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Old 30th December 2006, 02:45 PM   #1
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Talking Active Aura 3" speakers, odd grounding connections?

I've just finished a pair of active speakers using Aura NS3-193-8A widerangers.. I used a TDA7375 as the power chip and a opa4134 for the Linkwitz circuit (yes, I know, insane to use it on 3" speakers ). It seems to work just as planned, but now I started worrying about the strange groundings.. or at least I haven't seen similar anywhere else

Click the image to open in full size.

I use a 2x6V trasformer, which supplies the OPA4134 transform circuit through lm7805 and 7905. The ground 0V is connected as the signal ground too. The 7375 amp requires at least 12V, so I connected it between the "-6" and "+6V" lines, before the regulators of course. Now, the audio signal becomes grounded, sort of, through the supply filter caps. Can this somehow cause the circuit to oscillate under certain conditions, maybe? So far it seems to work fine, as said, heat sink isn't getting hot and no strange noises whatsoever. All "problems" I can think of, is that the supply filter caps appear to be in series for the 7375 amp, so they only have half the capacity.

Here's the connections:
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Old 30th December 2006, 02:51 PM   #2
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Oh, and the "transf.box" in the schematic is that black computer power supply box on the right end of the pic. There's about 2M of power cord between the speaker and the supply box. The box doesn't have any switching power supply parts inside; only 50VA trasformer, caps and a diode bridge.
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Old 31st December 2006, 09:25 PM   #3
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Hmmmm... I see what you mean. Because the signal ground is not connected at the amp, it has to return via the filter caps. And you can't connect the signal ground from the Linkwitz circuit because it's tied the the center rail. Hmmm..... Gotta think about that one.

But hey, it works! Can't the TDA7375 be run with a slpit rail supply? (I don't know the chip).

It would be interesting to hear what others have to say.

BTW, what is the voltage on the rails before the regulators? You indicate 2x6V, but it should be closer to 2x8V with no load. That doesn't leave you much headroom on your amp.
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Old 1st January 2007, 11:10 AM   #4
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Quote:
Originally posted by panomaniac
But hey, it works! Can't the TDA7375 be run with a slpit rail supply? (I don't know the chip).

BTW, what is the voltage on the rails before the regulators? You indicate 2x6V, but it should be closer to 2x8V with no load. That doesn't leave you much headroom on your amp.
The voltage is about +/- 9V unloaded, so it's just at the limit for the tda7375 chip (max 18V). I used quite much recycled components; the 7375 is intended for car radios and for 2-4 ohms load impedances, so not a perfect choice for these speakers In fact, usually my speakers have reached mechanical exursion limits before amp power stops.. but now the amplifier runs out of power first That was expected of course, because with LT these three-inchers reach about 50-60 Hz out of one litre cabinet.

Other opinions, anyone?
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