School me on the EQ section of the pathogen distortion

[acuevo]

Please bear with me, I’ve been building pedals for a few years but i’m a noob at understanding and tinkering with the circuits. I apologize if these particular EQ circuits have been discussed elsewhere, i’m sure they have. I’ve been searching and just not quite able to wrap my head around them.

Anyway, to the point. I built a pathogen and also breadboarded one to tinker with and see what i could get out of it.

So far, i’ve replaced the hard clipping diodes (D1 and D2) with a red LED and a blue LED. I’ve also replaced one of the soft clipping diodes (D4) with a blue LED. Finally i changed R22 to a 100k resistor to bring the overall output level down some, as using the LEDs made it insanely loud.

It sounds pretty good!! those small changes are subtle but fun. I used the blue LEDs as that was what i had laying around, but i’m relatively pleased with the result. My trouble is i lost a LOT of bass and the mid character has changed quite a but. If i max the bass knob out its still on par with the original circuit maxed out, it just drops off super early without any real adjustable area. The mids knob works but seems to have less range (even if i do turn down the bass knob). Overall it sounds pretty scooped and i’d like to try to get some mids back if i can.

So i guess my questions are… did changing R22 make me lose some of the make up gain for the EQ section, thus making the mids and bass more static? Or did changing to LEDs affect the tone that much that now the EQ section needs a rework? I played with the tonestack calculator online using the James dual bass capacitor passive circuit (which seems pretty similar) but using the values from the pathogen it seems like the bass already goes almost all the way to 0db and changing anything more seems like its going to mess with the treble and the mids even more.

Sorry for the wordy post if i’m unclear with what i’m asking i can try to explain it better.

 

[jesuscrisp]

Does it sound correct if you swap the parts back to stock on your breadboard? There's always the chance of something else being wrong or not making contact.

Else, R22 and C23 form a filter and swapping R22 to a much lower value will affect the tone quite a bit. Try bumping up C23 to 2n2 and see if that helps.

 

[acuevo]

*Facepalm* I didn’t even consider that changing the resistor would change the filter for that segment. Thank you for that suggestion! Yes i originally tested the board as “stock” to make sure everything worked as it should and all was well.

I swapped in a 2n2 for C23 and it really helped a lot! The bass still seems to roll off rather quickly but there is more bass available now. Overall things seem just a weee bit darker. The mids knob is working pretty well now.

Do filters in the feedback loop like that function the same as a basic high pass filter?

I actually really am loving how it sounds. The original circuit is great for lead stuff, my goal for this was to get a nice heavy rhythm sound and its going QUITE nicely so far.

 

[jwin615]

Try swapping C14 to 470-680nf
That should give more bass on the end of the sweep, I think.

 

[jwin615]

Isn't this the circuit that's the wampler triple wreck with 2-3 value changes?
Maybe compare to that schem.

 

[acuevo]

Isn't this the circuit that's the wampler triple wreck with 2-3 value changes?
Maybe compare to that schem.

Yeah its the same circuit. Differences are one of the Vref resistors and one of the mids capacitors. I’ve been considering seeing how the mids will respond, but i feel like the Vref resistor may not change much? Correct me if i’m wrong. I can’t remember the value on the triple wreck, but i believe its a 6.8k on the pathogen. Also i think the overall power supply on the triple wreck is less involved.

I’ll give that a try with C14 as well, thank you!

 

[jesuscrisp]

Vref resistors won't make a difference and I wouldn't try for higher values for C14 for increasing bass.
Increasing it to 470-680n will only make it act at even lower frequencies, which will make for even less audible changes.
If anything you might want to decrease it to start shelving on a higher frequency. Sounds counter-intuitive, but might help to actually drop it to 47n or so.

 

[jwin615]

Vref resistors won't make a difference and I wouldn't try for higher values for C14 for increasing bass.
Increasing it to 470-680n will only make it act at even lower frequencies, which will make for even less audible changes.
If anything you might want to decrease it to start shelving on a higher frequency. Sounds counter-intuitive, but might help to actually drop it to 47n or so.

Not questioning you, pure question...
How does raising the cutoff /corner freq of a variable hpf allow more bass?
Tone stacks arent my string suit but since this isn't in a feedback path, I don't get it. At least this early today(or that late last night).

 

[jesuscrisp]

How does raising the cutoff /corner freq of a variable hpf allow more bass?

It's about perceived bass, which in guitar tone is really about the 100-250Hz area. What you see here is a passive James tonestack. It doesn't boost bass, it cuts frequencies by shelving at a certain corner frequency. Putting in the values of the Pathogen into a tone stack calculator you will see that after halfway, it mostly allows frequencies below 100Hz to pass through. Due to the linear taper, frequencies up to 100Hz are basically maxed at halfway, turning it up further only increases lower frequencies than 100Hz, which adds a good bit of low end, but it's less noticeable. It is probably done so it feels bigger at halfway, but ultimately a log taper would give better response throughout the sweep, which is also something I'd recommend to make the bass control more "actually usable". Dropping C14 to 47n will also make the bass control affect the fullness of the sound more.

