Low Pass Filter, High, & Band (MidRange) -- Active - Page 1
Forum section: electronics / general

author: ElectronicFanatic1
author_rank: Contributor
timestamp: February 12, 2012, 10:39:26 pm
content: Does anyone know of an good ICs that will do the job as a lowpass/highpass/bandpass filter? help would be greatly appreciated.-Mitch

author: amspire
author_rank: Super Contributor
timestamp: February 12, 2012, 11:13:17 pm
content: There are a number of IC's from several manufacturers. But we need the filter specifications first, and perhaps the application. To make a suggestion, we need to know things like frequency range, input voltage level range, what supply voltages you want to use, what kind of filter performance you expect.The filter IC's are brilliant devices, they are a lot of fun to play with, but they are not perfect. They might meet your needs. They might not.Richard

author: ElectronicFanatic1
author_rank: Contributor
timestamp: February 13, 2012, 01:09:35 am
content: Mainly looking for Lowpass for a subwoofer application - Cutoff at around 200Hz .. and supply voltage anywhere from ±12 to ± 20 .. and its does have to beperfectbut itd be nice to get it as close as I could.

author: amspire
author_rank: Super Contributor
timestamp: February 13, 2012, 02:56:32 am
content: Quote from: ElectronicFanatic1 on February 13, 2012, 01:09:35 amAssuming you are looking at a filter to go before the power amplifiers, and not after, then you could use a filter IC.A good place to start is the design tools, as they often let you find the best chip. So I would start here:http://www.linear.com/designtools/software/(scroll down to Filter Simulation)http://www.national.com/en/webench/webench_filters.htmlhttp://www.maxim-ic.com/products/filters/National Semiconductors has now been purchased by TI (Texas Instruments).Of the three companies above, I would choose the first two ahead of Maxim as the supply will probably be more reliable, but Maxim do make some very nice IC's.Run the tools and get a list of IC's that will do the job. Then you can check on Digikey and Mouser to get an idea on availability and price.But I have never seen one of these IC's used in an Audio amplifier. The noise and distortion figures are often not as good as you can get with a good op-amp based circuit. They often work best with input over 1 volt RMS, and they can get pretty noisy with a quiet 1mV audio coming in. Also, the secret to a good active crossover design is a fairly constant total output as you sweep over the crossover region, and nothing very ugly happening with phase shifts. It is not a trivial design at all, even if you using IC filters.I would just do a web search for "Active crossover" schematics, and try and find a site that seems to know what it is talking about. If you find a good circuit, you can change the frequency just by changing the filter caps in inverse proportion to the frequency. So say you wanted a crossover to be 20% lower then a design that you find. You do this by making all the filter capacitors 20% LARGER.Richard

author: lowimpedance
author_rank: Super Contributor
timestamp: February 14, 2012, 01:50:49 am
content: As Richard suggested, find schematics etc so try herehttp://www.sound.au.com/index.html, has heaps of good info.John

author: NiHaoMike
author_rank: Super Contributor
timestamp: February 14, 2012, 02:55:55 am
content: Nowadays, the approach is to use a DSP. TI is the best known name in that field. They also make the best audio amplifier chips I know of, including some that interface to a DSP over I2S.

author: ejeffrey
author_rank: Super Contributor
timestamp: February 14, 2012, 10:47:15 am
content: A lot of IC filters from companies like Maxim are not really suitable for audio crossovers. They are generally switched-capacitor filters with high order and/or high Q. They are great for anti-aliasing filters used with ADCs or DACs, although they often require a cleanup analog filter to remove the clock noise. The problem is that a crossover is always used when there is some desired signal at the cutoff frequency. An excessively sharp filter will cause ringing and other weird behavior in the crossover, and be difficult to match to the high-pass conjugate feeding the main speakers. There are filter ICs that can be programmed for more suitable filters, you just have to make sure you choose correctly. Analog filters are easy to make for these frequencies: a single op-amp can make an arbitrary 2nd order section easily, and a 3rd order filter with uglier math. DSP is the most flexible and allows you to use FIR filters, although their value in an audio system is debatable.