passive pre amp

[Andrew Pratt]

thomas provided me with this link to a passive pre amp



Any thoughts Jon?

[JonMarsh]

This is a "cute" project, and probably sounds pretty good for the minimal bucks involved. The main bonus of this concept is eliminateing an active gain stage with it's colorations. (there are some fairly low coloration active gain stages, but not for low bucks- when you consider the discrete and passive devices required, power supplies, etc).

The real achilles heal is the pots- wiper contacts are prone to noise and low level distortion. A "level 1" upgrade is going with a good dual gang Noble pot from Welborne labs or some other source.

Level two is a good passive mutlipole attenuator from DACT; there's are about 24 position.

Level three is a Shallco based attenuator with 46 steps, like my Marchand PR41, which also has input selection.

But for what you need to do right now, Andrew, this will get you going. Note that if you go this "cheapie" route, you'll have to manually balance the right and left gain; that will prove to be a real pain over time, I expect. Unless you just leave it at a fixed position. That's the biggest reason I'd recommend spending a few bucks on a better attenuator.

In fact, if you want to do something a little more elaborate, I may have an extra Duncan conductove plastic slide attenuator with engraved aluminum panel I could send you. I'll check this weekend- will have to go through a few boxes to find it. But then it would be more like a conventional pot setup. Also, it's 10K input resistance, which may be lower than you want, but should work OK with the CD player.

Regards,

Jon




Earth First!
_______________________________
We'll screw up the other planets later....

[Andrew Pratt]

Jon at this point I'm open to any suggestions you have...incl your spare parts I do agree though that a single volume knob for both channels would be much more user friendly

[Lex]

Well, it certainly looks "airy" Interesting project.

Lex

[JonMarsh]

BINGO!!!


Andrew, I found the stash of mixer parts, including the Duncan conductive plastic sliders, eustachions, etc. I do have one extra dual 10K control (there's one which is committed to a preamp project I started about 10 years ago and haven't finished... I'm bad, but I'm getting better... I hope), I'll just have to steal a mounting plate and knob from one of the single slider sets. BTW, slider can be either black or white.

I'll assemble that and then photo it, so you can see what it looks like this weekend. Maybe it will be too wonky a Pro look for you, I don't know... some people like that, though, we know who we are.

Regards,

Jon


Later, from the bowels of the laboratory.....







Earth First!
_______________________________
We'll screw up the other planets later....

[Andrew Pratt]

Jon priorty one is sound looks are secondary (to a point!) but definately the black one if possible.