All I see is C1 as the reactive component. The coupling cap is reactive by nature, but it is used just as a DC blocking coupler. It is not there for any effect caused by its reactive component; it's just acting as a DC blocker. R's, of course, are just dissipative. The 'lytic is not there to alter the circuit response the way C1 does, although at very low likely subsonic frequencies it doss induce a rolloff.
What are the 2 reactive components, outside of the coupling cap? Maybe I'm looking at the wrong picture, but I see only one other cap in the circuit. Resistors are not reactive; they are dissipative. A reactive component, such as a cap or inductor, have voltage and current offset by an angle. Both of them can store energy, one in an electric, and the other in magnetic field. In resistors the voltage & current are always in step; i.e. zero degrees of angle between them, and resistors cannot store energy.
Ahh, what you looked at was only the thumbnail of an attached picture. If you klick that to view the complete picture, you will see the posted schema.
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Is R1 & R2 a zobel attenuator to show a resistive load to the output in order the dac output doesn't see a capacitive load or to flat it for the next input stage ? Idem for the second zobel R3 & R4 ?
Both in // are giving a 5 K output impedance ? Low enough for the next input stage: 50K or 100K input impedance of audio industry standard
So C3 + R2 is not a simple low end high pass, C3 just a simple DC blocker to secure if DC.
Then C2 & C1 a 12 dB low pass together to tame HF spread? Or simply filtering each 10K R to make the Ref less noisy for the next stage (same goal) ?
What I wonder is if C3 really works to be a DC blocker or to shape a high pass with R2, beneficial for the next amp stage (pre or amp) ?
Both in // are giving a 5 K output impedance ? Low enough for the next input stage: 50K or 100K input impedance of audio industry standard
So C3 + R2 is not a simple low end high pass, C3 just a simple DC blocker to secure if DC.
Then C2 & C1 a 12 dB low pass together to tame HF spread? Or simply filtering each 10K R to make the Ref less noisy for the next stage (same goal) ?
What I wonder is if C3 really works to be a DC blocker or to shape a high pass with R2, beneficial for the next amp stage (pre or amp) ?
What does the rest of the circuit look like? What DAC chip are you using?
To me this looks like a DC blocker and a basic RF filter (if the caps are indeed 10pF). It’s just a way to be nice to whatever the next stage is.
Once we know which chip you’re using, we can probably find hints in the application notes.
To me this looks like a DC blocker and a basic RF filter (if the caps are indeed 10pF). It’s just a way to be nice to whatever the next stage is.
Once we know which chip you’re using, we can probably find hints in the application notes.
Here's what the frequency response looks like. The 10pF caps are HIGHLY suspect. It would result in a cutoff frequency of a whopping 56MHz. Let's have a look at that application note and we can probably figure it out!
EDIT: C3 and R1 are reversed compared to the original, but it doesn't matter.
EDIT: C3 and R1 are reversed compared to the original, but it doesn't matter.
I just follow the original post to try to understand the questioned shematic.
Yup I'd also like the OP gave the true shematic of the DAC to know more about dac chip model and all the passive parts values (caps).... We don't know for instance if there is oversampling made before the output...
@jean-paul
10 pF is not impossible if the goal was only to filter RFI, EMI gardbage. Think to it as you live in a >= G Hz nasty environment nowadays ! But indeed with this values, can not be sonic filter for the ears (reconstruction filter). For that 50 Khz would be a better value if one doesn't want to waste the phase too much before the -3dB.
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but yeah probably something like 1 nF ?
I tried that value as simple 6dB low pass before the RCA of DAC having a CFA for I/V with just 50K hz -6dB feedback filter before the passive low pass of the RCA output. I removed the 1 nF Class I cap though as it sounded better w/o....
I tried that value as simple 6dB low pass before the RCA of DAC having a CFA for I/V with just 50K hz -6dB feedback filter before the passive low pass of the RCA output. I removed the 1 nF Class I cap though as it sounded better w/o....
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I have a few new 510pF caps and my multimeter shows right value. It is cheap UNI-T UT133A, the lowest line in capacity is 9.999nF. It shows 0.007nF with these capacitors, I think it could be some error at so low values, so I assume it is 10pF not 6-8.
I think right answers about filtering external RF were already here.
At left side signal goes to op amp buffer to headphones amplifier. DAC chip has voltage output, the question is not about DAC but only about such a filter at line out. Perhaps the developers did this so that the headphone amplifier would not be excited while working with the line output ?
I think right answers about filtering external RF were already here.
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Yes, but if you tell us which chip it is, we can look at the data sheet and the typical application and get some hints from there.
The bandwidth of any audio amplifier is way too low for gigahertz range signals to have an impact. The biggest issue these days is switchmode noise, but that’s typically in the 100kHz-1MHz range. A 56MHz cutoff makes no sense.
And there is perhaps the limited bandwith of some passive parts when used as filter, as well.