Vermes
Advanced Member level 4
Assumptions:
- tip on LM3886TF
- preamplifier on a system controlled via I2C (the choice was TDA7439 because it can be connected into equalizer series and has gain, volume, balance, bass, middle, treble adjustment
- supply – 200W transformer, soft start, Schottky diodes
- control - 2x16 LCD + pulser, Atmega8 controls the operation of the amplifier
- housing – lacquered Diora deck
Some elements used:
- 2x28V 200W transformer
- 2x16 LCD blue/white
- heat sink from Sony amplifier
- 4x10000uF capacitors
- TDA7439
- Atmega8
- meters
- 8xBYW29 diodes
It is good to start with power amplifier, which is based on schematic and board from AVT kit. Then a power supply on Schottky diodes can be created with separate bridges on + an – of the supply. All that together with the PCB should be connected to the 2x28V 200W transformers, flooded with resin. It gives a strong, long bass, gentle and strong soprano. Also a soft start for transformer was home made. In addition, on the PCB there is a +8V and +5V power supply of the preamplifier and driver, there is also a relay which switches on the power amplifier.
The back of the housing was not processed. Necessary holes were cut, sanded and covered with clear lacquer in spray. Front of the housing had to be modified. A rectange of aluminum sheet (with previously cut holes for LCD, VU and pulser) was glued to the aluminum frame of Deck, using anaerobic glue. Then everything was sanded and lacquered. Sheet treatment for the panel was the most time consuming part of the project, because it was home made without specialistic tools. The effect is very interesting, because sand makes deeper pits in the aluminum than in steel, so the surface is rough, what is presented in one of the pictures.
PCB of preamplifier is shown in the photos. The preamplifier is based on TDA7439, signal is taken from 4 double chinch sockets, then goes through a selector and gain (in TDA) and through the relay to R/S sockets (output/input of the external equalizer), goes back to TDA, where you have adjustment of volume, corector and balance. Then the signal is fed to the terminal. The board is also equipped with systems that adapt the signal to drive indicators.
The driver is based on Atmega8 and Bascom. Front panel has no buttons except the pulser knob. Encoder has a pressed axis and that button is used for turning on/off the amplifier, changing functions. It is very useful and front of the amplifier is „empty” thanks to that. Processor controls TDA7439 and also has a clock on DS1307. Programming can be done via DB9 socket on the rear panel of the housing. The device has a function of delayed turning on the columns and delayed turning off the terminal.
Pictures:
**broken link removed**
**broken link removed**
**broken link removed**
**broken link removed**
**broken link removed**
**broken link removed**
**broken link removed**
**broken link removed**
**broken link removed**
**broken link removed**
**broken link removed**
**broken link removed**
Link to original thread (useful attachment) – LM3886TF + preamp własnego projektu na TDA7439
