DIY 1x15 bass cab is displaying some strange behavior, need help

[NickFaneMusic]

Hey guys, looking for some technical help with a bass cab I built.

The issue I'm having is that once the amp is wired in (using a basic mono 1/4" jack from AllParts and an Eminence Legend CB158), the tone coming through the speaker is very faint and distorted. Even stranger is when I place my finger on the banana plug on the + jack of the speaker and the end of an input cable running through the amp, the speaker creates a loud sine-wave sound that changes in pitch, seemingly randomly. The amplifier, speaker cable, internal speaker wire and speaker aren't variables, so I'm wondering if the jack I'm using is the incorrect kind, or if the one I bought is simply faulty.

I took it upon myself to do this project on my own without much wiring experience other than patching some guitar joints and learning about circuitry from an old Navy manual, so I won't be offended if you point out something totally moronic that I've done or not done. Just looking for answers. Thank you.

 

[agedhorse]

Oh, don't do that, you are coupling in phase output signal back to the input oft he amp and causing oscillation. It's a good way to damage your amp.

Is this a new driver or an old one, and can you confirm that it's in fact in good working condition?

What is the output connector on your amp?

 

[NickFaneMusic]

Oh, don't do that, you are coupling in phase output signal back to the input oft he amp and causing oscillation. It's a good way to damage your amp.

Is this a new driver or an old one, and can you confirm that it's in fact in good working condition?

What is the output connector on your amp?

That makes sense and I feel dumb for not realizing.

I've been using the Ampeg head for gigs, and when run through an Acoustic B115 I have it sounds fine. The output connector seems like a standard 1/4" jack. The amp's an Ampeg PF500 for reference. The speaker is actually used from Guitar Center but I tested another speaker that has been working with the same circuit and it had the same issues.

 

[agedhorse]

Are you sure you didn't accidentally wire from ring to sleeve rather than tip to sleeve?

You might measure the input resistance to the speaker at the jack to see if maybe you have a shorted speaker.

You will want to be very careful, these possible faults can damage an amp almost instantaneously (depending on the amp and the exact fault)

 

[NickFaneMusic]

The way I have it wired follows this diagram. Is there an additional wiring that I need to consider? I'm sorry, I'm new at this and realizing now that I bit off more than I can chew.

http://300guitars.com/wp-content/uploads/2008/03/spkr-dia-11.gif

 

[agedhorse]

Ahhh, the diagram is wrong for a start. The minus wire needs to go to the sleeve not the ring.

 

[beans-on-toast]

Just to summarize:

Your speaker cable should have a standard ¼” plug at each end. The jack on the speaker cabinet should be a standard tip and sleeve jack. There should not be a tip-ring-sleeve plug or jack in the picture. The speaker cable should be two wires, NOT a shielded instrument cable. Wiring is tip connects to tip, sleeve connects to sleeve.

Speaker [+] should connect to jack tip terminal.
Speaker [-] should connect to jack sleeve terminal.


Switchcraft 11 jack:
[Invalid or Expired Link Removed]

 

[NickFaneMusic]

Just to summarize:

Your speaker cable should have a standard ¼” plug at each end. The jack on the speaker cabinet should be a standard tip and sleeve jack. There should not be a tip-ring-sleeve plug or jack in the picture. The speaker cable should be two wires, NOT a shielded instrument cable. Wiring is tip connects to tip, sleeve connects to sleeve.

Speaker [+] should connect to jack tip terminal.
Speaker [-] should connect to jack sleeve terminal.


Switchcraft 11 jack:
[Invalid or Expired Link Removed]

Thank you for sharing the graphic, it's very helpful! I'm fairly certain that's how I've wired my rig though. It's only the two wires, correct?

 

[NickFaneMusic]

The jack I'm using is the same kind as in the graphic. Honestly I don't know the terms very well, so what's a "ring" on an input jack?

 

[beans-on-toast]

Thank you for sharing the graphic, it's very helpful! I'm fairly certain that's how I've wired my rig though. It's only the two wires, correct?

Yes only two wires.

 

[beans-on-toast]

The jack I'm using is the same kind as in the graphic. Honestly I don't know the terms very well, so what's a "ring" on an input jack?

If you look at a stereo plug, also called TRS or tip, ring, sleeve, it has three contact points. From the end you have the tip, below that, the short collar is the ring, next comes the sleeve. This allows you to connect three wires. The two black rings are insulators that separate the sections.

TRS plug

An instrument connector or a 1/4” speaker plug, also called a TS or tip speeve plug, has two wires connections. The tip at the end and the sleeve after the black insulator.


TS plug

Some people call the sleeve the ground or return connection.

The jacks are available in TRS or TS formats. A standard TS jack has two terminals like in the one in the pdf document above. A standard TRS jack has three terminals.

TS jack, two terminals, Switchcraft 11

TRS jack, three terminals, Switchcraft 12B

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I don’t want to overly complicate things but there are jacks that have little contact switches built in. The switches, also called shunts, can be either normally open or normally closed when a plug is not inserted. Inserting a plug will close or open the shunt. A jack that has a shunt has an additional terminal. So you can have a TS jack with three terminals for instance. You can have more than one shunt on a jack. They offer a number of different models with all kinds of shunting options.

TS jack with one normally closed shunt, three terminals, Switchcraft 12A

 

[NickFaneMusic]

Thank you both for your help. So if I'm to understand what you're saying, I should check to make sure I have the proper cable for the jack, as well as ensuring the proper terminals are connected of course.

 

[beans-on-toast]

Thank you both for your help. So if I'm to understand what you're saying, I should check to make sure I have the proper cable for the jack, as well as ensuring the proper terminals are connected of course.

Good cables are pretty inexpensive and made well. If you buy one, look for a speaker cable with Neutrik ¼" plugs. S

The problem with soldering one yourself is that the space between the wires is tight and chances of a short once you screw on the cover is greater. All it takes is one errant strand of wire shorting. A typical two conductor speaker cable will be stranded copper, rubber jacketed. The gauge can vary: 18ga, 16ga, 14ga are all fine. Here is one example: Invalid Link Removed

Speaker cable