If going to make one TDA7293 working at AC25 x 2, driving 4 ohms bookshelf speakeers, what will be the minimum VA of the transformer will be needed? Since I wanna built something compact and slim, I try rread through the TDA7293 odf file but still can't make sense, could anyone please help? Thanks!
It's in German, but...
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Thanks again.
Since I have two slim (43mm overall height) transformers rate at 150VA 240V / 25V x 2 don't wanna waste, since here the mains supply is at 220V, therefore the output should not exactly right at 25V x 2.
My speakers are rated at 4 ohms, therefore I am wondering I use just one transformer or use both but parallel them as one 300VA transformer, maybe I try using one transformer first, with 10 x 5600uF smoothing caps, and fit everything in a 180mm x 300mm x 50mm slim case, if no good, then maybe take out the transformer put in another case as external PSU, but will then using both but parallel as one 300VA transformer.
I don't expect much from a chip amp although I know they could be real great, but since I wanna save cost, and I never really play loud, plus I am going to use CPU fan to help cooling, I think as long as the dynamic impedance of the speakers stay stable, there should have no problems?
Since I have two slim (43mm overall height) transformers rate at 150VA 240V / 25V x 2 don't wanna waste, since here the mains supply is at 220V, therefore the output should not exactly right at 25V x 2.
My speakers are rated at 4 ohms, therefore I am wondering I use just one transformer or use both but parallel them as one 300VA transformer, maybe I try using one transformer first, with 10 x 5600uF smoothing caps, and fit everything in a 180mm x 300mm x 50mm slim case, if no good, then maybe take out the transformer put in another case as external PSU, but will then using both but parallel as one 300VA transformer.
I don't expect much from a chip amp although I know they could be real great, but since I wanna save cost, and I never really play loud, plus I am going to use CPU fan to help cooling, I think as long as the dynamic impedance of the speakers stay stable, there should have no problems?
With lover voltages, long as you keep the gain low enough not to exceed the maximum voltage available, it should not be a problem...
Remember a 25VAC transformer will give 25 x sqrt(2) - diode losses from rectifier... so you are looking at about 35V rails....
When you divide 35 by your load (4 ohms), you will see that the chip can not handle enough current to deal with that voltage...regardless of transformer... and this hold true for most chips currently available....
So your solutions to are, get 8ohm speakers, or lower voltage tansformers...
Remember a 25VAC transformer will give 25 x sqrt(2) - diode losses from rectifier... so you are looking at about 35V rails....
When you divide 35 by your load (4 ohms), you will see that the chip can not handle enough current to deal with that voltage...regardless of transformer... and this hold true for most chips currently available....
So your solutions to are, get 8ohm speakers, or lower voltage tansformers...
it's much much worse than that.
The reactive speaker load on continuous soundwaves can have an impedance around 60% to 70% of the nominal impedance for some narrow bands of frequency.
That alone increases the current demand by about 50%.
But on discontinuous sound, particularly fast starting or fast stopping signals, the effective impedance for the fast transient can be as low as 35% of the nominal impedance.
Your amp should be designed to meet this requirement.
Then how about parallel 2 x TDA7293 for one channal with the same transformer? Since add one more amp PCB still far much cehaper then buy a new transformer or speakers....... but as told before, I have 2 transformers in hand both rated at 150VA / 25 x 2, will 150VA enough for parallel 2 x TDA7293 per channal?
all the power from the transformer must be heatsinked in the amplifier and dissipated in speakers voicecoil
your suggested case is small, heatsinks probably too and I don't know what your bookshelf speakers can withstand
therefore there is little to gain from more transformer wattage
try one transformer for stereo, you already have it!
your suggested case is small, heatsinks probably too and I don't know what your bookshelf speakers can withstand
therefore there is little to gain from more transformer wattage
try one transformer for stereo, you already have it!
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