Combo design with an external speaker jack

[kjc]

Greetings all,

First time post from an admitted novice.

I am building a combo tube amp and I wish to directly wire the internal speaker and at the same time install an external speaker jack. My goal is to have the internal speaker 'turn off' when an external speaker is plugged in.

I'm trying to create a combo/head 'combo'....

I imagine a stereo jack is involved. Can someone describe how to do this.? Maybe post a diagram.

Thanks in advance.

[Enzo]

Not "stereo" by which I assume you mean a TRS jack.

If all you want is for the external jack to kill the internal speaker it is simple. The ground will be common to both speakers. So tun a wire from ground to the negative of the internal speaker and also to the sleeve contact of the EXT jack. Now the tip contact of the EXT jack has to have the extra cutout contact. Run the hot wire from the amp to the tip contact of the EXT jack. At this point you can now plug an external speaker into the jack and it will play.

From the cutout contact of the jack, run a wire to the positive terminal if the internal speaker. The cutout contact is that extra contact that touches the tip contact of the jack when nothing is plugged in. It is the contact that is usually grounded on an input jack to keep amps quiet when no guitar is plugged in. Plug something into the jack and it lifts the tip contact away from the cutout contact. The two contacts act like a switch.

Now when nothing is plugged in, the power from the amp output flows out to the EXT jack, through the closed contacts there and on to the internal speaker. And then of course the current returns through the ground connection. The internal speaker makes sound. When you plug into the EXT jack witha speaker, now the contacts are opened so nothing gets to the internal speaker, and the current flows through the external speaker.

[kjc]

I see the light

Enzo,
Thank you for the information and the kind and detailed way it was delivered.
- KJC

[Regis]

Not "stereo" by which I assume you mean a TRS jack.

If all you want is for the external jack to kill the internal speaker it is simple. The ground will be common to both speakers. So tun a wire from ground to the negative of the internal speaker and also to the sleeve contact of the EXT jack. Now the tip contact of the EXT jack has to have the extra cutout contact. Run the hot wire from the amp to the tip contact of the EXT jack. At this point you can now plug an external speaker into the jack and it will play.

From the cutout contact of the jack, run a wire to the positive terminal if the internal speaker. The cutout contact is that extra contact that touches the tip contact of the jack when nothing is plugged in. It is the contact that is usually grounded on an input jack to keep amps quiet when no guitar is plugged in. Plug something into the jack and it lifts the tip contact away from the cutout contact. The two contacts act like a switch.

Now when nothing is plugged in, the power from the amp output flows out to the EXT jack, through the closed contacts there and on to the internal speaker. And then of course the current returns through the ground connection. The internal speaker makes sound. When you plug into the EXT jack witha speaker, now the contacts are opened so nothing gets to the internal speaker, and the current flows through the external speaker.

Enzo, I'm not understanding what kind of jack used here, is it a normal shorting jack like used for inputs, a stereo trs jack, or what? Is there a switchcraft part number?

[Enzo]

My only mention of "stereo" was to tell him that was NOT what he needed.

But you are right, i never did mention exactly what jack I want

A plain old vanilla tip shorting jack is what we need, yes.

Switchcraft? Plain old 12A, or 112A, or N112A. Basic tip cutout contact type.

Any "mono" jack with a cutout contact on the tip.

I prefer to use the Cliff type jacks. They are easier to understand visually for the novice, plus the plastic body eliminates any potential problems associated with grounding the negative side of the signal. Usually that is not a problem, but especially in solid state stuff, many amps do not return the speaker to ground. There is often a sampling resistor for feedback - like a .1 ohm 10 watt or something. Ground that and the system doesn't work right. Plastic jack solves that.