Homemade amplifier on TDA 7294 (part 1). Scheme, description

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Homemade amplifier on the TDA7294 chip (part 1). Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Transistor power amplifiers

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Part I

Which tells about me and the TDA 7294 chip

I want to make a reservation right away: I am an electrical engineer by education, and even a railway engineer, and I also work not in electrics, but at a rail welding plant. I don’t deviate from the topic - I’ll return to the piece of iron, but I’ll bring it up to this: the first is to an old anecdote put in the epigraph, the second is that my knowledge in electronics is rather superficial and at one time came down to squeezing out a pension from a granny to buy radio components for the next receiver ...

When I conceived a self-built and self-designed car amplifier, the question immediately fell into two. Actually the amplifier and the power supply to it. As for the amplifier, the choice fell on the TDA 7294 chip. In the annotation, it was advertised in such a way that tears welled up in my eyes. And all for $5. Little believed. Even taking into account the anecdote told above.

Amplifier circuit (without power supply)

(click to enlarge)

The money is not big even on the scale of the railways, so I bought two TDA 7294s at once, made the seal with lightning speed, soldered everything, turned it on ... and praised the Lord our God, for the first time in my life it worked right away. Scheme on two TDAs, connected to a bridge to a load of 8 ohms. I applied a sinusoid from 0 Hz to 25 - 30 kHz with an amplitude of up to 1 V to the input. The output signal was perfect: it did not cut anywhere in the entire range up to Uout = 38 - 40 V (RMS), then at Uin > 0.85 V the signal already deteriorated. I tried to take readings immediately, so that the load equivalent would not blush and smoke, and even so that I would not change my 8 ohms. According to all pre-revolutionary arithmetic, it turned out that the equivalent power was about 180 W (RMS). The load strove to smoke and become red-hot, which confirmed pre-revolutionary arithmetic. I think for $5 x 2 it's cool.

Well, how will all this sound on live acoustics? I connected two S90s in series (4 ohms each) and hung up a voltmeter, applied a signal (music) from an auto-CD to the input - it played great, and the amplifier itself did not make noise, as its "brothers" sometimes do with the inscriptions "HI-FI amplifier ". The larger the inscription, the louder the noise.

Well, what if now to the fullest and to hell with it, with distortion? The voltmeter needle jumped over 40 V. The first who ordered to live long were the tweeters, then the mid-range speakers began to set up a smoke screen. The woofers turned out to be the most persistent and tenacious ... These are my first losses, then - more.

Let's summarize: the bridge circuit gave clean Uout = 38 V, that is, 180 W (RMS) into 8 Ohms, but at the limit of possibilities it turned out, whatever one may say, Uout = 43 V, and power - 230 W. All this was measured at low frequencies: a bridge circuit was made for a subwoofer.

Part II

Part III

Publication: cxem.net

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