I'd like to make a pair of simple RC (1st order) passive high pass filters to go between my preamp and power amp. Does anyone know the typical output impedance of a preamp and the typical input impedance of a power amp?
I need to have some idea if there's a value for the resistor that would be large enough to be easy for the preamp to drive and small enough to make the input impedance of the power amp irrelevant.
Both preamp and power amp are solid state and I'll be using single ended inputs.
I need to have some idea if there's a value for the resistor that would be large enough to be easy for the preamp to drive and small enough to make the input impedance of the power amp irrelevant.
Both preamp and power amp are solid state and I'll be using single ended inputs.
Measure?
Best if you can measure the impedances.
I do not remember exactly how, but you use known resistor
and calculate. You have got to have an AC-meter.
Best if you can measure the impedances.
I do not remember exactly how, but you use known resistor
and calculate. You have got to have an AC-meter.
Preamps are usually down around 200 to 1000 ohms, and
of course there are exceptions.
Power amps usually are 10K to 47K. Again, plenty of
exceptions.
of course there are exceptions.
Power amps usually are 10K to 47K. Again, plenty of
exceptions.
You'd do best by using small C, large R (to swamp out source impedance effects), then buffer them before the power amp. That way, you won't have to load the preamp down very much. Good buffers are cheap, easy to use, and sonically transparent.
All you need to do is put a capacitor in between the pre-amp and power amp. Pick a value that provides -3db at the frequency you want. You won't need an additional resistor but it might not hurt to load the pre-amp with 10K or so unless it's already loaded by another amp. This assumes you have an oscillator and meter.
If no test equipment is available, certainly the amp mfg. can provide you with the input impedance so you could calculate the value.
If no test equipment is available, certainly the amp mfg. can provide you with the input impedance so you could calculate the value.
jlambrick, may I ask what the purpose is of this filter?
You have got some input from others here but my advise is to really use a resistor and a cap. If the preamp as normal use R = 2k2 and C = 3n3 => 21.9 kHz (if this was the wanted frequency). The preamp MAY get into trouble if a cap is directly connected to the output, the amp amaybe can't take heavy capacitive loads.
You have got some input from others here but my advise is to really use a resistor and a cap. If the preamp as normal use R = 2k2 and C = 3n3 => 21.9 kHz (if this was the wanted frequency). The preamp MAY get into trouble if a cap is directly connected to the output, the amp amaybe can't take heavy capacitive loads.
Jlambrick,
I had a similar question, check out this thread
http://www.diyaudio.com/forums/showthread.php?s=&threadid=3709
I had a similar question, check out this thread
http://www.diyaudio.com/forums/showthread.php?s=&threadid=3709
Hi guys,
Thanks for all the suggestions.
Here's what I'm trying to do: I'm driving some tower speakers with limited bottom end with my power amp. There are subwoofers which are self powered to take the response low.
I'd like to limit the low end going to the towers in order to preserve the dynamic range as much as possible. I've taken a lot of care to provide a really high quality signal to the amp so I was thinking that a passive filter (using really top notch components) with a cutoff around 80 Hz would be a good way to go. This would minimize any distortion from an additional gain stage.
Thanks for all the suggestions.
Here's what I'm trying to do: I'm driving some tower speakers with limited bottom end with my power amp. There are subwoofers which are self powered to take the response low.
I'd like to limit the low end going to the towers in order to preserve the dynamic range as much as possible. I've taken a lot of care to provide a really high quality signal to the amp so I was thinking that a passive filter (using really top notch components) with a cutoff around 80 Hz would be a good way to go. This would minimize any distortion from an additional gain stage.
If that's all you're trying to do, life is sweet. Get the load z spec from whomever makes your power amp. Use a simple series cap to give you a pole at whatever the corner frequency is of your tower speakers. This will result in a third order acoustic highpass characteristic at that corner frequency. Then all you need to do is cut off your subwoofer with a complementary LP filter at that frequency.
The source impedance of your preamp will be pretty negligable here.
The source impedance of your preamp will be pretty negligable here.
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