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Old 1st July 2005, 06:56 AM   #1
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Default freq. responce help on mini amp

heres my amp:

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Click the image to open in full size.


I built it so I'd have something portable, that I could take with me somewhere and plug into some floor speakers ( or small more portable bookshelf speakers)

Its based on the TDA7264 chip by ST. I adapted it for single supply operation and am useing 32 volts to run it ( regulated printer power supply) I've noticed that without a lot of bass boost ( I have to use my computer's EQ and boost the bass in volume controll ) the chip says its power bandwidth is from 20hz-20 khz. How come my lack of bass? I notice that on some really low notes you will see the woofers moving, but no gutteral sound will be made. I'm running it through my marantz sp1200's, when I use my fisher amp and its doing only 5 watts you can feel that bass. ( the amp has a power meter on it so I can see where it peaks and rms's out) Would an op-amp fix my bass problem on this amp, or does the chip really stink that bad? Also, since my power supply is only 940 ma, could it be a lack of amperage thats causeing the bass rolloff? what about my input caps? their the reccomended 1uf 50 volt caps ( I found very small ones ) ? could it be my output dc decoupling caps? their 470 uf 25 volt, should they be bigger? can the pot affect frequency responce at all? any help would be greatly appreciated! thanks!
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Old 1st July 2005, 07:16 AM   #2
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... would help to drop the schematics...

Yes, could be that your dc-coupling cap is too small or lower quality...

mic
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Old 1st July 2005, 05:59 PM   #3
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http://www.st.com/stonline/books/pdf/docs/4541.pdf

I also ordered this chip, Its basicly the same accept the gain is adjusted externally. See page 2 of 9, it shows the schematic for single supply operation, thats how I adapted this one. ( obviously minus the gain resistors, and I didnt include the mute circuit on my amp, their the same though.)

http://www.futurlec.com/Philips/TDA7264.shtml

heres my chip. Retards, they list it as a philips...its made by ST, haha.

so what do you mean by dropping the schematic..listing the links here for you to see or just going at it without one

Hmm.. Ill try the output caps, what value would you reccomend I replace them with?
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Old 1st July 2005, 11:15 PM   #4
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Click the image to open in full size.

heres the circuit board, the output caps are right behind the connector on the board, the yellow wire is right and white is left ( denoting which cap is left/right) their 470 uf 25 volt. Should I use larger caps? because these are substituted from the other schematic.. maybe 1000 uf? what voltage would they have to be for 25 watts ?
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Old 2nd July 2005, 02:53 AM   #5
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I read a few application notes. It looks like c9 and c10 are 10x small than they should be or usually are.

Play it safe go with 50volts
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Old 2nd July 2005, 03:45 AM   #6
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ok. Yeah, my filter cap is 1000 uf 35 volt, I have a 50 volt one I'm gonna use instead. wow.. so do you think 22 uf would suffice for output caps?
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Old 2nd July 2005, 10:47 AM   #7
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Quote:
Originally posted by ThSpeakerDude88
ok. Yeah, my filter cap is 1000 uf 35 volt, I have a 50 volt one I'm gonna use instead. wow.. so do you think 22 uf would suffice for output caps?

The 1000uf 35volt cap should be OK. You need to change c9 and c10 to around 4700uf.
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Old 2nd July 2005, 11:28 AM   #8
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Quote:
Originally posted by ThSpeakerDude88
so do you think 22 uf would suffice for output caps?

By output caps do you mean c9 and c10 on the application notes. If you do 22uf is much to small. Incease from 470uf to 4700uf
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Old 2nd July 2005, 11:34 AM   #9
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oh ok! Well, I have to replace the filter cap too, I plan on running my amp at over 35 volts ( up to 40 with a saftey tolerance) and right now I'm running it at 32 volts, so I dont have much of a headroom. Ill try the 4700 uf. Hey by the way, I have 2 caps in my capacitors box ( I desolder tons of componenets and use them again) Their 4700uf 25 volt, short and big modules that came off of a JBL pro amp. The thing is I dented the cans while getting them off ( I pried against each other with a screw driver...yes this was before I knew as much about electronics, the only reason I took apart that amp was because I learned a harsh lesson on proper bridging of an amp...) anyways, the caps seem to be fine otherwise. Think they'll do for now?
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Old 2nd July 2005, 11:49 AM   #10
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I wouldnt use anything less than supply voltage. You can test one channel with the 4700uf caps. You have by running them in series,that will gave you 2350uf 50volts. If you get more bass in one channel,it the output caps.
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