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In Reply to: RE: Inexpensive Power Transformers posted by Triode_Kingdom on June 10, 2017 at 10:00:32
Hi Triode Kingdom,
I get what you're saying about not being crazy about the idea of an umbilical-type arrangement. A lot of the benefits of that arrangement are the distance of the power transformer from the rest of the preamp, as well as the fact it is in a separate metal enclosure.
You can get just about all of those benefits by using a larger chassis and placing the power trans/supply and preamp circuitry at the other end of the box. The power trans can also be in its own box inside the chassis for shielding. Shield the wires from the power supply, route close to the chassis plate, etc., to minimize radiated fields.
I've been thinking about the same thing. The chassis for this will be constructed from an aluminum extrusion with a 3" X 8" cross-section. I bought a 4' length, so I can cut it to practically any size. If it's about 14" deep, that would allow positioning the PT and power supply circuitry a reasonable distance from the phono section. I'm planning to shield the phono tubes (all 9-pin), and it might also be possible to add a small mu-metal shield around the PT. I think this will work well. :)
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Hi Triode Kingdom,
I've had a project on the back burner forever with similar design parameters...a pre-amp I plan to put in a rack-mount case, which is almost 19" wide, I think. Obviously plenty of room to separate the noise-makers from the noise-takers.
Btw, I recently took a class about EMI/RF interference - it was great and went a long way to explaining a lot of typical layout and wiring practices. One fundamental tenet was to, whenever possible, shield or otherwise mitigate noise sources, as opposed to noise 'victims.' I suppose one could always do both, especially if weight and cost aren't huge factors (this was an aerospace-centric class; weight is obviously critical), but often the biggest overall dB/$ payoff will be had when attacking sources.
Distance is a key strategy, since, depending on the type of noise, typical diminution is on the order of 1/(separation distance) or even 1/(separation distance)^2...you get the idea. Shielding can also yield significant benefits, as can good wiring practices.
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