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another electronics question

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NutmegCT

NutmegCT

Great Pumpkin
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sorry guys - think i'm in way over my head ...

Trying to add a simple (ha!) volume control to a 6v audio circuit.

Output is from an 8pin DIP audio amplifier chip, 400mW.

Using the output directly to the speaker (a small 8 ohm), the volume is just a tad high. I added a 5k ohm potentiometer between the chip and the speaker positive, and there's no sound whatsoever for 90% of the turning range. Last bit of turn and the volume zaps up to max very quickly.

Also tried the same using a 10k ohm pot. No difference.

How do I figure the correct size of potentiometer?

The audio amp chip is an LM386N, RadioShack # 276-1731. Vs = 6v, Rl = 8 ohm, P out = 125mw, f = 1kHz, pins 1,8 open.

Edit: Both pots are audio-taper, 5k (or 10k) ohm, .25 watt.

I know that the source impedance should normally be no greater than 1/10th (0.1) of the pot's stated resistance. Further, the load resistance or impedance should be 10 times the pot's resistance to prevent the taper from being adversely affected. But I don't know how to measure the source impedance and load impedance. Dumb me.

Thanks anyone!
Tom
 
The volume potentionmeter must installed to the input pin of your amp chip, not the output pin and speaker.

The center tab of the 10K pot should be attached to the input pin of your amp chip. The input that was attached to that amp pin is now attached to one of the outer tabs of the pot. The other outer tab of the pot is connected to ground.

Don't worry about the impedances for this type of amp.
 
How can I stop my Betamax from flashing 12:00? /bcforum/images/%%GRAEMLIN_URL%%/smile.gif
 
Don - I've done exactly as you said, trying first the negative chip input and then the positive input.

Center tab to chip input pin; line input to pot left tab; ground to pot right tab.

With either attempt, the pot has no effect at all. It's "full on" regardless of the pot setting. Does this with the 5k as well as the 10k pot. It's like it was before I added the pot. There are no extra connections, other than what I used when I added the pot.

Argh.

Tom
vping: pull the plug /bcforum/images/%%GRAEMLIN_URL%%/smile.gif
 
> ... trying first the negative chip input and then the positive input.

Use the Positive input with the Negative input connected to ground. Is that what you did?

Do you have a capacitor between the output pin and the speaker to block DC flow?
 
> How can I stop my Betamax from flashing 12:00?

Ask the guys at the store where you buy tapes for it.
 
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