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A volume control for all seasons...?

195.44.216.248

Posted by Gary on August 1, 2000 at 16:26:41

Okay,

It's late at night (in the UK) and I'm losing sleep. I need some help please. I have two preamps, a Croft Super Micro (tube) and a Russ Andrews passive with an active gain (ss) attached (if that makes sense).

I'be been contemplating building a stepped attenuator to try and realise more potential out of these preamps or to audition the benefits of a true passive preamp. (I'm using Kimber KCAG cables, are these low enough capacitance to use with a passive?)

What I'd like to do is try a reasonably cheap/easy build, but I want the following options.

a) Ladder stepped attenuator - best possible sound?
b) Small steps betweeen each setting.
c) Some sort of balance control.

Now I've seen the following.

1. Marchand Electronics PR41 passive preamp.
Pros - Very nice, Shallco, 47 steps (1.25db per step), balance control (0.6db per step on one side at a time).
Cons - Expensive ($695 for kit with prebuilt attenuators). Main attenuator is a series attenutor, not the ultimate (I'd always be wondering if it could be better...)

2. Michael Percy Audio Shallco kit
Pros - Reasonable price, $273 for two mono Shallco ladder 47 step switches with 184 Holco resistors to boot. Offers both small steps and easy balance control, albeit by adjusting two mono controls.
Cons - I don't think my soldering skills are up to it. Quote "...either the Shallco or Elma switches require a high degree of soldering skill and a great deal of care and precision". I'd weep if I ruined one of these babies just as I put the last resistor in.

3. The Parts Connection - mono Shallco 32 ladder step
Pros - Ladder, 32 steps, preassembled at $400
Cons - Not as fine gradation as the 47 steps (will I notice the difference?)

4. Placette Audio passive preamp.
Pros - 128 steps, remote control
Cons - No balance control (that I know of), expensive experiment ($1200).

I was just looking at Electronic Tonalities $40 attenuator kit and I take on board the fact that you'd only probably use 2 or 3 settings, but it doesn't solve my balance control problem (either my ears or my cartridge is out of whack).

Therefore, my proposed solution is this (based on the Rothwell Passive preamp that's on sale in the UK).

Use 3 ladder attenuators, 1 stereo 12 position (4 wafers?) and 2 mono 12 position.

The main stereo pot would contain coarse steps, 0 to 132 db (in steps of 12db). Each mono pot would contain fine steps of 0 to 11db (in steps of 1db). The main signal would come into the main stereo pot which is then wired to each mono pot.

To use, set the broad listening level with the stereo pot, and then attenuate each side with the separate mono pots to the required level. In theory, you should have steps ranging from 0 to 132db in steps of 1db, with a balance control range of 12db. (Or 0 to 66db with 0.5 db steps and a balance range of 6db).

Pros - Cheap to build (someone -sorry can't remember who - mentioned that Mouser sell these switches at $3.17 each). Easier to build, only 12 positions to fit resistors in. Fewer resistors to wire (can possibly upgrade to better ones later at a reasonable cost). Balance control. Small steps. Ladder attenuator construction.

Cons - Three controls to use (though I envisage that the main coarse control would soon only be used in 2 or 3 positions once a user had found an optimum range, and that the fine steps would be used more often). 4 resistors in signal instead of 2.

My queries are these.
1. Is this a viable idea? Could anyone point me in the right direction as regards parts , wiring diagrams etc?
2. Does anyone offer prebuilt 47 step Shallco ladder attenuators?
3. Have I finally, really and truly lost it?

All feedback will be much appreciated.

Thanks,

Gary

This post is made possible by the generous support of people like you and our sponsors:

Kimber Kable

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