Question on attenuating a small signal

Let me start off by apologizing since this is not concerning a guitar amp.

What I'm trying to do is find the correct potentiometer resistance to control a signal coming from the speakerphone port on a Cisco IP phone. I'm building a device for work to power some intercom speakers but the level coming out of the phone (~2-4 watts I'd guess) is overloading the "MIC" inputs on my bogen amplifier. Once I turn the volume on the phone down, it works fine--no clipping. The only problem with that is the intercom software turns the volume back up on the phone to maximum; there is no way around this.

Here is the information I know:

The speakerphone output on the phone:

• About 2 watts, no greater than 5w
• Was originally connected to 8ohm 2" speaker
• This is the signal I want to attenuate

The amplifier I'm plugging connecting the speakerphone leads to:

• Going into a Low Impedence MIC Input
• 35 Watts output to 70V horns
• Has independent Vol/Bass/Treble (if that's important)

My proposed plan was to wire:

• Speakerphone output to lug 1 of the pot
• Wire lug 2 to the terminal block on the box
• Wire lug 3 to ground

My questions:

• What resistance potentiometer do I need? Will a 10k work? Linear ok?
• Is the impendence differences going to give me problems? I know the MIC input in low impedence, will the 8ohm speakerphone output be ok?
• Am I missing anything other than just attenuating the signal with a pot?

I'm fairly handy with a soldering iron so that's no issue.

Here's a semi-crappy phone picture of the project.



Let me know if you need anything else and a big THANK YOU in advance!

Matt D

 

Thanks Skip.

The only problem with turning down the volume on the phone, is the intercom software turns the volume back up to full when it broadcasts. What I really need is a trimmer that I can set-and-forget.

I'm debating on making a radioshack trip and just picking up a variety of pots. I've got spare phone if I melt this one.

Any more thoughts?

 

Ok so I found this link: http://amps.zugster.net/articles/attenuation

I think this might be more of what I'm looking for.

Another question: Can a 1/4 or 1/2 watt resistor handle a 2-3 watt load? I would think it would melt or something.

Thanks!