Missing Build Docs / Schematics

We live in a "Me first" world and people often forget that other people have lives and struggles of their own. Hang in the Robert, you and all of us are doing the best we can. You have hands down the best pcbs of any site and I can't imagine how crazy it must be running this entire business by yourself while maintaining your sanity in your personal life. The order I placed with you a few days ago will put my project list up to 16, so thanks to you, I'll be plenty busy for weekends to come. Rock on and keep truckin'!
 
Does anyone have the schematic for the ‘Scenario Preamp’? The cornerstone Gladio SC. I could’ve sworn I seen it on a thread her, somewhere. And, if not, Robert, can we PLEASE?! get the schematic???
 
Mbens11 said:
Does anyone have the schematic for the skeptical buffer by any chance
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While there is no official one posted from PedalPCB, I did attempt to trace the PCB (PCB568).

I first posted this on 6/26/2023. I have revised my post and the schematic on 6/28/2023.

I applied some information I recalled about producing a bipolar voltage supply from Tagboard Effects in order to better trace the power section. I also had the resistors/capacitors mixed up on the first section of IC1.

I am 90% accurate that my schematic is correct.

All parts on my schematic match the current BOM for the Skeptical Buffer.
 

Attachments

  • EUNA Schematic Revision 41024_1.png
    EUNA Schematic Revision 41024_1.png
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@Robert I’m sorry to keep asking, but I’ve been trying to wait patiently for a while now. Can I PLEASE get the updated schematic for the pot and kettle?? I ordered a new revision board just to get the trace for the 4th switch, but the usps has it in limbo at the moment.
 
marksescon said:
While there is no official one posted from PedalPCB, I did attempt to trace the PCB (PCB568).

I first posted this on 6/26/2023. I have revised my post and the schematic on 6/28/2023.

I applied some information I recalled about producing a bipolar voltage supply from Tagboard Effects in order to better trace the power section. I also had the resistors/capacitors mixed up on the first section of IC1.

I am 90% accurate that my schematic is correct.

All parts on my schematic match the current BOM for the Skeptical Buffer.
Click to expand...
I tried it on the emulator software and that doesn't work. Maybe there's still something wrong in your schematic.
I advice to open a new thread about it. Maybe somebody can see what's this mistake, if it is there.

EDIT: I guess there's something about the bias of the op-amp. Check R1 and R5.
 
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Elijah-Baley said:
I tried it on the emulator software and that doesn't work. Maybe there's still something wrong in your schematic.
I advice to open a new thread about it. Maybe somebody can see what's this mistake, if it is there.

EDIT: I guess there's something about the bias of the op-amp. Check R1 and R5.
Click to expand...
That threw me off initially as well, but according to a couple other builders (Breakfast Audio, Niche Devices), TL072 (dual op amp) runs on +17V/-17V, meaning ground, or better stated, “0V,” is half the op amp supply. If you think about the power supply as potential and absolute numbers, it makes sense.

R5 is biasing the op amp. I’ve seen synths and studio equipment schematics that employ the same stuff as well. I also suspect R7 plays some sort of role as well but I am not sure and basing this purely on the Eunuch where R7 is connected to the bias voltage.

Furthermore, if you look at the Eunuch Buffer (https://www.pedalpcb.com/product/pcb581/), which is the Skeptical Buffer minus the elaborate bipolar voltage supply and runs on 9V/0V, R100 and R101 forms a voltage divider, equaling half the op amp power supply or 4.5V. (Eunuch can run at higher voltages, but 9V is the ‘starting’ voltage.)

I postulate that if you want the Eunuch to match the headroom of the Skeptical Buffer, you may need to run the Eunuch at 35V 30V.

EDIT:

I have also attached a picture for what I believe is the Eunuch Buffer schematic so that you may try that in LTSpice or any other simulator. I pieced it together based purely on speculation and looking at the picture of the PCB on the product page.

Note:
  • Pin 8 and 4 of IC1 are now attached to +V and ground (or 9V and 0V, respectively)
  • The addition of the voltage divider network (R100, R101) and C11. The part values are numbers I pulled out of thin air, but as long as R100 and R101 are of equal resistance, the circuit should theoretically work.
  • R5 and R7 are now attached to Vref (VEE, 4.5v).
 

Attachments

  • EunuchBuffer Schematic.png
    EunuchBuffer Schematic.png
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marksescon said:
That threw me off initially as well, but according to a couple other builders (Breakfast Audio, Niche Devices), TL072 (dual op amp) runs on +17V/-17V, meaning ground, or better stated, “0V,” is half the op amp supply. If you think about the power supply as potential and absolute numbers, it makes sense.

R5 is biasing the op amp. I’ve seen synths and studio equipment schematics that employ the same stuff as well. I also suspect R7 plays some sort of role as well but I am not sure and basing this purely on the Eunuch where R7 is connected to the bias voltage.

Furthermore, if you look at the Eunuch Buffer (https://www.pedalpcb.com/product/pcb581/), which is the Skeptical Buffer minus the elaborate bipolar voltage supply and runs on 9V/0V, R100 and R101 forms a voltage divider, equaling half the op amp power supply or 4.5V. (Eunuch can run at higher voltages, but 9V is the ‘starting’ voltage.)

I postulate that if you want the Eunuch to match the headroom of the Skeptical Buffer, you may need to run the Eunuch at 35V.

EDIT:

I have also attached a picture for what I believe is the Eunuch Buffer schematic so that you may try that in LTSpice or any other simulator. I pieced it together based purely on speculation and looking at the picture of the PCB on the product page.

Note:
  • Pin 8 and 4 of IC1 are now attached to +V and ground (or 9V and 0V, respectively)
  • The addition of the voltage divider network (R100, R101) and C11. The part values are numbers I pulled out of thin air, but as long as R100 and R101 are equal, the circuit should theoretically work.
  • R5 and R7 are now attached to Vref (VEE, 4.5v).
Click to expand...
I understand what they are saying but the TL072IP datasheet says max 36V.

Also if you run the Eunuch Buffer at 35V and the TL072 can only handle 17V wouldn't it fry the chip?

Can someone check me on the datasheet to make sure I am reading it correctly.
 
ThePanda said:
I understand what they are saying but the TL072IP datasheet says max 36V.

Also if you run the Eunuch Buffer at 35V and the TL072 can only handle 17V wouldn't it fry the chip?
Click to expand...

You are right, as the Eunuch product page denotes a range from 9V to 30V. I will correct my original post. Running Eunuch at higher voltages to match the headroom of the Skeptical is a wild proposal that I haven’t substantiated. I am not entirely sure it’s true, just a suggestion I based on people turning synth modules into guitar pedals.
 
ThePanda said:
understand what they are saying but the TL072IP datasheet says max 36V.

Also if you run the Eunuch Buffer at 35V and the TL072 can only handle 17V wouldn't it fry the chip?
Click to expand...
Vsupply is the max operating potential.

Vs=(V+)-(V-)

TL07X devices have a Vs_max of 42V. The 36V spec refers to the max on the input pins (i.e., common mode voltage and voltage differential), not the supply absolute.

EDIT: The 36V spec only applies to M-suffix (military), NS, and PS packages; all others are -0.5–0.5V.
 
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