Testing an Audio Input Jack

[Palbert]

I've been trying to build simple amplifiers and they are not working for some reason. I know my speaker is fine so I think it may be my input jack. I'm using a mono jack with leads soldered on so I was wondering how to test it to see if I am getting a signal.

 

[Triode]

If you have a plug with exposed wires you could just plug it in, touch a multimeter set to continuity test, or resistance if it doesn't have that, to one of the solder points and it should show continuity (low resistance) with one of the wires coming from the plug, and the other contact should show continuity with the other wire. If you don't have a plug with wires free stick the test probe against the back of the jack and it should show continuity with one of the contacts and the side of the jack near the front should connect with the other.

 

[Palbert]

So I should be checking the resistance between the two solder points i.e. between the ring and the tip. Or is it between one of the solder points and the end of the wire attached to that point?

 

[Triode]

Between one solder point and the wire attached to that point.

 

[Palbert]

I tried three jacks and they all showed continuity for both leads. I'm just doing a simple transistor amplifier with resistor feedback. 3907 transistor with a 10K-ohm and 470-ohm resistors. 10K on "top" of feedback chain and 470-ohm on "bottom".

 

[Palbert]

My jacks are fine because I set up an op-amp feedback system and I got sound (distorted though it may be) so I'm not sure what the deal was. Thanks though!

 

[audioguru]

I'm just doing a simple transistor amplifier with resistor feedback. 3907 transistor with a 10K-ohm and 470-ohm resistors. 10K on "top" of feedback chain and 470-ohm on "bottom".

1) A 2N3907 was an old very rare dual transistor. Maybe you used a common 2N3904 or 2N3906 transistor?
2) Your explanation of the extremely simple circuit is meaningless.
Please post the schematic and show the complete and correct part number of the transistor and the power supply voltage.

I set up an op-amp feedback system

Again, your explanation of the extremely simple circuit is meaningless.
Please post the schematic.

 

[Palbert]

Google Image Result for https://www.tpub.com/neets/book7/0071.GIF

^^ There's the link to the schematic I used. I used the resistors as mentioned before and I was in fact using a 2N3904, 8-ohm speaker, and 9v source instead of 10.

 

[audioguru]

You are shorting the output of your preamp with an 8 ohm speaker. A speaker is driven from a power amplifier, not this preamp.
If the transistor is biased properly then it should have a load of 4700 ohms (4.7K) not 8 ohms.
Your circuit is also missing an output coupling capacitor.

A transistor is never biased with a single resistor to the positive power supply because then it becomes a thermometer and every transistor will work differently. It needs some negative feedback. The bias resistor can connect to the collector instead of the positive power supply voltage. Usually the base is biased from two resistors making a voltage divider and an emitter resistor is used for negative feedback.

Your choice of wrong resistor values causes your transistor to be saturated so it does not amplify. It is turned on as hard as it can.

EDIT: Reduced the bias resistor value.