Every speaker builder now the moment when you have an idea for your own customized speaker and you are searching for an amplifier which fits the needs. Most of the chinese Amplifiers has a horrible background noise or large transient noise. Nothing is worser than to see your own build speaker which is ruined through a bad amplifier.
Analyze the needs and find the right components
The idea was to build an amplifier which fits most of the needs of an speaker builder. A decent sound, enough power and universal. Most of the people build a 2.0 or 2.1 speaker system. So this amplifier should support both. In most cases the subwoofer needs more power than the speaker. A 4 Channel amplifier whit bridgeable stages would be nice. So you can bridge Stage one and two for the right Stereo channel and three and four for the left Stereo Channel if you wanna use 2.0. If you wanna use 2.1 you can bridge two Stages for the subwoofer and use the other two stages for the speakers. After searching for a good and not so expensive 4 Channel amplifier i found the TDA7377 which fits the needs. Now we have an amplifier but if you use 2.1 you do not want that the subwoofer plays all frequencies. So we need a low pass filter for the subwoofer. Moreover you also want to adjust the volume of the whole system and adjust the subwoofer level. Honestly it would be great to have also a bass boost and treble adjust function. So many sound functions would be nice. After searching i found the PT2033 audio processor which supports it all and have a input channel selector. Now we have choose our main Chips.
Building the amplifier
In the top left you see the TDA7377 amplifier with four amplifier stages. This Chip makes a line audio signal to a high power signal for the speakers. I add also a low pass filter on the Stand-by pin which delays the power on of the TDA7377 to hide the transient noise. The rest of the amplifier is from the typical application circuit from the datasheet.
In the top right you see the audio signal switches. With this switches you can select the audio inputs of the four TDA7377 stages.
In the bottom left you can see the PT2033 audio processor. This Chip sets the volume level, bass boost, treble, inputs and the subwoofer filter. This Chip is programmable over a I²C bus via a microcontroller.
In the top middle you can see the +9V Supply regulator for the PT2033. Its an LDO with a high power supply rejection ratio (PSRR). A high PSRR suppresses unintentionally frequencies in the power supply which the user may can be hear over the speaker.
In the bottom right you can see the connectors for the speaker, the header to select the decoupling capacitors from the speaker out, the power supply plus filtering of the TDA7377 and some signal headers for the microcontroller.
The finished amplifier
- Output power: 2.0 (Stereo) up to 2x35W @4Ω; 4.0 up to 4x10W @2Ω; 2.1 up to 2x10W @4Ω + 35W @4Ω
- Mode selection over DIL switch and Jumper (no soldering needed)
- Three audio inputs with JST XH 3 (2.54)
- Active lowpass filter for subwoofer
- Subwoofer volume adjustable from +37,5dB to -37,5dB
- System volume adjustable from 0 to -78,75dB
- System treble adjustable from +14dB to -14dB
- System bass adjustable from +14dB to -14dB
- Noise free turn on and turn off
- AC and DC Power supply input possible (10-18V DC or 8-12V AC)
- Good sound and a low price
- Controllable over I²C
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