Increasing C14 as you said shifts the shelf to a lower frequency, actually killing a lot of the guitar frequency range that would make it sound big. Basically just adding low bass rumble but no actual body.

 

[acuevo]

Thanks guys! For your help and patience. This is all interesting stuff.

Over 100hz would definitely be more useful than all the sub-bassy stuff. I have an actual abasi pathos as well and interestingly enough the bass is incredibly overbearing in that circuit, i have to turn it way down (like below 9o’clock) to get to manageable levels. The stock pathogen (with the 1N4148s) is not nearly as bad. I wonder if wampler possibly used a log pot for the bass in the original.

At any rate, this thing is sounding great to my ears (i love me some LED clipping). I’ll try a 47n for C14 tonight and see how it goes.

Thanks again guys for all the help!

 

[andrewsrea]

LED clipping requires higher forward voltages to engage than 1N4148 diodes (over double). Lower frequencies require more energy to be produced, thus will trip the forward voltages sooner than higher frequencies. In essence, the LED clipping diodes created a high-pass filter in the circuits between IC 3.1 and IC 3.2, until the gain control is at a point where all audible frequencies are exceeding Vf (significant amount of gain for the upper mid-range and above).

To bring back the bass and mids without drastically changing R22 or C23, you might want to experiment with simply strapping a 1nF cap across D1 or D2. You may want to experiment with the cap value to find which brings the results you are after.

Addressing those frequencies at IC 1.2 requires drastic change, where subtle changes earlier are probably the better move. Sometimes the frequencies you are trying to boost on the back end, are no longer there due to earlier filtering (and there is a lot early on, rolling off frequencies below 723Hz).

Then if loudness is still a problem, try swapping out the A100K Volume for an A50K. It will make your volume control more usable in its range of motion and lower your output impedance a bit, perhaps making it more friendly for downstream pedals. if you can still find a 'sweet spot' using the stock A100K, then don't mess with what works.

Hope this helps.

 

[acuevo]

LED clipping requires higher forward voltages to engage than 1N4148 diodes (over double). Lower frequencies require more energy to be produced, thus will trip the forward voltages sooner than higher frequencies. In essence, the LED clipping diodes created a high-pass filter in the circuits between IC 3.1 and IC 3.2, until the gain control is at a point where all audible frequencies are exceeding Vf (significant amount of gain for the upper mid-range and above).

To bring back the bass and mids without drastically changing R22 or C23, you might want to experiment with simply strapping a 1nF cap across D1 or D2. You may want to experiment with the cap value to find which brings the results you are after.

Addressing those frequencies at IC 1.2 requires drastic change, where subtle changes earlier are probably the better move. Sometimes the frequencies you are trying to boost on the back end, are no longer there due to earlier filtering (and there is a lot early on, rolling off frequencies below 723Hz).

Then if loudness is still a problem, try swapping out the A100K Volume for an A50K. It will make your volume control more usable in its range of motion and lower your output impedance a bit, perhaps making it more friendly for downstream pedals. if you can still find a 'sweet spot' using the stock A100K, then don't mess with what works.

Hope this helps.

I’ll give this a try as well. When you say “across” do you mean in parallel with one of the diodes to ground? Or in parallel with the circuit (one side of the cap on either side of one of the diodes)?

 

[andrewsrea]

I’ll give this a try as well. When you say “across” do you mean in parallel with one of the diodes to ground? Or in parallel with the circuit (one side of the cap on either side of one of the diodes)?

Yes - 'across' means parallel. You can actually just temporarily solder the cap leads to the diode leads to 'audition' them.

 

[acuevo]

Thank you everyone for the suggestions, I think i’ve landed on a few value changes and tweaks that i am satisfied with. I’ll post back later with a list!

 

[acuevo]

I'm going to try to do this from memory since i don't have my notated schematic in front of me lol.

D1, D2 and D4 remain the red/blue LEDs i had in there at first.

I reverted C23 and R22 to the original 330p and 680k values, changed the volume pot to a 50k as suggested and volume is more manageable now.

In messing with the TB tone stack - i found a 47n for C14 to be a little too "woofy" (to use a technical term). So i split the difference with a 68n and thats working pretty well for me now.

I experimented with C21 and changed it to the 1n found in the wrecktifier - i liked what it did but wanted just a little LESS of what it did, if i remember correctly i put a 560p in there. Made it a little more juicy i guess you could say?

Finally - i thought the brightness cap C25 was a little too dark when engaged, so i swapped that for a 3n3 - if my math is right (and theres a very good chance its wrong) this makes the cutoff for the filter around 5khz or so. Its a more subtle difference when using it but it works better in my opinion - especially if i ever want to use it for recording.

I haven't actually done this part yet, but i'll also be changing the bass pot to an A100k instead of a B100k. Now that i changed the filter in IC1.2 back to stock the bass control is absurd again and having it change more gradually will make dialing it a lot easier.

If y'all are interested i can post demos down the road and a side by side with a pathos. The differences are relatively subtle, but work great for me. In my opinion the pathos works great as a lead pedal but was lacking for a heavy rhythm sound. I set out to mod it to my taste to do that and by golly it worked out pretty darn good! Thanks to all of you for the help!