Horswispr's Full Review: Solen 5.1uF 400V Polypropylene Capacitor
If you're into restoring vintage loudspeakers, occasionally you're going to have to replace capacitors in the crossover network of speakers you buy on eBay or Craigslist. The crossover network is responsible for routing the proper signal to the woofer, midrange (if the speaker is a three-way), and tweeter. Capacitors are usually in the signal path on the way to the tweeter, as they are "high pass" filters, allowing higher frequencies to pass through, and rolling off lower frequencies.
Solen capacitors (as well as Daytons and other brands) are readily available through Parts Express and other on-line vendors, and they (both Solens and Daytons) are known to be good quality capacitors for loudspeaker crossovers. They come in various values (measured in microfarads) and are generally quite cost-effective. More on this particular capacitor in a minute, but first a little background.
Dead tweeters?
If you receive a pair of older loudspeakers, and one of the tweeters is dead, it's quite possible that the tweeter is OK, but something in the signal path has gone bad. You can run a low level signal directly to the tweeter to see if it's working. Alternatively, you can hook up a nine volt battery to a couple of short wires and touch the the tweeter leads. If you hear a popping sound (it's not loud or damaging), you at least know that the tweeter is passing signal, though you don't know if there's distortion. If I hear signal passing through the tweeter, the first thing I usually check is the wiring and all solders on the way to the tweeter. Is a wire disconnected? Is there a "cold solder" issue? If these two tests prove "negative" (all seems well), my next step is to replace any capacitors on the way to the tweeter. (Note that with older Acoustic Research speakers, the problem is often in the continuous midrange and tweeter potentiometers they used--another issue entirely.)
Many vintage loudspeakers have only one capacitor on the way to the tweeter, making replacement fairly easy if you're good with a soldering pencil. The value of the old capacitor is usually printed on it. If there's a "mystery capacitor" in the circuit, proper values for a given loudspeaker model number can generally be found via a Google search. If not, the folks at Parts Express may be able to provide advice.
Dynaco A-25s, the speakers I know best, have only one capacitor on the way to the tweeter. The woofers are run "wide open." Several times, I have received pairs in which a tweeter is dead or putting out a reduced volume level. The capacitor value for the Dynaco crossover is 5.0 microfarads (uF), so I chose a 5.1 (the closest value) for capacitor replacement in Dynaco A-25s.
Solen 5.1s.
The Solen 5.1s reviewed here are physically larger than the original capacitors found in Dynaco A-25s, and they also have higher voltage ratings (400V). They're more than adequate for speaker crossover applications. As the picture shows, they're nice looking little black cans, about 1 1/4" long and 7/8" in diameter. The polypropyine dielectric found in these capacitors is said to be better than those in the "cheap" capacitors used in most mass-produced '60s and '70s loudspeakers, and the tolerance is rated at 5%. Parts Express sells 5.1s for $3.99 each, meaning that you can "re-cap" a pair of Dynaco A-25s for under $10. I belive Solen makes both less and more expensive capacitors than the ones reviewed here. These are Solen's high quality capacitors designed for use in most loudspeaker crossovers. A quick check of Parts Express's website will reveal the many alternatives available.
Some hobbyists make a habit of re-capping all of their vintage loudspeakers, but there's controversy out there about whether new capacitors really make a difference in the sound of older speakers if the original capacitors have not faltered. "Capacitor drift" is a possibility with older capacitors, even if the loudspeakers initially sound OK. If a capacitor's value drifts slightly "north" (say, from 5.1 to 6.1), then the effective crossover frequency of the tweeter is very slightly dropped, meaning that your tweeter will be working a bit harder at the bottom of its range, and there might be a very slight midrnage peak at the crossover frequency. Conversely, if a capacitor drints "south," (say, down to 4.1), then a midrange dip can occur, as the crossover frequency heads north. Capacitor resistance can also increase over time with older capacitors, leading to a drop in tweeter output. Given all of the above, it's probably best to replace capacitors in pairs. I generally subscribe to the "if it ain't broke, don't fix it" philosophy, but I have noticed an unusually high degree of clarity in Dynaco A-25s and KLH 6s that were re-capped.
Installation.
I found the Solens to be easy to install. Working through the "woofer holes," I first glued in the caps (the affectionate term for capacitors), then soldered the leads in. The capacitors' wires are long, strong, and bend easily, so attaching to the crossover network was no problem. The folks at both Solen and Parts Express told me that hot glue wouldn't hurt the capacitors, so that's what I've used to attach the capacitors to the crossover board.
Sound.
I haven't listened (in a "controlled" environment) to enough capacitors from different brands to say for sure that I can hear what a Solen sounds like versus what a comparable Dayton sounds like. Some engineers I've spoken with say that capacitor "sound" is just more audio voodoo, like $1000 interconnects and $2000 speaker wires. But I can say with confidence that every Solen-recapped speaker pair I've listened to sounded wonderful. In several cases, recapping has "fixed" the problem when a Dynaco A-25's tweeter was silent or down in level. Compared to non-recapped Dynacos, the sound with new caps tends to be unusually clean, clear, and non-screechy through the critical midrange. The one recapped pair of KLH 6s I've heard sounded really articulate and clean, while retaining the KLH 6s characteristic mellowness.
Conclusion.
If you're restoring vintage loudspeakers, capacitor replacement will rear its not-too-ugly head at some point. Solen capacitors have a good reputation, and so they're the brand I chose when it became a necessity to replace capacitors in the Dynaco A-25s I was restoring. I have found them easy to work with, and the sound, to my ears, is excellent. I recently ordered some Daytons (even less expensive at Parts Express) for future projects. If I can hear a difference, I'll update this review. But my hunch is that the sound will be comparable. Most engineers I've chatted with say that the elite capacitors (more expensive and with tighter--less than 5%--tolerances) are "overkill" for crossover networks in vintage loudspeakers. Solen 5.1 400V capacitors have worked well in the loudspeakers I've restored this far, and they get my strong recommendation.
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