High headroom Preamp Pedal Schematic Design Help

hydr41n

hydr41n

New member
Hi Guysss!!! Does Anyone have a time to help me create a schematic for this idea? Or is this thing even gonna work 🤣

I don't know if i get it right for this idea since I'm a still a noob and just read some documents and research. Any feedback, critics to Enlighten me is very very welcome!

This is basically the Scenario Preamp in the core.

Ideally run this on 28v > 30v
OPAMPs -> TL072 / OPA2134 *if i have the budget
JFET -> 2N5457 / J201 *if i have the budget

// === POWER SUPPLY SECTION ===
// 18V DC Input -> Boost to 30v
+18VDC_IN ---> [EMI Filter] ---> [Input Diode Protection: 1N5819] --->
[Electrolytic Cap: 470uF/50V] || [Ceramic: 100nF] --->
[TDK-Lambda I3A4W005A150V-003-R DC-DC Boost Module] or any alternative idea??
→ Set Output to +30V (via trim pin)
→ Optional LC Filter: 10uH + 220uF/35V Low ESR Output Cap
→ Clean +30VDC rail for all circuits

// === INPUT BUFFER ===
[Guitar In] ---> [OPA2134 U1A] (Buffer & Splitter)
- Main Path: U1A output → Volume Pot (100kA) → C1 (100nF)

// === EARLY GAIN STAGE ===
C1 ---> Gate of Q1 (J201 - First Gain Stage)
Drain: R4 (12k) to +30V
Source: R5 (1.5k) to GND
Gate Bias: R6 (1M) from V+, R7 (1M) to GND
Optional bypass cap C4 (2.2uF, SW1 for Custom/Flat)
Drain output ---> C2 (100nF)

// === VOICING SWITCHES ===
- SW1: Custom/Flat (Q1 bypass cap toggle)
- SW2: Bright switch (120pF across Volume pot)
- SW3: Deep switch (220nF cap before Q1)
- SW4: Q2 Bypass cap voicing toggle (2.2uF on source)

// === TONESTACK ===
C2 ---> Tone Stack Node:
- Treble: Treble Pot (250kB) → C4 (250pF) to GND
- Mid: Mid Pot (250kA) → R11 (15k) to GND
- Bass: Bass Pot (1MB) → C6 (100nF) to GND
→ Shared tone stack output through C5 (10nF)
Output of tone stack ---> C3 (100nF)

// === POST-TONESTACK BUFFER ===
C3 ---> [OPA2134 U2A] (Buffer Stage)
- Feedback: R12 (100k) in parallel with Rboost (1.5k) + Cfb (220pF)
- Input R13 (100k), +IN to GND via 100k
U2A Output ---> C8 (100nF)

// === DRIVE ===
C8 ---> Gate of Q2 (J201 - 2nd Gain Stage)
Drain: R14 (12k) to +30V
Source: R15 (1.5k) to GND
Gate Bias: 1M Reverse Audio Pot:
+30V --[1M RA Pot]-- Wiper to Gate --[100k]-- to C8, bottom to GND
Optional: Bypass cap C9 (2.2uF, SW4)
Drain output ---> C10 (100nF)

// === LOCAL NEGATIVE FEEDBACK LOOP ?????? ===
Q2 Drain ---> Rfb (220k) + Cfb (220pF) ---> Source of Q2 (R15)

// === ROTARY FILTERS ===
Q2 output (C10) ---> Filter1 (Rotary High Cut)
- 6-pos rotary caps (330pF–3.3nF)
→ R20 (100k) to GND
Then → Filter2 (Rotary Low Cut)
- 6-pos rotary caps (2.2nF–10nF)
→ R21 (10k) to GND
Output of Filter2 ---> C11 (100nF)

// === MIXING STAGE ===
C11 + Clean tap from U1A (pre-gain) ---> [OPA2134 U1B] (Summing Mixer)
- Clean path attenuated via internal trim: [50k trim pot] + [10k resistor] from U1A output ****not sure if I need a phase inverter here!!!!
- Dirt path via internal trim: [50k trim pot] + [10k resistor] from Filter2
- Feedback R18 (100k), +IN to GND via 100k
- Clean/Dirt ratio adjustable 0–100% via internal trims (default set 60:40? need to test -> clean:dirt)

