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#31

Build Reports / Re: Polyphemus [One Knob Overd...

Last post by Devinimpson - June 04, 2026, 09:15:43 AM

This all started with Jessenator giving me the bullying me for building in 125B instead of 1590B. I threatened to put a mosfet boost in a 1590XX just to spite him. That's not where I ended up, but the idea for this circuit did come to me while contemplating mosfets and revenge.



Polyphemus is a one-knob overdrive/distortion with internal voicing options that allow it to be tailored to a variety of rigs and use cases. The idea was, to do all the dialing in up front, then screw the thing shut and just rock! As it's built around a Super Hard On of sorts, it only seemed appropriate to name it after the original one-eyed monster!



The circuit consists of three gain/eq stages. The first stage is a high shelf filter that boosts everything above a set frequency by 20dB. Everything below that frequency stays at unity gain. The second stage is a simple mosfet boost, which is pushed by the first stage into clipping. The final stage is a low shelf, set at a similar frequency to the first. This flattens out the eq again. This makes for a "transparent" overdrive that emphasizes harmonics and retains clarity, since higher frequencies are saturated more and sooner. It also greatly lowers the noise floor!



Switches 1 and 2 set the capacitance/cut-off frequency in the HPF stage. Switches 3 and 4 set the capacitance/cut-off frequency in the LPF stage. HPF and LPF interact to shape the character of the gain, as well as the frequency response. Flat, transparent overdrive, various kinds of mid boost or treble boost, mid scoop, even distortion/fuzz is achievable. Heat sets the range of the Gain control. This is so that the headroom can be adjusted to suit your pickups and maximize the range of the Gain Control. Output is a volume control. With Heat dialed in, there is a moderate change in volume from the lowest to the highest Gain setting (maybe 6dB). I like to set Output so that the lowest Gain setting is about unity with bypass, but you could attenuate or boost to taste.


Here's a demo:

geometry dash


There's a little dedication to Jessenator on the PCB. 😘 I built mine in a 125B, as is my preference, but it'll fit into a 1590B with top mount jacks. Side jacks are possible, but you'd have to push the Gain knob up to accommodate them. And, of course, it's in green, Jessenator's preferred solder mask color.


As always, I have extra PCBs. If you want one, DM me.

That is a really tidy build, and the internal voicing idea makes a lot of sense for a one knob pedal. I like the approach of setting the character once inside the enclosure, then keeping the outside simple enough to just plug in and play.

#32

Open Discussion / Re: The secret M117 flanger

Last post by Scruffie - June 03, 2026, 09:37:05 PM

Thanks for that, so it's just using one half of each CD4013? What an odd design choice... Definitely not using the chip handling oscillator division in parallel? That might make a little more sense in lieu of a clock buffer, given the BBD's have equal clock capacitance to an MN3007.

The BBD's were in series in the original which it did look like was the direction it was heading in the gut shots Jessenator sent me, is parallel confirmed?

Are you able to measure the clock frequencies as well out of interest?

If someone posts some decent gut shots it shouldn't be too hard to trace and confirm seeing as we already have the 117 schematic.

I'll PM you. Let me know if you need different angles than what I captured.

Thanks, unfortunately to get a good look at the traces you'd need to unsolder the pots.

But, I thought of a much simpler solution... just test for continuity between pin 2 of both MN3004, if it beeps, they share the same clock.

If it doesn't beep, check pin 2 of one doesn't match to pin 12 of the other.

Still no beep? Then it's time to test the CD4013 for continuity.

Probed around in mine. One half of the inner 4013 handles generating the two phase pulses for each MN3004. The  outer 4013 is then the other half of the clock circuit although I believe based on photos earlier in the thread that there is a single oscillator feeding the two flipflops. BBDs are in parallel like the original design.

#33

Open Discussion / Re: The secret M117 flanger

Last post by museums - June 03, 2026, 04:09:48 PM

If someone posts some decent gut shots it shouldn't be too hard to trace and confirm seeing as we already have the 117 schematic.

I'll PM you. Let me know if you need different angles than what I captured.

Thanks, unfortunately to get a good look at the traces you'd need to unsolder the pots.

But, I thought of a much simpler solution... just test for continuity between pin 2 of both MN3004, if it beeps, they share the same clock.

