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TDA7293Pro – Bench Testing

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TDA7293Pro – Bench Testing

The TDA7293Pro is a specialized power amplifier meant for active speakers. The input is fully balanced. This will ensure no interference when the speakers are far away from the mixer. On board is also a speaker DC protection circuit. A relay will open when there’s DC at the output of the TDA7293, thus preventing the speaker from damage. The op amp for the balanced input is powered by a 7815 and 7915 voltage regulators, whereas the dc protection circuitry has a dedicated 9V supply from a 7809. 

The TDA7293Pro is meant to drive 4Ω speakers. As such the rails voltages are +/- 28Vdc. The power transformer is a 20-0-20VAC. The the tests below were conducted at +/-28Vdc rails.

10kHz Full Power into 8Ω

10kHz Full Power into 8Ω 10kHz Clipped Waveform into 8Ω

The plot on the left is the TDA7293Pro at 10kHz Full Power into 8Ω. This display is just before clip. The maximum voltage swing is 50Vp-p. That is 17Vrms. Thus power output is 36W into 8Ω. We can expect about 60W into 4Ω. I will know the exact figure when my 4Ω dummy load is ready.

The right display is when the TDA7293 is over driven. The top and bottom clipped waveforms are symmetrical with no signs of instability even at 10kHz into 8Ω. This is actually a very good clipping behavior. 

10kHz and 20kHz Square Wave into 8Ω

10kHz Square Wave into 8Ω
Rise Time = 4.0us | 10Vp-p
20kHz Square Wave into 8Ω
Rise Time = 2.8us | 10Vp-p

The plot on the left is at 10kHz. No oscillations are observed at the top and bottom. Rise time is at 4.0us. The right plot is at 20kHz. As before, no oscillations are seen. However, in these two plots, the trailing edges are not as smooth as the leading ones. This indicates there’s some capacitance affecting the negative slew rate. I wouldn’t worry too much about this because it’s not audible. 

TDA7293Pro Schematic

The schematic above shows the components I used for the TDA7293. I set the amplifier’s gain at 30dB. The bootstrap capacitor is a 47uF/100V. Even though the TDA7293 datasheet doesn’t have a zobel, I installed one out of caution. The values are 0.1uF with 4.7Ω seen at the output.

The Mute and Standby functions are set in Play Mode permanently. This is achieved by tying the 10K and 22K resistors to 9V which is supplied by the LM7809 voltage regulator.

The specifications of the TDA7293Pro are as follows:

Power Output = 36W into 8Ω | 60W into 4Ω
Input Sensitivity = 1.0V RMS (Unbal) | 0.5V RMS (Bal)
Input Impedance = 20K
Rise Time = 4.0us at 10kHz Sq into 8Ω
Voltage Gain = 30dB

Power Supply Specs
Power transformer = 20-0-20Vac
Supply Rails = +/- 28Vdc
PSU caps = 20,000uF

I did some some minor changes so I’m expecting a new batch of pcbs for final testing. Once I’m satisfied, I will offer this pcb for sale. As it stands now, the TDA7293Pro passed with flying colors. Stay tuned for updates.

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