Precision Fidelity C7/A: To modify or leave as is?

Just for the record, the original C7 was designed by me when Precision Fidelity had just moved to Santa Rosa, CA in 1977. The company was sold to The Hill Group, a holding company in San Diego in 1978. They eventually sold the designs to Bruce Moore who ran the technical end after that. I went to National Controls to design A/D convertors and exited the audio scene.

I'm delighted that the C7 and the M80 stereo power amp have become such beloved instruments. As an technically inclined artist, it is satisfying to know that my creations have provided so much pleasure for so long.

I never heard an actual C7 but I built one from the schematic a long time ago. As I recall, it sounded very nice, just lacking a bit in dynamics. From looking at your system, I think you would appreciate the improved sound quality that V-Cap coupling caps should provide. Richard is absolutely right that cap upgrades can be risky. They will change the sound, and sometimes a modern cap can be a step backwards. I happen to like the sound of V-Caps very much, both the original Teflon and the newer CuTF series, but that is not a universal reaction. I suspect your C7 uses some mylar film caps from the late 1970s, and V-Caps should be a major improvement in inner detail and (probably but less certainly) tonal balance. If I were you, I would do it. In the unlikely case that you are not happy, you can always put the originals back in.

By the way, if you need a copy of the schematic, send me an email through the Audiogon system. I have one in my files somewhere. As I recall, it shows the original circuit as well as later updates.

Hello,
I must commend your design. I recently purchased a C7 and I love it. For some reason the owner's manual and full schematic are scarer than hens' teeth.
Any chance you have either?
I would gladly pay any costs.
Thank you
Lloyd Foster

I remember there was a guy by the name of Joe Bermudez involved in that company. The power supply design reminded me a bit of an Audible Illusions as well as some early C/J product. I fixed one about 10 years ago. Hasn't been back since.

Here's something from High-endaudio:

PRECISION FIDELITY C-7 (LATER MODELS)
I sold this model when my store opened back in 1981. This is a "Classic Preamplifier", with a design far ahead of not only its own time, but even up to today. In fact, our current audio market is begging for an updated version of the C-7.

The C-7 was essentially a high quality (tube) phono-stage with two volume controls, a couple of extra (passive) inputs and no line-stage. This is "the dream design" of today's audiophiles who have phono-centric systems, like me. (My own preamplifier, the Jadis JP-80, was heavily modified to copy the basic design of the C-7.)

It's been some time since I heard one of them, but I remember their sheer natural quality and the cleanness and quietness that is consistent with no line-stage. The people who bought them, if they could live with the low-gain, loved them. (I'd love to hear a modified version, with the best caps available today. I would love even more to hear an all-out modern version of this design.)

I remember that the original C-7 had some design problems that translated into sonic problems, so look for the "A" or "Revised" versions. (I can not provide the schematics to make these revisions.) The C-7 should be modified with better capacitors, just like all the other preamplifiers from this era. They also require a high quality step-up device for low-output moving coils.

Recent- One reader just purchased a C-7 based on the above advice. His take:

"...soundwise - Wow! Lumi is taking a long rest. This thing sounds a bit dark (like most passives in my system, probably the amp), but it is so dynamic, immediate, transparent, and not greasy or euphonic or juicy. I'd venture to say it is rather accurate. Of all medium priced preamps that I've tried, and I've had many, including many Bruce Moore designs, this one is by far the best sounding, with great MM phono. It beats Magus by a wide margin and phono is a lot quieter (uses two solid state regulators). Thanks for a great suggestion..."

Bottom Line- If I was on "a strict budget" for a preamplifier, and with the choice of ANY model ever made, the C-7 (modified) would be my first choice.