BLENDING COUPLING CAPS IN SET

BLENDING COUPLING CAPS IN SET

A few nights ago I had a nightmare that woke me up...I was in Studio 54 and I was wearing an Arnold Palmer powder blue polyester leisure suit, with shiny white shoes and matching shiny white belt and a toupee...and everyone was laughing at my disco dancing.

I was so upset I couldn’t go back to sleep so I heated up my soldering iron and put my 300B SET on the operating table. It was 4AM.

As you know the great fun of SET is the fact that there are so few parts in the signal path, which makes each part extremely critical in terms of sound quality. That is the benefit and fun of ultra-simplicity. That also explains why direct coupled circuits, which are superior in most ways, are no fun to play with..there are no coupling caps to fudge around.

When SETs arrived in America one of the shocks was the anti-film cap revolution. In a world dominated by polypropylene capacitors the notions that oil/paper caps like our grandfather used was not sensible, and then to add insult to injury, we heard from our Japanese bro’s....don’t use aluminum electrolytic power supply capacitors, use oil caps in the power supply.

AudioNote made a major contribution by having manufactured to their spec oil coupling capacitors which are now available from Angel Instruments,(www.angela.com) and this is where the fun begins. The debate goes like this...oil caps sound better than film capacitors because film capacitor have a “plastic” coloration, which can be heard in SET, and probably can not be heard in other types of circuits. There may be some sense in this because polypropylene caps are plastic, and all capacitors ring to some degree. But from a technical point of view the best quality polypropylene caps produce less “normal” distortion, and sound like they have better transient response. Oil caps sound softer, but they don’t have the plastic coloration of film caps.

There are some designers who swear by each, but that is not the real point of this debate, because only you should decide which colorations works for you, which brings me back to my night in the operating room. I started to experiment and listened to different brands of polypropylene caps and different version of the AudioNote oil caps, using mostly voice and Ry Cooder music to get a sense of the “tune” that I liked.

I decided that a .01 MIT polypropylene in parallel with an AudioNote ..1 mfd oil was exactly what I liked with my system; it was the right blend of speed and midrange juice. Let me assure you that the differences in different blends of oil/film were very obvious, which again is the great advantage of SET, and I was using Western Electric 300Bs, which makes this type of examination very easy.

How long did it take to change coupling capacitors...about 15 minutes for each amplifier, which brought me to about 8 AM, when I finally went back to sleep and had this dream.....I am back at Studio 54 and Cameron Diaz, wearing a very skimpy dress dances over to me and sticks her juicy tongue in my ear and wants to know if she can come back to my house to listen to 300Bs.

e-mail Dr. Harvey "Gizmo" Rosenberg: drgizmo@meta-gizmo.com