What value for the coupling caps?

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Having the schema below, what values should I use for C1 and C2?
2002tii(thank you!) gave me the following formula:
f = 1/(2*PI*R*C) and having f @ 10hz
C2 should be at least 160nF(R = 100K + 1K), so 1uF would be ~ 2Hz

C1 should be at least 1.29uF(see those 4K7+4K7+4K7 in paralell with the 100k)

Is this right?
Any recommandations?
Do you know where I could find more details about calculating the values for the coupling caps?

Thank you :)
 

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li_gangyi, I am trying not to, but you don't know me ;)


mcp, what do you mean by cascaded opamps? the signal is going through multiple opamps?
if that's it, well, I think the signal(in my case) is going through multiple opamps as well, not on the DAC board, but on the signal path before the preamp stage, the signal goes through 3 more opamps, so in total 4 opamps from digital to preamp. each opamp has it's own set of coupling caps.
 
mcp, I think you already understood I am a beginner...
No, i am not aware.....;)

What do you mean by "have your filter inputs and outputs de-coupled"?
If you do not use any capacitors to separate one network from the other, you will be "direct-coupling" them. Any DC on the input will be amplified at the output. But you are not interested in amplifying DC. You are working on AC signals, like an active crossover to separate music signals. By having a capacitor at the input, it will prevent the input from been injected with DC from the source. A capacitor on the output also prevents any DC emitting from the output of the opamp from being injected into the next stage. Hence, the stages are "de-coupled".
 
mcp said:
No, i am not aware.....;)

Now you know it :smash:

If you do not use any capacitors to separate one network from the other, you will be "direct-coupling" them. Any DC on the input will be amplified at the output. But you are not interested in amplifying DC. You are working on AC signals, like an active crossover to separate music signals. By having a capacitor at the input, it will prevent the input from been injected with DC from the source. A capacitor on the output also prevents any DC emitting from the output of the opamp from being injected into the next stage. Hence, the stages are "de-coupled".

The schematic above is from the digital in board in my receiver, and the signal is comming directly from the DAC(AK4527BVQ) at C1. It is going through the opamp, C2 and then out into a board where the signal to be amplified is selected(a lot of switches/relays over there).
So from what I understood, C2 must be the (de-)coupling cap at the output of the stage(DAC board). C1 is the (de-)coupling cap before the opamps. Is this right?

And then a question about the 10uF caps.
As originally C1=10uF/35V and C2=10uF/35V, I was trying to figure out what else I could use over there, smaller values eventually since with 10uF I see myself forced into elcos, which as we all know, are far from being the perfect caps. Another question: are 35V caps really required?

The nasty thing is that there isn't a lot of space, the space between the leads is some 5mm, so even going with some lower values like 2uF or even 1uF I can't get some nice MKPs, only MKTs, still, I think these are better than the elcos(correct me if I'm wrong).

:dead:
 
So from what I understood, C2 must be the (de-)coupling cap at the output of the stage(DAC board). C1 is the (de-)coupling cap before the opamps. Is this right?
Yes, that is correct.
Another question: are 35V caps really required?
The opamps will probably have rail voltages of +/- 15V. If so, 35V caps is about minimum.
the space between the leads is some 5mm, so even going with some lower values like 2uF or even 1uF I can't get some nice MKPs, only MKTs
Maybe you can solder them under the PCB if there is enough space.
 
mcp said:

The opamps will probably have rail voltages of +/- 15V. If so, 35V caps is about minimum.

Yes the the opamps are on +- 15V rail.
But the caps ar not on the rails, they are on the signal path. No difference?

Maybe you can solder them under the PCB if there is enough space.
I can solder on the other side, but the leads for an MKP are not that long, and the distance between them is 25mm. How can I put them in some 5mm?
Then again, the board is positioned vertically, the MKP's are not light and I can't fix them properly onto the board, so there might be some some problems sooner or later.

Thank you very much for all your help, much appreciated :)
 
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