Hi Guys...i am building the circuit that i have supplied a link to but can't find any info about how it works, setting up or testing, so far i have built the input stage and the top filter (u1a and u1b) respectively, on feeding the input with a gorgeous sinewave, everything looks good untill the signal comes out of pin 9 where is is ringing badly? i don't know what to expect at the output, i am assuming that as the frequency changes, the voltage at the output rises and falls respectively as it does on mine, i expected a clean rising and falling D.C voltage at though instead of a peaky waveform at the Cathode of D1 though, can anyone give any insight to this circuit please?

I am aiming to be able to hook up my signal generator and sweep though 40Hz-16Khz and seeing the leds sweep through from bottom to top as the frequency rises.....or am i mistaken about what this circuit does?

Neil.

http://www.aaroncake.net/circuits/3chspec.asp

http://www.aaroncake.net/forum/topic.asp?TOPIC_ID=8847&

Neil.

 

Hi again, Neil.
I think that type of peaking filter has a bandpass that is too narrow to do what you want.
You need filters that have a flat bandpass then complementary slopes like the crossover network for a speaker.

 

Just to show you what AudioGuru is talking about, here's an AC analysis on the part of the circuit before the LED drivers.

See the attached schematic & simulation.

 

A few minutes ago, I posted this on the other website:

 

These graphs show me EXACTLY what i was seeing on the scope as i varied the input frequency, a sudden spike instead of a gradual rise and fall....you guys are so bright!!!!!

i have a couple of projects i really need to finish then i am going to sit down with a book or two and learn this stuff, is there a formulae for calculating filter frequency response?

Neil.

 

There are lots of different types of filters.

For this type of thing, you need three different types:
1) A low-pass filter for the low frequencies - everything below a certain frequency can go through.

2) A bandpass filter for the midrange frequencies - usually specified by a center frequency and a width. Everything outside the band is rejected. This consists of a high pass with a low frequency roll-off, and a low pass with a high frequency roll-off. They can be combined into one stage.

3) A high-pass filter for the high frequencies - everything below a certain frequency is attenuated.

These ranges don't have to be absolute. A Butterworth type filter will provide smooth transitions between the various frequency ranges.