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Need an easy project? Simple & sweet passive pre

Redboy

a few good watts
I built a passive pre based on the information found in LPD's thread recently. The best part was the way things just came together, in a way that they rarely do.

The key to the success of the project was the box I used - I didn't have to drill a single hole! You should be able to find one of these boxes without looking too hard - it's an older data switching box like this (shown with original guts already removed):

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I bought the rest of the parts from Parts Connexion, an AK sponsor - find the link at the bottom of this page. I've ordered from them several times and they're great! Great product, great service, and quick shipping.

Parts I used...
  • Potentiometer: Noble stereo 100K volume pot
  • (2)Resistors: 11K Shinkoh Tantalum film
  • (2 pairs) Connectors: Connex RCA input jacks, inside chassis mount
  • Some short bits of CAT-5 wire
...about $45 for some really nice parts. Or you could do it on the cheap for less than $10. Your choice.

I chose to paint the box. This was my first time using hammered texture paint, and it did not turn out well! :no:

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Next thing is to wire it up and solder that sucker! Read ashok's detailed instructions in LPD's thread. Here's how I laid mine out:

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Note that the left and right inputs are above, and outputs are below. Make sure you tighten these things as much as you can! I'm not particularly fond of the way this layout looks (I'd prefer to have inputs on one side, outputs on the other) but I wanted to keep the wiring as simple as possible and this was the ticket. No drilling required, either! Keep it simple!

In my parts list above, I noted that the input jacks should be "inside chassis mount." This means (counterintuitively, I think) that the nut will be on the outside of your box. The beauty of doing it this way is that if you absolutely loved the way this preamp sounded, but wanted to put it into a nicer looking case, you could do so without having to warm up the soldering iron! Just unscrew and pop the whole assembly into your new box. For now, I'm content with my badly painted switching box.

So, how does it sound? Ah yes, that. I had this little pre over at ejfud's house the other day, and in initial non-scientific trials, we both liked it better than the Channel Islands pre he had running at the time. To quote mhardy6647, "YMMV"

So, what are you waiting for? Order some parts, put it together. It's that simple! :yes:

Enjoy.

Nate
 
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Sure. The lighter colored wires are connected to "ground", the darker ones go from the wiper to output positive. Each twisted pair goes to a channel:

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Thanks. Super-simple, and you say it sounds good? Cool! :thmbsp:

By typical serendipity, just yesterday I saw a small pile of those (well, very similar) data switching boxes at the scrap-recycling place. I never paid attention to them before, and am still not sure how they are used, but thinking they might come in handy for the upcoming computer-system upgrade I have in mind, hoping they might serve as a means of switching two computers between two monitors, I picked up two of them. Think I'll go back and get another, and try this project. So simple, it should be quick! :D
 
Not difficult. A miniature DPDT switch and some more wire. And a little more fiddling. That one's next.

I'm probably going to build the uber-low budget version of this for comparison, too.
 
I had tried a passive pre before and it seemed to suck the life out of the music.

I then went to a simple two tube pre I found in an old Glass Audio article and have been very happy.

I'd like to try the passive pre again. Is there a trick to keeping the life in the music?
 
I think the sonic end result hinges on system synergy to a large extent. Some systems suck with a passive, others demand it.

chasaboo, I'd like to see that two tube pre you mentioned. Got pics or info?
 
I'm going to try building a tube buffered passive preamp around a PCB I acquired from a notorious Hong Kong knockoff of high end gear.

I'll build it soon, assuming I don't wind up with a different preamp or get distracted by a shiny object.
 
Indeed it is! :tresbon:

I'm content with this passive for the time being. I've really enjoyed listening lately, and I've spent less time inhaling solder fumes...
 
I think the sonic end result hinges on system synergy to a large extent. Some systems suck with a passive, others demand it.

chasaboo, I'd like to see that two tube pre you mentioned. Got pics or info?

It's in Glass Audio Vol. 3, No. 2 and by Rozenblit. If you look it up online I'm sure you'll find a schematic and people who have built it. It's very simple. :thmbsp:
 
A great use for these, with multiple inputs is to run your "serious listening" inputs directly into it and then run the front speakers line level outputs of another system into another input. In my case I have a Lexicon DC-2, it's bass management allows me to "steer" the LF signal to a powered subwoofer. I keep a cd changer, and other Mid Fi stuff hooked to the Lexicon, and run the system that way for casual music AND HT use. For serious listening the signal goes direct from my AH! cd player or TT/Phono stage through the passive to my amp.

I had been looking for a way to "protect" my front speakers from the crazy LF output that DTS/5.1 is capable of, while allowing full range "pure" 2-channel use!
 
I'm probably going to build the uber-low budget version of this for comparison, too.

I just did that. Used the $3 RS stereo pot the el cheapo RCA's, and a plastic project box. I didn't have 11k resistors on hand so I used 10k.

It sounds pretty good but there's a channel imbalance in the pot. I plan to measure it and put a compensation resistor on the side that needs it. At regular listening levels it isn't all that obvious but when you go from dead stop to I-can-hear-it-now the left channel comes on first and at low levels you can hear the slight difference. The change from "off" to "on" is a bigger step than I expected but nothing outrageous.

Ray
 
Hammered texture paint

Redboy...

I've never used that paint but your photos make it look great....what did you not like about it????

I've never used the krinlke-look paint either but have seen it and like it OK (but probably difficult to dust?)
 
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