After all the raving about Duelund resistors, on this forum and elsewhere, I decided to give them a try in my SDA SRS 1.2TL loudspeakers. I ordered ten CAST Silver resistors, with 10 watt rating and longer leads, directly from Duelund. The longer leads cost $6.70 per resistor. The total cost, inclusive of shipping from Brandby, Denmark, was $650, or $65 per resistor. I placed the order on 2/14/13 and received the merchandise on 3/25/13. I was initially quoted a delivery time of 3 weeks, but the factory had to attend to some other unforeseen issues before my order could be processed. When Duelund was able to process my order, they were nice enough to ship it by FedEx International Priority Service.
The long length of the Duelunds (5.3") usually presents placement problems. Over two years ago, I replaced the stock crossover circuit board with a custom 4" x 12" board (discussed here). I was able to get all five resistors to fit on the underside of the board. I could have ordered the shorter, 3" long version, but the shorter resistors have 5 watt power ratings. Furthermore, Duelund said there was a small improvement in sound quality with the longer 10 watt version.
Figure 1. Duelund resistor placement mockup.
Paper cutouts with the same footprint as the Duelund CAST resistors were arranged on the back of a prototype sample of my SDA SRS 1.2TL crossover board. I ordered long leads and asked how long the "long leads" were. This is the response I received from Duelund:
"They are made so they easily cross each other on the middle of the resistor. I make them by hand, so I just make them looong."
Based on that vague, non-quantitative reply, and knowing that the resistors were 5.3" long, I guessed that the leads would be at least 4" long. The actual leads measured 4.2" to 5.1" long and are spaced 4.8" apart
Figure 2. Actual resistor arrangement.
Due to the locations of the resistor through-holes and obstructions on the back of the board, the 11.5 ohm resistor had to be stacked on top of the 2.7 ohm resistor.
Figure 3. What a mess - Duelund resistors installed. The leads are covered with 3/16" shrink wrap.
The resistors were secured to the board with a pad of hot glue at each end.
Figure 4. Cutout in the Sonic Barrier Black Hole damping material.
Sonic Barrier Black Hole damping material is placed between the circuit board and its same-size structural support board. I cut away the damping material in the area of the stacked resistors to avoid excess pressure on them. I found out the hard way that Duelund resistors are somewhat delicate.
Figure 5. Licorice sticks, bricks and regular looking resistors. Clockwise from bottom left: original ceramic
metallic resistors, Duelund carbon resistors, Mills MRA-12 wire wound resistors.
The blue painter's tape labels shown in figure 5 were required because the resistor labels were black type printed on transparent adhesive. Since the resistor body is black, the label lettering was difficult to read closeup and impossible to read more than a foot away. I have 20/20 uncorrected vision.
Noise spectrum measurements with an oscilloscope showed that the Mills passed a cleaner signal than the cermet resistors and the Duelunds passed a cleaner signal than the Mills. The increase in transparency was immediately apparent, but it was more modest than I expected. The noise spectrum of a 1000 Hz test signal from an MCP BR2822 LCR meter was analyzed after it passed through no resistor (only the leads of the meter and oscilloscope) and then through 2.7 ohm and 22.5 ohm ceramic metallic (original SDA resistors), Mills MRA-12 and Duelund CAST Silver resistors. The Fast Fourier Transform noise spectrum plots are from a Tektronix TDS 2012 oscilloscope. All FFT measurements were taken within a few minutes of each other.
It is easier to see differences in the plots if you save them and view them in succession.
Figure 6. 1000 Hz test signal straight in from LCR meter.
Figure 7. FFT plot of 1000 Hz test signal from 2.7 ohm ceramic metallic resistor.
Figure 8. FFT plot of 1000 Hz test signal from 2.7 ohm Mills MRA-12 resistor.
Figure 9. FFT plot of 1000 Hz test signal from 2.7 ohm Duelund CAST Silver resistor.
Figure 10. FFT plot of 1000 Hz test signal from 22.5 ohm ceramic metallic resistor.
Figure 11. FFT plot of 1000 Hz test signal from 22.5 ohm Mills MRA-12 resistor.
Figure 12. FFT plot of 1000 Hz test signal from 22.5 ohm Duelund CAST Silver resistor.
Figure 13. One lead of one of the 11.5 ohm resistors broke off with normal handling during installation. I
soldered it back on. Duelund is sending a replacement.
In all my years and years as an electronics hobbyist since teenage, I have never had a component lead to break...until now...with my $65 a piece boutique resistors.
Figure 14. SDA SRS 1.2TL crossover board with Mills MRA-12 resistors.
Figure 15. SDA SRS 1.2TL crossover board with Duelund CAST Silver resistors on the back.
Figure 16. Leftover tinned silver wire from clipped resistor leads. Maybe I'll melt it down and make a piece
I received this reply when I asked Duelund about break in time for the CAST Silver resistors:
"5 days good playing."
Since I didn't know what a day of good playing was, I assumed it to be a typical day's listening, say 10 hours, rather than an entire 24 hour day. That would generously put "5 days good playing" as 50 hours. I let the radio play overnight and while away from home. I did not notice any changes while casually listening nor while reviewing my listening notes and spatial placement charts. After 66 hours of straight playing time, I sat down for a critical listening session. Again, I didn't hear any improvement over the initial critical listening session which was done 24 hours after installation. I primarily listen to instrumental jazz. I might have heard some difference after longer break in time if I had played a wider variety of vocal music.
I found the Duelunds to be a little more transparent than the Mills MRA's, although I paid a hefty premium for that added transparency. I would feel better about the financial investment if the degree of improvement had been on the order of that realized with the premium grade Sonicap capacitors and Solen and Jantzen inductors previously adopted. In addition, the quality issues I encountered with broken and loose leads were not confidence inspiring. I would have to think long and hard about using these in a future project.
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