SD-1 to OD-1???

[MartyMart]

Well, what I originally intended to do was very similar to that. Before a couple of days ago - and finding out about the quad opamp version of the OD1 - I had scanned and meticulously "traced" the OD1's PCB with that exact intention. If anyone out there that has the quad version could send me a scan of the PCB (top and bottom) I would be incredibly grateful.

On its way to you soon sir !!

Marty.

[Regan]

Mike,
A few questions,
Is there enough room for a small daughter board with the quad chip?
Which quads did you try?
Hmmmm, is it a matter of paralleling the opamps? I wonder if piggybacking two duals would work fine.
I'll have to take a look when I'm less tired.
Regan

[analogmike]

Mike,
A few questions,
Is there enough room for a small daughter board with the quad chip?
Which quads did you try?
Hmmmm, is it a matter of paralleling the opamps? I wonder if piggybacking two duals would work fine.
I'll have to take a look when I'm less tired.
Regan

IN this case it's easier to cut traces and run jumpers than a daughter board. But you just gave me an idea... tack 1/2" wire leads onto the quad op amp chip. Use a 1" lead on pin 4. Then you can move 3 of the legs down one slot (4 5 and 6) and pin 7 can go to pin 4, saving cutting of any traces.

I also forgot to mention that you have to bend leg 2 and attach to leg 1 on the chip and leg 13 to 14 (leave holes empty on new pin 2 and 13).

It's not so easy to describe but you can figure it out, that's why it's called DIY  

[Gregr]

This is an ancient subject but I'd like to comment about the coupling capacitor values. If you look at the schematics for the 14-pin and 8-pin versions you will see that the resistors to analog ground following the capacitors are also different. They scale accordingly.

The high pass filter before the input buffer C1 and R2 are 47n and 100k for the dual op amp version vs 100n and 220k for the quad. Both set the high pass corner at 7.2Hz. Similarly this is the case for the 47n and 1M vs 100n and 470k feeding the output buffer. Is is also the case for the 4.7n-100k combination vs 47n-10k combination which feeds the clipping stage. The corner frequencies are the same despite the sizes of capacitors used.

I'm comparing the schematic dated April 1, 1978 with one dated December 26, 1980.

I've modified an SD-1 to match that of the dual op-amp OD-1 and am satisfied with the results, but I think a higher fidelity op amp for the clipping circuit and low pass filter is necessary to get the clarity of the original OD-1.

Am I missing something?

[Steben]

Given the circuit I find it astonishing a different opamp can give clarity or the opposite.
Only a really big signal (let's say the output of another pedal) gets you most of the time in opamp clipping area.
But with guitar at the input you need a guitar with let's say at least 2V output.

[Gregr]

It's a simple circuit. The NPN input and output buffers have been standard in Boss pedals for decades. I don't believe they contribute to the midrange congestion. Save for the chip used for clipping and tone control circuits there really isn't anything left.

[Gregr]

Boss SD-1 schematic link
Boss OD-1 schematic link (4558C version with switching omitted from the diagram)

Call me cuckoo, but the only differences between the SD-1 and OD-1 according to the two schematics linked above are:

SD-1 to OD-1:
R1 >> 1K
C2 >> 0.0047uF
C6 >> 0.018uF
C4 >> 10K resistor (see below)

This last weird cap to resistor change requires a bit of extra trickery.  If you look at the second opamp stage of both pedals, you can see that:
In the SD-1: 
R7 is connected to pin 3, and 4.5volts is also connected to pin 3 via the capacitor C4.
In the OD-1:
R7 is connected to pin 2, leaving 4.5volts connected to pin 3 by itself via a 10K resistor.

I'm guessing you could solve this problem by doing this:
1. lift the end of R7 from its hole
2. desolder the wire from lug 3 of the tone pot
3. solder this wire to the lifted leg of the R7 resistor
4. swap C4 for a 10K resistor

Just make sure you're lifting the resistor leg that was leading towards C4 and pin 3 (maybe someone can confirm which side leg this is?)



Hopefully that trick should work.  Finish it off by desoldering the other two wires from the tone pot and put tape on the ends or something so they won't short out against anything.

I'm just going on the differences I can see in the two schematics and don't want to kill your pedal.  Perhaps some other forumites can confirm that this will actually work first?

This is a far easier solution that is functionally equivalent:

-Remove C5
-Remove the wire that connects pin 3 of the tone pot to the hole on the board labeled 8
-Put a short across C4
-Change C2 from 18nF to 4.7nF