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Old 7th February 2014, 09:04 PM   #1
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Default TDA7293 parallel chip questions

Hello all. Long time lurker here. Thanks for all the great information. I have an ESP Project 03A under my belt and want to tackle a bigger chip amp. I have a question about an ebay TDA7293 board. Lots of amps and power supplies available from china these days. It is this one:

http://www.ebay.com/itm/TDA7293-Amplifier-Parallel-BTL-Mono-350W-Power-Amplifier-Board-/120952105312?pt=US_Amplifier_Parts_Components&hash =item1c294ea960

If the link doesn't work it is ebay item number:

120952105312

I can't tell from looking at the board what the NE5532 does. Does it drive all 4 chip amps or does it act as a preamp making the whole board more like an integrated amp? I can't see any pot used as a volume control.

Also, in regards to paralleling these 7293 units. Would 4 of these in parallel make them more tolerant of higher supply rails? I have a 500VA 30-0-30 transformer burning a hole in my pocket right now. It is giving me +44VDC/-44VDC. I would be driving an 8 ohm load, but would be nice to have the flexibility to do 4 ohm loads in the future. It seems dividing the current among the four units would allow them to operate at the higher voltages with less risk. Or am I off in space?

Thanks again,

SS

Last edited by Steadysupply; 8th February 2014 at 12:35 AM. Reason: clarification on link
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Old 7th February 2014, 10:52 PM   #2
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Paralleling doesn't have much to do with the supply voltages, more to do with spreading out the heat generated and increasing the maximum available current. The board you linked to (link doesn't work btw) says its BTL meaning 'bridge tied load' - this effectively halves the impedance of the load seen by the chips. So when you drive a 4R load with that, its necessary to have 2 chips in parallel or you'll get audio cut-outs when the chip overheats. Even so, driving 350W is going to be very marginal in practice - it would need some really serious heatsinking to achieve this power level with only 4 chips. Putting 4 chips in parallel for single ended use looks to me like overkill unless you have a 1R load but it would allow you to use a more wimpy heatsink.
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Old 8th February 2014, 02:20 AM   #3
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That makes sense. I originally thought all 4 chips were operating in parallel. So if I understand correctly, this board advertised as "Parallel - BLT Mono" two of these tda7293s are operating in bridged mode, and they are both operating in parallel with the other two TDA7293 units.

The board has a total of 4 TDA7293 chips.

I still don't see what the NE5532 does in this circuit.

Thanks again!
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Old 8th February 2014, 11:23 AM   #4
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Yep, that's how I read it - 2+2 which makes it OK for driving a 4R load. I also have no idea what the 5532 is bringing to the party except it might invert the drive to the anti-phase pair of chips with one opamp.
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Old 8th February 2014, 11:41 PM   #5
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Looking at the board, I think we see :
- 5532 left side is input buffer with HF-filter, and some gain probably
- 5532 right side is inverter / phase-splitter
- 5532 supply is MOSFET (610/9610) followers from 18.2V zener strings
- each bridge section has its own mute/standby circuit
- current sharing resistors from the chips' outputs even though it's master-slave config with only one feedback network, bootstrap cap, etc.
- only very basic local decoupling on the power stages
- only a "global" Zobel/snubber back-to-back from the outputs

I personally would not agree with some of these design choices but if it works reliably (let's hope so), who cares... given the price of the module.
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Old 9th February 2014, 01:02 AM   #6
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It is funny that there are Three sellers of that very same board, with Three different prices!!

jer
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