Parts list:
Capacitor (C) - 10 µF (microfarads), 50V - serves as both the coupling capacitor and the high-pass filter capacitor
Resistor (Rf) - 2.4 kΩ (kiloohms), 1/4W - fixed resistor for the high-pass filter
Potentiometer (P) - 10 kΩ (kiloohms), linear taper, rated for at least 24V - acts as a variable resistor for the gain control
Non-inverting input resistor (R1) - 1 kΩ (kiloohms), 1/4W
Feedback resistor (R2) - 9 kΩ (kiloohms), 1/4W
Op-amp (U1) - OPAx134 series (e.g., OPA134PA), rated for ±2.5V to ±18V dual supply or 5V to 36V single supply - a rail-to-rail operational amplifier
TPA3118 mono digital amplifier board - rated for a supply voltage range of 8V to 26V, and up to 3A of output current.
Wiring instructions:
1. Connect the bass guitar input signal to one end of the resistor Rf (2.4 kΩ). Connect the other end of Rf to one end of capacitor C (10 µF, 50V). The resistor Rf and capacitor C form the high-pass filter.
2. Connect the other end of capacitor C to the non-inverting input (+) of the op-amp (OPAx134).
3. Connect one end of resistor R1 (1 kΩ) to the junction of capacitor C and the non-inverting input (+) of the op-amp.
4. Connect the inverting input (-) of the op-amp to the junction of resistors R1 and R2 (9 kΩ). Connect the other end of R2 to the ground (GND).
5.Connect the wiper (middle pin) of the potentiometer P (10 kΩ) to the junction of the capacitor C and the non-inverting input (+) of the op-amp. Connect one end of P to the output of the op-amp and the other end to the ground (GND). The potentiometer P acts as a variable resistor for gain control.
6. Connect the other end of resistor R1 to the output of the op-amp.
7. Connect the output of the op-amp to the audio input of the TPA3110 amplifier board.
8. Connect the speaker to the output of the TPA3110 amplifier board, observing the correct polarity (positive and negative terminals) according to the board's specification.
9. Connect all GND points together: the GND of the op-amp, the GND of the TPA3110 amplifier board, and the GND of the external power plug.
I used chat GPT to design an ultra-simple bass amplifier around the TPA3110 and I was following along until step 5, but step 6 says I should connect R1 to the output of the op amp but there is already something connected there. Where did I mess up? Also, how do I "connect all ground points together" when it gets to step 9? Should I physically link the grounds, or does it mean they should all go to the chasis? Thanks for your help!
Those wiring instructions came from chatGPT? If so, it has created the world's first (to my knowledge) resistor (R1) with three (count 'em) ends. The first end in 3), the second end in 4) and the final end in 6).
Ah ok, so it was Chat GPT messing up haha. Is there a way to redesign the amp? The input is supposed to be a high pass filter at 65hz with an op amp to amplify my bass guitar's signal to line level, and the TPA3110 based board is the smallest amp circuit I could find for my needs. The potentiometer is a volume knob. Can you suggest a way to salvage the design, or should I scrap chat GPT's suggestion completely?
I think the design can be salvaged yes. The high pass filter - I think the 10uF probably needs reducing in value to 1uF to get the 65Hz cutoff, the 2k49 going to GND. The 9k and 1k resistors can re-arranged to give a gain of 10 for the opamp stage. That means the 9k between pin6 and pin2, 1k between pin2 and GND. Then the pot connected between the output of the opamp (pin6) and the TPA3110. Assuming that's the desired configuration.
Doesn't even show if single or dual supply
and no power supply decoupling.
assuming your using 9 volts common with MI pedals
then a single supply circuit would be entirely different.
Bass guitar E = 41 Hz low B = 31 Hz
typical high pass protection would be closer to those
values with a 3rd or 4th order filter.
not a basic 6 dB input filter.
Input filter usually set to below 20 Hz
bass pickup around 8k to 12k
So the typical MI input impedance be around 1 meg
and no power supply decoupling.
assuming your using 9 volts common with MI pedals
then a single supply circuit would be entirely different.
Bass guitar E = 41 Hz low B = 31 Hz
typical high pass protection would be closer to those
values with a 3rd or 4th order filter.
not a basic 6 dB input filter.
Input filter usually set to below 20 Hz
bass pickup around 8k to 12k
So the typical MI input impedance be around 1 meg
You might be better off with a simple google search of proven TpA3110 designs in this case. Chat GPT uses predictive guess of the next word based on context of preceding words. There is no sanity check or assurances they make sense. It’s fine for talk and making shopping lists, basic correspondence emails, cover letters, or ad copy - wordy things. Even computer code is based on text. But precise wiring architecture and nodes that need to be connected, maybe not.
For example “TPA3110D2 schematic” and image returns this which might be a lot more useful.
If you want to have some gain greater than native 20dB gain of TPA3110D2 then you need to add an opamp gain block.
Even so, you really need to read the datasheet to understand the operation, limitations, and setup jumpers etc.
For an opamp line level gain block, use standard google search or go to Rod Elliot’s site.
Not everything can be done so easily by chatbots (yet). 🙂
For example “TPA3110D2 schematic” and image returns this which might be a lot more useful.
If you want to have some gain greater than native 20dB gain of TPA3110D2 then you need to add an opamp gain block.
Even so, you really need to read the datasheet to understand the operation, limitations, and setup jumpers etc.
For an opamp line level gain block, use standard google search or go to Rod Elliot’s site.
Not everything can be done so easily by chatbots (yet). 🙂
Last edited: