bluedmc777
Active member
Is this on the actual boss pedal or clone?
This Week on the Breadboard: Boss OD-3
- Thread starter Chuck D. Bones
- Start date
Is this on the actual boss pedal or clone?
On the actual Boss pedal.
Chuck D. Bones
Circuit Wizard
I blew the dust off of the breadboard and made a few more tweaks. This is (probably) the final version. I added a MID switch, a GAIN switch (good idea Jason!) and retuned the tone controls. The MID switch selects between the stock notch (left position), slight notch (middle) and deeper notch (right). It's subtle, but noticeable. Totally optional. The GAIN switch kicks Q5's gain up by about 9dB for a little more bite. Definitely noticeable. Totally optional. I wasn't satisfied with the tone controls, so I made some adjustments. With BASS at 3 (10:00), the TREBLE control mimics the Boss OD-3 TONE control pretty well, but it goes a little darker below 1 and quite a bit brighter from 8 on up. With Bass at 6 and TREBLE at 7.5, the response from Q5-D to the output is pretty flat. U1 can be any dual opamp. Q1 needs to have a high Vp. Q2 and Q3 should be matched (see notes) for best performance, but the circuit will work fine as long as the two are close. PF5102 is hard to find these days. Any high-gain JFET with a Vp below 2.5V, such as J113, will work for Q2, Q3 and Q5. D5 & D6 should be Si; Ge is too leaky.
This is a low-medium gain OD. It's not gonna sound like a DS-1, BD-2, FF, BB, TS, TB or BMP. Max output is over 5Vp-p. Input impedance is high, output impedance is low. Should work pretty well anywhere in the pedal chain.
This is a low-medium gain OD. It's not gonna sound like a DS-1, BD-2, FF, BB, TS, TB or BMP. Max output is over 5Vp-p. Input impedance is high, output impedance is low. Should work pretty well anywhere in the pedal chain.
bluedmc777
Active member
Just realized I don’t even have the actual Boss OD-3 lol… I have the Aion Helios.
Chuck D. Bones
Circuit Wizard
The Aion Helios is a Rat clone. The Heliodor is their OD-3 clone. The Heliodor is a faithful reproduction of the OD-3. Aion recommends the 2SK209-GR as a direct replacement for the 2SK184-GR. J201 may work also. As always, it's more about the specs than the part numbers so plan on screening whatever JFETs you decide to use.
bluedmc777
Active member
Heliodor that’s it lol
In the Kanengomibako schematic you posted, it shows the power supply and switching circuits. In the power supply, are Q7, R30 and C26 a capacitance multiplier? I believe the BD-2 also employs a capacitance multiplier. I assume the idea is to reduce power supply ripple (moreso than the more typical single big electrolytic), at the cost of a voltage drop (and more components/board space). What are your thoughts on using cap multipliers in pedal power supplies?
Random thinking-out-loud idea... With the BD-2, I believe at least one person has re-implemented it using integrated opamps. Using that idea as inspiration for the OD-3: instead of using opamps, could one or more of the gain and/or clipping stages be replaced by a CMOS logic chip (e.g. cd4007)? I'm just thinking, I've generally enjoyed the overdriven CMOS sound (such as this great example
), and I like the OD-3. Could the marriage of these two ideas be an instant ear-gasm?!
Random thinking-out-loud idea... With the BD-2, I believe at least one person has re-implemented it using integrated opamps. Using that idea as inspiration for the OD-3: instead of using opamps, could one or more of the gain and/or clipping stages be replaced by a CMOS logic chip (e.g. cd4007)? I'm just thinking, I've generally enjoyed the overdriven CMOS sound (such as this great example
), and I like the OD-3. Could the marriage of these two ideas be an instant ear-gasm?!
Chuck D. Bones
Circuit Wizard
Interesting idea. It could work. I have not tried putting diodes in the feedback loop of a CD4007 gain stage. The open-loop gain of a single CMOS stage is maybe 30dB (32x) on a good day. The discrete gain stage Q13, Q14 & Q11 (Kanangomibako sch) has considerable more open-loop gain and it is non-inverting. That means a single CMOS gain stage is not a drop-in replacement, but there are ways of accomplishing what you're suggesting.Random thinking-out-loud idea... With the BD-2, I believe at least one person has re-implemented it using integrated opamps. Using that idea as inspiration for the OD-3: instead of using opamps, could one or more of the gain and/or clipping stages be replaced by a CMOS logic chip (e.g. cd4007)? I'm just thinking, I've generally enjoyed the overdriven CMOS sound (such as this great example
Yes, it is a crude form of C-multiplier. I've seen this in high-end audio tube amps.
The C-multiplier provides more filtering. Whether that extra filtering does any good is open to debate. There is a concept in engineering known as "good enough." Once a design meets the requirements (assuming one knows the requirements), further improvements provide diminishing returns and may in fact be detrimental. Increasing the parts count makes production more expensive and might reduce reliability. I do not use active power filtering in my pedal designs. Consider this: we don't want noisy DC power anywhere inside the enclosure. If we need all that extra filtering, the problem is with the power source and should be dealt with there.
As for diodes in the feedback loop of a CMOS stage: check out the RunOffGroove 22/7. They use a CD4049 to implement a Big Muff, with dioes in the feedback loop. I haven't built one of these, but hope to some day.
But in my idea, this is actually where I would deviate from the OD-3: omit the clipping diodes entirely, and obtain clipping from overdriving one or more CMOS gates. I'm not sure if that's even doable! But it sounds like a cool idea.
That's kind of what I was thinking. If I'm using a modern, high-quality, regulated + isolated power supply for my pedals, the DC should be pretty clean. Maybe not "audiophile clean", but certainly good enough for guitar pedals. I like overkill, but as you said, overkill can go too far and be detrimental.
Chuck D. Bones
Circuit Wizard
We are wandering off-topic here. I'll PM you.
I've been rocking my Heliodor (OD-3 clone) with the above mod as my primary overdrive for quite a while now. I recently discovered one small limitation of this mod: when you get into the almost-clean drive settings, the maximum volume is limited.
So on my actual Boss OD-3, I put the 3k3 resistor back, but changed diodes d10 and d11 from 1n4148 to red LEDs. This seems to have a similar effect as the resistor change. And I think it might also make the driven sound a little less compressed. I was going back and forth between my Heliodor with the 1k mod and the OD-3 with the red LED mod. The difference between the two is definitely subtle, so confirmation bias may be at play.
But I thought I'd throw this out there for anyone else who's interested in more OD-3 mods.
Chuck D. Bones
Circuit Wizard
Good idea changing D10 & D11. Red LEDs, IR LEDs or series-connected Si diodes are all good options. One could also try a resistor in series with D10 & D11 to reduce compression. I'm thinking something around 470Ω would be a good starting point.
D6 & D7 provide limiting after the 1st stage, so there may be some more headroom available by series pairs of diodes or LEDs for D6 & D7.
D6 & D7 provide limiting after the 1st stage, so there may be some more headroom available by series pairs of diodes or LEDs for D6 & D7.
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