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| Subject: | Re: LF: Re: Passive high-pass filter circuits? |
| From: | [email protected] |
| Date: | Thu, 03 May 2007 20:20:54 -0400 |
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| In-reply-to: | <009101c78dc0$c1836700$0b01a8c0@server> |
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> The source and load Z are both 600 ohms.
From your description, the source might be close to that over the range of interest, but can you be sure about the impedance seen by the telco "repeater coil" into the mic input? It will make quite a difference to a simple passive filter.
Assuming the figures are reasonably close and the load is mostly resistive in nature, a turnover at 1 kHz and 6 dB down by 250 Hz can easily be exceeded by a single series capacitor (actually two in this case, since it's a balanced line). A .27uF in series with each side of the line will do the trick.
If it turns out either impedance is actually lower than you are figuring, you might need a higher value of cap to prevent excess rolloff of lows. And, if either is higher, you might need smaller caps to attain adequate hum suppression. Some experimentation may be needed, in other words.
John
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