Hello everybody,
Will someone please explain to a newbee why do I need decoupling output caps in my simple DAC, how do I find whether I have some DC in my output and from where this DC is coming there.
Many thanks for your explanation and best regards,
Ignat
Will someone please explain to a newbee why do I need decoupling output caps in my simple DAC, how do I find whether I have some DC in my output and from where this DC is coming there.
Many thanks for your explanation and best regards,
Ignat
You might not need them, it depends on your DAC’s particular design and implementation. You can measure whether there is DC offset on your DAC’s outputs by connecting a voltmeter set to read DC volts to the audio signal output jacks of the DAC. Read the offset on both channels, as they may be different. Capacitor coupled (AC coupled) outputs will essentially read zero volts of DC offset. If your DAC was designed to have DC coupled outputs it still will have a small DC offset which is considered normal. If, however, the rest of your system cannot tolerate even a small (millivolts) DC offset, then you should capacitively AC couple the signal outputs to remove the offset entirely. The selection of a subjectively good sounding signal coupling capacitor is one of those hotly debated audiophile topics.
Last edited:
Many thanks Ken, brief and clear. So will try the proverb "best cap is no cap". It is a very simple dac based on CS1842 + TDA 1543x2. Originally implementig different mods-electrolityc and foil caps and in one schematics without any. Anxious to check the output DC offset as soon as I am back home.
Cheers,
Ignat
Cheers,
Ignat
Just for your additional info - I have measured the DC at the outputs without output caps and any load - it is 2 mV on both channels. Not sure whether I have to engage the digital input when measuring-please advise.
Thanks
Thanks
But the answer is simple, if the cap has a large enough value the voltage drop across it can be made arbitrarily small, and thus any non-linearities it possesses can be made arbitrarily small. So large electrolytics are usually the answer - be generous with the value to allow for aging. 3dB cutoff at 1Hz or lower is a guideline. You don't want a "good-sounding" cap, you want no distortion of the signal, so no sound from the cap!
Note not to use X7R or similar ceramics as coupling caps - they are microphonic! (as well as quite "distorty" - though not such an issue here as the voltage is small if correctly sized).
Those are actually coupling capacitors, and are connected in series with the signal, which travels "through" them.
They are intended to block any DC voltage present at the circuit output, and sometimes are also intended
to cut off the lower audio frequencies.
Decoupling capacitors are usually connected from each DC power supply terminal to ground,
and improve the power supply performance.
Try it and see. But regardless, always turn volume to minimum before turning the power on/off,
or switching inputs, etc.
The TDA1543 is a single +5 VDC chip. That would imply a 2.5 VDC output offset.
But the IC was designed for low cost applications. So your output pin DC measurements could be correct.
Pause for a moment and consider capacitor functions.
And correct function names for each function.
DC power supplies uses and need larger electrolytic capacitors.
To filter out AC ripple and noise.
You add "Bypass" caps to shunt higher frequency noise.
Also to reduce the ESR of the larger filter cap.
Audio amplifier "series" output caps block the DC offset.
Capacitors associated with that part of the circuit.
Small value, low voltage & low cost.
Great place to start
This is a great area to analyze and improve sonic performance.
Then is the low pass additional filtering of sampling noise to keep it simple.
Then you will find small "shunt" capacitors to ensure EMI compliance standards.
Exclude them.
But the IC was designed for low cost applications. So your output pin DC measurements could be correct.
Pause for a moment and consider capacitor functions.
And correct function names for each function.
DC power supplies uses and need larger electrolytic capacitors.
To filter out AC ripple and noise.
You add "Bypass" caps to shunt higher frequency noise.
Also to reduce the ESR of the larger filter cap.
Audio amplifier "series" output caps block the DC offset.
Capacitors associated with that part of the circuit.
Small value, low voltage & low cost.
Great place to start
This is a great area to analyze and improve sonic performance.
Then is the low pass additional filtering of sampling noise to keep it simple.
Then you will find small "shunt" capacitors to ensure EMI compliance standards.
Exclude them.
As for me, I don't care about the DC component at the DAC's output, if it is <=5-6mV. (usually it is less).
Alex.
Yes, you are right, thanks. I have omitted them in my setup and there is no problem, at least audible
Cheers