|
Tweakers' Asylum Tweaks for systems, rooms and Do It Yourself (DIY) help. FAQ. |
|
|
|
Tweakers' Asylum Tweaks for systems, rooms and Do It Yourself (DIY) help. FAQ. |
|
In Reply to: How do you make a VERY GOOD passive pre posted by EdS on May 15, 1999 at 14:24:14:
Hi there,Simple. Find a 4-Deck, military surplus 24 position Switch with 24 or more positions and SOLID SILVER COIN CONTACTS. These are notably better than the Elma Switches. If you scour a few Surplus Stores you should be able to find this for little money (< $ 50).
Buy a good hand full of Holco Resistors. Solder these together with the switch so that they form a Ladder attenuator. For this the whole thing switches two resistors each in each position, so that a constant Input Impedance is presented. More on this here:
http://www.slip.net/~arinc/
I personally use a 30 Position Switch (I have another 2-deck one as balance control) and use mostly 2db Steps with a few larger ones near the bottom.
In order to avoidHigh Frequency Rolloff, it is advisable to keep the Value of the pot low, about 10k is an acceptable compromise.
The only fly in the ointment is that most consumer grade DAC's and CD-Players have lousy Output Stages that are not happy to drive a load of 10kOhm....
So you could then use a simple Valve Buffer-Stage which also gives some gain (say a 5687 per Channel). This will allow a very high Input Impedance with an ability to drive the Pot.
I myself use such a scheme in my own Preamp with good succes. It has no less transparency as the the volume controll without the Valve-Stage but dynamics and tone are much better (more realistic)....
As to sand-filling the case. Sand will damp mechanical resonances, but it will not help with RFI. Furthermore, sand has a tendency to get EVERYWHERE.
What I personally would siuggest is that you look around in home improvement stores. There is one in the UK that sells excellent looking small Drawers made from plywood. The size is about 12" by 8" and they are raw wood. I'm sure you can find something similar.
The UK based place also sells various Handles and other trimmings for furnituer. In there is included an excellently lloking large diameter round knob, which looks made as the volume control knod. This again is raw wood, so you could stain both box and knob in the same (or a slightly different) colour.
Simply house the Attenutor and Input/Output Jacks in there. Even better, if you have found your "ideal" Cable, build the thing with the Interconnect Cables attached. The unit is open underneath (actually it used to be the open top to put something into the drawer), some plywood can be used to fill this in.
I PERSONALLY recommend the use of thin copper foil to shield the interiou, this will make a real difference. As for damping, use some Bitumen Pads on the inner surfaces to damp these. Some strategically (in resonance nodes) located lead-strips also can be used.
As we are already doing a lot of wood, I suggest to try seating the thing on various different Wood blocks (try different wood for different sound).
Anyway, you now have a ecologically sound (it will mostly decompose when thrown away and you recycle some miliary waste - the switches) Volume Control which will take some serious beating.
Later Thorsten
This post is made possible by the generous support of people like you and our sponsors:
Follow Ups
- Re: How do you make a VERY GOOD passive pre - Thorsten 10:11:51 05/17/99 (3)
- Re: How do you make a VERY GOOD passive pre - AlanC 19:01:23 05/17/99 (2)
- Re: How do you make a VERY GOOD passive pre - Thorsten 05:11:16 05/18/99 (1)
- Since when does +18 db = passive ??? (NT) - Sean 21:57:49 05/21/99 (0)
Top of Page ]
[ Contact Us ]
[ Support/Wish List ]
[ Copyright © 2025, Audio Asylum, all rights reserved ]