// === ***OPTIONAL FILTER SECTION ***INTERNAL SWITCH===
C13 ---> SW6: Low-end rolloff <85Hz (220nF + 10k) --->
Then → SW7: High-end smoothing >6kHz (10k + 470pF) --->

// === OUTPUT DRIVER ===
→ Level Pot (100kA)
Wiper ---> [OPA2134 U2B] (Low-Z Line Driver)
- Feedback: R22 (100k) in parallel with Rboost2 (1.5k) + Cfb2 (220pF)
- Input R23 (100k), +IN to GND via 100k
U2B output ---> Output Jack
 
Last edited:
hydr41n said:
// === TONESTACK ===
C2 ---> Tone Stack Node:
- Treble: Treble Pot (250kB) → C4 (250pF) to GND
- Mid: Mid Pot (250kA) → R11 (15k) to GND
- Bass: Bass Pot (1MB) → C6 (100nF) to GND
→ Shared tone stack output through C5 (10nF)
Output of tone stack ---> C3 (100nF)
Click to expand...
Can you show an example schematic with such a tone stack?
 
temol said:
Can you show an example schematic with such a tone stack?
Click to expand...

1753946462666.png

Sorry for my bad drawing. If I understand it correctly, I think it would be like this? I initially saw samples of tone stack on D-style preamap section. But idk if I write it correctly on my text format schematics or if i even understand it correctly.
 
hydr41n said:
I can 🤣

I chatgpt the OPAmps components 🤣 and maths for the biased for jfets and power section! other sections are just from D-style schematics.
Click to expand...
Haha it was the section headers formatted like ChatGPT that really gave it away. I didn’t mean to shame. You can learn a lot from ChatGPT but I’d highly recommend you get yourself a breadboard and some components and try putting it all to use.

Start with something simple like a fuzz face. If you’re really new, coppersound sells silicon fuzz face breadboard kits that have components and teach the basics. From there you can expand into bigger and better things and eventually get to where you can build out your vision of this pedal, but coming to it from a better place of understanding. You might be diving in a little too deep to start with this being your first idea/attempt.
 
No worries I know I'm a noob and pretty new with this field, that is also why i am asking for help 🤣 . i build my first scenario preamp but i have my ideas and i want to make it happen *i know i am taking a big leap with this but i want to make it happen. but as you know i can't put it rn into a schematics, i dont have the proper knowledge. All i have is basic understanding, ideas and AI for sourcing alternative components or how the opamps woks etc. I already ordered on coppersound diy kit but it will take months to arrived. I was researching for a week for this and wanted to get input from you guys.
 
Last edited:
hydr41n said:
No worries guys! I'm a noob and pretty new with this field, that is also why i am asking for help 🤣 . i build my first scenario preamp but i have my ideas and i want to make it happen *i know i am taking a big leap with this but i want to make it happen 🤣. but as you know i can't put it rn into a schematics, i dont have the proper knowledge. All i have is basic understanding, ideas and AI for sourcing alternative components or how the opamps woks etc. I already ordered on coppersound diy kit but it will take months to arrived. I was researching for weeks for this and wanted to get input from you guys.
Click to expand...
Hey we all started from somewhere at some point. I don’t know where you’re located but I’d imagine you could probably find a way to get a breadboard for relatively cheap from somewhere closer that won’t take months to ship. If you already built a scenario preamp then you know how to source components, unless perhaps you bought it as a kit from somewhere like Musikding, but they also sell breadboards!

Anyways, still highly recommend you try to breadboard a simple circuit like a fuzz face, LPB-1, elektra, or something like that. Then once you’re comfortable with how it all works try to build this idea out. That’s how you can make this happen. It’ll be a process for sure but it’s worth it!
 
AceHyzer said:
Haha it was the section headers formatted like ChatGPT that really gave it away. I didn’t mean to shame. You can learn a lot from ChatGPT but I’d highly recommend you get yourself a breadboard and some components and try putting it all to use.

