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Old 21st April 2005, 08:32 AM   #1
Deltat is offline Deltat  United States
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Default My senior Design Project

Just thought id let you guys see my project see what you guys think. Its a subwoofer amplifier based on the Tripath TK2350 evaluation board. My power supply is +/-45Vdc. The preamp stage has a MAX260 switched cap filter which i have programmed as a 4th order butterworth(can easily change to bessel if you guys think thats better) with an adjustable cutoff frequency from 60Hz to 120Hz in 5Hz steps. Next is a PGA2311 stereo volume IC, im only using one channel of course. The gain is from -30dB to +30dB in 3dB, then 2dB then 1dB steps as the gain gets higher. All of this is adjusted with optical rotary encoders and an Atmel Mega16 micro. Also the LCD displays the volume and x-over settings.

Now the issues. I didnt buffer the signal between the Max260 and the PGA2311. I dont think the 260 is able to drive the 2311. Would that cause this rumbling i get? Its not a ground loop for when i increase the x-over i hear higher frequency noise.
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Old 21st April 2005, 08:36 AM   #2
Deltat is offline Deltat  United States
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sorry that was an old pic heres a newer one. Also i would post a schematic of my pre-amp so you guys can help me figure out whats wrong, but i dont know how to get it to fit size wise and be ledgible.
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Old 21st April 2005, 08:37 AM   #3
Deltat is offline Deltat  United States
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and here is the front
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Old 21st April 2005, 08:15 PM   #4
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Hey Deltat, that piece looks really nice!

Please post sch. we always wanna se that

Wished i could do that programming though, have some PGAs and WM8816 i would like to do something with
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Old 21st April 2005, 08:43 PM   #5
Deltat is offline Deltat  United States
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The programming was pretty easy actually. Im not a software guy, infact i HATE it.

Heres a schamatic of the pre-amp board. Ignore the power pins on the LM833. Its an 8-pin chip but i used the schemic from a lm324 since i did this on my home computer with evaluation version. Also the LP filter after the PGA2311 is to block the switching noise generated on the MAX260. With a max fclkc/fo ratio of 200 the clock frequency was in the audio range, 12k-24kHz.
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Old 21st April 2005, 10:46 PM   #6
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Default Hi

You should build an active crossover(low pass).12/db per octave is adequate for a quick experiment,this should only require a handful of parts.Substitute this for the MAX260 circuit you have.Having a clock frequency in the audio range is not good. harmonics will find their way into your output stages.I assume you looked at your signal with an 0-scope?
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Old 21st April 2005, 10:57 PM   #7
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Generally speaking, switched cap filters suck for audio. The clock that drives the capacitor switches always finds it's way into the audio. I'd replace that thing with an opamp circuit. You could put in some reed relays to switch some of the components if you must have a variable cutoff frequency.

I_F
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Old 21st April 2005, 11:08 PM   #8
jleaman is offline jleaman  Belgium
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Really nice work. Id like something like this in my pre-amp..
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Old 22nd April 2005, 12:18 AM   #9
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WOW, that is great looking.

My next project needs a display just like that.
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Old 22nd April 2005, 12:27 AM   #10
jleaman is offline jleaman  Belgium
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It looks like this is a mono amplifier ..?
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