Thanks guys.
Yes, the I is in the datasheets. And the TDA1543 datasheet even shows an I/V using a 1.2k resistor, which should mean 2.3mA * 1.2k.
But the TDA1541 has a "typical" output of 4mA. As I understand it, the TDA1541 can not be used with a passive I/V like the TDA1543.
The TDA1545 has an output of just 1mA and the datasheet shows an I/V with 3.9k resistor. That makes perfect sense to me. But then the TDA1541 screwed things up for me.
I'm not completely clueless here. But there evidently are things I don't quite understand.
Yes, the I is in the datasheets. And the TDA1543 datasheet even shows an I/V using a 1.2k resistor, which should mean 2.3mA * 1.2k.
But the TDA1541 has a "typical" output of 4mA. As I understand it, the TDA1541 can not be used with a passive I/V like the TDA1543.
The TDA1545 has an output of just 1mA and the datasheet shows an I/V with 3.9k resistor. That makes perfect sense to me. But then the TDA1541 screwed things up for me.
I'm not completely clueless here. But there evidently are things I don't quite understand.
Some more.
The 2.3mA of the TDA1543 and a passive I/V of 2.4kOhms result in about 2Vrms. Ran it in LTSpice.
I'm getting there. But I still have some questions.
I read this about the TDA1543:
"The DAC outputs an analog current proportional to the digitally encoded input signal, and the current is drawn through the output resistors, one for each channel, to produce the output voltage."
Continues...
"The TDA1543 is run at 9 V instead of the normal 5 V. This is done to give the chip enough headroom to output a standard 2 Vrms output signal. The result will be a dangerously warm chip unless heatsinking is used."
What does "headroom" mean here?
Second. Some of the popularity of the TDA1543 is related to the fact that you can use it with a passive I/V. From that I conclude that the TDA1541 cannot be used without a passive I/V. Am I correct? How about the 4mA? If you cannot simply use a 1.5k resistor with the TDA1541, why?
The 2.3mA of the TDA1543 and a passive I/V of 2.4kOhms result in about 2Vrms. Ran it in LTSpice.
I'm getting there. But I still have some questions.
I read this about the TDA1543:
"The DAC outputs an analog current proportional to the digitally encoded input signal, and the current is drawn through the output resistors, one for each channel, to produce the output voltage."
Continues...
"The TDA1543 is run at 9 V instead of the normal 5 V. This is done to give the chip enough headroom to output a standard 2 Vrms output signal. The result will be a dangerously warm chip unless heatsinking is used."
What does "headroom" mean here?
Second. Some of the popularity of the TDA1543 is related to the fact that you can use it with a passive I/V. From that I conclude that the TDA1541 cannot be used without a passive I/V. Am I correct? How about the 4mA? If you cannot simply use a 1.5k resistor with the TDA1541, why?
quantran said:
I noticed the Vref pin. But not that it is not on the TDA1541. I think I know what "Vref" stands for. But what does it do? I checked some TDA1543 schematics. Didn't get any wiser.
I also noticed that the DDDAC gets an output of 1.6Vrms from 8.4V. The 47 Labs claims the Progression DAC has an output of 2.1V. I guess the latter must be 2.1Vp.
phn said:
As you have yet read in datasheet and as other have yet told you, TDA 1541 and TDA1543 are output current DAC which require an external *active* I/V converter (i.e. a properly connected op amp or other circuit able to guarantee its input behaviour as a "virtual ground" in order to obtain the maximum current constance - and linearity). So calle "voltage output" DAC, especially if they are of multibit type, simple use an *internal* I/V active converter (i.e. an op amp integrated on the same chip): DAC of this class are inherently current sources, not voltage sources. The real difference with the two "flavour" of DAC is that I/V section is internal or external to the DAC IC, nothing more!
About "Vref". TDA 1541 and TDA 1543 have either Vref connection but, with TDA 1541 (which require dual supply), "vref" is just the ground connection. Besides, the Vref pin of TDA 1543 is to be used as a bias reference for external I/V converter and not for arranging a "passive" I/V converter with resistors. Overriding the question of supplyng TDA 1543 with near the double of voltage for what it's designed for, with IC must be kept in mind that all mode no written down in datasheet may easily turn in a written out of IC itself... be careful with experiment, especially when no internal schematic is provided in datasheet (as is in this case).
Curiosity: why you need to change TDA 1541 (or 1543) in "native voltage out" when they are not thought for?
Hi
Piercarlo
Re: Re: TDA1541 and TDA1543 questions
But I have read the datasheets, more than once. I think I have made that more than clear here.
The datasheets may say they require active I/Vs. But we know there are lots of TDA1543 DACs with passive I/Vs.
My problems are not related to the datasheets per se, but my limited knowledge about electronics. For example, I knew what passive and active I/Vs are. But I did not knew you could set the voltage (if that's the right word for it) with a passive I/V. That I learned yesterday. Hence I wrote: "The 2.3mA of the TDA1543 and a passive I/V of 2.4kOhms result in about 2Vrms. Ran it in LTSpice." That was a revelation to me.
I don't. The I/V does that. I just didn't know how a passive I/V works. Now I do.
I will try to figure out the rest of your post.
Piercarlo said:
But I have read the datasheets, more than once. I think I have made that more than clear here.
The datasheets may say they require active I/Vs. But we know there are lots of TDA1543 DACs with passive I/Vs.
