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Old 1st July 2003, 11:31 PM   #1
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Default another noob GC up 'n' runnin'

First try! (knocking on wood). I've got my single channel running through a speaker I don't mind frying, so it doesn't sound great, but for 1/2 stereo on that speaker, it does sound pretty decent. It's been playing about an hour now. It's funny, but the heatsink (2.5 x 5 x 0.5") is hotter than the chip even at the far end of the heatsink. I have managed to keep the feedback resistor and power capacitor's lengths very short. Were there any other lengths that needed to be kept short as well? I followed the directions on the Decibel Dungeon site for the most part, but did not put the 100R and 0.22uf components between power ground star and mains ground as I did not have them. I gathered from Fedde's site that since they "sounded better with them" that they weren't essential. I'll put them in later. I haven't put the power capacitor bypass caps on yet as I saw some diagrams where they were omitted. I saw some schematics where people had put a cap across pins 1 & 4 and will try that later, but didn't do that this time either.

Questions: How long should I keep the fuses on the power rails from the supply? I'd like to start on the other channel tonight but have no more fuse holders.
I asked this above, but were there any other lengths than feedback resistor and power input capacitors that needed to be as short as possible? I have the mains switch and volume pot on the front panel while the signal inputs and mains plug are on the rear panel, which makes for a bit of wire length coming from inputs/plug to switches and then back to the chip. I'd also like to later hook up the switch on the front panel to be able to select an input source.
I am running a single 50K pot now for the volume, but will be replacing it soon with a 100K stereo pot I got from RS (hope the quality is sufficient). It is dual ganged, but in addition to the normal three connections on one side of the pot, there is an additional fourth connection on the rear. Could someone tell me what this connx is for?

thanks for the help.

Tim S

p.s. those big-*** honkin' yellow cylinders are 2.2uf caps that a local DIYer I know gave me. Said they were good quality. If size is any indication....
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Old 1st July 2003, 11:42 PM   #2
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good start on the project....maybe stand off that heatsink an inch if you can.....and becareful with those fuse holders they like to melt and are not really meant for this application...keep us posted!!!

Cheers!!The DIRT®
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Old 2nd July 2003, 12:25 AM   #3
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Getting the heatsink off the base will help, no doubt. Any recommendations on fuse holders? Also, is it internal heat that melts the fuse holder or contact with something else? I intended to order the wall mount holder from parts express and was surprised with what they sent me. I didn't know it wasn't meant for amps/audio/.... so I used it anyway. Hope I don't regret it. Anyway, I'll pull them off as soon as I can. Any Idea how long the rails should be fused before they can be assumed OK? thanks

tim s
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Old 2nd July 2003, 01:50 AM   #4
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Panel mount fuse holders are the way to go...cheap also....and saves you from tearing the cover off...but they should not blow anyways ...is the heat sink finned or is it bar stock>??..
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Old 2nd July 2003, 07:07 AM   #5
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is the black thing at the back of the picture (centre of the back of the case) the mains inlet? is so, i would use bigger wires, and i would move it away from the signal connections. if not, im a moron
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Old 2nd July 2003, 10:10 PM   #6
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yeah, that's the mains inlet. I hope that it's not a problem being so close to the signal inputs, as my woodworking tools are not great and it'll be a big pain in the **** to move something now that it's somewhat assembled. The mains inlet is about 2" away from the closest signal input. Someone please let me know if I need to do something.

No problem to beef up the wires. They're 18ga now. A local DIYer said that that would be plenty since the coils in the transformer were probably higher gauge than that. Since I will be running two transformers, I should run bigger wire. I'm just not thinking far enough ahead. oh well....

I've raised the heatsinks (aluminum bar, no fins) and they stay much cooler now. The chip has always been fairly cool to the touch.

tim s
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Old 2nd July 2003, 10:30 PM   #7
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the mains outlet should be fine, but if you have an oscilliscope (cant spell) you could check the output to see if it is amplifing 60Hz (or whatever your mains frequency is).

they look very thin (like cat5 cable) in the picture, i always use huge wire for mains connections. i just strip the outer insulation off of some mains cable (6A+ normally) and use those wires.
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Old 2nd July 2003, 10:47 PM   #8
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<they look very thin (like cat5 cable) in the picture, i always use <huge wire for mains connections. i just strip the outer insulation <off of some mains cable (6A+ normally) and use those wires.

I don't know how thin cat5 cable wires are. They are pulled from thermostat wire, but that is solid copper and I'm pretty sure that it is bigger than the cat5 wires, as I've heard of people braiding the cat wires. fat stinkin' chance braiding these. However, I'll still probably replace them with heavier gauge wire (can't hurt....but then what do I know).

I'm sure you use huge wire. Don't y'all run 220V over there?

tim s
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Old 2nd July 2003, 10:51 PM   #9
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your mains input is fine where it is......dont be afraid to run the wire longer in your cabinet to keep it away from the signal wiring....focus on that.....and if you run a second transformer 16ga would be preferable and each on its own fuse


DIRT®
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Old 3rd July 2003, 06:36 AM   #10
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Quote:
Originally posted by timsch75
&lt;they look very thin (like cat5 cable) in the picture, i always use &lt;huge wire for mains connections. i just strip the outer insulation &lt;off of some mains cable (6A+ normally) and use those wires.

I don't know how thin cat5 cable wires are. They are pulled from thermostat wire, but that is solid copper and I'm pretty sure that it is bigger than the cat5 wires, as I've heard of people braiding the cat wires. fat stinkin' chance braiding these. However, I'll still probably replace them with heavier gauge wire (can't hurt....but then what do I know).

I'm sure you use huge wire. Don't y'all run 220V over there?

tim s

cat5 is computer network cable, very thin, the conductor is less than one millimetre thin.

it just looks thin in the picture.

230-240 actually
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