"that" Overdrive [documentation]
- dylan159
- Resistor Ronker
Information
Here's my latest creation, that Overdrive! No, not that one, this one!
You might know I like to be very straightforward or to clean up other designs usually, this began as a test to see if I could be more flamboyant with my designs. Also I wanted to take on the difficult challenge of making an overdrive pedal which doesn't borrow heavily from known designs. In the end my minimalist approach is still there, and this isn't a physically big circuit and the values are all common: despite extensive breadboard testing, I didn't have to give up on that.
We all know which is the predator in this category, and we know it's green now, I wanted to refresh on that a bit. For example, we know the pre gain low shelf is very important to keep a clear distortion, and it's very important to me, but what if we could make that rolloff steeper, and maybe that way being able to push it lower? The most obvious solutions would be a tiny input cap or an active high pass filter at the input, but I'm not a fan of either approach, either because of interactivity or because of having the noise of an active stage before all of my gain. Instead I thought, what if we feed back more of the low frequencies? what if instead of the usual shelving lowpass formed by the feedback network in an inverting op amp we try to make it second order?
Same thing for the post-gain lowpass. First order passive filters are ubiquitous, and they work ok. Even the green pedal, with its active tone control, in practice doesn't go far off at all from the response of a cut-only first order lowpass, once you combine the active stage with the fixed lowpass before it. A second order filter here is relatively unexplored, and can be used among the other things to preserve more of the nice lower treble while still keeping the bees in the nest with the steeper rolloff. This is the final iteration. I've messed with some things while getting ideas, like parallel resistors+capacitors in the feedback for more of a custom-fit frequency curve (but for the grounded leg that would have given me more bass not less!), switchable clipping, fixed frequency gyrator mid control... In the end I tend always to simplify though. For the feedback I settled for two parallel networks, one traditional with variable gain, one a fixed second order lowpass, which then get mixed together. The response of the gain stage looks like this (stepped gain pot, you can see the bass cut is sharper than with a traditional green pedal): But I know glassy and clean bass isn't for everyone, so I added a bass control which in practice isolates the additional network, leaving you with something more familiar (again green for reference): Finally there's the S-K lowpass. A trick here is to switch between the usual buffer and a gain stage, which increases the final Q. That's what the resonance switch does. The small peaking near the cutoff is very very effective in giving you more sounds. The boosted Q value has been chosen to be still low and usable but different enough. The 100KC dual pot is a bit unfortunate, but other values can be used with scaling, and A taper if wired in reverse. Here's a sweep of both modes: Build pic: Vero: Demos:
You might know I like to be very straightforward or to clean up other designs usually, this began as a test to see if I could be more flamboyant with my designs. Also I wanted to take on the difficult challenge of making an overdrive pedal which doesn't borrow heavily from known designs. In the end my minimalist approach is still there, and this isn't a physically big circuit and the values are all common: despite extensive breadboard testing, I didn't have to give up on that.
We all know which is the predator in this category, and we know it's green now, I wanted to refresh on that a bit. For example, we know the pre gain low shelf is very important to keep a clear distortion, and it's very important to me, but what if we could make that rolloff steeper, and maybe that way being able to push it lower? The most obvious solutions would be a tiny input cap or an active high pass filter at the input, but I'm not a fan of either approach, either because of interactivity or because of having the noise of an active stage before all of my gain. Instead I thought, what if we feed back more of the low frequencies? what if instead of the usual shelving lowpass formed by the feedback network in an inverting op amp we try to make it second order?
Same thing for the post-gain lowpass. First order passive filters are ubiquitous, and they work ok. Even the green pedal, with its active tone control, in practice doesn't go far off at all from the response of a cut-only first order lowpass, once you combine the active stage with the fixed lowpass before it. A second order filter here is relatively unexplored, and can be used among the other things to preserve more of the nice lower treble while still keeping the bees in the nest with the steeper rolloff. This is the final iteration. I've messed with some things while getting ideas, like parallel resistors+capacitors in the feedback for more of a custom-fit frequency curve (but for the grounded leg that would have given me more bass not less!), switchable clipping, fixed frequency gyrator mid control... In the end I tend always to simplify though. For the feedback I settled for two parallel networks, one traditional with variable gain, one a fixed second order lowpass, which then get mixed together. The response of the gain stage looks like this (stepped gain pot, you can see the bass cut is sharper than with a traditional green pedal): But I know glassy and clean bass isn't for everyone, so I added a bass control which in practice isolates the additional network, leaving you with something more familiar (again green for reference): Finally there's the S-K lowpass. A trick here is to switch between the usual buffer and a gain stage, which increases the final Q. That's what the resonance switch does. The small peaking near the cutoff is very very effective in giving you more sounds. The boosted Q value has been chosen to be still low and usable but different enough. The 100KC dual pot is a bit unfortunate, but other values can be used with scaling, and A taper if wired in reverse. Here's a sweep of both modes: Build pic: Vero: Demos:
Last edited by dylan159 on 16 Jun 2021, 09:17, edited 3 times in total.
Personal blog/archive: https://bentfishbowl.wixsite.com/electronics
Find me at https://discord.gg/bMuhX4TkZM Audio Electronics discord server.
Find me at https://discord.gg/bMuhX4TkZM Audio Electronics discord server.
- dylan159
- Resistor Ronker
Information
Thanks, you can build it if you like it!
