Hey all,
I am currently working on a sure electronics amplifier based on TDA7492.
These integrated bridged amplifiers, specified at max. 20v/4 ohms, sell
for under 35 dollars including 19V power supply on ebay and different
sites.
The sure one comes in a nice case, featuring:
- Cinch Input
- 3,5mm stereo jack input
- 3,5mm stereo headphone jack
- Rotary encoder for volume setting
- Mute by pressing rotary encoder
- 2 fading leds showing volume
Circuit consists of:
- TDA7492 for main out amplification
- SCM4809 for headphone amplification
- PT2033 as source selection and volume control
- PIC16F1503 for controlling the PT2033 via I2C, both amplifiers MUTE
input and the power of PT2033 via fet by rotary encoder and switch. It
also senses both 3,5mm jacks by the jack detect pins
As I need to reprogram the flash (Programming pins equal I2C pins and
are on a nice pin header together with program enable pin and 5V/GND),
because the amplifier always boot up in mute mode, and there is no
real datasheet of PT2033 available, I have the important parts here:
I2C address is 0x88 (8 bit-W; 0x44 for 7 bit). The PIC always sends 7
Bytes:
- Volume/Attenuation from 0x28 (very silent but not muted) to 0x00 (full
volume) (datasheet states 64 attenuation steps so 6 bit...)
- Input select: 0x4D with headphone, 0x5D without. 0x5C if AUX is
plugged in. So we have the two LSBs for channel selection (0: AUX IN0,
1: Cinch IN1. The higher bits may do some gain things as the chip does
not do any output control.
- Other bytes are always the same: 0xC0, 0xE0, 0x80, 0x6F, 0x7F
where we miss:
- 2 bits gain select (may be in byte 0 MSB or byte 1)
- 5 bit subwoofer attenuation (output not connected in this application)
- 4 bit each for Treble/Bass control
- Loudness switch bits (1 or 2)
- Datasheet states "individual channel output volume adjust and tone
control" - as we see just one byte changing, at least volume seems to be
set for both channels together. On Unmute/Input switch, the output is
lineary faded in steps of 1. Rotary encoder inc/decs in steps of 3 or
sometimes 4.
- Datasheet shows more settable attenuators/volumes, not everything
matches the description...
I already asked the Princeton Technology Corp. for more information,
until today I only received the answer of the customer service that my
request has been forwarded to the tech people :)
I hope this information helps someone.
My custom firmware would implement:
- balance (if possible)
- Auto-Power on
- Input select
- maybe individual volumes per input (unfortunately, there is no eeprom
so this function would be of little use)
- Output select
Watch this topic
Disable multi-page view