I'm looking for some help in understanding impedance matching. I'm hoping one or more of you technically savvy electronics folks will jump in and give me a simple circuit recommendation.
Specifically I want to try to build a passive "pad" that goes between the output of a Fishman Prefix Plus built-in guitar pre-amp and the input of an IRig HD2 guitar-audio-to-usb converter. My issue is that, as it stands, I have to turn the volume control of the pre-amp as close as I can to it's minimum value (like 0.01, which is iffy), and set the gain of the Irig input hard to it's minimum value to get any kind of decent sound. Anything else results in lots of distortion. I'm trying to get a clean guitar sound.
I get the feeling that by using the extreme lowest setting on the pre-amp I am not in the sweet spot of the pre-amp design. I feel like it makes the sound tinny ... I'm always lacking bass when I use the device (compared to just plugging my guitar into the Yamaha Stagepas PA). It's just my noob idea that the amp was probably designed to be used in the middle, rather than at the extremes of its gain settings.
So, I'm thinking about making a passive "pad" that basically consists of two resistors.
input O------- R2 --------+----------------O output | R1 | ground O------------------- +----------------O ground
My basic, very limited, understanding is that such a passive pad consists of a voltage divider created by resistors R1 and R2. I really have no idea what values to use, although I sort of think their ratios should be about 9:1 where the value of R2 is about 9 times greater than the value of the "shunt" resistor "R1". Rather than just guess, I thought I would ask the community.
The specs for the devices are copied from the user manuals Here is what I see:
FISHMAN Guitar Pre-amp
Nominal Input Level: -20dBV Input Impedances: 20MOhm Output Impedance: "Less than 3.5kOhm" Nominal Output Level: -12dbV
IRIG HD2 audio-to-usb converter
Maximum Level: from 307mvpp to 8.36Vpp Gain Control Range: 28.7 dB Input Impedance (guess): 380 kOhms
I cannot find the actual input impedance specification for the IRIG HD2. There is a reference in the user manual that it is a "high-Z input". I am guessing it is simllar to the input impedance for the IRIG2 which IS specified as 380kOhms.
So, given those specs, what should be the values of R1 and R2?
Any other thoughts on what I'm trying to do here? I'd sure like to get a good sound and a feeling of control instead of a tinny sound and a pre-amp that is turned down to 0.01 ....