Start with something simple like a fuzz face. If you’re really new, coppersound sells silicon fuzz face breadboard kits that have components and teach the basics. From there you can expand into bigger and better things and eventually get to where you can build out your vision of this pedal, but coming to it from a better place of understanding. You might be diving in a little too deep to start with this being your first idea/attempt.
Click to expand...
Thanks for the advice! yes i started doing my mods from a simple boost to become OD to Dist or Fuzz by patching schematics basically 🤣 even i dont have the best of knowledge of how the hell all the parts works, i pretty much have the logical thinking or you can say common sense for this kind of thing since i love to code.
 
AceHyzer said:
Hey we all started from somewhere at some point. I don’t know where you’re located but I’d imagine you could probably find a way to get a breadboard for relatively cheap from somewhere closer that won’t take months to ship. If you already built a scenario preamp then you know how to source components, unless perhaps you bought it as a kit from somewhere like Musikding, but they also sell breadboards!

Anyways, still highly recommend you try to breadboard a simple circuit like a fuzz face, LPB-1, elektra, or something like that. Then once you’re comfortable with how it all works try to build this idea out. That’s how you can make this happen. It’ll be a process for sure but it’s worth it!
Click to expand...
I get my components from digikey. but yeah you are right, maybe i should just get breadboard to really start this.
 
hydr41n said:
// === POWER SUPPLY SECTION ===
// 18V DC Input -> Boost to 30v
+18VDC_IN ---> [EMI Filter] ---> [Input Diode Protection: 1N5819] --->
[Electrolytic Cap: 470uF/50V] || [Ceramic: 100nF] --->
[TDK-Lambda I3A4W005A150V-003-R DC-DC Boost Module] or any alternative idea??
→ Set Output to +30V (via trim pin)
→ Optional LC Filter: 10uH + 220uF/35V Low ESR Output Cap
→ Clean +30VDC rail for all circuits
Click to expand...
How do you plan to power the opamps? You either need a symmetrical power supply or a reference voltage from a voltage divider.


hydr41n said:
+IN to GND via 100k
Click to expand...

GND... It depends on whether you have a symmetrical power supply or a reference voltage (Vr)

But...
Take a proven hi-gain circuit with opamps, add a few things, remove a few. There will be time to come up with your own schematics later...You currently have a need, but you're approaching it from the wrong angle. Before asking a forum to evaluate a schematic composed of random blocks, it's worth spending some time looking at other, ready-made solutions. And using what's available.And if you really want to start your own, more challenging way, ltspice is a very easy-to-use program. There are tutorials – you can draw a schematic there and see what the output will be, you can even upload a WAV file and run it through the circuit.Draw the schematic by hand and post it on the forum. I'll draw it for you in ltspice, and you can test and learn from it.
 
temol said:
How do you plan to power the opamps? You either need a symmetrical power supply or a reference voltage from a voltage divider.




GND... It depends on whether you have a symmetrical power supply or a reference voltage (Vr)

But...
Take a proven hi-gain circuit with opamps, add a few things, remove a few. There will be time to come up with your own schematics later...You currently have a need, but you're approaching it from the wrong angle. Before asking a forum to evaluate a schematic composed of random blocks, it's worth spending some time looking at other, ready-made solutions. And using what's available.And if you really want to start your own, more challenging way, ltspice is a very easy-to-use program. There are tutorials – you can draw a schematic there and see what the output will be, you can even upload a WAV file and run it through the circuit.Draw the schematic by hand and post it on the forum. I'll draw it for you in ltspice, and you can test and learn from it.
Click to expand...
Thanks! I supposed I am pretty excited with this idea that i skip many steps! you are absolutely right, i need to approach it from the different angle and study the existing circuit blocks to build this. I am currently using the scenario preamp as my basis for how it splits the signal for clean and a gain section pattern. I want to use cascading jfets instead for my gain section but i will study how can i biased this properly and how to power it up properly. I will need your help guys again for feedback and insights after i am done with the schematics.
 
Once you get a breadboard you'll need to approach this project in stages. First you'll need to learn how to breadboard and transfer schematic to breadboard. You'll need to understand the concept so I recommend going through a few of these first. You need to walk before you can run otherwise you'll get super discouraged and rage quit.

From there, take the training wheels off and breadboard something purely from a schematic. There are tons on the shop site. Start small and work your way up.

