LocoDantes
11-16-2010, 04:05 PM
Hi, all. I'm new here -- I've been lurking a while to get my bearings, and making my first post with some trepidation.
I'm planning to build some 4430 clones (a thoroughly beaten dead horse, I know). I'm going to copy the N3134 crossover, so I built a simulation in SIMetrix (a fairly straightforward SPICE package), thinking I could use the simulation to predict the effects of Lpads that aren't exact matches for the factory version, varying coil resistances, and so on. I expected/hoped that my curves would resemble those posted here (http://www.audioheritage.org/vbulletin/showthread.php?9745-Quick-amp-Dirty-4430-Inspired-Two-Ways-Part-I&p=43075&viewfull=1#post43075), but alas, they don't. I was hoping someone might be able to shed light on what I'm doing wrong.
Here's the simulation schematic:
48574
Some explanation: SIMetrix allows multi-step analyses where component values are determined by expressions that include variables, said variables being stepped through specified intervals. R202 and R201 are swept with the varibles mid_sweep and high_sweep, respectively, and the expressions are given in the diagram. Those variables are in the range [0,1], corresponding to the control position (0 being full CCW and 1 being full CW). I used 6 ohms and 34 ohms as the values for the legs of R202 based on the measurements posted here (http://www.audioheritage.org/vbulletin/showthread.php?9745-Quick-amp-Dirty-4430-Inspired-Two-Ways-Part-I&p=42474&viewfull=1#post42474), and the values for the series resistances of the inductors came from here (http://www.audioheritage.org/vbulletin/showthread.php?5209-4430-help%21&p=47766&viewfull=1#post47766). I used 8 ohm resistive loads as per the standard test fixture (did I do that right?). LF and HF are the probes for the voltages plotted below.
Here's the output of the simulator with both controls wide open (full CW - mid_sweep=1, high_sweep=1):
48575
It should (I think) look like the green curve in the top graph in Giskard's post I referenced earlier. Note the ~2 dB peak around 1.7kHz in Giskard's graph which is notably absent in my sim's output.
Now, the output of my sim with R201 set to full CCW (high_sweep=0) and R202 swept from 50% to 100% (mid_sweep stepped from 0.5 to 1) which should correspond to 0 dB to +4 dB:
48576
This should resemble the red curves in the second graph in Giskard's post, but it appears to be overdamped.
I've stared at this trying to figure out what's wrong, and it's probably something really stupid that I've done. Please feel free to point it out.
I'm planning to build some 4430 clones (a thoroughly beaten dead horse, I know). I'm going to copy the N3134 crossover, so I built a simulation in SIMetrix (a fairly straightforward SPICE package), thinking I could use the simulation to predict the effects of Lpads that aren't exact matches for the factory version, varying coil resistances, and so on. I expected/hoped that my curves would resemble those posted here (http://www.audioheritage.org/vbulletin/showthread.php?9745-Quick-amp-Dirty-4430-Inspired-Two-Ways-Part-I&p=43075&viewfull=1#post43075), but alas, they don't. I was hoping someone might be able to shed light on what I'm doing wrong.
Here's the simulation schematic:
48574
Some explanation: SIMetrix allows multi-step analyses where component values are determined by expressions that include variables, said variables being stepped through specified intervals. R202 and R201 are swept with the varibles mid_sweep and high_sweep, respectively, and the expressions are given in the diagram. Those variables are in the range [0,1], corresponding to the control position (0 being full CCW and 1 being full CW). I used 6 ohms and 34 ohms as the values for the legs of R202 based on the measurements posted here (http://www.audioheritage.org/vbulletin/showthread.php?9745-Quick-amp-Dirty-4430-Inspired-Two-Ways-Part-I&p=42474&viewfull=1#post42474), and the values for the series resistances of the inductors came from here (http://www.audioheritage.org/vbulletin/showthread.php?5209-4430-help%21&p=47766&viewfull=1#post47766). I used 8 ohm resistive loads as per the standard test fixture (did I do that right?). LF and HF are the probes for the voltages plotted below.
Here's the output of the simulator with both controls wide open (full CW - mid_sweep=1, high_sweep=1):
48575
It should (I think) look like the green curve in the top graph in Giskard's post I referenced earlier. Note the ~2 dB peak around 1.7kHz in Giskard's graph which is notably absent in my sim's output.
Now, the output of my sim with R201 set to full CCW (high_sweep=0) and R202 swept from 50% to 100% (mid_sweep stepped from 0.5 to 1) which should correspond to 0 dB to +4 dB:
48576
This should resemble the red curves in the second graph in Giskard's post, but it appears to be overdamped.
I've stared at this trying to figure out what's wrong, and it's probably something really stupid that I've done. Please feel free to point it out.