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To use the mute function, simply connect a three-position switch connector on M / ST. A key can be used for panel mounting enclosure and connected by wires to the connector. The link is as follows the thread of the connector means connecting the second born and the wires on the other side borns. The operation is as follows when the key is to GND and the circuit is muted to V + when the circuit starts up. This process has a delay determined by capacitor C5 and C6. If you do not want or do not need to mute just connect the first and second borns or even need to use a connector just make a jumper to connect the dots. An unbalanced audio line output signal from a professional sound card should be connected to 6.3mm female TS (Tip-Sleeve) plugs J1 and J9 to the amplifier. The audio input can be shorten to ground when removing the TS plug to mute the amplifier. Most TS plugs have a built-in switch for this. Transformer T1 should be a toroidal transformer type for minimum electromagnetic trayfield which reduses audio hum and noise. In my case I started with an existing 2x 15V AC 0.75A transformer which is sufficient for around 2x 10Watt RMS. Choose a 20V..35V AC / 30..50VAC transformer when more power is needed. Don't forget the conversion from AC to DC: 15VAC x sqw(2) = 15VAC x 1.41 = 21VDC. The input voltage (positive and negative) may not exceed 50VDC. The supply shown includes a "loop breaker", which is intended to prevent earth/ ground loops to prevent hum when systems are interconnected. Please be aware that it may not be legal to install this circuit in some countries. The diodes must be high current types - preferably rated at no less than 3A (1N5401 or similar). The loop breaker works by allowing you to have the chassis earthed as required in most countries, but lets the internal electronics "float", isolated from the mains earth by the 10 ohm resistor. RF noise is bypassed by the 100nF cap, and if a primary to secondary fault develops in the transformer, the fault current will be bypassed to earth via the diodes. If the fault persists and the internal fuse (or main power circuit breaker) hasn't opened, one or both diodes will fail. Semiconductor devices fail short-circuit, so fault current is connected directly to safety earth. Difference in THD is rarely audible. If you can hear a difference between 7293 and 3886, I would say it is the difference between mosfet and bipolar in common/most amp designs (they can be designed to sound more similar I believe), where mosfet amp tend to sound "muddy"?
If using a normal power supply for the amp tests, apply power (±35V via the safety resistors) and verify that the current is no more than 60mA or so – about 6V across each 100 ohm resistor. No load current can vary, so don’t panic if you measure a little more or less. Verify that the DC voltage at both outputs is less than 100mV. Using another 100 ohm resistor in series with a small speaker, or an oscilloscope, apply a sinewave signal at about 400Hz to the input and watch (or listen) for signal. The signal level needs to be adjusted to ensure the amp isn’t clipping, and the waveform should be clean, with no evidence of parasitic oscillation or audible distortion.I have not fitted a heat sink to the TDA's yet, since I wanted to first have my circuit work without any obvious problems in idle mode and then worry about heatsinking next. On the first try I had both TDA7293 chips soldered to the board. I have shorted the audio input signal to ground. As readers will know, there are already several power amplifier projects, two using IC power amps (aka power opamps). Both have been popular, and this project is not designed to replace either of them. However, it is significantly smaller than the others, so it makes building a multiple amp unit somewhat easier because the space demand is much lower. It’s quite simple to include 4 amps (two boards) into a small space, but be aware that good heatsinking is essential if you expect to run these amps at significant power levels. As the frequency of the signal rises, the impedance lowers. At a frequency of 20kHz, the impedance has dropped to roughly 19kOhms. The TDA7293 specifications might lead you to believe that it can use supply voltages of up to ±50V. With zero input signal (and therefore no output) it might, but I don’t recommend anything greater than ±35V if 4 ohm loads are expected, although ±42V will be fine if you can provide good heatsinking. In general, the lower supply voltage is more than acceptable for 99% of all applications, and higher voltages should not be used unless there is no choice. Naturally, if you can afford to lose a few ICs to experiments, then go for the 42V supplies (obtained from a 30+30V transformer).
If you want to know how 7293 will perform in comparison to 3886, you have to know how mosfet amps sound in general, then you could benchmark the 7293 with another mosfet amp (where they have similar characteristics in sound). I'll bet 80% at least will prefer 3886. determined by the physical wiring of the IEC connector if a fused type is used. With a fused IEC connector, the fuse is before the switch and it cannot be removed while I had to do "everything" to beat the mini-crescendo with 7293, so I used big transformer, especially because the mini-crescendo had a "fuller sound" and used big trafo. Big transformer will for sure improve the characteristics of the amp in bass region and "power". I only asked one experienced man for his opinion about the two amps. He didn't explicitly say which one was better, only that the mini-crescendo had more body and fuller sound. That would be fine I guess except that the footprints are not quite compatible; specifically, the 7293 has a dedicated BOOTLOADER pin (12) which drives the bootstrap capacitor, whereas on the 7294, the bootstrap C is driven by the OUTPUT pin (14), and pin 12 is NC.
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Do you actually see any chance this might be a temperature problem? Because with the input signal shorted there should be barely any heat needing dissipation, right? Also, since the explosion occurs literally within less than one second after power up I wouldn't expect a heatsink to be having much of an effect on that? If you want to build this project a PCB layout as well as TDA7293 BOM are provided for free, as is, no warranty. Enjoy! I have attached my circuit diagram to this post. Please be aware, that I have already figured out and fixed the follow mistakes made:
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