Programmable Active Crossover(analog)

I have designed a Software programmable active filter(analog) .The picture shows one channel of the finished circuit.
It is a 2-way Linkwitz-Riley configuration(24dB/oct).The devices shown on the blue sockets have 4 software adjustable potentiometers inside each one,by tying the wiper to one end of the pot you create an adjustable resistor.Different crossover points are achived by changing the resistor values(software controlled),256 discrete resistor values can be programmed(approx. 100hz crossover step resolution).

I am using a "Basic Stamp"microcontroller to program the resistor values.I am using the "I2C" protocol for communication with the digital pots.The quad pots are from Analog Devices(part number is AD5263).

It is my intention to further develop this project and have some PC boards made up in the near future.I will share the details for those who have an interest in this x-over.I do not have any formal documentation at this point,my main objective was to get the prototype built and get some initial data.

My initial bench tests of the prototype are very positive,It looks like the channel balance is within .2 db between the LP/HP sections at the programmed crossover point.

All comments are welcome.

Regards Bob C.


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For Analog_SA

Hello: The design goal of any piece of audio related equipment should be that installed components should not alter the sound quality in any way.Any electronic component will always change the original signal in some way.The audibility of any distortion is what's important(IMO).

The only thing "Digital"about these pots is that their ohmic value is controlled by software commands.There is no digital conversion of the audio signal...I want to clarify this point for people not familiar with these devices.

The basic Filter circuit that was used is the Linkwitz-Riley 24dB/oct.I have built a few active crossovers using fixed value resistors in the past with excellent results,you can build an active crossover(analog) with specifications that are the equal of any commercial offering.

The basic question you are asking me is how much will the replacing of fixed value resistors with "digitally controlled" pots degrade the sound.

I can report to you that I do like the "Sound" of this crossover if it does indeed have a sound.To my ears it does not distort the sound in any way that I find objectionable.The Speakers that I am using are drivers from Parts express, RS 7-inch woofer paired with a Planar tweeter.

I should also mention that I am able to download new crossover points during live listening with no audible switching transients!..
This is extremely beneficial when you are tweaking your crossover settings.

I will update with a progress report in the near future.

Regards Bob C.