TDA1543 setup (alternate I/V output)

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Folks, I've got a large number of TDA1543 chips I'll use in a power DAC for my tweeter (400Hz+). I've calculated them to be able to deliver around 100mW into a 16ohm load, wich is ample, but I can't really figure out how I should make the output stage.

I want all the mA the DACs can deliver to be sent through my speaker to drive it, and if I use an I/V resistor plus cap coupling, I'll leak all the power over the I/V leaving nothing to drive the speaker with won't I?

Should I make an impedance correction network on the speaker ensuring 16ohm across it at all frequencies (including DC), and use this complete network as most people would use an I/V resistor (see the attached pic)? Measure and tweak to get it linear? Any other suggestions?

My suggested I/V network:
 

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nice idea....

just quick calculation, 100mW in 16 Ohm is resulting in a Voltage (effective) of 1.26 Volt. With the TDA1543 running on 8 Volt this is easy to do. My dac design gives 1.56 Volt RMS at the output

The only question I may have is the current.... at "full" power you need roughly 80mA for the 100mW in 16 Ohm

I know that the maximum effective signal current 0dB signal coming from a TDA1543 is 720 uA ...

You will need therefore 80mA/720uA = 110 DAC chips :att'n:

These 110 DAC Chips will consume like 6 Ampere 50 Watt power disapation...
Next question, how are you planning to drive 110 parallel TTL inputs ?

If you all do this, great stuff, not easy, I know... Just built a prototype with 60 DAC's in parallel.... So basically you need 4 times this ...

The idea of imepdance correction is kind of the right things if you don not want to go for 1000 DAC chips , never the less I am not sure how the dac reacts when the speaker unit is unloading current when it swings back after a pulse signal. the output impedance of the dac is pretty high...

If 1.2 Volt is enough for you, why not make a very simple MOSFET source follower ? than you just work with a few dacs, improving the sound and drive the tweeter strongly.

Any way, it sounds very interesting and it would be fun to try !!!!


regards
doede
 
I just did the calculations and came up with 93 chips needed for 100mW into 16 ohms, I'm not quite sure why I got a different number than Doede, but even so thats a LOT of DAC chips! Driving all these and keeping the jitter low between them is going to be tough as is the PS and getting rid of all that heat.

I second Doede's suggestion, I use a cascoded mosfet follower to drive a tweeter and it works very well (great for headphones too).

John S.
 
Thanks Doede, John

I'll probably go the MOSFET route then, you are suggesting something like the Headwize project at This HeadWize article ? Any recommendation on wich transistor that'll provide the best sound in this simple circuit?

I'd also like some recommendations on how to do the DAC and it's O/P stage. I can use as many TDA1543s as I like, I have a wide range of quality capacitors, I've got microphone transformers too (1+1:1+1 Lundahl) if that'll improve anything...

Regarding a chip for you, Klaus, I'll probable be able to spot you one. My email is down at the moment, try it in a day or so.
 
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