If it doesn't beep, check pin 2 of one doesn't match to pin 12 of the other.

Still no beep? Then it's time to test the CD4013 for continuity.

Probed around in mine. One half of the inner 4013 handles generating the two phase pulses for each MN3004. The  outer 4013 is then the other half of the clock circuit although I believe based on photos earlier in the thread that there is a single oscillator feeding the two flipflops. BBDs are in parallel like the original design.

#34

Open Discussion / Re: The secret M117 flanger

Last post by Scruffie - June 03, 2026, 12:21:13 AM

If someone posts some decent gut shots it shouldn't be too hard to trace and confirm seeing as we already have the 117 schematic.

I'll PM you. Let me know if you need different angles than what I captured.

Thanks, unfortunately to get a good look at the traces you'd need to unsolder the pots.

But, I thought of a much simpler solution... just test for continuity between pin 2 of both MN3004, if it beeps, they share the same clock.

If it doesn't beep, check pin 2 of one doesn't match to pin 12 of the other.

Still no beep? Then it's time to test the CD4013 for continuity.

#35

Open Discussion / Re: The secret M117 flanger

Last post by jessenator - June 02, 2026, 09:33:10 PM

If someone posts some decent gut shots it shouldn't be too hard to trace and confirm seeing as we already have the 117 schematic.

I'll PM you. Let me know if you need different angles than what I captured.

#36

Open Discussion / Re: The secret M117 flanger

Last post by Scruffie - June 02, 2026, 02:35:26 PM

Sounded like a separate modulation underneath the main modulation to my ears.
Maybe they have one 4013/14013 running as divided by 2 from the first clock?

I have noticed this sound from my pedal as well. There is a subtle 2nd modulation effect taking place in the background. It would be amazing to be able to mod the clocks to really take advantage of the fact this is basically two flangers running simultaneously! Again, the unobtanium schematic for this version is the key.

My guess is because of the MN3004's piss poor clock to gain ratio and the fact there's two almost certainly in series what you're both actually hearing is basically a tremolo along with the flanger.

If someone posts some decent gut shots it shouldn't be too hard to trace and confirm seeing as we already have the 117 schematic.

#37

Open Discussion / Re: The secret M117 flanger

Last post by museums - June 02, 2026, 01:57:48 PM

Looking at the Peavey DSC-4 dual clock chorus. It has 4 controls, 2x speed and 2x depth controls for each "clock". It really only has one clock, but 2x LFOs(072s) that look to be combined into a comparator(U3-B)and fed into the 3101. I would think this could confuse or glitch the 3101 but it makes for a very lush chorus.
Perhaps something similar is occuring in the MXR. Or it is somehow creating a decade of the LFO?

There are a bunch of dual LFO choruses from that era and in practice the clock just sees a different pattern of rising and falling voltages over time than with a single LFO. The LFO with the higher depth control generally has more influence over the movement of the overall voltage. With both depth controls in the middle you can get interesting non-linear LFO movement.

IIRC the Peavey is a little different because it has two different LFO shapes.

#38

Open Discussion / Re: The secret M117 flanger

Last post by Scruffie - June 02, 2026, 01:51:39 PM

Did anyone consider the possibility that maybe it's just being used for something very dull, like switching? For that fancy new LED?

#39

Open Discussion / Re: The secret M117 flanger

Last post by jwin615 - May 28, 2026, 05:10:00 PM

Looking at the Peavey DSC-4 dual clock chorus. It has 4 controls, 2x speed and 2x depth controls for each "clock". It really only has one clock, but 2x LFOs(072s) that look to be combined into a comparator(U3-B)and fed into the 3101. I would think this could confuse or glitch the 3101 but it makes for a very lush chorus.
Perhaps something similar is occuring in the MXR. Or it is somehow creating a decade of the LFO?

#40

Global Annoucements / Re: Jan 2026 restocks

Last post by BricksnBeatles - May 21, 2026, 12:27:31 AM

I appreciate it guys and I haven't quit. I just need to find my motivation again, somehow.

I'll be in Hville in a couple of hours. I'll swing by and Rochambeau ya if that helps.

A good beating might be needed. I don't mean that in a perverted way, lol.

What a tease :p