I designed the TDA7293Pro primarily for professional applications but I made sure it’s up to HiFi standards. This way, it can be used commercially or in the home.
The pcb measures 3.9″x3.6″ only. It’s small enough to be installed in a speaker like in Active Speakers or an array for a multi-channel amplifier. The block diagram above shows what is contained within the pcb.
The input is fully balanced. This is necessary because in commercial use, a bunch of active speakers would likely be mounted on the walls of say, a church. Driving them would be a mixer that’s located somewhere else. Without a balanced line, you’ll pick up all sorts of noise.
Immediately after the balanced amp is a trimmer pot. This is to adjust the TDA7293 sensitivity so that you can reference it to 0dBu or 0dBV. After calibration, the TDA7293Pro full power will be at 0dB (RED LED).
To prevent the trim pot from loading the TDA7293 input, I installed a buffer. This serves to isolate the TDA7293 from the pot. The output of the TDA7293 is sensed by a DC protection circuit. Should the amplifier fail for any reason resulting with DC at the output, a relay will instantly disconnect the amplifier from the speaker. This speaker protection circuit is extremely effective in use. No fried voice coils.
As for the TDA7293, I decided to power it for 4 ohms. Rail voltages are therefore +-28Vdc. Closed loop gain is set at 30dB. For best sonic quality, no ceramic caps are in the signal chain. The 2.2uF at the input is a film cap. The feedback cap is a Silvered Mica. Other upgrades include a 47uF/100V cap for bootstrapping and another film cap for the output zobel.
Grounding is exemplary. The bottom ground plane is used for signal ground only. “Dirty” grounds like power and decoupling grounds are all at the top ground plane. This attention to detail is unheard of in diy amps.
That’s not all. On board the pcb are 3 voltage regulators. LM7815 and 7915 are for the op amp and a 7809 for the output relay. It even includes two power supply filter caps of 3300uF/50V. All that’s required to get it to work is a power transformer, a bridge rectifier and a heatsink.
The Gerbers will be with my pcb maker soon. I’m just waiting to finish other designs before sending them out.