Question about jacks from a beginner

[samuelzero]

Hello everyone.  I have a question about what I assume to be an extremely simple modification.

I'm looking to convert a headphone jack into an external speaker output on a small practice amp.  I would like for the amp's internal speaker to be disconnected when a connector is inserted in the jack.

The patient is an Orange Crush 10, which is a tiny little 10 watt solid-state practice amp with a 6.5" speaker.  I can't quite explain why, but I love the damn thing.  The word on the street is that it they actually sound quite good through a better speaker, so I'm ordering a 1x12 cab from Avatar with a Celestion G12H30.

The Crush has a 1/4" headphone output which I never use, and I'd like to turn that into my external speaker jack. Though I'm not a master-solderer by any stretch, I can handle swapping pickups in my guits, so I'm assuming I have the necessary skills. 

It's not clear to me how I should configure the jack to allow for the internal speaker to work when no cabinet is connected.  Any thoughts?

Also, I'm aware of the inherent dangers involved with capacitors retaining deadly voltages. Would this simple mod put me in any danger? 

I appreciate any insight you can provide.

Best,

samuelzero

[nashvillebill]

Just unplug your amp and wait a few minutes, that will let the caps bleed off...if it were a higher-powered amp, I'd use a resistor to discharge the power supply caps but yours doesn't have much rail voltage, so I personally wouldn't worry about the caps discharging (for this small amp ONLY!!).

What you need is called a mono switching jack, normally closed.  There are many more complicated flavors out there, but what you need is the basic version that has 3 terminals.  One terminal is ground.  The second terminal is where you solder the wire coming FROM the amp.  The third terminal is where you solder the wire going to your internal speaker.  (Note, you'll have to check out the jack to figure out which terminal is which). When you don't have a plug in the jack, the jack makes the connection between the amp and the internal speaker.   When you plug in a plug, the plug physically moves the contacts open and the amp's output is sent into the plug instead.

[teemuk]

Personally, I wouldn't tamper with the headphone jack: It's likely a switching one already and can be converted to a speaker jack just by replacing the attenuating resistor divider with jumper wires but this still begs a question why. For instance, I bet the PCB traces that go to headphone jack are rather thin and I wouldn't trust them at conducting speaker current. The whole mod also lowers resale value and there is a serious risk that things are done poorly and the PC board gets ruined.

This can be done so much easier. (By the way, didn't we discuss this topic already some time ago? Can't you people use the search function?) Anyway... You can buy another switching jack – similar to what nashvillebill described – and fit it inline with the speaker leads. It was already explained how a switching jack works. One additional note: You should use an isolated "plastic" jack because it may be that the "ground" of the speaker should actually not be connected to ground directly (very good chance for that in modern SS amps). Mount the jack to an external metal bracket and bolt it to the amp's cabinet. When you want to use external speaker just "plug in", otherwise the combo uses its internal speaker.

See this site for inspiration:
http://www.rru.com/~meo/Guitar/Amps/Kalamazoo/Mods/speaker.html#ejack
Just ignore the fact that it discusses a tube amp. All the same, you have two wires running from the amp to the speaker. It's all that matters.

See, what an easy mod to do without even opening up the amp, figuring out the circuit design and PC board layout, removing components, and without ruining the resale value of the amp. You still have the headphone jack left and the mod is easily reversible as well.

[samuelzero]

Thanks very much to both of you for your responses.

Teemuk - sorry about making you post redundant information.  I tried a few searches, but I didn't find what I was looking for.

My reasoning on using the headphone jack is simply that it's already mounted.  I was thinking I would disconnect whatever is currently feeding it and just tape those wires off and leave them dangling inside the cabinet. Then wire the jack inline as you describe. 

Though it may make more sense to just add another jack as you suggest.

Either way, thanks again for both of your help.