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Again on NOS TDA1543 DAC active filter
Again on NOS TDA1543 DAC active filter
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Old 11th October 2018, 08:31 AM   #1
ygg-it is offline ygg-it  Italy
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Default Again on NOS TDA1543 DAC active filter

Sorry to bother you again on this old dac (TDA1543), but I'm going to build an active opamp IV filter at the output.

I need to know which order should be and, overall the cut off frequency.

What I don't understand is why many have cut at 10KHz (and not 20Khz or more) and they say are completely satisfied about the sound.

TDA 1543 I/V stage education needed!!

Can you please give me a quick guidance about which should be a good sounding IV bending curve at the output of a NOS DAC like TDA1543?
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Old 11th October 2018, 10:41 AM   #2
DF96 is offline DF96  England
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The filter given in your link appears to have a 40kHz cutoff, so it is not a reconstruction filter unless oversampling has been used.

What is "good sounding" can be a matter of taste.
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Old 11th October 2018, 11:14 AM   #3
ygg-it is offline ygg-it  Italy
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Hi I'm referring to post #22 and successive: 10Khz cutoff (I ve simulated too)

TDA 1543 I/V stage education needed!!
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Old 11th October 2018, 01:17 PM   #4
lcsaszar is offline lcsaszar  Hungary
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Most commercial implementations use a 3rd order Besseĺ filter, tuned to a cutoff frequency just beyond 20 kHz.
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Old 11th October 2018, 02:08 PM   #5
abraxalito is offline abraxalito  United Kingdom
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I've recently put up opamp-based schematics for I/V and filter stages for a TDA1387 DAC here : AliExpress AD1865 R2R DAC

You might find something useful there as there are similarities between the chips.
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Old 11th October 2018, 02:44 PM   #6
ygg-it is offline ygg-it  Italy
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Quote:
Originally Posted by abraxalito View Post
I've recently put up opamp-based schematics for I/V and filter stages for a TDA1387 DAC here : AliExpress AD1865 R2R DAC

You might find something useful there as there are similarities between the chips.
But your scheme's curve is flat for hundreds of KHz?!!

This confuses me even more...
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Old 11th October 2018, 02:55 PM   #7
abraxalito is offline abraxalito  United Kingdom
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That's just to illustrate the effect of hanging a 2n2 capacitor on the inverting input of the I/V opamp - not really recommended. I posted up a post-filter which has a 3rd order roll-off beyond 20kHz and I'm going to suggest a CLC filter prior to the I/V which does NOS droop correction as well as attenuation beyond 22kHz or so.
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Last edited by abraxalito; 11th October 2018 at 02:59 PM.
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Old 12th October 2018, 08:13 AM   #8
ygg-it is offline ygg-it  Italy
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Ok, assuming I'm building a separate opamp filter of 3rd (or 4th) order to cut off after 20-22KHz and provide the necessary voltage gain - thus I can run a bank (1..2..4...8...) of TDA1543 at 5V without heatsink- (I need +6.3 db gain at least because I'd like to use AD828), I need now to design the IV.

I have in mind two solutions:

1) do the IV conversion with a simple opamp with the right feedback resistor followed by the AD828 opamp filter (like in the datatsheet). In this case I need one opamp stage more.

2) do the IV conversion with just a resistor across the TDA outputs before the AD828 opamp filter. Much more simple.

Which do you suggest in such situation?
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Old 12th October 2018, 09:33 AM   #9
DF96 is offline DF96  England
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If you are using an opamp to do the IV then this stage needs to implement some filtering because an opamp output cannot follow the transitions at the output of the DAC. It need not be the main filter, though.

TDA1543 with 5V supply cannot use simple 'resistor to ground' passive IV - see my website for details. You need 6V minimum, and 8V would be better.
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Old 12th October 2018, 01:30 PM   #10
abraxalito is offline abraxalito  United Kingdom
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I don't much like either 1) or 2) as they stand as each has weakness. But whether those weaknesses matter depends what you're going to be feeding the output of your DAC into. For example, if its a datasheet application chipamp then either will be sufficient, go with whichever is easier to build.
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