Question about Ground of an IC

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#24
RoyAaron said:
I've attached the sheet for the NS8002A module.
Click to expand...

The circuit on that pdf shows the first amp stage configured with a 20k input resistance. It is actually marked Ri and that sets the input impedance in that configuration to 20k. The 0.39uF (all these caps are coupling caps, decoupling are the caps across power rails)

So 0.39uF and 20k form a high pass filter with a -3db point of approx 20Hz

A 1uF ceramic will work fine and lower the -3db point to 8Hz. For high end audio we would more likely use a film cap but ceramic is perfectly OK for this.
 
#26
Mooly said:
The circuit on that pdf shows the first amp stage configured with a 20k input resistance. It is actually marked Ri and that sets the input impedance in that configuration to 20k. The 0.39uF (all these caps are coupling caps, decoupling are the caps across power rails)

So 0.39uF and 20k form a high pass filter with a -3db point of approx 20Hz

A 1uF ceramic will work fine and lower the -3db point to 8Hz. For high end audio we would more likely use a film cap but ceramic is perfectly OK for this.
Click to expand...
One last one (hopefully) . . . should I add a coupling cap to the output of IC2. If so, then would 1uF be OK?
 
#28
RoyAaron said:
One last one (hopefully) . . . should I add a coupling cap to the output of IC2. If so, then would 1uF be OK?
Click to expand...
It is like Rayma says, coupling cap sizes are determined by what it works into and what sort of lower frequency cut off point you want.

If the NS8002 board has a coupling cap at the input then that is all you need. If you add one after IC2 you must sure any DC bias paths remain intact such as the one to IC3 inverting input (with extra resistor as I showed earlier).
 
#34
Things sometimes get misinterpreted or assumed (by all concerned 🙂)

You mentioned a bunch of 474nF caps which would be an odd value. I wondered if you knew how the values were arrived at from the markings. 104 would be a 100nF for example.

RoyAaron said:
Would my adding a 118nF cap after IC2 be a problem (f=70Hz, R=20K)?
Click to expand...
I took this face value. 118nF (an odd value but you didn't say it was four 0.47uF in series ) after IC2 will appear in series with this one:

RoyAaron said:
The NS8002 spec sheet shows a 0.39uF cap before a 20K resistor upon input.
Click to expand...

So I said 88Hz, you got 87.5Hz. Those are just rounding errors.
 
#36
RoyAaron said:
But aside from what errors you might uncover I have a question about grounding as pertains to the three ICs (MC33171N [spec sheet also attached]).
Click to expand...
My observation is those opamps aren't designed for audio and have too low a GBP. Also they are micropower at 200µA supply - serious low distortion audio opamps tend to be in the 2mA to 4mA supply current range in order to be fast enough to give low distortion at high audio frequencies.
 
#38
Mooly said:
Things sometimes get misinterpreted or assumed (by all concerned 🙂)

You mentioned a bunch of 474nF caps which would be an odd value. I wondered if you knew how the values were arrived at from the markings. 104 would be a 100nF for example.


I took this face value. 118nF (an odd value but you didn't say it was four 0.47uF in series ) after IC2 will appear in series with this one:



So I said 88Hz, you got 87.5Hz. Those are just rounding errors.
Click to expand...
Mooly,
Please have a look at Tillotson's #36.
I looked at the LM4562 and it certainly appears to be a better amp.
But there are different flavors of "high fidelity." That is, while I certainly want to avoid distortion I am not driving a 60 watt speaker hoping for concert hall quality.
Do you think the MC33171Ns would still suit me?
-Roy
 
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