Distortions

Hi guys!

This bad behavior is to be expected.
The TDA 1543 /45 are current output dacs and need to see a virtual ground at the output pin.
If you look at the data sheet , you will see that the output compliance ( the AC voltage that the DAC can "see" in the output pin ) is only + - 25mV.

See the pag. 7 of the PDF , Analog outputs

http://www.ptsoundlab.com/secnumerique/dac/zeoovertda1543/TDA1543_.pdf

Good work , Isaac!

Cheers :MILD:

Jorge

 

Hi,

Nope, set up correctly the TDA1543 will provise the full CD Standard voltage output without clipping and quite reasonably low distortion.

You are quite wrong about this as an absolute limit. It is a limit that needs to be complied with IF you want to get rated linearity at high levels.

You CAN get a lot more output from the DAC, using passive I/V conversion, but there are a number of specific limits one needs to be aware off AND because of the tolerance of the DAC's in series one tends to find that if you push towards the limits you need to trim both I/V resistors and Refernece resistor on the TDA1543 for each chip to get the maximum output without clipping.

BTW as one can see from the Datasheet in the same section you mention the limit (if we accept a somewhat poorer than specified high level linearity) is V signal P-P = Vdd - 3V centered at 1.8V + 0.5 * (Vdd-3V). In other words, ir we entertain the specification maximum of 9V supply voltage we can get a 6V Peak-Peak Signal swing, enough to have a little headroom for a 2V RMS/5.6VPP signal of CD Standard.

The problem is that full scale current of the TDA1543 is specified as 1.95mA-2.65mA.

In order not to clip the Chip for digital full scale at 2.65mA you need an I/V conversion resistor of (Vdd-3V)/2.65mA or in our case 2264 Ohm, using 2K2 is acceptable therefor if we have a 9V Supply for the TDA1543 and ONLY with a 9V supply. BTW we get "only" 4.29V PP (1.5V RMS) from a 0dbfs signal with a chip having 1.95mA full scale current. In other words, for a Chip with a lower specification limit Ifs we would have to increase the I/V resistors from 2K2 to 2K87 and for a "bogey" Chip with 2.3mA full scale current we need 2K4 as I/V resistor.

HOWEVER, if e had only a 5V supply for the TDA1541 we would be limited to 2V PP (0.7V RMS) output and 750 Ohm I/V conversion resistors.
Anyway in order to get the lowest distortion we must then trim the reference resistor on the TDA1543 to place our quiescent voltage at 1/2 of the signal swing + 1.8V above ground, in our 9V example this will be at 4.8V. In most cases doing so establishes a close to minimal distortion condition.

So, as we can see we may require depending where the TDA1543 chip falls in the tolerance field a different I/V conversion resistor value and we must trim individual Chips for correct offset. Failing to do sugests to me that at least 50% of all DAC's will not make best use fo the individual chips in the given circuit.

This makes clear that values of the reference and I/V conversion resistors must be adapted to the actual supply voltage applied to the DAC AND to the actual chip.

Ciao T

 

It only depends what is for you "reasonably" low distortion. In that department our mileage may vary.

[[ You are quite wrong about this as an absolute limit. It is a limit that needs to be complied with IF you want to get rated linearity at high levels. ]]

And who don't want that linearity? Linearity is a bad thing?.

[[ BTW as one can see from the Datasheet in the same section you mention the limit (if we accept a somewhat poorer than specified high level linearity) is V signal P-P = Vdd - 3V centered at 1.8V + 0.5 * (Vdd-3V).]]

This is DC voltage compliance and is not the some thing as AC voltage compliance...I hope you know the diference.

Obviously , this low linearity is only obvious in systems , with high resolution and not in SE systems , where de distortion of the DAC with an voltage swing greater than the other , can serve to compensate for the same problem in a SE amp , if the phase of that distortion is oposite.

Arrivederci J.

