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