Boss - SD-1w Super OverDrive (Waza Craft)

All about modern commercial stompbox circuits from Electro Harmonix over MXR, Boss and Ibanez into the nineties.
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guiddruid
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Post by guiddruid »

Gut shots - https://imgur.com/a/UPaObOE

Not the best photos, sorry - cables get in the way. Really needs all the wires to be de-soldered to get a proper look at it.
Input is top-right of the circuit (W1 & W2), then heads down the right-hand-side, across & back up the left-hand-side. Looks like there ground plane on the component side of the board is split to improve input/output separation.
Most of the caps are through-hole.
A lot of SOT-23 transistor pairs "C6" and "DG". There are a couple of 8 pin ICs in there too. "99M"?
Lots of un-populated components.

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Post by roseblood11 »

Not worth tracing it. It's just a stupid SD-1...
These waza craft pedals are quite expensive, although production must be much cheaper than it was in the 80s. And they still use these unbelievably cheap caps and crappy ribbon cables.

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Post by guiddruid »

There are indeed no opamps in the circuit, unlike the original SD1 - the 8 pin ICs are switches (see below).

Opamps look to have been replaced with discrete transistor circuits. The drive and tone stages are not identical.

Input + drive stage is Q2(XG), Q18(DG), Q3(DG), Q4(JY), Q5(XG), Q6(XG)
Q4(JY) is controlled by the switching circuit, probably to mute & reduce bypass noise.
Passives & clipping diodes look very slose to original SD1 - clipping diodes D4,D5,D6 have same idents as in original SD1 schematics. IC2 is doing some switching here...

IC2 sw 2 controlled by S/C toggle switch. Doing something with the inverting input of the drive gain stage
IC2 sw 1 controlled by S/C toggle switch. Is creating an inverted copy of the toggle switch control (connects to IC3)

Tone stage is Q8(DG)/Q7(C6), Q9(XG), Q10(XG)

This is followed by Q12(DG)/Q11(C6), then Q20(XG),Q21(XG),Q23(DG)/Q22(C6). IC3 seems to be a bypass path around theese last 4 transistors.

IC3 sw 1 controlled by toggle switch. Connected to the final gain stage (Q20,Q21,Q22,Q23)
IC3 sw 2 controlled by inverted toggle switch. Connnected to the previous gain stage (Q11 + Q12)
So IC3 looks like it is switching in a whole additional gain stage

Main switching control circuit looks to be identical to original SD1 (and all other Boss pedals), which should help with identifying some of the other components. (Seems a bit weird to use a mix of discrete analog switching components and the 8 pin bilateral switch ICs)

Should mean DG = SOT23 NPN transistor

Code: Select all

  c
[-+-]
[+-+]
 b e
Also JY = SOT23 N channel JFET in switching circuit, not sure which way round drain & source are

Code: Select all

  g
[-+-]
[+-+]
 ? ?
IC2 & IC3 are Toshiba TC7W66FK, dual bilateral Switches

Code: Select all

io1 1  8 vcc
oi1 2  8 ct1
ct2 3  7 oi2
gnd 4  6 io2
---
XG = SOT23 something
C6 = SOT23 something, possibly PNP?
C1 = smaller than SOT23. Switching diodes of some kind. Clipping circuit & on FET gates.
C3 = some other diode. Used with the DG/C6 pairs.
D13 = C2 = diode at power supply connection

dv8r601
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Post by dv8r601 »

Jy is a bav199 double diode
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dv8r601
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Post by dv8r601 »

And also most sot23 jfets source and drain are interchangeable.

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Post by guiddruid »

Thanks dv8r601 - that doesn't make sense, given where they are in the circuit though. The NXP datasheet for BA199 also says the markings would be "JYp", "JYt" or "JYW", and that's not the case here.

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Post by guiddruid »

Found a good reference for SMD markings; http://caxapa.ru/thumbs/588912/smd-codes.pdf

Have some promising candidates for some of the mystery 3 pin devices.

JY, SOT23 N channel JFET in switching circuit
2SK208, IDSS classification 1.2 to 3.0 mA
g
[-+-]
[+-+]
s d

DG, NPN transistor of some kind, bistable for footswitch + gain stages
2SC2713
c
[-+-]
[+-+]
b e

C6, transistor of some kind (Q7, Q11)
MMBA811C6, PNP
c
[-+-]
[+-+]
b e


Nothing sensible for XG yet...

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