I just finished build #2. I used the alternate values (shown on the schematic and I think also earlier in this thread). I definitely prefer the alternate values with my humbucker guitar. I couldn't make up my mind with my single coil guitar, maybe a slight preference towards the stock values. The differences between stock and alternate values aren't night and day; they are subtle but noticeable. To my ears, there is more treble/high end at lower gain with the alternate values. (Although, both guitars are long overdue for a string change, so maybe I'm overcompensating a bit on the highs due to the strings.)
I haven't yet done a side-by-side comparison of the CMOS Overdrive to anything other than the Madbean Mysterioso, which is an almost-clone of the Blackstone Appliance Mosfet Overdrive (BAMO). I haven't been hunting for any particular sound, but I do like trying out different dirt pedals (my wife might say obsessively so). Of all the dirt pedals I've built and tried, I kept coming back to the boring old Boss OD-3... that is, until I tried the Mysterioso. I immediately thought to myself, this is the tone I've always wanted but didn't know I wanted. A normal person would be content to stop once they found "the" sound, but are we not all obsessives in this hobby? I think the Mysterioso was the first dirt pedal I used that wasn't based on some diode clipping scheme. So I went searching for more CMOS-based designs. I found the RunOffGroove Double-D (also cd4049 based, like the Mysterioso/BAMO), and Chuck's tweaked version. That led me to this cd4007 project. (I actually have a prototype CDB-mod Double-D PCB, needs just a little refinement.)
So with all that as a preamble: to my ears, Chuck's CMOS OD certainly has some "family resemblance" to the Mysterioso, but it's definitely its own thing. I really like the sound of these meant-for-digital-applications CMOS logic chips being used in analog mode and overdriven. I've seen a lot of people describe the sound as "tube like"; I can't say if that's true, since I've had so few opportunities to really get a tube amp's power section to break up. Whatever it's called, it's a sound I personally find pleasing.
Chuck's CMOS OD has a great EQ. It's not terribly common to have a mid control on an overdrive pedal, and the few I've tried never seemed to make a big difference. But the mid control on the CMOS OD is really effective. Likewise, so are the bass and treble controls. So my prediction is, if you build this pedal and like the overall character of the overdrive sound, then I'd be surprised if you couldn't make it work with the rest of your gear because the EQ gives a lot of flexibility. I'd also suggest either building two like I did, or socketing those components that have alternate values listed.
All this is based on strictly playing at home. My band was on hiatus during covid. We all got vaccines, had one rehearsal, now everyone is busy with summer life, so I haven't had an opportunity to try the CMOS OD in a band mix. I do have high expectations for it in a band context, though, largely because of the excellent EQ.
Hopefully all the PCBs I sent out have arrived or arrive in the next couple days. I'm eager to see everyone's build and hear their thoughts!
Slightly amusing side note: when I had #2 nearly finished, I did a power-on sanity test. I thought it sounded kinda dull, but it was working so I thought I'd finish assembly and then do a longer play-test with it. Sure enough, once I had everything pretty much done, and all my tools and soldering iron put away, I was admiring my work, when I noticed I had forgot to populate C12! Argh, something that would take two seconds to do before it was all put together, now I have to tear it down, get my tools back out, etc. So 20 minutes later, I was actually able to play it without the dull sound!
The MID control is certainly tunable. By changing C5, C6 and/or R9 we can have different Q and center freq. I set it for a fairly low-Q (wasn't going for the stuck wah tone) and 600Hz.
That's the plan for mine after gaining it up a bit. Sounds awesome, but found myself wishing there was more on the gain knob. Been meaning to do some experiments to boost the distortion when I have some time.
I somehow missed this thread and board but an old friend of mind used to call it his purple headed yogurt slinger. I am sure if given enough time I could paint that monster.
@Chuck D. Bones your knowledge of circuits astounds me! I absolutely love your threads and read them while scratching my head and hoping something sticks.
I somehow missed this thread and board but an old friend of mind used to call it his purple headed yogurt slinger. I am sure if given enough time I could paint that monster.
That's the plan for mine after gaining it up a bit. Sounds awesome, but found myself wishing there was more on the gain knob. Been meaning to do some experiments to boost the distortion when I have some time.
1. No JFETs
2. More gain
3. Even better midrange control
OK, three goals.
The first thing you need to know about these CMOS gain stages is the most you can get out of each gain stage is about 40dB. You can go just so far by increasing the feedback resistor.
The output impedance is a few KΩ, so you have to be careful about loading them.
Lowering Vdd increases gain. There is a sweet spot around 4V.
In the CMOS OD, I deliberately set the gain of the first stage low to accommodate the MID boost/cut circuit. In the Deluxe, I used an opamp for the MID boost/cut which left all three CMOS stage available for making large gain.
I tried putting diode hard clippers on the output of one or two of the gain stages. There was more compression, but the tone was not what I was after.
I somehow missed this thread and board but an old friend of mind used to call it his purple headed yogurt slinger. I am sure if given enough time I could paint that monster.
@Chuck D. Bones your knowledge of circuits astounds me! I absolutely love your threads and read them while scratching my head and hoping something sticks.
I somehow missed this thread and board but an old friend of mind used to call it his purple headed yogurt slinger. I am sure if given enough time I could paint that monster.
@Chuck D. Bones your knowledge of circuits astounds me! I absolutely love your threads and read them while scratching my head and hoping something sticks.
I still have several boards available, don't be shy about asking! (Also: I think I'm going to make a revision that additionally has space for a surface mount Q1, allowing you to use either a through-hole or SMD transistor. If you're not afraid of SMD soldering, the SMD J201 seems to be readily available.)
Looks like I have band rehearsal on Thursday, so hopefully I'll soon have a report on using it in a live mix.
I still have several boards available, don't be shy about asking! (Also: I think I'm going to make a revision that additionally has space for a surface mount Q1, allowing you to use either a through-hole or SMD transistor. If you're not afraid of SMD soldering, the SMD J201 seems to be readily available.)
Looks like I have band rehearsal on Thursday, so hopefully I'll soon have a report on using it in a live mix.
I'd recommend lower gain JFETs for Q1, such as J201. The PF5102 kinda muffles the high-end s bit. The 2SK193 is a very good one because it has extremely low capacitance. The 2N5457s that are available are at the low end of their gain range, so they should work well too.
I think the Mysterioso was the first dirt pedal I used that wasn't based on some diode clipping scheme. So I went searching for more CMOS-based designs. I found the RunOffGroove Double-D (also cd4049 based, like the Mysterioso/BAMO), and Chuck's tweaked version. That led me to this cd4007 project. (I actually have a prototype CDB-mod Double-D PCB, needs just a little refinement.)