 

Hi,

Well, I consider this:



"reasonable"

It certainly is better than any Speaker or Mike at "full scale".

I know the difference. BUT, as you will find, if you actually for a moment use your own head, instead of deafly following others, it is a clipping voltage limit that applies to DC and AC.

What sort would that be? Those with >5% THD average for realistic levels at the listening position (eg low output imedance amplifiers with low sensitivity speakers?).

Actually, the difference between 0.1% THD (2nd harmonics dominant) at digital full scale and the kind of hard clipping shown in the pictuires posted here earlier is more than a little obvious, even with low resolution (eg low sensitivity speaker based) systems.

Ciao T

 

OK...the old argument , why pursuit low distortion, if the mikes or speakers are the principal culprits.

That way all amps must sound the same , as the distortion of the transducers is the greater in the reproducing chain..

[[ it is a clipping voltage limit that applies to DC and AC.]]

When the clipping voltage limit is reached the distortion become maximized , but Current Source DAC "likes" to see a short at is output.

[[ What sort would that be? Those with >5% THD average for realistic levels at the listening position (eg low output imedance amplifiers with low sensitivity speakers?).]]

Obviously , we belong to different camps in that department , certainly for you the crux, is a full range high sensitivity speaker current operated...please enjoy.

As the French say:

À chaqun son pied!

Ci vediamo...Jorge

 

You are already learning how football should be played with José Mourinho... the world's best football coach...

Now you've just started to learn how audio electronics should be played with Jorge Santos... the world's best home hi-fi engineer...

Those are the men who revolutionate... they are revolutionists... they bring revolution to your homes!

Learn or loose...

 

Hi,

Not at all, my argument is -60db 2nd harmonics (or 0.1% THD at digital full scale ) that is monotonic falling with level is a sonically very harmless form of distortion. Haveing 1/100's of that mount of high order distortion is much more objectionzble.

I am not arguing that everything sounds the same, but that distortion must be considered in the cointext of audibility. You complain over "high distortion" without qualifying and considering the impact. That is just plain idiotic.

Well, they do? Aer you quite sure about that? I mean not just parroting others, but have you actually done extensive experiments (or at thge very least anbalysed the actual circuitry inside the DAC and attempted to understand it?

I am not saying that. However, if you use a low efficiency moving coil speaker and drive it from a voltage source you are establishing the exact conditions to maximise distortion and compression. That is a simple fact.

As the key two distortion menchanisms in speakers relate to 1) the current in the voicecoil in a cubed function and 2) the excursion in a squared function it is VERY easy to see that typhical "High Fidelity" speakers (low efficiency = high current, small diameter drivers = high excursion) must be high distortion devices, compared to the typhical High efficiency Speaker (high sensitivity = low current, large diameter = low excursion).

Draw your own conclusions. And occasionally supplement parroting plainly false statemenst with actual empirical work. You may find the results rewarding.

Ciao T

 

Perhaps Tube Dude and 3dsonics would care to take this discussion into a separate thread or pm?

 

Isaac,

Why? The issue still is the NOS DAC based on the TDA1543 ship... so, what is your problem?

 

Relative distortion levels of high vs low efficiency speakers?

 

Hi,

You may forgive me, however, Jorge raised the issue of speakers claiming with a certain type of system/speaker certain things are not audible. I merely pointed out that there where conditions that suggested that his contention was wrong. As I do not like when people make unsupported statements I provided the rationale behind my disagreeing with his contention.

I'll not mention speakers again unless other table the subject first, I promise.... ;-)

Ciao T

 

That's fine, I was just requesting that it go to another thread.

 

Ok, fair point! But... the argument in favor of the NOS DACs, which have incredible distortion as your scope clearly showed, is precisely the fact that this distortion is always much less than speakers'distortion... which in turn leads us to the question of knowing what levels of distortion we should have to be able to listen and identify what the scope so clearly shows... it is inevitable!

