Hey, im making a stereo Linkwitz-Riley crossover with one output being connected a sub with its own amp, and the other to a pair of midrange speakers with their own amps, and i have a few things im unsure about...
1. Volume control - am i right in thinking the volume control, the standard dual log 10K pot, should be connected before the crossover? The only potential issue i have its that if the input signal is reduced before the opamps, the opamp noise will be a higher percentage of the output signal than if the pot was after the crossover, although this would mean a four pole pot, and the resistance from all the pots will not be the same.
2. Audio opamps - i know what the usual opamps used for audio are, but is using the MAX494 a good idea, it has low noise, is rail-to-rail (although this isnt important), low power, "precision" quad opamp?
3. I intend to create the negative supply with a charge pump IC, however, will the ripple from the output effect operation, or is it best to put the output from the charge pump through a linear regulator first?
Thanks, Matt
1. Volume control - am i right in thinking the volume control, the standard dual log 10K pot, should be connected before the crossover? The only potential issue i have its that if the input signal is reduced before the opamps, the opamp noise will be a higher percentage of the output signal than if the pot was after the crossover, although this would mean a four pole pot, and the resistance from all the pots will not be the same.
2. Audio opamps - i know what the usual opamps used for audio are, but is using the MAX494 a good idea, it has low noise, is rail-to-rail (although this isnt important), low power, "precision" quad opamp?
3. I intend to create the negative supply with a charge pump IC, however, will the ripple from the output effect operation, or is it best to put the output from the charge pump through a linear regulator first?
Thanks, Matt
1) The source impedance of the pot might affect the filter response,
so you need to consider that. Is this the main volume control, or the
level controls used to determine the relative levels of low vs high?
In either case you might need to buffer the output from the wiper.
2. This is probably not your best choice, partly due to the limited
voltage swing of the device. Maybe some other quad and higher
supply voltages.
3. You can always RC filter the negative supply ripple if you need to.
I suggest putting a little distance between the charge pump and the
analog circuits. Will it be able to deliver some real voltage, like 10-15
volts?
so you need to consider that. Is this the main volume control, or the
level controls used to determine the relative levels of low vs high?
In either case you might need to buffer the output from the wiper.
2. This is probably not your best choice, partly due to the limited
voltage swing of the device. Maybe some other quad and higher
supply voltages.
3. You can always RC filter the negative supply ripple if you need to.
I suggest putting a little distance between the charge pump and the
analog circuits. Will it be able to deliver some real voltage, like 10-15
volts?
1) The crossover is driven directly by an opamp with a gain of 1, with the volume control, which is the main volume control just before that, so the driven impendance shouldnt be a problem
2) After another look, i found the max414 which has lower noise and can operate with a larger voltage range, although it has higher operating current then the max494. Also, the limited operating voltage of the max494 shoudnt be a problem if its only dealing with line level voltages?
3) Well the input to the charge pump will be about 12-15V, with an output of 10-11V maybe, but looking again at the max voltages for the opamps, if i chose a max494 or 414 i will have to use a linear regulator to keep the supply voltage within the excepted range, which is 10.5V for the 414, but at least 20V comes from the charge pump and power supply.
Thanks, Matt
2) After another look, i found the max414 which has lower noise and can operate with a larger voltage range, although it has higher operating current then the max494. Also, the limited operating voltage of the max494 shoudnt be a problem if its only dealing with line level voltages?
3) Well the input to the charge pump will be about 12-15V, with an output of 10-11V maybe, but looking again at the max voltages for the opamps, if i chose a max494 or 414 i will have to use a linear regulator to keep the supply voltage within the excepted range, which is 10.5V for the 414, but at least 20V comes from the charge pump and power supply.
Thanks, Matt
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