My problems are not related to the datasheets per se, but my limited knowledge about electronics. For example, I knew what passive and active I/Vs are. But I did not knew you could set the voltage (if that's the right word for it) with a passive I/V. That I learned yesterday. Hence I wrote: "The 2.3mA of the TDA1543 and a passive I/V of 2.4kOhms result in about 2Vrms. Ran it in LTSpice." That was a revelation to me.
Piercarlo said:
I don't. The I/V does that. I just didn't know how a passive I/V works. Now I do.
I will try to figure out the rest of your post.
phn
Passive I/V with a resistor, in theory, is not a proper way to convert current to voltage. In fact this works with most DAC chip. However, in most cases, except for tda1543 and may be tda1545, you will not get a voltage large enough to drive an amp.
Loading the DAC chip with a resistor to ground will cause linearity error because these DACs are designed for output to be connected to virtual ground. If the resistor is small enough linearity error may be acceptable and the DAC may even sound good subjectively. If you increase the passive i/v resistor to certain value depending on DAC chip, it will cause heavy distortion and may not even work.
Practice show that tda1543 work with large i/v resistor and most other chips don't. That is because the tda1543 is internally different from other chips. This allows it to tolerate large i/v resistor. This is unusual. The designers of tda1543 or may be some one here would know why.
However it's still a good idea to keep the passive i/v resistor as small as possible. That's why people stack up 8x or 16x tda1543. By this way the i/v resistor can be reduced by 8 or 16 times and still give the same output voltage.
Cheers
Passive I/V with a resistor, in theory, is not a proper way to convert current to voltage. In fact this works with most DAC chip. However, in most cases, except for tda1543 and may be tda1545, you will not get a voltage large enough to drive an amp.
Loading the DAC chip with a resistor to ground will cause linearity error because these DACs are designed for output to be connected to virtual ground. If the resistor is small enough linearity error may be acceptable and the DAC may even sound good subjectively. If you increase the passive i/v resistor to certain value depending on DAC chip, it will cause heavy distortion and may not even work.
Practice show that tda1543 work with large i/v resistor and most other chips don't. That is because the tda1543 is internally different from other chips. This allows it to tolerate large i/v resistor. This is unusual. The designers of tda1543 or may be some one here would know why.
However it's still a good idea to keep the passive i/v resistor as small as possible. That's why people stack up 8x or 16x tda1543. By this way the i/v resistor can be reduced by 8 or 16 times and still give the same output voltage.
Cheers
It must be DC coupled. The output of the TDA1541 is sinking 2mA at zero analog output. This current varies between 0 and 4mA from negative to positive analog output peak. The other restriction is that the voltage at the current output pin must not go beyond 25mV. Therefore a passive I/V resistor of as low as 6 ohms or so should be used. In order to get full 2V output, about 160x voltage gain will be necessary (assuming 6 ohms I/V resistor), and noise problems may arise. The virtual GND opamp I/V stage is much simpler.
Hi Oshifis,
To check I have understood this right: About 1541, 25/2=12,5ohm is the highest allowable resistor? Output with 6 ohm will be 6*2=12mV?
A parentesis: About the CD 2V out std I find this unnecessary as not even a poweramp needs this much. Wouldn´t 0dBu=0,775V be enough? Or why not the semiprostd 300mV/10k? If we go for 6ohm load and 0,5V out we then only need 40x gain.
To check I have understood this right: About 1541, 25/2=12,5ohm is the highest allowable resistor? Output with 6 ohm will be 6*2=12mV?
A parentesis: About the CD 2V out std I find this unnecessary as not even a poweramp needs this much. Wouldn´t 0dBu=0,775V be enough? Or why not the semiprostd 300mV/10k? If we go for 6ohm load and 0,5V out we then only need 40x gain.
The higher the i/v resistor value the higher the output.
I have checked and most people say around 35R is what gives the best sound. The tda1541 should have a minimum output power and the minimum resistor value should be around 15R but I need to confirm that!
What I propose is not that thing at all, it is to replace the opamp by a discrete ( non chip component) stage.
What my question is : what resistor value should I use to buffer the transistor in a push-pull class A stage.
I will use a capacitor and filters at the output of the tda to filter noise and DC so it is not polluting the discrete amplifier.
Thank you!
I have checked and most people say around 35R is what gives the best sound. The tda1541 should have a minimum output power and the minimum resistor value should be around 15R but I need to confirm that!
What I propose is not that thing at all, it is to replace the opamp by a discrete ( non chip component) stage.
What my question is : what resistor value should I use to buffer the transistor in a push-pull class A stage.
I will use a capacitor and filters at the output of the tda to filter noise and DC so it is not polluting the discrete amplifier.
Thank you!
HI ozmikeh ! I looked at it and I don't think ill use that. I prefer tweek my own i/v and set proper resistance and filters values. 
Also I wonder why they use the tda1545A ??????
The Rudolf i/v comes with a filter and noise canceller and DC blocking cap at the end of the i/v, I wonder why he chose to put it at the end and not at the beginning , any idea ???
Also I wonder why they use the tda1545A ??????
The Rudolf i/v comes with a filter and noise canceller and DC blocking cap at the end of the i/v, I wonder why he chose to put it at the end and not at the beginning , any idea ???
they use TDA1545A to avoid putting the signal through SPDIF which has some issues.
I think it might be because putting it at the end means you're blocking DC on a bigger signal. Thus the capacitor has less effect on the micro-dynamics?
I'm sure Rudolf is/was a member on here, you may be able to find him and ask him.
I think it might be because putting it at the end means you're blocking DC on a bigger signal. Thus the capacitor has less effect on the micro-dynamics?
I'm sure Rudolf is/was a member on here, you may be able to find him and ask him.
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