jonheal Wrote: > 1. Is the OPA134 a good choice? Digi-Key has several varieties > (OPA134UA-ND, OPA134UA/2K5-ND, OPA134PA-ND)Yes, in fact I have been using the > dual version (OPA2134) in my active crossover. The OPA2604 is also not bad.
> 2. I included the capacitor and resistor in the circuit because I saw no > harm in blocking DC voltage, UNLESS it will have an adverse effect on > signal quality. Will it?It won't, but tied together like they are, the > "averaging" resistors and the highpass filter interact with each other. The main effect is that the 21.5k resistor cuts your gain by more than half. DC isn't a big deal going through a single buffer stage. The power amp for the sub probably has a DC blocker on its input. If you want to include a DC filter, put in a second buffer amp. > Also, the page I borrowed most of this circuit from specified a cutoff > frequency 7.4Hz based on a function that included capacitance and > resistance as factors. Is there any advantage to increasing the value > of the capacitor and decreasing the value of the resistor (or vice > versa) to achieve the same cutoff frequency? > In general, increasing the resistor value and decreasing the capacitor value will make the filter an easier load to drive but increase the sensitivity of the filter's behavior to the input impedance of the op-amp. Going the other way will draw more current from the preamp outputs but be less affected by the op-amp. > 3. Are metal film resistors and polypropylene capacitors the best to > use?I think that they're the most cost effective for DIY circuits. You can get some pretty fancy capacitors from DIY audio shops like the "wondercap" and "auricap" and such, but I have used the Panasonic polypropylene film capacitors for my own circuits. > 4. Will the voltage I apply to the OpAmp make a difference? (I think the > specifications said 15V, nominal.)You want to have the voltage supplies > exceed the maximum signal you wish to reproduce by about 2V. Otherwise, anything within the specified range for the op-amp is fine. +/-9V is easy to achieve with batteries. Which reminds me -- you will want some sort of power supply reservoir capacitors between +V and ground and between -V and ground. Something like a 100uF electrolytic capacitor in parallel with a 1uF film capacitor should work for just one op-amp. -- John Stimson ------------------------------------------------------------------------ John Stimson's Profile: http://forums.slimdevices.com/member.php?userid=218 View this thread: http://forums.slimdevices.com/showthread.php?t=20907 _______________________________________________ audiophiles mailing list [email protected] http://lists.slimdevices.com/lists/listinfo/audiophiles