I guess you mean the wiring? For a variable resistor it doesn't matter which end goes where
I guess you mean the wiring? For a variable resistor it doesn't matter which end goes where
Personal blog/archive: https://bentfishbowl.wixsite.com/electronics
Find me at https://discord.gg/bMuhX4TkZM Audio Electronics discord server.
Find me at https://discord.gg/bMuhX4TkZM Audio Electronics discord server.
- 287m
- Breadboard Brother
yeah, right. Its just habits for matched A and B. Haha
thanks for some design circuit, enjoyed that in this pandemic shit
Anyway, perf try onboard. Dunno when pots came.
- dylan159
- Resistor Ronker
Information
Nice! is that single sided just how I like it?
I'm glad you had fun with my circuit. I think the board rules cover it as long as we're here, but if you want to share the layout elsewhere, can you please use the same license as me, since it's sharealike?
Personal blog/archive: https://bentfishbowl.wixsite.com/electronics
Find me at https://discord.gg/bMuhX4TkZM Audio Electronics discord server.
Find me at https://discord.gg/bMuhX4TkZM Audio Electronics discord server.
- 287m
- Breadboard Brother
Yes, single sided. Still in progress to shrink it, didn't like the empty space.
of course! As always, linked to original thread. So, they must visit fsb to see schemo and know original owner.
Now the question, is there night and day difference if use linear tone pots?
of course! As always, linked to original thread. So, they must visit fsb to see schemo and know original owner.
Now the question, is there night and day difference if use linear tone pots?
- dylan159
- Resistor Ronker
Information
I'd think that if it's possible to not visit here and take the layout without context, that could be a leak not covered by the forum rules. not really too worried about it, I just enjoy knowing if the idea spreads.287m wrote: ↑14 Jun 2021, 04:50 Yes, single sided. Still in progress to shrink it, didn't like the empty space.
of course! As always, linked to original thread. So, they must visit fsb to see schemo and know original owner.
Now the question, is there night and day difference if use linear tone pots?
linear will work, just worse sweep. I'd rather use log in reverse or try different values beforehand.
Personal blog/archive: https://bentfishbowl.wixsite.com/electronics
Find me at https://discord.gg/bMuhX4TkZM Audio Electronics discord server.
Find me at https://discord.gg/bMuhX4TkZM Audio Electronics discord server.
- dylan159
- Resistor Ronker
Information
both that and for a smoother VI curve, thanks mostly to the summed bulk resistance. In particular bat41 is very soft itself, this way you get that with an higher Vf. Two pairs of 4148 work well too, and single pair also, it's to taste.
Personal blog/archive: https://bentfishbowl.wixsite.com/electronics
Find me at https://discord.gg/bMuhX4TkZM Audio Electronics discord server.
Find me at https://discord.gg/bMuhX4TkZM Audio Electronics discord server.
- mictester
- Old Solderhand
Information
"That"'s a superb sounding overdrive! The BAT41s take the edge off a bit - you can add the edge back in by switching to two pairs of 1N4148s - it's actually worth making the diodes switchable. The controls have ranges that are entirely useable - it's a really good project!
"Why is it humming?" "Because it doesn't know the words!"
- dylan159
- Resistor Ronker
Information
Thank you! Have fun with the diodes, I think I said it in the first message, but you're free to try which you like best, as long as it doesn't mean clipping this op-amp or any after it. It's pretty safe here.mictester wrote: ↑14 Sep 2021, 12:03 "That"'s a superb sounding overdrive! The BAT41s take the edge off a bit - you can add the edge back in by switching to two pairs of 1N4148s - it's actually worth making the diodes switchable. The controls have ranges that are entirely useable - it's a really good project!
Personal blog/archive: https://bentfishbowl.wixsite.com/electronics
Find me at https://discord.gg/bMuhX4TkZM Audio Electronics discord server.
Find me at https://discord.gg/bMuhX4TkZM Audio Electronics discord server.
- Jarno
- Resistor Ronker
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saw this in "new replies" and fully expected this to have some kind of THAT silicon, like THAT2181 or maybe THAT300/320/340
"It crackles....., but that's ok"
- dylan159
- Resistor Ronker
Information
No, you see, it's that overdrive, not THAT overdrive
Personal blog/archive: https://bentfishbowl.wixsite.com/electronics
Find me at https://discord.gg/bMuhX4TkZM Audio Electronics discord server.
Find me at https://discord.gg/bMuhX4TkZM Audio Electronics discord server.
- dylan159
- Resistor Ronker
Information
Little update on the circuit, called "what if you don't always want a second order low-pass though?". This little tweak adds a third mode, a more traditional first order RC filter, at the very small cost of a different kind of switch. Having them side by side I still prefer the second order filters most of the time, with an higher cutoff they can be still bright but without that annoying crackle of higher harmonics. Still, it can be useful to have, so I put the time soldering it in and posting this new schematic.
The second small update is the output rewired so that it doesn't get boosted when engaging the resonant filter. At first I had decided against it to keep the output impedance low, but honestly an extra 1k is nothing, or even beneficial to isolating cable capacitance. The grounded leg resistor has been increased to keep the original gain and response.
The second small update is the output rewired so that it doesn't get boosted when engaging the resonant filter. At first I had decided against it to keep the output impedance low, but honestly an extra 1k is nothing, or even beneficial to isolating cable capacitance. The grounded leg resistor has been increased to keep the original gain and response.
Personal blog/archive: https://bentfishbowl.wixsite.com/electronics
Find me at https://discord.gg/bMuhX4TkZM Audio Electronics discord server.
Find me at https://discord.gg/bMuhX4TkZM Audio Electronics discord server.