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Old 18th July 2004, 08:13 AM   #1
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Question Bigger or larger capacitors in Active Crossovers...make a diff?

Most of the stuff I've seen uses around 0.1uF. But if I use a larger capacitor, say 0.33uF, my resistor values drop. So lower resistors, but higher capacitance. If I go the other way (0.03uF) I get higher resistors, but lower capacitance.

So does it matter at all, or does the small values used have no effect? Sound, stability?
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Old 18th July 2004, 08:21 AM   #2
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I truly believe that its a good idea to use the bigger caps if you can get some nice ones. One reason is that bigger resistors are noisier than small resistors and therefore contribute more to the bag ground noise. I try not to go above 22 kohm in most cases.

Then there is the case of the mox filter this gives the user a chance to play arround and achieve the same frequency response with both small and large caps and resistors. So my advice would be to try it and see whats best for you.

As for the noise, it might be pretty academic unless you have a lot of active filters in your signal path.

I hope this helps you

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Old 18th July 2004, 08:50 AM   #3
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I did not think it mattered, but when I had a 'hum' problem I tried higher capacitor / lower resistor values and the hum disappeared.
Higher resistor values seem to make the circuit more susceptible to pickup from the transformers magnetic field.
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Old 18th July 2004, 09:28 AM   #4
johnf is offline johnf  Germany
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Default Re: Bigger or larger capacitors in Active Crossovers...make a diff?

You may get some hiss with really high resistance values (ca. 100K+). You may also see large output offsets if you are using bipolar opamps. The offsets can cause clicks when you plug things in, which admittedly is probably an inconsequential nuisance.

If you get your signals to line level early on and don't let impedances go much above, say, 33K, you should have no trouble with hiss.

On the last crossover I built, I used 0.15 F Wima MKP4 capacitors, the largest value I could get with a 10mm lead spacing. The resulting ca. 20K ohm source impedances were no problem at all through eight NE5532 opamp stages that filter and pass (consumer) line level signals. If I were to do it again, I would use less expensive and more readily available 0.1 F parts.
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Old 18th July 2004, 04:35 PM   #5
johnf is offline johnf  Germany
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I did some really crude tests on my line-level crossover. The hiss from its ca. 20K metal film resistors is perhaps 10 dB below that from its 50K Alps RK27 input volume control, when the pot is wide open and not connected to a source. Here, I would not be too worried about increasing the resistors to a similar value.

Like 'consurt_ee_um', I find hum is the bigger problem, in this case, from an ungrounded receiver.
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