The other part of my vinyl journey, involves phono preamplifiers. First off with a ceramic cartridge a phono preamplifier is not required. The Viking console had no preamp neither did our Sears consolett. When I added the Shure M3D to the Viking I used an inexpensive “Daveco” preamp designed for the purpose of converting from a ceramic to a magnetic cartridge. When I graduated to my own turntable I stuck with the M3D cartridge. The electronics I was then using was the Sinclair Stereo 60. It was modular system intended to mount in a turntable plinth. The power amplifiers proved to be very unreliable but the preamp worked fine, I used it until the late seventies. Sinclair spared every expense in their products, they were designed to be as cost effective as possible. They had that DIY feel to them, manuals full of schematics hook-up details suggestions for modification. I loved it. The preamp sounded fine to me at the time.
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http://diy.torrens.org/Sinclair/index.html
Then along came the CBC installing two new FM radio transmitters. Their test tones came blasting through my speakers! At that point I purchased a low TIM preamplifier kit.
I had previously ditched the Sinclair power amplifiers and had built low TIM power amplifiers from kits. The preamplifier was from the same company “Unitronics” or something to that effect. Upon construction I found that it was rather noisy. They were using a zener in the emitter circuit of a differential pair at the preamplifiers input. It was there to form a constant current source. Replacing it by a simple resistor got rid of the noise. I Mounted it in a Hammond steel chassis box with a Hammond blank aluminum front panel. In addition to the phono preamplifier stage I added the “Bass- Summing Amplifier” from the April 1981 Popular Electronics”.
https://worldradiohistory.com/Archive-Poptronics/80s/1981/Poptronics-1981-04.pdf
It was always cool watching a warped record play, the high compliance woofers would move in and out in opposite directions. Some amps had a rumble filter to solve that problem, but that sacrifices bass. By blending the stereo channels together below a set frequency that out of phase rumble is cancelled out. Because most stereo records have mono bass already nothing is sacrificed by the process. It was very cool to flip the switch in and out and see that slow in and out motion stop but the sound was totally unaffected. I also added Scott’s pre-synth circuit. I had switching for five stereo inputs, plus tape monitor. Back then I used Letraset dry transfer lettering to label all my projects. Then I would add a couple sprays of a clear coating. Forty some years later that coating is falling off now leaving a clean blank panel.
Receiving the inaugural issue ”0” of Glass audio, my (never totally dead) interest in tubes was revived. From GA I discovered the back issues of “Audio Amateur” as well. Having purchased (or was about to purchase) the Sony MC cartridge from “Addison” I needed a pre-preamplifier. So I built Joe Curcio’s pre-preamplifier, It worked like a charm. I was even able to use it with my CD-4 Demodulator, but the front and rear channels came out reversed as the single stage amplifier inverts phase.
Audio Amateur issue 2, 1985 featured Joe Curcio’s “Daniel” preamplifier. I built my own version via old school point to point wiring techniques. No circuit board required by me although they were available for sale from Old Colony Sound Lab. Chris Paul proposed a modification to greatly reduce the output impedance of the preamp referred to as the Mu follower. I used that circuit. Using 6DJ8 tubes it sounded fantastic. People had been dumping their vinyl, thinking that CDs were so much superior in sound quality. I remember telling them that my records sounded as good as CD’s. Latter I would revise that statement to say that they sound better than CDs! I tried different tubes including Ampex, Brimar Philips SQ (special quality) 6922 and JAN (Joint Army Navy tubes) 7308’s. I wasn’t intentionally “tube rolling” it was just that I was lucky enough to have accumulated a lot of this old tube “junk” as it was being discarded no longer required for its original purpose. Hamfests, Triode Electronics and Antique Electronic Supply were useful suppliers as well. The final tube swap was to the E288CC. This tube has been described as a 6DJ8 on steroids. It is electrically a bit different than the 6DJ8, I ended up rebiasing the first stage for proper operation but it sounds damn good. With my cartridge now switched over to the Audio Technica AT-ART9XA it is hard to imagine anything sounding better. I don’t expect any more upgrades for a long, longtime if ever.
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