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In Reply to: help with basic potentiometer questions posted by Darren on March 24, 2000 at 08:31:13:
Darren,Curcio Audio has a very simple DIY passive preamp schematic at their site:
www.curcioaudio.com They even provide part #s from Digi-Key (a good parts source). Good luck w/ your project.
I've been looking for someone's passive pre project. Was thinking that they were just too simple for anyone but myself to need direction. Thought I could understand enough of schematics to get by. I guess not. Really too bad that the chassis isn't available anymore, it looks really nice.Thanks
Darren,The first few times I looked at this schematic I was at a loss too. However, what I did was to eliminate most of the switches as a starting point. Then I laid out some wire and two old junk pots so I could "mock up" the wiring layout. Once I got the idea of how everything went together I could look at the schematic and make sense of what was on paper.
BTW, check out www.meci.com for a good selection of inexpensive pots and switches. I scrounged my passive pre-amp from old electronic junk from my workplace (best items scored were the 1% tol. wirewound pots, about $50 each from Spectrol, tossed into a junkbox!). My biggest expense was the RCA jacks.As far as a chassis goes, check your local metal working firms, they may have or could make you a very simple chassis for peanuts.
If the rat shack version works out moderately well, I'd like to go through with the full stepped attenuator like the DACT mentioned above. Will have to consider a basic layout like Curcio's then and anticipate the 4 or 5 pairs of RCA's will be a significant cost.As for the chassis, I did get the name of a refrigeration company nearby that's made things for the tube guys and tweakers around here. Seems like pretty solid stuff. Was wondering about shielding though. Will the metal used (thickness or type) make a material difference where noise is concerned? Would you recommend bare or insulated wiring?
Darren,
Definately do a "test" system first, it gives you a chance to really learn how to wire, solder, etc. The Curcio design is a good simple starting point, I'm certain subbing in DACT attenuators will be easy once you get the hang of how things work.As far as chassis sheilding goes, I'm using old alum chassis (~2mm thick) totally inclosed. Each chassis is aprox. 2.5"H x 6"W x 9"L. I live less than a mile from a 50KW FM radio station. If the passive were subject to RFI I would know it. I run only 'line level' inputs; CD, FM, tape because phone equip IS susceptable to RFI. If you're really concerned about EMI/RFI try this, look up "roofing &/or sheet metal contractors" in the yellow pages. Find one that sells to the general public and buy some 20 oz roofing copper. BTW thats 20 oz/sqft copper. You can cut it w/ heavy shears and line your chassis w/ it. I used it on my CDP and it does help reduce any stray EMI. In fact, if you want something really different, have them make you a chassis from copper. I know the outfit I buy from would bend a chassis for me for about $50. I you added some nice wood side caps then polished and lacquered the copper you'd have a very unusual but beautiful passive preamp. Good luck on your project.
Good luck w/ your project.
Not sure if you are going to use DACT input selection control or not. If you do, you need to know that their input selection switched source and ground at the same time - which might be different to your test switch.
As for the preamp chassis. Mine is aluminum - using my old shoe box size integrated amp.
Can't comment about shielding, no problem here.
Next item to look at - solder, something like Wonder solder, Carders, WBT (I was told to avoid using this),…..
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