Scott's JEL FF Preamp

JE Labs Full Function Preamp with Built in SUTs (Step-up Transformers)

2x NOS Ken Rad 76s, 2x NOS RCA 6SL7s, 2x NOS RCA 6SN7s

Hashimoto Power Transformer and chokes, Altec 4722 mic transformers

Angela/Jensen and Sequa PIO signal caps, NOS Russian PIO caps, German F&T and NOS Sprague Atom electrolytics,

Tekman CF resistors and Riken CC resistors

Built for Scott Matthews

Complete on 3/1/10

Project Summary:

This JEL FF preamp has the most functional phono stage I have built so far. The phono section has two inputs - one for a low output MC cart stepped up via Altec 4722 mic transformers and the other for a regular MM cart. The phono section also has two output - low Z output via 76-6SN7 linestage and high Z ouput bypassing the linestage that requires 250K impedance.

My experience with this circuit tells me that the preamp is very sensitive to the quality of tubes used. Which is why I wanted to use nothing but all NOS American tubes in the preamp. I usually buy a whole lot of tubes then select the ones that I am most happy with my ears and with my tube tester. I have realized over the years of experience that, in spite of what the sellers say, you don't actually know how good the tubes are until they are plugged into an amp.

All primed up, ready to be painted....

All painted in cherry red. Scott wanted to match up his JEL 2A3dx stereo that I built to the preamp, hence the color.

The best time to take pictures is when it's overcast outside. It's been raining a lot here in Nor Cal and we have been missing some bright sunlight lately. I took the amp outside a couple of hours before the sunset and I just got the best lighting possible to take pictures of the preamp.

Input legends are as follows: preamp output, regular MM cartridge input, MC cart input, high Z phono out, line input 1, line input 2, and line input 3. The red binding post is phono ground.

Beautiful Hashimoto irons!

The right toggle controls phono input between MC and MM cartridges (MC input will be routed to the Altecs first before feeding into the phono stage, whereas MM feeds directly into the phono stage). The left toggle selects the input impedance of the Altec between 38 ohms and 150 ohms.

The wiring is intensive in this build. Lots of routing bewteen switches. I somehow managed to build a preamp that is dead quiet in spite of these wires everywhere. I think the key is careful planning with grounding scheme and component placement to keep the leads as short as possible. I also like the recitified heaters for the tubes as well as the voltage divider network that keeps the heater voltage lifted around 75 VDC above the ground. This not only insures safe operation of the tubes, but it also keeps hum and any other spurious noises away.

A whole lotta oil to keep things smooth....

I really really really like this preamp. The 76 tubes in the line stage seems to do the wonders to the soundstage - you can really feel it and see it with your ears when listening to classical music. The sound feel "wide and spacious". The preamp also add some serious bass to the sound without making it muddy. The phono stage sounds very passive and accurate. I only have MM carts in my setup and I could only test the "regular" phono stage in the preamp with what I have. I am anxious to test the Altec irons when I make a visit to Mike McKee in Davis, CA this week. He's one of my clients for whom I built a JEL FF preamp. He's got a turntable with a Denon MC cart that he graciously agreed to let me test the preamp with. I will add my comments as well as Mike's after the test. Stay tuned!

Verdict:

Before I ramble about how wonderful those Altecs were, here is the speccification of Mike's turntable:

Slate Plinth designed and mfg by Oswaldsmill Audio

Lenco L75 running gear

“PTP” – Peter Top Plate structure for the running gear

Schick 12” tonearm

Uwe ebony headshell

Denon DL103 fitted with a Soundsmith ruby cantilever and OC diamond stylus

I was simply amazed. I have never heard a TT sound that good. If I said it sounded like high quality CD, I would only undermine how it truly sounded. The music sounded incredibly life-like and every note had life to it. I am now seriously giving a thought about having a MC cart setup like this for my system. I only wish those Altecs were more readily available.

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