Any good TDA1541A DAC kit?

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You want to convince me that TDA1541 with max 4x OS capabilities will swing faster the outputs than the BB DAC's (rated at 8 and 16x) and the Phillips datasheet is wrong when it says the settling time is 1 micro second?

I think nowadays people use TDA1541A which has a plot of distortion vs freq at 8fs (fig4). Also what's the DNL spec for your beloved BB DACs - do you have it to hand?
 
Well, to give you credit for something, I become curious to test the new, fast, low noise ADA4897-1 in my PCM61 DAC. I need an adaptor single-dual now...


Would this ADA4897-a make the issue of high input impedance of opamp I/V's with the dac rise time. Ie, would its input impedance not start to rise so far into the mhz that a DAC would never see it ?
 
I think nowadays people use TDA1541A which has a plot of distortion vs freq at 8fs (fig4). Also what's the DNL spec for your beloved BB DACs - do you have it to hand?
You made a funny :)
I was using BB DAC's as examples just because... they did build lots of r-2r dac's. BB developed many DACs in the ladder configuration - 16, 18, 20, another 20, 24 bit. Phillips developed... two r-2r: 14 and 16 bit.
And when BB was laser trimming their resistors, Phillips decided to continue their development of r-2r with TDA1543 - 16 bit with performance below 13 bit (-75dB)...
Would this ADA4897-a make the issue of high input impedance of opamp I/V's with the dac rise time. Ie, would its input impedance not start to rise so far into the mhz that a DAC would never see it ?
The DAC current is 1...2mA. Voltage 2V. That means 1..2 kohm resistance. I think the output impedance of the OpAmp that can drive 100 ohm at 1MHz and 80mA will be just fine. BTW it's a SiGe CMOS part...
 
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You made a funny :)

I'm always hopeful that I can entertain as well as educate :p

I was using BB DAC's as examples just because... they did build lots of r-2r dac's. BB developed many DACs in the ladder configuration

Yep, but you missed out PCM53.

Phillips developed... two r-2r: 14 and 16 bit.

To borrow a phrase from Thorsten - this is patently untrue. You're as bad as him at digesting datasheets.

And when BB was laser trimming their resistors, Phillips decided to continue their development of r-2r with TDA1543 - 16 bit with performance below 13 bit (-75dB)...

You're talking full scale THD figures here? What's the relevance to audio? Oh and yet another patent falsehood :)
 
Hi,

You want to convince me that TDA1541 with max 4x OS capabilities will swing faster the outputs than the BB DAC's (rated at 8 and 16x) and the Phillips datasheet is wrong when it says the settling time is 1 micro second?

I never claimed that the Philips Chip settles faster than the BB ones. Nor have I indeed made any of the other claims you attribute to me.

The BB chip is rated to settle to +/-0.0006% of full scale, which is +/- 2LSB for 16 Bit and +/- 4LSB for 18 Bit. As for 1uS, this is TDA1541, I was referring to the later and by far more common TDA1541A which is specified to settle TO +/- 1LSB (+/-0.0003%) in under 500nS. It is anyones guess what the settling time to +/-4LSb would be like...

Past that, settling time TO +/-1LSB is much longer than the RISE TIME. And the rise time is what may cause a feedback amp to slew. It is also important to note that almost all I/V circuits are integrators, placing additional demands on the op-Amp to charge/discharge the integrator capacitor.

Well, to give you credit for something, I become curious to test the new, fast, low noise ADA4897-1 in my PCM61 DAC. I need an adaptor single-dual now...

Why?

According to you (post 186) 12V/uS slew rate is all that is needed. Maybe you should try a TL072 instead?

Ciao T
 
What part of which datasheet did I get wrong? My quip about the Fet switches in you favourite VGA?

Yep. Incidentally it was a little more than a 'quip' but we'll let that slide for now :)

If they do not use switches, what do they use, do you have any reference that shows what is used?

Why would you believe what I say when you don't believe what ADI says? I'd only be quoting from that - that DS and the related parts using the same architecture plus ADI's design support materials are my only source.

Even if you didn't read the explanations the fact that the attenuation vs control voltage plots are smooth without step jumps might tell you something which undermines your FET switch opinion.
 
