492
Item nr.
Most efficient Home Sound amplifier in the history of mankind (second only to my later amplifiers).
Production | The Netherlands, 2019.
Price was 3 €. |
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Semi- conductors | TDA7297. |
Cabinet | Plastic. |
Power | USB Charger, 0.3W. |
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 Pmax = (Vcc - 2 Vth)2 / 2 Z, and assuming a threshold voltage Vth 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. |
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Condition | 10. |
Value (est.) | 3,3€. |
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.