DIY Bluetooth Mixer with Adjustable Overall Gain

If you're interested in building a DIY Bluetooth portable mixer, check out this article.

The DIY TFM241BT Bluetooth portable mixer commonly uses perforated boards.

The Bluetooth module is the CSR8645, which offers good performance. You can later upgrade to the CSR8670 or CSR64125. You will need 7 pieces of 5532 op-amps.

Main features include:

· 2 channels with 3.5mm balanced inputs (6.35mm connectors are too large). These inputs can be used for a mic (+27dB output to L+R) or a line input (+9dB output to L or R).

· 3-band equalizer.

· One Bluetooth input (the CSR8645 can connect to two devices simultaneously).

· One FM input.

Outputs:

· RCA unbalanced output and isolated 3.5mm balanced output.

· Signal reception via FM antenna.

· The battery is from a Hasee smartphone, 3Ah, with an overall power consumption of 0.5A. Theoretically, it can last for 6 hours, and you can also plug it in to use.

The battery used is from a Hasee mobile phone, 3Ah, with an overall current draw of 0.5A. Theoretically, it can be used for 6 hours, and it can also be powered by an external source.

Over time, the TFM241BT Bluetooth portable mixer will inevitably face issues such as poor contact. Since PCB is now commonly used, the design can be upgraded.

Upgrades include:

· Full PCB construction with a modular design.

· Addition of a simple reverb circuit.

· Support for more microphone types.

· No need to redo the enclosure, as the knob layout remains the same, with only minor adjustments to the connectors.

Final product as shown below:

Specifications:

· Power input: DC 5V 3A

· Li-pol Battery: 3.85V 3.9Ah

· CH1 Balanced/Unbalanced input: 0~1V rms (dynamic, condenser, or wireless mics)

· CH2 Unbalanced DC Bias input: 0~1V rms (electret microphone)

· Pre-gain: 0~+11~+26dB

· High (15kHz): -15~-1~+10dB

· Mid (800Hz): -6~-1~+4dB

· Low (50Hz): -9~-1~+7dB

· Attenuator:-∞~0~+6dB

· Reverb delay: 140~800ms

· Reverb repeat:0~100%

· CH3 FM: FM srereo, frequency range-∞~0~+6dB, attenuator -∞~0~+6dB

· CH4 Bluetooth: CSR8645-AptX, name HIFI, attenuator -∞~0~+6dB

· Overall gain: -∞~4.4~+10dB

Feature Overview:

· CH1 supports balanced or unbalanced signal input, and can connect dynamic, condenser, or wireless microphones, as well as instruments.

· CH2 features bias power and supports unbalanced electret microphones.

· Both inputs have adjustable pre-gain to amplify weak microphone signals, as well as a 3-band equalizer and reverb processing, where the delay time and repeat rate are adjustable.

· FM supports full-band stereo reception with automatic station memory.

· Bluetooth supports APT-X lossless transmission and can connect to two devices simultaneously.

· The level indicator visually displays the output signal strength.

· Outputs include isolated balanced and unbalanced options, suitable for connecting to various power amplifiers.

· The built-in high-capacity battery allows continuous use for 6-8 hours and includes a battery indicator. It uses a standard USB 5V charger.

· The power section uses an MC34063 to provide a ±9V dual voltage for op-amp operation.

Completion.