| downhere |
I've gotten the Powersupply working giving me a steady +-25V, but when I connected the amp to the powersupply, and switched on the thing with a 10ohms resistor on the outputs, it combusted rather spectacularly.
However my DMM only showed 0.1 or 0.2V of difference, right before it blew up. What could possibly be wrong with the circuit? Any connections I should double check?
Should I cut off all the unused pins right to the edge? I left 2mm sticking out.
Thanks in advance! The chip LM3875 looked fine tho, didn't get warm or anything. |
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| li_gangyi |
| wad was the wattage of the 10R resistor?? |
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| downhere |
| Quarter watt... which was what I had lying around. |
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| li_gangyi |
| which is also why it blew...you gotta use high wattage resistors here...I'll bet ur amp is doing fine... |
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| downhere |
| Ah thanks... I might sacrifice one of the extra speakers I have lying around instead then. Would that be ok in place of a proper high wattage resistor? The only one I have is a 120R one. Simlim tower's a little to far away for me today. |
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| li_gangyi |
hey~!! You're from Singapore as well?? Well guess what...you could try a mail order company if you really wanted to..like RS and farnell
www.rscomp.com.sg
and
www.farnell.com (choose Singapore)
if you're really lazy and dun wanna spend 7 bux for the shipping...just use a junk speaker...I could lend one of mine to u... |
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| downhere |
Haha yeah I am... I didn't know we had mail order in Singapore. :) Guess I'll start buying things again.
Using the innards from an altec lansing computer speaker set. ACS48. They've got an 80VA toroid inside and a nice little powersupply section that i just snapped off the PCB. Works fine.
I'll try the junk speakers later. :) Thanks for the help! |
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| li_gangyi |
| yeah...guess u could've got better trafo's instead...how does it sound?? and some pics of course~!!! |
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| downhere |
Nope amp didn't work. I got +18V DC at the outputs, 12V AC. + a humming sound. Any ideas as to what I've connected wrongly? I'm going through the schematic now again.
Is this oscillation? Do I need to put the caps even closer? Which caps in particular? |
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| li_gangyi |
| can u lemmi see the schmatic u used?? izzit inverted or non...and wad kinda value caps did u use for decoupling?? any input cap? |
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| downhere |
Used the gainclone from here.
http://www.euronet.nl/~mgw/diy/amps...3875_schema.jpg
Used paralleled caps .1uf caps for the .22uf cap, cos I didn't have one lying around, a carbon resistor at 21.5k and 1k metal film for the feedback bits, and 47uF cap instead of the 22uF cap.
other than that, all per schematic. I didn't differentiate between signal ground and power supply ground tho. Just connected them all to one star point.
Inputs were +-25V as stated before, cos the other trans I had was +-40 and I wanted to test the amp first.
No input cap. I didn't connect the input to anything.
All ECs are the right way, nothing's touching, 1000uF caps are abt 1.5 cm away from the power pins.I'm going to wrap all the pins with electrical tape next to make sure nothing's touching AT All.
Are you interested in getting resistors and capacitors? I need to get a collection of them so I can build more of these amps, like 50 of the most commonly used values. They're rather easy to put together, and I'm working on a step by step way to solder all 9 components for a little surround sound amp. I can break the order up and mail the parts to you.
The speaker is 6ohms. And I'm not sure why I'm getting AC and DC at high voltages. |
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| li_gangyi |
| okie..first off...you need to have tt 22k or else it will have a DC offset..next is to check if the power supply is present on bothrails...tell me when u're done with these 2...must be a pretty simple problem...and try it without the zobel (R3 and C2 on the outputs) |
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| downhere |
I feel like an idiot. I went to order more samples of the 3875 for more tries, then found that the chip I had was the 3876!!!
Wrong pins. I should have connected it to the pins 9&10. I'll go get more parts and fix it... Sheesh. |
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| li_gangyi |
| if you want any of those chips...tell me I can mail a pre-soldered part with almost all the stuuf for ya... |
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