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Old 9th July 2003, 07:07 PM   #1
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Default Help me out, please...

Ok, i've been working this whole week on trying to get my Gainclone up and running...and i've had some successes despite many failures. Here's where i am, and the problem :

My power supply is running fine....+24V, 0, -24V


When i assemble the entire circuit, put the 10ohm resistor on the speaker outputs to measure the DC offset....i get 3mV. When i hook up an input, and speakers....no output at all.


For a while, i assumed it was my pot...so i left it completely out of the circuit when i tried assembling with entirely new parts. Still, 3mV DC offset.



Anyone have this problem?

-Maz
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Old 9th July 2003, 07:11 PM   #2
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are you sure you have it wired up correctly? have you tried a different chip? (new one)
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Old 9th July 2003, 07:13 PM   #3
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Yes...i'm using my 4th out of 5 chips i got. First one i blew up, second one the pin came off on.... third one I set up this morning, with the 3mV result. 4th one is hooked up now, and giving me the same thing.

I had hoped it was just a bum chip, and/or every other component in the circuit.....but when i built this new circuit an hour ago, it reproduced the exact same results.


as far as wiring it up correctly, i am using the giant drawn "how to wire" picture from Nuuk's website...and crosschecking my polarities and whatnot with the Peter Daniel schematic. I've quadruple checked everything...even continuity to make sure its not a cold joint or something.


-Maz
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Old 9th July 2003, 07:25 PM   #4
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Originally, i had it hooked up to a 100k pot, ...but i omitted it on this hookup to see if it was the problem. It wasn't.
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Old 9th July 2003, 08:57 PM   #5
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nothing, eh?
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Old 9th July 2003, 09:02 PM   #6
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if your certain you have everything connected to the correct pin, i cant help you much. your using LM3875? are you sure your connecting the components to the correct pins? have you checked the datasheet, not just the circuit diagram?
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Old 9th July 2003, 09:09 PM   #7
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Do I see it correctly that -24V wire is connected to signal ground? Signal ground wire doesn't sem to be connected to pin 7.

Is it aluminum plate everything is resting on?

Did you isolated both grounds and chip case from that plate?

Your input should go to pin 8, which is also connected through 220k resistor with pin 3. Pin 3 is output, pin 7 connected directly to signal ground.

V+ goes to pin 1, V- goes to pin 4. Signal ground and PS capacitors common ground connected together.

Ground to speakers output is taken from common point between caps.

You can go wrong if you do all this.
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Old 9th July 2003, 09:22 PM   #8
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Looks like to me your input ground is attached to your -24v rail.
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Old 9th July 2003, 09:24 PM   #9
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Hard to see , but like peter stated it looks like the run from pin 3 is wrong and dont bend the pins(except NC),This can break the delicate connections inside the chip.
ron
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Old 9th July 2003, 10:09 PM   #10
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Hi Magnetmaz,

Maybe it would be helpfull if you could post a list of all the pins and their quensient Voltages. This would force you to measure them again and help us to determine what's wrong. I'm pretty sure we can help you a long way if you post the list.

Regrads,
Thijs
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