D6 D7
D8 D9
EQ
2
3 1
C5
R15
R16
C12
R17
C9
C8
TREBLE
2
3
1
GND

QUARK VINTAGE OVERDRIVE 7
DRILL TEMPLATE
Cut out this drill template, fold the edges and tape it to the enclosure. Before drilling, it’s recommended
to first use a center punch for each of the holes to help guide the drill bit.
Ensure that this template is printed at 100% or “Actual Size”. You can double-check this by measuring
the scale on the printed page.
Top jack layout assumes the use of closed-frame jacks like the Switchcraft 111X. If you’d rather use
open-frame jacks, please refer to the Open-Frame Jack Drill Template for the top side.
LED hole drill size assumes the use of a 5mm LED bezel, available from several parts suppliers. Adjust
size accordingly if using something different, such as a 3mm bezel, a plastic bezel, or just a plain LED.
0 1 2
CM
0 1
INCH
x: 0, y: -1.20
ø15/32”
x: -0.775, y: -1.20
ø5/16”
ø3/8” ø1/2”
0.385”
0.625” 0.625”
ø3/8”
OUT DC IN
125B
FOOTSWITCHLED
x: -0.65, y: +1.71 x: 0.65, y: +1.71
ø9/32” ø9/32”
x: +0.775, y: +0.66
ø1/4”
x: -0.775, y: +0.66
ø1/4”
x: 0, y: +0.66
ø1/4”
CENTER (0,0)

QUARK VINTAGE OVERDRIVE 8
ENCLOSURE LAYOUT
Enclosure is shown without jacks. See next page for jack layout and wiring.
125B

QUARK VINTAGE OVERDRIVE 9
WIRING DIAGRAM
125B
IN +VGND N.C. N.C. OUT
PCB
IN
GND +V +V JACK GND JACK
OUTIN
GND GND PCB
OUT
Shown with optional 9V battery. If battery is omitted, both jacks can be mono rather than one being stereo.
Leave the far-right lug of the DC jack unconnected.

QUARK VINTAGE OVERDRIVE 10
LICENSE & USAGE
No direct support is offered for these projects beyond the provided documentation. It’s assumed
that you have at least some experience building pedals before starting one of these. Replacements and
refunds cannot be offered unless it can be shown that the circuit or documentation are in error.
All of these circuits have been tested in good faith in their base configurations. However, not all the
modifications or variations have necessarily been tested. These are offered only as suggestions based
on the experience and opinions of others.
Projects may be used for commercial endeavors in any quantity unless specifically noted. No
attribution is necessary, though a link back is always greatly appreciated. The only usage restrictions
are that (1) you cannot resell the PCB as part of a kit without prior arrangement, and (2) you cannot
“goop” the circuit, scratch off the screenprint, or otherwise obfuscate the circuit to disguise its source.
(In other words: you don’t have to go out of your way to advertise the fact that you use these PCBs, but
please don’t go out of your way to hide it. The guitar effects industry needs more transparency, not less!)
DOCUMENT REVISIONS
1.0.0 (2021-03-19)
Initial release.