Then do research. I mean, LOTS of reading. Learn how tone stacks work, gain stages, boosters, clipping. Your breadboard will be your friend here to help solidify the learning.

fig

Thread 'Resources'

Post links to supplies, tools, tutorials, cat videos, that turbo-lift blooper reel. Anything related to breadboarding (makes sense huh?)
  • Like

Then work backwards. Have a shower thought of "What happens if I make a Red Llama circuit with a Baxandall tone stack?". Put it on a breadboard using those circuit legos you've drilled into your head. Congrats, this is your first original circuit!! Then draw a schematic based on your breadboarded project.

THEN it's time to tackle the OP project. Now that you've built up some sort of knowledge base (including schematic drawing) you may or may not notice that the application of all those stages won't work. Build and tweak everything in stages on a breadboard. Your original idea may sound good on paper but not in real life. It happens.
 
BuddytheReow said:
Once you get a breadboard you'll need to approach this project in stages. First you'll need to learn how to breadboard and transfer schematic to breadboard. You'll need to understand the concept so I recommend going through a few of these first. You need to walk before you can run otherwise you'll get super discouraged and rage quit.

From there, take the training wheels off and breadboard something purely from a schematic. There are tons on the shop site. Start small and work your way up.

Then do research. I mean, LOTS of reading. Learn how tone stacks work, gain stages, boosters, clipping. Your breadboard will be your friend here to help solidify the learning.

fig

Thread 'Resources'

Post links to supplies, tools, tutorials, cat videos, that turbo-lift blooper reel. Anything related to breadboarding (makes sense huh?)
  • Like

Then work backwards. Have a shower thought of "What happens if I make a Red Llama circuit with a Baxandall tone stack?". Put it on a breadboard using those circuit legos you've drilled into your head. Congrats, this is your first original circuit!! Then draw a schematic based on your breadboarded project.

THEN it's time to tackle the OP project. Now that you've built up some sort of knowledge base (including schematic drawing) you may or may not notice that the application of all those stages won't work. Build and tweak everything in stages on a breadboard. Your original idea may sound good on paper but not in real life. It happens.
Click to expand...
Thanks for this! gonna read/try this and try to understand from this circuit blocks. i just ordered resistor kits, breadboard, fets and opamps so i can test it physically not just on paper, excited to build this legos 🤣
 
TL072 max voltage is 30v. I wouldn't push it to that.
2134 is 36V
At 30v, you'll need 50/63v electros, which will be pretty large.
Honestly, 18V is going to give you enough headroom for anything.
 
jwin615 said:
TL072 max voltage is 30v. I wouldn't push it to that.
2134 is 36V
At 30v, you'll need 50/63v electros, which will be pretty large.
Honestly, 18V is going to give you enough headroom for anything.
Click to expand...
Thanks! I see so 18v will be enough, is the 2134 an overkill for my use case?
 
This is basically the Scenario Preamp in the core.
...
To be honest I don't know how to make schematics. I can only read basics, but make it? I can't, I know it sounds ridiculous.
...
1753946462666-png.100223


...

i have my ideas and i want to make it happen *i know i am taking a big leap with this but i want to make it happen.
Click to expand...



*Claims to not know how to draw a schematic, draws one when prompted.*



That last sentence I quoted is the key — you have ideas you want to make happen.

That's what got me to finally learn how to read schematics, I had ideas I wanted to make happen.
There's tons I still don't know/understand, but I'm a step closer to making my ideas happen because I learned the basics of reading a schematic and THEN started to breadboard thnigs.

Honestly, that long list of ChatGPT stuff gives me a headache — I don't understand the underlying basic info it's trying to convey.
Would be so much easier to read a schematic to try and help you...

So... TAKE that SCENARIO schematic and break it down and build it back up as your own on the breadboard.

This idea of yours, it's exciting; enjoy your journey.
 
hydr41n said:
Thanks! I see so 18v will be enough, is the 2134 an overkill for my use case?
Click to expand...

IMO... High-end low-noise op-amps are great for EQs and compressors — anything that's clean where a noisy opamp would degrade your signal.

For any DIRT circuits where you are degrading your signal anyway, well, then any standard op-amp will do: JRC4558, TL072, LM1458...

However, if it sounds good to your ears it IS good, so audition the opamps on your breadboard.
 
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