Help with Active Crossover-Equalizer
I have the Kinergetis subwoofer towers. The equalizer/crossover has in input buffer followed by op amp crossovers to a final bass boast op amp circuit that now uses the LM6171 tricky op amp. The input buffer is there to provide a low impedance drive for the crossover circuity. The entire circuit is direct coupled with an output cap to block dc at the end. The input buffer amp is an Elantec el2001 70 bandwidth buffer that failed. I replaced it with a el2002 op amp that is very similar to the el2001 except that is has like 170 mgtz wideband buffer. I was told by the headphone geeks that it is slighly better sounding. It also draws more current, slighlty faster slew rate and higher bias current. When I installed the el2002 and looked at the input offset it increased from 70mv with the EL 2001 to over 200mv with the el2002When I tried the unit it worked but now it started to motorboat (oscilate) when the turned the volume all of the way up. Also my power amps protective circuity would cut off detecting dc or something. I suspect that the final lm617 op amp is the one that is oscillaing.
el2002 is said to be a fairly stable buffer. Is is possible that the higher input offset is multiplying to higher levels through the filter chain (dc coupled) and causing the final equalizer op amp which is an LM6171 to saturate at high ouput and go into oscillation?
Any suggestion to troubleshoot this?
Another approach is to try to locate the EL2001 lower bandwidth op amp which should be more stable and give up some performance, but it has been obsolete for years.