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#71
Build Reports / Polyphemus [One Knob Overdrive...
Last post by Aleph Null - February 09, 2026, 04:26:20 PMThis 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:
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.
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:
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.
#72
Open Discussion / Re: Got bored, building a bass...
Last post by jimilee - February 08, 2026, 05:06:23 AMQuote from: phreek on February 08, 2026, 12:17:48 AMHere's a while thread on the Sun on FSB. There's a vero layout, on page 2. I don't read much past that.Quote from: jimilee on February 05, 2026, 09:04:05 PMhah I wish I was better with schematics! Hell if I were I'd cook up a sunn beta bass pre and be done with it lolQuote from: jessenator on February 05, 2026, 07:56:40 PMSadly byoc has closed up shop. Had a final sale end of 2024. Don't recall the reasons.I think the BYOC schematics are linked by someone over on pedalpcb.
I have a mbp Promenade in my build queue. I wonder of aleph null's Otolith could be optimized for bass (maybe just cap values?) That's a very versatile beast and can do super sludgy to punchy.
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https://www.freestompboxes.org/viewtopic.php?t=25813
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#73
Open Discussion / Re: Got bored, building a bass...
Last post by phreek - February 08, 2026, 12:17:48 AMQuote from: jimilee on February 05, 2026, 09:04:05 PMhah I wish I was better with schematics! Hell if I were I'd cook up a sunn beta bass pre and be done with it lolQuote from: jessenator on February 05, 2026, 07:56:40 PMSadly byoc has closed up shop. Had a final sale end of 2024. Don't recall the reasons.I think the BYOC schematics are linked by someone over on pedalpcb.
I have a mbp Promenade in my build queue. I wonder of aleph null's Otolith could be optimized for bass (maybe just cap values?) That's a very versatile beast and can do super sludgy to punchy.
Sent from my iPhone using Tapatalk
#74
Open Discussion / Re: Got bored, building a bass...
Last post by jimilee - February 05, 2026, 09:04:05 PMQuote from: jessenator on February 05, 2026, 07:56:40 PMSadly byoc has closed up shop. Had a final sale end of 2024. Don't recall the reasons.I think the BYOC schematics are linked by someone over on pedalpcb.
I have a mbp Promenade in my build queue. I wonder of aleph null's Otolith could be optimized for bass (maybe just cap values?) That's a very versatile beast and can do super sludgy to punchy.
Sent from my iPhone using Tapatalk
#75
Open Discussion / Re: Got bored, building a bass...
Last post by jessenator - February 05, 2026, 07:56:40 PMSadly byoc has closed up shop. Had a final sale end of 2024. Don't recall the reasons.
I have a mbp Promenade in my build queue. I wonder of aleph null's Otolith could be optimized for bass (maybe just cap values?) That's a very versatile beast and can do super sludgy to punchy.
I have a mbp Promenade in my build queue. I wonder of aleph null's Otolith could be optimized for bass (maybe just cap values?) That's a very versatile beast and can do super sludgy to punchy.
#76
Open Discussion / Got bored, building a bass. Ne...
Last post by phreek - February 05, 2026, 06:10:57 PMSup gang! It's been a minute.
Firstly, WTF happened to BYOC?!
Nextly, is there a bass muff layout somewhere? Also, what bass pedals are you rocking? Gonna be looking for ideas for more sludgy, doom-esque kind of affair.
Whatcha got?
Firstly, WTF happened to BYOC?!
Nextly, is there a bass muff layout somewhere? Also, what bass pedals are you rocking? Gonna be looking for ideas for more sludgy, doom-esque kind of affair.
Whatcha got?
#77
General Questions / Re: all-silicon Cosmopolitan o...
Last post by Aleph Null - February 04, 2026, 07:46:53 PMNah. Just slap a BS170 in the stock circuit and see what it does. You might have to change R12 if the bias is way off, but it probably won't be.
#78
General Questions / Re: all-silicon Cosmopolitan o...
Last post by jessenator - February 04, 2026, 07:31:58 PMQuote from: Aleph Null on February 04, 2026, 04:52:42 PMWhat about using a mosfet for Q3?So something like this for the output stage?
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#79
General Questions / Re: all-silicon Cosmopolitan o...
Last post by Aleph Null - February 04, 2026, 04:52:42 PMWhat about using a mosfet for Q3?
#80
General Questions / all-silicon Cosmopolitan or Di...
Last post by jessenator - February 01, 2026, 06:11:59 PMRead in the build doc for the cosmo that Q3 can be subbed, theoretically with some other component changes. Wondering if anyone has tried it and come up with a tone they like there. Haven't breadboarded this one yet as I spent my time with another circuit:
As far as the dizzy tone, the PPCB forum came together with an NPN version of the Gnat (Buzzaround), which I like quite a bit. I was experimenting with it this weekend going through each, seeing what I could and couldn't replace with silicon.
Q1 and Q2 are just a darlington, but I still wanted to see if I could sub with equivalent low-beta with and without the resistor across C-B. Zero luck there.
Tried medium gain in Q1 (286) with no resistor. It sounded pretty decent with a low-ish gain (84) with a 2M2 across C-B. This was all still with an AC127 in Q3. Okay, but the sustain dropped off, might need to adjust a few other values, but not sure which.
However trying to replace Q3 with silicon was a dead end. Looked at some other schematics out there, tried adapting that final stage, even adding another gain stage before the final volume. Just sounds bad. Not even "different," just bad.
Seems like a similar situation with the Cosmo needing that germ in Q3... If anyone's got some insight on that one, I'd appreciate it.
IF what I'm looking for is better served up in a different circuit I'm open to direction. Just had this idea in my head to have two flavors of the same basic circuit.
As far as the dizzy tone, the PPCB forum came together with an NPN version of the Gnat (Buzzaround), which I like quite a bit. I was experimenting with it this weekend going through each, seeing what I could and couldn't replace with silicon.
Q1 and Q2 are just a darlington, but I still wanted to see if I could sub with equivalent low-beta with and without the resistor across C-B. Zero luck there.
Tried medium gain in Q1 (286) with no resistor. It sounded pretty decent with a low-ish gain (84) with a 2M2 across C-B. This was all still with an AC127 in Q3. Okay, but the sustain dropped off, might need to adjust a few other values, but not sure which.
However trying to replace Q3 with silicon was a dead end. Looked at some other schematics out there, tried adapting that final stage, even adding another gain stage before the final volume. Just sounds bad. Not even "different," just bad.
Seems like a similar situation with the Cosmo needing that germ in Q3... If anyone's got some insight on that one, I'd appreciate it.
IF what I'm looking for is better served up in a different circuit I'm open to direction. Just had this idea in my head to have two flavors of the same basic circuit.