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Old 30th January 2004, 12:44 AM   #1
abpea is offline abpea  United States
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Angry No Joy!

Sheeeze... I decided to put a gainclone together today using PD's scheme. It's just three resistors... how can a person mess that up.

I soldered two GCs together today and neither one made a sound. Here is a picture of what I did:

I removed pins 2,5,6,9,10,11. Soldered a 22k resistor across pins 3 and 8. I also soldered a 680R resistor to pin 8. Next I soldered a 220R resistor to pin 7 then I soldered a 22k resistor across the ends of the 220R resistor and the 680R resistor.

I hooked up an old speaker to pin 3 and to the 680R resistor. Then I attached a 12v battery to pin 1 and 4.

I'm using an MP3 player as my source.

Turn everything on and... nothing!!

Can anyone give me a pointer as to the obvious mistake (that I can't see) I'm making???

Thanks for your help -
Bruce
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Old 30th January 2004, 02:41 AM   #2
abpea is offline abpea  United States
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Here's a picture of my layout:
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File Type: jpg pic_1a.jpg (67.0 KB, 428 views)
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Old 30th January 2004, 04:38 AM   #3
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Default Re: No Joy!

Quote:
Originally posted by abpea
I attached a 12v battery to pin 1 and 4.
I'm using an MP3 player as my source.
Turn everything on and... nothing!!
Thanks for your help -
Bruce

Geeeee....... I cannot see any groundloops in the pic....
did you make them?

J-P.
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Old 30th January 2004, 04:53 AM   #4
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did you bother with the negitive rail? lol
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Old 30th January 2004, 05:04 AM   #5
abpea is offline abpea  United States
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I have two star ground points.

The first one has the two capacitors and the speaker neg wire connected together.

The second one is where the 680R, 22K and 220R resistors all meet. Then I connected the two points together with a wire.

Can't see it very well in the picture above.

This is my first p2p wiring project, always used a pcb before. Anyway, thanks for your help I appreciate your comments very much.

Should my two star ground points be connected somewhere else (another ground point) as well?
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Old 30th January 2004, 05:17 AM   #6
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Might also help if you mount the chip on a heatsink. Hint Hint.
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Old 30th January 2004, 05:47 AM   #7
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also,
you state you used a 12 volt battery. +/- 12 volts is the lower limit from what I have read. even if you had a voltage divider on the 12 volt battery, you would have had +/- 6 volts, not 12. Try 2 wall wart power supplies at the very least...

don't give up yet.
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Old 30th January 2004, 06:01 AM   #8
Alex S is offline Alex S  Singapore
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I thought the croc clip was the heatsink

Come to think of it, dunno what the other clip (the left) is gripping, so the whole thing could be shorted out
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Old 30th January 2004, 06:18 AM   #9
banana is offline banana  Hong Kong
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22K from pin3 to pin8;
680R from pin8 to ground;
220R from input to pin7;
22K from input to ground.

Is that all the resistor that you've connected?

If you are running your chip from a single 12V battery, then that is a single power supply. In this case an input cap, an output cap and most importantly a "DC bias" are necessary, somthing like the two "RA" on figure2, page5 of the spec sheet. Otherwise, your chip will always reference to the negative supply rail and would not swing AC.

Besides, LM3875 spec sheet say the mininum supply voltage is 20V, which is the mininum total DC voltage across V- and V+.
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Old 30th January 2004, 09:01 AM   #10
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Default wow, this is way out maaaaaannnnnnnn

Quote:
Originally posted by Alex S
I thought the croc clip was the heatsink

Come to think of it, dunno what the other clip (the left) is gripping, so the whole thing could be shorted out

you can see one croc holding the 3875 by it's non insulated body, so the whole grip stand is in this case ground.... and then the other croc holds something else... but what is it?

but i have to admit , your first trials look way much cooler than mine!

Jean-Pierre
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