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TDA7294 Datasheet related question

Started by polo16mi, August 25, 2009, 06:22:28 PM

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polo16mi

Hi:

I had been studing the TDA7294 datasheet and noted something that im in doubt.

At the page 6/13 they says there that the RMS Continuos Output Power is:

Vs=+/-35V,  RL=8 ohms   60 W min   70 W typical.
Vs=+/-31V,  RL=6 ohms   60 W min   70 W typical.
Vs=+/-29V,  RL=4 ohms   60 W min   70 W typical.

I dont understand fully something.  I have a 24+24/6A  tranny, and maked a power source with a rectifier bridge with 4 diodes (6A60), a 100nf ceramic cap in parallel with each of them, 4 electrolitic cap (4700/63v each, 3 for rail), and 2 100nf poliester cap (one for rail).   I guess that i ll get around 34V CC for each rail.  If i use this power source, i wont use a 4 ohms speaker with this tension?

I hope expresed clearly enough.... :-\



J M Fahey

Hi Polo.
Your calculations are right, and you have built a good power supply.
The datasheet says you shouldn´t load it with 4 ohms.
Practice says that for light (Hi Fi home) use, you *can* use 4 ohms (or 2x8 ohms) speakers, you'll burn nothing.
Practice (and the datasheet agrees) says that for heavy, continuous  work (guitar amp, DJ equipment, etc.) you will have problems, at least overheating it or worse.
Practice also says that Marshall MG100, which uses a 7294 (Or 7293) with close to +/-35V and 4 ohms, burns so much that Marshall supplies a plug-in miniboard for musicians to self-repair them.
Given the low cost, I would use *two* boards with your power supply, each of them driving one 8 ohms speaker.

polo16mi

Thanks JM. Good answer. Then...im looking the differents answer that i got of us, and wondering now if i got this right.

I already started another topic asking for a "just one preamp stage driving two identical power stages" and looks like it is posible.. Looks that isnt a bad idea at all.

You had confirmed that i have a good PS enough for two 7294 power stages.

So, the roadmap that i planning now, is....

-At first try, i ll make just one power stage, use the " 8)Coihue micro 8)"  as a preamp and see if them are enough power to play with the guys.
-I ll keep another "ace in the hole" (it is right?) and, if i short of power, add one more power stage with one more speaker.

that all....for now...

Thanks a lot at all you guys... i learning a lot, and getting comforting little success




joecool85

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