As a matter of fact, we can clearly identify the NOS DAC distortion when we listen to it almost regardless of the speakers we use, that's the reason why some people like it so much and others don't... because it has a sound of its own (distortion). So, I guess you are right, that old argument is indeed pointless.

Distortion may sound pleasant in certain contexts - valve amps are the major example - however distortion should not be the goal at all... we only talk about "benign distortions" because we are not able to eradicate it completely and we are always awear of it... that's why we've been changing our equipments, searching

One thing is certain... everyone likes when there is no distortion (except if the music is bad or the distortion is comming from the music itself) whereas some people tolerate some kinds of distortion and even like it, and others simply don't.

That's the major issue behind all audio discussions... should we crave for zero distortion or find the pleasant one?

 

Like Isaac I'm just wondering if we shouldn't split this thread both so that Chris can continue to get the advice he wants about his DAC, and the distortion audible or otherwise should go elsewhere. Then the major issue can be discussed ad infinitum as I'm sure it will!

 

Can you now? I'll bet you that if I set up a blind test between my NOS DAC and any other CDP (one that wasn't familiar to you) you would not be able to say which was the NOS DAC (ie, you wouldn't be able to hear the 'distortion' which would clearly identify it) .

Michael.

 

You see here's another case of what the figures say, and what you acyally hear is different.
Mike, I'll do a blind test between a NOS dac and another unfamilar unit, I can tell it by the 'presenation it gives' nothing more. T.

 

Hi,

PLEASE NOTE, what Isaac's scope showed was CLEARLY a defective unit. A well set up Non-Os DAC using TDA1543 and using Passive I/V conversion to direct output looks like this:



47 Laboratory 4715, waveform of 1kHz sinewave at 0dBFS, from stereophile.com

What Isaac measured showed what happens if you do not set up you chip correctly. That is why I took the pains pointing out how to do it right.

Put most simply, with 9V supply the TDA1543 with passive I/V can output 2V RMS for 0dbfs with relatively low distortion. If you trim the Reference resistor you can achieve as little as 0.01% THD (-80db) with selected chips. On average you get -60db or better THD/N with the DAC correctly trimmed.

Note that the datasheet suggests a typhical THD/N for the TDA1543 of -75db and a guranteed limit of -70db when employed as per datasheet. The slight increase of worst case THD/N when using the passive I/V correctly may be objected to by scope jokeyes on principle, but is comparably harmless, in the context.

Ciao T

 

Hi,

I see that the thread has been (illadvisedly) split off. I feel that discussion has remained relevant to the original topic as confirmation to Chris that his DAC is indeed faulty and needs to have the reference resisito and/or I/V conversion resistors and/or PSU adjusted to operate as it is capable of.

Ciao T

 

Michael,

It might happen... but only if your set-up would be so f**ked up that everything would always sound the same regardless of the solution being used or if you would be using two NOS DACs...

Maybe I will come to Lisbon tomorrow and we could do this if you want... I never heard a NOS DAC and I don't remember the sound of your DVD player either... I'm all blind.

Besides, I have what I think is a very strong argument in favour of the objectivity, in some circumstances, of a non-blind test... it was what just happened to me:

I took my Moon Eclipse to Tube Dude's place to compare it with his CD player, and nobody else was hopping more than me that the Moon could be better... for a start I even didn't like the Eclipse with Tube Dude's system and his CD player was so much better that I could not believe where all that money went...

My mind was trying hard to believe otherwise but my ears didn't let it...


PS: Isaac's scope showed a distinct distortion using a 15kHz (not 1kHz) sinewave which is characteristic of a normal NOS DAC.

 

OK - trying to follow this to learn a bit about the DAC.

3D - you've identified 3 possible remedies in your post avove. Is this a case of pick one of the 3 as you please to bring to DAC back to spec., or is further investigation needed to identify which of the 3 remedies is correct?

Thanks,

Stuart.