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Analog Line Level Preamplifiers , Passive Pre-amps, Crossovers, etc.

Big Dumb Input Selector
Big Dumb Input Selector
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Old 27th April 2011, 03:29 AM   #1
SnowplowTortoise is offline SnowplowTortoise  United States
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Join Date: Feb 2010
Default Big Dumb Input Selector

This is a small project I just finished up. It is a 6-way input selector with five sets of RCA jacks in the back and one in the front. Grounds are also switched to reduce ground loops. It is strongly based on this insanely detailed tutorial. I resisted labeling each set of jacks with a specific device because that stuff tends to change fairly often for me. It's maybe hard to see in the pictures (also in reality), but there are just the numbers 1-6 stamped into the metal.

As described in the tutorial, I added 10k resistors between all grounds, though I don't completely understand what this does or why it is necessary. Whatever the reason, it seems to work well as I hear no extra sounds as a result of putting this box in the signal path.

The wood is some leftover walnut and the metal is aluminum. Insulated RCA terminals from Ebay and a 6-way, 4-pole, non-shorting rotary switch is all there is to it.

Thanks for looking.
Attached Images
File Type: jpg Input Selector 1.jpg (242.3 KB, 178 views)
File Type: jpg Input Selector 2.jpg (235.0 KB, 171 views)
File Type: jpg Input Selector 3.jpg (193.4 KB, 172 views)
File Type: jpg Input Selector 4.jpg (91.1 KB, 165 views)
File Type: jpg Input Selector 5.jpg (87.0 KB, 163 views)
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Old 27th April 2011, 01:36 PM   #2
Mooly is offline Mooly  United Kingdom
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Big Dumb Input Selector
Very nice I like the style of it.

I guess the resistors tying the grounds are just to keep everything at the same potential, perhaps to avoid clicks as the selector is turned. Just because we refer to something as "ground" doesn't mean that it is of course. Any source equipment that is not directly connected to mains earth could be though of as having its "ground" as floating... so I think that is all the resistors are for.
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Old 29th April 2011, 03:38 AM   #3
SnowplowTortoise is offline SnowplowTortoise  United States
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Join Date: Feb 2010
Thanks Mooly. I was wondering what harm the unused inputs could cause while they are completely disconnected from the active circuit - that makes a lot more sense now. Glad I had the good sense to know what I don't know and heed the advice of people who do!

One other bit of explanation - I would have done the normal thing and built this selector into my amplifier, but unfortunately the enclosure I used did not have enough space in the back. At least the two form a visually seamless team sitting next to each other on the shelf. Nearly twins, Id say.
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File Type: jpg DSC_3805.jpg (82.3 KB, 39 views)
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