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Old 23rd November 2003, 10:02 PM   #1
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Default TDA1543 DAC problems -- advice?

I have a 4x parallel TDA1543 DIY DAC rather similar to the Tnt-Audio Convertus design (no output stage).

I've had a real problem recently with a harsh and aggressive high end, especially sibilants. Or rather, I think the problem has been there a while, but it's really starting to bother me a lot.

I've tried a number of tweaks -- replacing the 7805 rectifiers with TL431 shunts, going to passive PS on the TDA1543, battery supply, various coupling caps (Auricaps, BG NPs), various IV resistors (Holco, cheap carbon film). I could try some more IV resistors....

I've noticed this with a number of different amps and IC cables, so I think it's the DAC.

Suggestions?


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Old 23rd November 2003, 11:21 PM   #2
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Try a different resistor-value(trim) for V ref (output from TDA 1543).

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Old 24th November 2003, 05:21 AM   #3
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Hi!
Only time I have experienced problems like You said was when my power supply was not good enough- are You sure that Your tl431 is in good working point - minimally 10mA through it. Do You have really good cap's after the tl431( like Black Gate's or similar- and on input receiver oscon's or similar)- TDA1543 won't be satisfied until it has REALLY good power supply. In my setup I have Riken on I/V and Vref and some silver PiO and MKP's in paralel as coupling cap's- maybe Your resistor and coupling cap's are the reason for that too.
happy diy is that
daniel
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Old 24th November 2003, 02:16 PM   #4
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Default interesting

Thanks for the ideas. The PS capacitance is rather light, 4x 220uF Cerafines at the TDA1543s, bypassed with 0.1uF at the pins. I tried alligator-clipping in a 2200uF cap, but it didn't seem to have much effect. The TDA1543 supply is passive, a 12V battery with about a 20R resistor to drop voltage, then the capacitors.

The CS8412 (receiver) supply is two TL431s, capacitance is also light, only about 220uF (cerafine) per supply bypassed with 0.1uF after the TL431. I think the TL431s are shuntingtha about 20mA.
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Old 24th November 2003, 03:19 PM   #5
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Now I'm no expert but since you have tried battery supply and all, guess that is not where the problem is.

Dunno if you have read about Doede's DAC. But he states very categorically that you need to trim the DAC with the right RREF and RLOAD AND voltage..to get the lowest distortion and best sound!

http://www.dddac.de/ma_dac23.htm


Hope this helps..

Cheers,
Bas

PS his voltages and resistance where calculated/trimmed for 8 parallel.
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Old 24th November 2003, 04:09 PM   #6
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Quote:
The TDA1543 supply is passive, a 12V battery with about a 20R resistor to drop voltage, then the capacitors.
Maybe omitting the 20 Ohm resistor and adding a discrete regulated supply for the TDA1543 will improve things. Or try a battery with lower voltage ( 6 V for example ) without any series resistor.

In other words: I think that 20 Ohm series resistance is not beneficial for correct operation the DAC chip. It also ruins the mOhm internal resistance of the battery so the advantages of using a battery are greatly reduced.

The advice to trim the DAC with the right Rref and Riv and voltage is a good advice too.
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Old 25th November 2003, 12:22 AM   #7
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Default 20R

I was pretty happy with the change going from the LM7808 to the passive supply, but I might try switching back just for curiosity.
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Old 25th November 2003, 04:59 AM   #8
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Hi!
Try to put TDA chip on a 5V and 1.5k for I/V and 1k for Vref. It is ( my opinion) best to do it with ELSO regulator - you can use LM329 in that regulator or TL431 (if you need higher ps for your TDA). I think that if You have tried battery on Your dac- ps is not Your problem (the minute I put battery in my dac there was no harshness in sound but I didn't like the sound overall so I have changed to regulators)- maybe as Bas said to try to change TDA working point. Also try 6.72V on TDA and 2k2 as I/V and 1k32 as Vref. Maybe 8V and 3k as I/V and 1k5 as Vref. If this doesn't work- see to find better resistors and cap's after the TDA- and if that doesn't work- well You are in trouble.
Maybe it is something wrong with input receiver than.....
TDA chip is great chip - only it is very sensitive to everything
daniel
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Old 25th November 2003, 05:02 AM   #9
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sorry, one more!
TDA will work with only TL431 as a regulator without any harshness or anything- correct combination of the components in power supply will also affect the sound tremendously
daniel
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Old 25th November 2003, 12:57 PM   #10
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Default tl431

With 4x TDA1543, there's quite a bit of current, about 300mA. Maybe you could use multiple tl431s?
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