Outboard level or volume control

Charles Calkins · « **on:** 26 Jul 2005, 01:08 am »

Hey Guys:
Anybody heard of such a gizmo. Herr Von Schweikert says I will need one if I want to keep my solid state amps for the woofers and tube amps for the mid and tweeter module.

Cheers
Charlie

JoshK · « **Reply #1 on:** 26 Jul 2005, 02:41 pm »

Those nude attenuators or whatever they are called that some use would be ideal for this purpose. Or Luminous Audio's passive preamp would work perfectly as well. Basically, tube amps have higher input sensitivities than solid state amps so the incoming signal needs to be trimmed to match the the output volume level of the solid state amp.

Charles Calkins · « **Reply #2 on:** 26 Jul 2005, 02:58 pm »

joshk:
Thanks for the info. I don't know what a nude attenuator is but I did look at the Luminous site and read about the Axiom preamp. This might be the best way for me. I like to keep things very,very simple. I'll send Luminous an email and get their input.

Cheers
Charlie

JoshK · « **Reply #3 on:** 26 Jul 2005, 03:02 pm »

If you know what the input sensitivity (measured in voltage) of the two amps are, or can get it from the manufacturer then you can do something even simpler. You do the math to determine the appropriate resistor to make the two amps match. Then you build the resistor into a pair of ICs or into a plug in RCA > resistor > RCA. Cheap and easy.

Davey · « **Reply #4 on:** 26 Jul 2005, 03:17 pm »

Charles,

Look at Figure 1 at the top of this Goldpoint page.

http://www.goldpt.com/how.html

A simple two resistor pad should be all you need to attenuate the input to your higher gain amp so it matches with the other one.

As Josh said, you could build this into the RCA plugs or maybe a small project box.

Josh,

The voltage gain specification (and probably not the input sensitivity rating) is the meaningful number that needs to be obtained/measured from the amps. Most ampliifiers are in the 25-30db range of voltage gain so a few db one way or the other should be all that's required for a simple pad.

Cheers,

Davey.

Charles Calkins · « **Reply #5 on:** 26 Jul 2005, 03:26 pm »

Davey:
I see what you mean. However I kind of like joshk's suggestion about the Luminous Axiom preamp. It would be adjustable whereas the resistor pads are not. Right? Or as usual am I missing something.

Cheers
Charlie

Davey · « **Reply #6 on:** 26 Jul 2005, 04:05 pm »

Charles,

Yes indeed....fixed resistors would not be adjustable. It seems to me this would not be a problem since this is most likely a one-time-only correction.

The Axiom volume control is certainly okay......however, it's $150.00 vice about $2.00 for a couple of resistors.

Your choice.

Cheers,

Davey.

JoshK · « **Reply #7 on:** 26 Jul 2005, 04:05 pm »

Charles,

Yes, it wouldn't be adjustable, the luminous would be.

Davey,

Your right, somehow I thought I recalled them being related.

Charles Calkins · « **Reply #8 on:** 26 Jul 2005, 06:05 pm »

joshk and davey:

I know that my NAD amps have a 29DB gain. I've looked at CJ's and they don't give a gain figure. ARC does and the ones I could find info. on have 28DB gain. So now I'm thinking that if I find amps with a gain of around say 27 to 29DB then I wouldn't need an output level control. Right?

Cheers
Charlie

Davey · « **Reply #9 on:** 26 Jul 2005, 11:54 pm »

Charlie,

I thought you already had the power amps. Why in the world would you want to find different amplifiers just to avoid using a level control? I'm confused.

I believe you're over-thinking the problem now. I would use your existing amplifiers, get a cheap potentiometer from Radio Shack, install it on the input of the amplifier with the higher gain (whichever that is) and adjust to your liking. Eventually you could replace the cheap control with fixed resistors of the same attenuation value or something like the Luminous control.

Cheers,

Davey.

Charles Calkins · « **Reply #10 on:** 27 Jul 2005, 12:33 am »

Davey:
Yes I've got two solid state NAD218THX amps driving my Von Schweikert speakers. What I want to do is keep the NAD's to drive the woofer module and get a tube amp or two to drive the mid and treble module. V.S. says better results that way. NADS are very good for woofers but lacking in the high ends. Still confused?

Cheers
Charlie