Biamp question re: matching levels

ted_b · « **on:** 21 Jan 2005, 10:52 pm »

I am toying with biamping my speakers. One amp has a 28db gain, the other a 27db gain. Will this require a gain level control (neither amp has one)? Are there inline gain controls to be had? My pre has 2 sets of outputs, but that doesn't address my slight gain issues. The 27 db amp will be a bass amp. Thx,
Ted

tkp · « **Reply #1 on:** 21 Jan 2005, 10:56 pm »

Since you have VMPS speakers, you can easily adjust the midrange pods to make up for the 1 db differences between the two amps.

ted_b · « **Reply #2 on:** 21 Jan 2005, 11:05 pm »

This is actually on another pair that I'm going to demo. They don't have pot adjustments.

Thx,
Ted

Davey · « **Reply #3 on:** 22 Jan 2005, 12:57 am »

You can pad the input slightly on the 28db amp. You can either use a potentiometer or a single resistor (of the proper value) in series which will form a voltage divider with the amplifiers input resistance.

You can compute an appropriate resistor (R) as follows: (Rload is the input resistance of your amplifier.)

Attenuation (in db) = 20*log(Rload/Rload+R)

So for example....if your amplifier has an input resistance of 47k ohms you would insert a resistor of approximately 5.8k ohms to achieve a 1 db attenuation.

Cheers,

Davey.

jermmd · « **Reply #4 on:** 22 Jan 2005, 03:53 am »

What test tones would be used to adjust the pots on the RM40's? Do you use pink noise or maybe a tone around the crossover frequency?

Joe M.

ted_b · « **Reply #5 on:** 22 Jan 2005, 05:59 pm »

Quote from: jermmd

What test tones would be used to adjust the pots on the RM40's? Do you use pink noise or maybe a tone around the crossover frequency?

Joe M.

Well, I'd personally stay away from the crossover frequencies and make sure I'm well into the midrange, like 500 or 1k (xover is 166). Same with tweeter, at 12k or so (xover is 10k). There are a number of test discs that have separate bands at these frequencies.

Ted