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Old 1st June 2008, 11:25 PM   #1
nodiak is offline nodiak  United States
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Default Newbie chipamp questions.

I bought a gc off ebay 3 years ago, mostly used as backup amp (like now).
I've never built a gc, but think this could use a few mods. I looked inside and it uses Brians LM3875 boards, but some differences to his kits.
It has 2 outboard 10,000uF Nichicon caps. I've read this isn't necessary and maybe makes it sound slower with bass emphassis. I'm thinking of removing them. Experiences with this?
It has a 250va 25v+25v Avel toroid. I use 4-8 ohm speakers and read 20-22v is a better match. Think it's worth it to change?
It's an integrated. I use 94db speakers (Hemp FR81.0HQ) and at 9:00 it reaches very loud volume. I don't know what rating pot it uses, but is there a general rule for what pot could give me more adjustment? (I do have Alpha B10K's on hand if applicable). And, the builder wired the current pot backwards as it turns counterclockwise for louder (it's been funny for awhile but time to correct it). Do I just resolder the wires in opposite order?
I would do any changes by refering to the users guide for instructions.
Any input appreciated.
Don
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Old 1st June 2008, 11:39 PM   #2
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The potentiometer will probably be a log type one, if reverted it would give a terrible adjustement, making the volume extremely loud by only turning it a bit and then keeping almost unchanged. Is that your problem? Then you should keep the central wire the same and flip the others.

My experience tells that increased capacitance sounds better in chipamps. There is a thread about adding a snubber to compensate for the drawbacks of big capacitors, you may try it if you feel that the amplifier isn't sounding properly.
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Old 2nd June 2008, 12:29 AM   #3
nodiak is offline nodiak  United States
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ionomolo, Thanks, I'll check the snubber thread for sure.
The volume control problem is that it is at 0db when set all the way to the right, then begins getting louder as you turn it counterclockwise. It adjusts smoothly tho. I looked and the pot seems to be a 100K (says 100KAX2 on it). There are 4 wires soldered to it. I have to go out now, can try to explain more later if needed. Would smaller K rated pot give more adjustability? I'd like to use up to 9:00 or so.
Don
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Old 2nd June 2008, 12:44 AM   #4
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100K seems a bit on the high side, but it has little to do with adjustability*. There may be pots that have a wider turning angle, and that's what it seems that you are looking for. i would go for a 50K log. 20K will be ok but a bit stressing for your source.

*High impedances will make the amplifier sound quieter at intermediate positions as they form a voltage divider (which is nonlinear) and this may actually give some problems, but before buying one you should try to reverse it as log pots aren't symmetrical.
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