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TDA7293Mod – Bench Testing

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TDA7293Modular – Bench Testing

This is the first time I’m working on the TDA7293 in Modular configuration, so it’s with some anxiety when I started with the bench testing. For those that are not familiar with the TDA7293, it has a feature that allows one amp to be used as a Master while the other as a Slave. In the Slave unit, only the power mosfets are utilized. This effectively double the number of power mosfets. It is equivalent to expanding the power stage of a discrete amplifier. This is not to be confused with mono-bridging.

To take full advantage of this modular construction, I will be working with rail voltages of +/-40Vdc. My aim is to see what kind of power output I can achieve when it is driving 4Ω loads.

Full Power into 4Ω

1kHz Full Power into 4Ω 10kHz Clipped Waveform into 4Ω

The plot on the left is the TDA7293Mod at 1kHz Full Power into 4Ω. This display is just before clip. The maximum voltage swing recorded is at 22.5V RMS. That works out to an incredible 125 Watts into 4Ω. Full Power into 8Ω is a respectable 70 Watts.

With such high power, the TDA7293MOD is encroaching into the low end models of discrete amplifiers like the Rotel RB-960BX. Power output in such amplifiers is typically about 120 Watts into 4Ω.

The right display is when the TDA7293Mod is driven into clipping at 10kHz into 4Ω. The top and bottom clipped waveforms are symmetrical with no signs of instability.

10kHz and 20kHz Square Wave into 4Ω

10kHz Square Wave into 4Ω
Rise Time = 4.0us | 10Vp-p
20kHz Square Wave into 4Ω
Rise Time = 2.4us | 10Vp-p

The plot on the left is the Square Wave response at 10kHz at 10Vp-p. No oscillations are observed at the top and bottom. Rise time is at 4.0us. The right plot is at 20kHz at 10Vp-p. 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. 

TDA7293Mod Specifications

Power Output = 125W into 4Ω | 70W into 8Ω
Input Sensitivity (@ 1kHz before Clip) = 0.60V RMS into 4Ω | 0.83V RMS into 8Ω
Input Impedance = 33K
Rise Time = 4.0us at 10kHz Sq into 4Ω
Voltage Gain = 30dB

Power Supply Specs
Power transformer = 28-0-28Vac
Supply Rails = +/- 40Vdc
PSU caps = 20,000uF

Conclusion

I am impressed by the power output of the TDA7293Mod. It has enough muscle to be used as a main amplifier. A added advantage of this TDA7293Mod is the extremely small pcb. It measures only 3-3/4″ x 2-1/2″. Eight units of TDA7293Mod can easily fit into a standard 19″ case for Home Theater or for commercial use as in multi-zone applications. And if higher power is needed, two TDA7293Mod can be Mono-bridged for an output of 140 Watts into 8Ω.

Due to it’s ease in construction, this TDA7293Mod is ideal for DIY. No oscilloscope, signal generators, THD analyzers, etc are needed. Just solder in a few resistors, capacitors and that’s it. As far as power amplifiers go, this is as idiot proof as it can get.

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