About Coupling & 
Power Supply 
Capacitors
 
 
    

A Good-Sounding Capacitor is Essential!

Coupling capacitors are used in all tube gear. The audio signal gets from one tube to the next through these electrical components. For over twenty years, audiophiles and audio designers have been aware that not all caps sound alike. Capacitors can make a huge difference in the sound of equipment.

In the original Counterpoint gear, I used polypropylene capacitors from Reliable Capacitor. Later we changed to Wondercaps. For the upgrades, I use different capacitors depending on the unit being upgraded, and the desired cost/benefit ratio.

• TRT. I used the TRT Infinicap Signature capacitor in the 90's at Counterpoint. This is a fairly neutral-sounding capacitor that is not overly expensive, and is an improvement over the original RelCaps or IAR caps, but it is dry-sounding and perhaps a bit grainy. It offers a lot of capacitance in a small space, an advantage in a crowded chassis.
  
  
• RTX. Next up in terms of size, cost, and sound quality, are Relcap's Multicap RTX polystyrene and tin foil capacitors. In terms of three-dimensionality and musical richness, these sound substantially better than the TRT parts. They are fast-sounding so you hear all the detail in the music, but they are never harsh. They always sound warm and sweet. They cost about twice as much as the TRT caps. They are also physically a lot larger: twice as fat and about 50% longer than the TRT's, so they cannot always be used.
  
  
• VTV (UltraTone). Used in 1998 and 1999 in many of my Premium GOLD upgrades, these silver-foil in oil caps were custom made for Vacuum Tube Valley in England using 98% silver foil wound with high-quality paper impregnated with nontoxic pure mineral oil as a dielectric. The leads are solid OFC silver plated and silver soldered internally to the plates. The oil dielectric is not a complete insulator -- I have measured a few tens of millivolts (open-circuit) of leakage when a couple hundred volts of DC is applied to one side of the cap. DIY user of these caps should be aware of that. These capacitors are notable in that they are not rounded and dull-sounding on the top end like other oil/paper caps. I found them to be sweet and liquid-sounding. However, they do have an audible opacity in the upper midrange. I moved to the Auricaps (below) which are more transparent in the midrange, just as sweet and liquid, and do not have any measurable leakage current. UPDATE: I've had to replace several of VTV parts due to internal breakdown, causing popping noises from the speakers. These were 630-V parts used in 250-V environments, so the parts cannot be considered reliable. The U.S. importer, Vacuum Tube Valley, reports that he is unable to locate the manufacturer to discuss reliability issues, or parts that he paid for and never received. Not recommended.
  

Auricaps. Switched over to these in 2000. These are remarkable-sounding polypropylene capacitors. They possess all of the the liquidity of the much more expensive VTV caps (above) with audibly more midrange detail. As of 2002 they have been downrated slightly and are now my second-best coupling capacitor. Manufactured by Audience.

DynamiCaps. In a class by themselves. Made by TRT. If the best of the premium standard-wound polypropylene capacitors (AuriCaps, Cardas, etc.) are "10s", then this capacitor is a 12. There's something magic about this part. When I listen to music through it, it is every bit as detailed and transparent as the other ones, but in the midrange there is a weight to the sound, a sonic rightness that none of the other caps produce. The sound is at the same time, more relaxed, less forward and more open. Even the best of the other caps sound oversaturated, like a TV with the color turned up too high, compared with this cap. In "TV terms" you could say it provides a natural color balance. Starting in July of 2002, this has become my premium capacitor. Manufactured by IAR-TRT.

What about V-Caps or SoniCaps? I don't like to mention parts that I've not used but have evaluated and found to be wanting. No sense dissing the manufacturer. But by not mentioning them, it appears that I am overlooking parts which have achieved good reputations in the audiophile DIY community. So, I have decided to mention that I have listened to parts from Reliable Capacitor, Hoveland, and many others, V-Caps, and Sonicap Platinums. I don't consider them a good value. The latter two brands cost more than Dynamicaps, my current choice, and none of them sound as much like straight wire (to me) as the Dyamicaps. For the DIY-er, Reliable's PPMT models were used in Counterpoint's products in the early 1980's and were partially responsible for the sound of those models.
     
When I listen to passive parts that are used in the signal path (resistors, capacitors, etc.), I always compare them to a pair of 1-inch bits of very high quality wire. Those parts that sound the closest to the wire are the ones I use. When a new part (or a part new to me) comes along, out comes the "listen box," with its six sets of input jacks, a six-position selector switch, and one set of output jacks. I instruct my technician to install the parts I am evaluating into the box, but not tell me which switch position is connected to which parts. Position A is always the wire bypass, and positions B through F get filled in order depending on how many parts I am evaluating. Since I don't know what parts are connected to the other positions, I can't play favorites. After I have listened and noted what each switch position sounds like, I open the box to see what parts are associated with that position.
    
So far, the Dynamicaps sound more like the straight wire than any other coupling capacitors that have come into the shop. That's not to say that they won't be bested, and when they are, I'll use the new parts. I'm not beholden to anyone.

IN HIGH VOLTAGE POWER SUPPLIES I used to use the fine ELNA Cerafine, but they were discontinued. Black Gate WKZ, N and NH are excellent and I use them as upgrade parts in power supply applications (not in the signal path), but lately I've started to use Continental Capacitors' "Type-A" oil-filled capacitors for power supply work. They can't be used in all the products, as they are physically too large. But when I can fit them in, I will. These are luscious-sounding capacitors, warm, round and very present. They make it sound like the singer or musicians are in the room with you, more so than the Black Gate parts, and more than any other oil-filled capacitor I've found.

Note: I don't sell capacitors! I use them in the upgrades -- contact the manufacturer if you want to buy some or have technical questions regarding these parts. Michael Percy Audio (www.percyaudio.com) is a good place to find good caps. Continental Capacitors is an industrial supplier and does not have a retail presence, but their salesman, Paul Lafferty, is available to be e-mailed at conticaps@gmail.com (OEM inquiries only -- quantities over 100 pieces at a time only, and he's not able to handle DIY inquiries).