Gerard's Ali TDA7297

492
Item nr.

Ali TDA7297 Amplifier

Most efficient Home Sound amplifier in the history of mankind (second only to my later amplifiers).

**Data for Ali TDA7297**
Production	The Netherlands, 2019. Price was 3 €.
Semi- conductors	TDA7297.
Cabinet	Plastic.
Power	USB Charger, 0.3W.

The Design

This amplifier project started as an illustration of AliExpress kits for a presentation. Gradually, my goal became to obtain an energy efficient amplifier. That is, an amp that consumes little power during the 8000+ hours per year that I don't listen to any music.

For a given power supply voltage and speaker impedance, a Bridged Amplifier can deliver four times more power than a classical single ended design. I hoped to run the amp from 9V instead of the 12V needed for my previous amp, the PrachtPatser. Thest showed that I can sufficiently annoy my house mate and neighbors running the amp from a 5V USB charger, giving a total mains power draw of 0.3W when the amp is silent. Using the formula P_max = (V_cc - 2 V_th)² / 2 Z, and assuming a threshold voltage V_th of 0.5V, power into my 4 Ohm speakers could be around 2W. When more power is required, supply voltage can be increased up to 16V, and the amp should then be able to drive 2x15W into 8 Ohm speakers. (But I felt no need to try this out.)

I didn't figure out yet, how a headphone can be connected to a bridge amplifier; the headphone shells have a common ground, but the amp outputs may never be connected. My later Simson amplifier does have headphone out.

Obtained	4/2019 from Ali plus Scrap parts.
Condition	10.
Value (est.)	3,3€.

This Object

Building cost of the amplifier are quite reasonable; all new parts were obtained from AliExpress. I paid 2.31 for for the Amplifier frame, a small PCB with TDA7297 amplifier IC including AUX entry, volume control, and heat sink. The Loudspeaker connectors were 15 cents each, and the DC jack was 13ct, which totals to 2.74. From my junk supply I got a three position double switch and a tiny speaker to serve as switchable monitor speaker, but these are not really necessary of course. Neither is a cabinet, but I saved some plastic box from the garbage dump to house all the parts. Add some screws and eight pieces of wire, and still remain under 3 euro's.

Here my old amp (the PrachtPatser) and the AliAmp together on one photo. The old amp required at least 12V DC to operate well, taking 2.3W from the mains. With a small 6V transformer, the new amp consumes about 1.2W continuously, so I save about 1.1W of Vampire Power, just over 2 euro's of electricity in about one year.

Hoe does the amp sound? That's hard to explain in words (if one word is allowed, is is: good!), but perhaps the pictures here say more than a thousand words. On the left is a scope image of the voltage over the loudspeaker when the signal to the amp is a 1000Hz square wave. At the rising or falling flank, there is hardly any overshoot or undershoot. The horizontal edge of the square is slighly sinking indicating a little loss on low frequencies. All in all, the amp output "looks" quite good. Meanwhile at the other channel (right), the flanks of the square wave cause a slight peak effect, but I don't know if this arises in the amp or in the feed cable.

Part of Gerard's Radio Corner.
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