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Old 10th September 2005, 03:24 PM   #1
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Default LM3875 GC Starts Today......i think

OK, OK, enough pondering and visualizing, it's time to buy hardware. The Fostex FE103E BLH's are complete. Now they beg for something to drive them.

Somebody catch me and shake me up if I'm about to go off in the wrong direction, but here's my plan:

Going to but either the LM3875 Stereo kit or the Dual Mono kit from ChipAmp.com...........any advice based on the above speakers??

Also going to buy the Snubberized Power Supply kit from same........see anything wrong with that?? Better suited option based on the above??

I'm thinking standard components for the first amp and with these speakers. Maybe get a little more exotic on the second project.

Looking at a Hammond 182P22 toroidal transformer (225VAC, 44V CT@5.11A, dual sec's 22V@10.22A)......OK....???

Somebody get me back on the pavement if I have veered off the road!!!!

Thanks in advance, because I know somebody here will give me some good advice, corrections, or "sounds good"...


Curtis
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Old 10th September 2005, 03:33 PM   #2
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I don't know crap about speakers, but your plan sounds fine to me.

If you're planning on driving a 4 ohm load, consider the LM3886 kit. I'm building a dual mono, just finished finalizing the chassis layout today. I think.

Wes
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Old 10th September 2005, 03:44 PM   #3
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The Fostex 103E are economically-priced 8-ohm speakers. They are touted as being very efficient when used in a back loaded horn design (Buschorn MkII in my case). I'm still teetering a bit on the dual mono or stereo configuration. I'll be running a CD changer, and later, a FM reciever/tuner of some sort. I'm planning on utilizing a 10K pot and rotary selector as I have no pre-amp. On this project, I'm seeking good sound, with some degree of economics in mind ( I'm in a small apartment and the room it will be in is 10'x13' vaulted ceiling, 3rd floor, neighbors all over). Reckon that 10K pot that radio shack sells (it's an Alph I believe) is worth fooling with for $2.99?


Thanks for the vote of support!

Curtis
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Old 10th September 2005, 05:20 PM   #4
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Is a 10K pot the recommended value in that circuit? I think 25K is recommended. If your pot is too large, you can get RFI. If your pot is too small, you might not get enough attenuation (amp too loud at lowest volume).

For three bucks, I'd try it, IF it was a logarithmic pot. Otherwise, the volume may get very difficult to control -- one end of th eknob will be very "busy", the other nearly useless.

If it is not a logarithmic pot, see if they have 50K linear pots. If they do, run a 50K resistor in parallel with the 50K pot. The pot will behave in a fairly logarithmic way. You can tune the resistor value to change the linearity (use excel graphing mode to help you).

I'm also quite economic-minded. I also know that there is little point in cheaping out on power supply when building an amp! So I used dual power supply boards but a single 300VA toroid. Note that I haven't actually BUILT a chip amp yet, so take my advice with a grain of salt.

Wes
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