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Hi,

Why would you believe what I say when you don't believe what ADI says? I'd only be quoting from that - that DS and the related parts using the same architecture plus ADI's design support materials are my only source.

Even if you didn't read the explanations the fact that the attenuation vs control voltage plots are smooth without step jumps might tell you something which undermines your FET switch opinion.

I did read the explanation.

I find it opens up more questions than it answers. They clearly show a ladder attenuator. There has to be some form of switching somehow to use this.

As for the smooth curve, if they use (for arguments sake) an amplifier block with adjustable Gm (say over a 7dB range which is easy to do with good linearity) and then a resistor ladder with 7dB steps they could achieve the precise result shown.

Ciao T
 
As for the smooth curve, if they use (for arguments sake) an amplifier block with adjustable Gm (say over a 7dB range which is easy to do with good linearity) and then a resistor ladder with 7dB steps they could achieve the precise result shown.

And where would the claimed 'FET switches' be if (for arguments sake) this were indeed the arrangement they were using?

<edit> This might help : http://www.analog.com/library/analogDialogue/archives/36-01/xAmp/xAmp.pdf
 
Why?

According to you (post 186) 12V/uS slew rate is all that is needed. Maybe you should try a TL072 instead?

Ciao T

Because that affirmation was for TDA1541 in 4x mode (topic of the thread is TDA1541). Faster OpAmp (more than 24V/us) might be needed for PCM61 in 8x mode - I have both of them so I can tell the difference.
 
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Hi,

Because that affirmation was for TDA1541 in 4x mode (topic of the thread is TDA1541). Faster OpAmp (more than 24V/us) might be needed for PCM61 in 8x mode - I have both of them so I can tell the difference.

Just looking at the initial steepness of the step current step into an I/V resistor (easily done by feeding a full scale squarewave into the DAC), I would suggest that for a TDA1541A an absolute minimum of around 30V/uS are needed to keep up with the current step, however this would still mean that we are constantly at or near the slew-rate limit of the Op-Amp even for a 1LSB step.

So it would seem at least sensible to allow for some extra slew rate to make sure we are well away from the slew rate limit, as even signals that do not cause the circuit to actually "slew-limit" may increase distortion appreciably. Based on this little set of notes I would think that the OPA627 might just about suffice.

HOWEVER, in practice, with a TDA1541A at 4 * OS I did find it subjectively beneficial to use a OPA637 instead, with a capacitor from -in to ground to set sufficient noise gain for the OPA637 to be stable. This capacitor also had a subjectively beneficial effect for the OPA627 and I would strongly recommend applying it regardless which Op-Amp is used, unless a CFB Op-Amp is used.

Ciao T
 
Hi,

And, even if I still hear distortions well, I trust measurements more.

Quite many years back I build an Amplifier based on a schematic in a magazine. It had phantastically low measured distortion. Yet I kept hearing distortion , lots of it. I put it on a distortion meter, which had the meter not even twitch. I gave up using this amp. Others had the same problem, much was written about this issue.

In the end this distortion was acknowledged to exist in the design, even though it could not be measured. Essentially it was a specific case of TIM/SID.

So, I do rather trust my ears if they tell me something is distorted, even if the meters and measurements tell me it is not...

Ciao T
 
So... YOUR measurement tool/method was flawed. That does not mean that ALL the tools/methods are flawed. Or that the measurements are useless.

However, in the subject at hand, you are basically trading SNR (using a compliant resistor for I/V you have a low signal) to avoid an eventual slew-rate induced distortion.
Small capacitors on inputs of fast OpApms (and on feedback) limit that slew-distortion well and they are not so much of a load to induce distortions.
 
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So... YOUR measurement tool/method was flawed. That does not mean that ALL the tools/methods are flawed. Or that the measurements are useless.

However, in the subject at hand, you are basically trading SNR (using a compliant resistor for I/V you have a low signal) to avoid an eventual slew-rate induced distortion.
Small capacitors on fast OpApms limit that distortion well and they are not so much of a load to induce distortions.

Have you ever owned a well setup TDA1541A DAC ?
 
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