The installation of custom printed circuit boards and Northcreek Music Coil SDA inductors worked out very well for my SDA SRS's and SDA SRS 1.2TL's. I decided to continue this process with one pair (of three) of my SDA CRS+'s (1989 version). These CRS+'s had the following previous modifications:
1. Original oak veneer replaced with teak veneer.
2. Stock resistors and capacitors replaced with Mills MRA-12 resistors and AudioCap PPMF polypropylene film capacitors.
3. Polyswitches removed and replaced with wire jumper.
4. Stock binding posts replaced with Cardas CCGR-S binding posts.
5. Stock SDA cable replaced with a custom effective 9 AWG cable made from Monster Z2 Reference speaker cable.
6. Mortite driver, passive radiator and tweeter seals.
7. Steel retaining rings and brackets for drivers, passive radiators and tweeters.
8. Dynamat Xtreme vibration damping material applied to driver and passive radiator baskets.
In addition to the circuit board and SDA inductor, all of the AudioCaps, except for the 40 uF shunt capacitor in the dimensional driver circuit, were replaced with Sonicaps. The largest capacitor Soniccraft stocks is 33 uF. Soniccraft informed me that they do not have the capability to make a custom 40 uF capacitor, although they do make custom capacitor values under 33 uF. I could have used a stacked pair of 20 uF capacitors as shown in figures 6 and 7, but one of the objects of doing a custom circuit board was to avoid the need for stacking components. Therefore, my mind would not allow me to use that option. I could have made the circuit board a little longer to accommodate the extra capacitor, but then the board would not be centered over the large inductor and some additional mechanism to prevent board flexing would have been required. Sonicaps in the shunt legs of the driver circuits might be overkill anyway.
Figure 1. Stock printed circuit board and SDA inductor at left. The new board is 32% larger.
Figure 2. Before: Stock printed circuit board with AudioCaps/Sonicap/Mills and SDA inductor.
Figure 3. After: Custom printed circuit board and inductor.
Figure 4. The inductor's cable tie buckles, topped with pads of hot glue, made convenient standoffs for the circuit board.
Figure 5. Mills MRA-12 sub-1 ohm resistors (0.1, 0.15, 0.5 ohm). In the future, when I am more dedicated to audio than I am
now, I will evaluate the sound of replacing the polyswitch jumper (the red wire in figure 6) with a small amount of resistance.
Figure 6. Stacked Sonicap 20 uF caps.
The yellow thing in figure 6 is a 40 uF AudioCap PPMF shunt capacitor for the dimensional driver. Sonicraft does not make a 40 uF capacitor. I would have had to parallel two 20 uF Sonicaps and stack them one on top of the other (figures 6 and 7) or place one 20 uF cap on top of the board and one on the bottom or make the board bigger to accommodate the additional capacitor or mount the cap combination somewhere off the board.
Figure 7. Stacked Sonicap 20 uF caps.
Figure 8. Test fitting for the new board.
Figure 9. It was a challenge fitting a larger board in that tight corner, but it worked out.
Figure 10. The new circuit board and inductor are held in place with a 4" aluminum threaded stud and aluminum nuts and
Inductor Conditioning and Measurements
The Northcreek inductors were conditioned on an Audiodharma Cable Cooker for 144 hours. Improvements in the inductor's output waveforms were seen up to the 111th hour. When the inductors were reinstalled after 144 hours, evidence of overcooking (blurred transients, loss of overall detail and clarity, diminished sound stage height) were heard. There was also some high frequency grain which I attributed to the new Sonicaps. The sonic weight of images sounded more like listening to FM radio than a CD.
These inductors showed the least pre-cooking output waveform distortion and the best post-cooking waveform improvement of my three Northcreek inductor pairs. Compare the pre-cooking output pulse train in figure 12 (left) below with the pulse train waveforms in figure 8 (right) of the SRS inductors and figure 20 (left) of 1.2TL inductors.
Prior to processing on the Cable Cooker, listening comparisons between the inductor-modified CRS+'s and their non-inductor-modified twins were done for an hour.
Figure 11. Inductor output pulse train at 0 (left) and 111 hours.
Figure 12. Inductor output single pulse at 0 (left) and 111 hours.
Figure 13. Inductor output pulse rising edge at 0 (left) and 111 hours.
Figure 14. Inductor output pulse falling edge at 0 (left) and 111 hours.
Figure 15. Cable Cooker (left) and inductor output pulse trains at 111 hours.
Figure 16. Cable Cooker (left) and inductor output single pulse at 111 hours.
Figure 17. Cable Cooker (left) and inductor output pulse rising edge at 111 hours.
Figure 18. Cable Cooker (left) and inductor output pulse falling edge at 111 hours.
The output waveform distortion of the CRS+, SRS, and SRS 1.2TL inductors was significantly reduced by processing on the Cable Cooker, but there were some curious variations in the results. The 1.2TL and SRS inductors showed similar pre-cooking output waveform distortion, but the 1.2TL inductors, which had 100 hours of prior use playing music, showed signs of overcooking after 58 hours and took 51 hours of recovery. The SRS inductors, which had 10 hours of prior use playing music, stopped displaying measured and audible improvement after 150 hours, but no evidence of overcooking was heard even after further cooking up to 243 hours. The CRS+ inductors started out with the least amount of output waveform distortion and showed the most improved post-cooking output waveforms. No audible or output waveform improvements were heard or seen with the CRS+ inductors after the 111th hour of cooking. Evidence of overcooking was heard after the 144th hour. Overcooking aberrations were gone after 12 hours of music play.
The only major variable, that I know of, between the three pairs of inductors may have been the amount of shellac absorbed in the coil windings. For mechanical stability and vibration reduction, shellac is vacuum impregnated between the coils and allowed to cure over a few days. Of course, there will be variations in the tightness of the wire windings and therefore variations in the penetration of the shellac. In addition to variations in mechanical stability, the hardened shellac may have had some effect on the dielectric properties of the wire's enamel insulation and also may have contributed to differences in dielectric energy absorption and release. I assume that the thickness of the enamel insulation was consistent among the three pairs of inductors.