I replaced the stock electrolytic and mylar capacitors and the ceramic metallic resistors immediately after acquiring my SDA SRS 1.2TL loudspeakers in December of 2001. I chose AudioCap PPMF series polypropylene resistors and Mills MRA-12 resistors for the upgrades. Sonicaps (the house brand at Sonic Craft) were not on the market at that time.
After Sonicaps became available, I noticed that some speaker modders who initially chose AudioCaps switched to them. Sonicaps were said to provide more overall resolution and more bass impact, although no one mentioned a "night and day" difference between the two. I sent an email to Jeff at Sonic Craft and asked his opinion on switching from AudioCaps to Sonicaps. I included a 1.2TL schematic. His advice was that replacing the AudioCaps with Gen I Sonicaps would not be "worth the money" and that better results would be gained by doing the following:
1. Replacing the 0.25uF cap with a 0.22uF/200V Sonicap Gen 2.
2. Bypassing the three 12uF AudioCaps with a 0.1uF Sonicap Platinum.
This upgrade supposedly would yield an across the board improvement from the middle midrange up. I wasn't adventurous enough to deviate that far from the original crossover design. I hope that a few of the brave souls reading this will try the recommendations shown in 1 and 2 on their SDA's. Please be gracious enough to provide us with a detailed report of your results.
A long time ago, I was advised by a Polk engineer to remove the silver mica bypass capacitors and the polyswitches. The bypass capacitors were used to improve the transient response of the stock mylar and electrolytic capacitors. In SDA's, bypass capacitors are not needed with faster film capacitors. Furthermore, they can introduce an artificial "airiness" and other artifacts that are not present in the recording. However, some people may find these effects sonically pleasing. Do what you like. The polyswitch is there to protect the tweeters. It is not needed if you have a quality high current amplifier and are not prone to overdriving it.
Based on prior knowledgeable advice and my own listening and modding experience with SDA's, I chose to decline the high frequency bypass option and go with replacing the AudioCaps with Gen I Sonicaps.
I requested pairs of Sonicaps matched as closely as possible to each other and to the nominal schematic values. The stock capacitors were 10% tolerance parts. Elliot at Sonic Craft called a couple of hours later and said that he was having trouble getting close to the 0.25 uF value and that if I wanted that value closely matched, it might delay my order. Elliot is the man who usually answers the phone when you call to order parts. He said that he had some 0.22 uF caps that were close to each other and asked if those would work. I agreed to take the 0.22 uF caps. My order was placed on Tuesday and I received my caps on Thursday.:)
Figure 1. An early birthday present for my SDA SRS 1.2TL's.
The measured values of the Sonicaps were as follows:
Table 1. Measured values of Sonicap Gen I Capacitors.
Carefully pinch the expansion tips of the standoffs and ease them out of the large inductor coil flange. The plastic expansion tips can become brittle with age, so care must be taken not to break them. Ask me how I know. If you do break one of your standoff tips to the point that it is not usable, don't get overly concerned. Although the original standoffs are no longer available, you can make a suitable replacement. One such replacement is a plastic bolt and plastic nuts.
The Sonicaps and the AudioCaps are about the same size, so there was no drama involved with orienting parts this time. There is more that one way of orienting the larger replacement parts on the circuit board. Use whatever orientation you find to be most stable for your circuit board. I say this because someone else's 1.2TL circuit boards may be different in size and shape from mine. Even if your board is the same as mine, you still may find another parts orientation advantageous.
The time to complete the first crossover from removal to re-installation, excluding the time to take pictures, was 1 hour 37 minutes. The second crossover took 1 hour 13 minutes.
Figure 2. Completed recapped crossover. Don't try this at home.:p
The completed recapped crossover for the left channel is shown in figure 2. The 13.5 uF cap is under the 27 uF cap. The lead lengths of the Sonicaps were more than adequate with the exception of one lead for the 27 uF cap. A 4 inch extension wire was required. The extension wire is the red wire at the bottom of figure 2.
The capacitor leads were covered with an appropriately sized piece of shrink wrap tubing prior to soldering. The tubing was shrunk with a 1600 watt hand held hair dryer.
A folded rectangular piece of 1/4" soft foam was placed under the caps. Once everything was soldered down, strips of Scotch 3850 packing tape were used to tightly bind the caps to each other to reduce vibration. Some people like to use hot glue. I prefer packing tape because it is easier to remove in the likely event that I desire future crossover upgrades.;)
Figure 3. The Mills MRA-12 resistors were placed on the bottom of the board.
Laying the caps lengthwise on the board left no room on top for the resistors. They were placed on the board bottom as shown in figure 3. The standoff near the upper left corner must be removed to properly solder a connection for a 12 uF capacitor. Notice that the solder hole for the capacitor butts against the standoff. You will need to take care to flatten the side of the solder bubble adjacent to the standoff so that it will fit securely back into the board.
Figure 4. Reassembled crossover assembly.
Figure 5. Who'd have thought that lurking behind this big, thick, and impressive
brushed aluminum plate was a little bitty circuit board?
The only manufacturer's literature published for the Sonicaps is what is on the Sonic Craft website. There is no mention of the required break in time, but Elliot said that 100 hours was required for them to reach their full sonic potential.
The right channel crossover was done first, then reinstalled and the sound compared to the left channel with my preamp set to mono and the SDA interconnect removed. The balance control was repeatedly moved back and forth from right to left. I heard the following changes:
1. The recapped right side had more tactile and apparently louder bass. I could feel more vibrations coming through the floor and my seat cushions. The sound level meter registered the same volume on both sides.
2. The bass on the recapped side sounded slower and less defined and articulate.
3. The recapped right side had more upper midrange and high frequency detail. It did not sound brighter. I could just hear more decay, overtones, and details like a singer's inhaling and exhaling between phrases was clearer. I could also more clearly hear the subtle clicking sounds of saxophone players working the keys.
4. Some percussion instruments in the backround were heard more clearly. I also heard some percussion sounds that were previously unnoticed.
5. Sounds at both sides of the sound stage had more weight and detail.
I had previously replaced the stock caps in some of my other SDA's with Sonicaps, so items 1-5 came as no surprise. However, as expected, the degree of improvement was nowhere near as dramatic going from AudioCaps to Sonicaps as when I went from stock to Sonicaps.
When listening in stereo mode after both recapped crossovers were installed, I noted that the sound stage width and depth remained the same, but some vocals and solo instruments in the center were now projected 1/2 to 1 foot higher.
After 25 hours, bass speed was back up to pre-recap level and the bass definition and articulation had improved a lot, but it was still not back to pre-recap level.
After 80 hours, more high frequency and midrange detail was heard. Voices were clearer and heavier. Piano notes were more dynamic and had more weight.
After 102 hours, bass definition and detail had surpassed pre-recap levels.
After 106 hours, the bass was a little bit punchier and heavier. The apparent sound volume was louder, although the sound volume was not measurably louder. However, when the noise floor is lowered by continued break in, the sound reaching your ears consists of a higher percentage of the music signal, therefore, the music sounds louder.
The concept is the same as if you and another person were having a conversation in a room where other people are talking. If the other people in the room lower their voices or stop talking altogether, your voice, and the voice of the person you are talking to, will seem louder, although neither of you raised your voices.:)
Between 106 and 150 hours, I heard no further changes, so I assumed the Sonicaps were all grown up.