4x12 Drop-Out problem

[kinkadornick]

Hello everyone,

I am having a minor issue with my Mesa 4x12 three-quarter back cabinet. It is one of the cabs with an 8 ohm input but also two 4 ohm inputs for "split stereo or bi-amp." There seems to be some strange volume drop outs when I'm plugged into either 4 ohm input. I wonder if this is some kind of wiring problem that could be easily fixed? It does NOT sound like a blown speaker or distortion, more like a quick fade/drop out in the volume...

Any advice would be appreciated!

 

[Eevil]

Check the jack that it connects the plug securely..

 

[guitarsawicki]

I noticed the same thing with Mark V 90 W head.I have Sundown A50 head, Boogie Mark V head, Mesa three-quarter 4x12 cabinet and Mesa 2x12 (C90/EVM12) metal grill cabinet.

Mark V 4 ohm output to left side 4 ohm input of 4x12 cabinet
A50 4 ohm output to right side 4 ohm input of 4x12 cabinet

Guitar to Mark V, fx send to Boss DC-2 Digital Dimension, output A to Mark V fx return, output B to A50 clean channel input.

Like you said, there seems to be some strange volume drop outs. Also the sound was not very good. It sounded great when:

A50 4 ohm output to 8 ohm input of 4x12 cabinet

Guitar to Mark V, fx send to Boss DC-2 Digital Dimension output B to A50 clean channel input.

4 ohm load is not the problem, because Mesa 2x12 (C90/EVM12) metal grill cabinet sounds great with Mark V and A50. So the stereo system is now two heads and two cabinets.

Mark V manual says that Boogie Mark series amps sound better with 8 ohm load. I have not noticed that.

 

[bandit2013]

I would check the connectors on the cab. Remove the 4 screws and pull the jack plate out. The 8 ohm jack has a bump switch in it. When a speaker cable is plugged into that jack, it disconnects the ground on one of the pair of speakers and connects them in series for the 8 ohm load. When the speaker plug is removed, the series connection gets broken, and the bump switch reconnects the ground to the one pair of speakers. Why I call it a bump switch, there is a inner connection on the 8 ohm jack that connects to the sleeve of the TS plug, this forces the finger to move which has a rubber bump on it to separate the contacts that maintain the ground or series connection. If there is any intermittency of the switch parts, the speaker may cut out on the one 4 ohm circuit. Not sure about the other side. Also the 4 ohm jacks use an isolation form, so the sleeve or threaded part is made of plastic. Same type of jacks you find on the amp itself. I would look inside those jacks for signs of life with a flashlight. Spiders often like to use them for some reason if they did not have the plastic plug caps. I had that issue with an amp, for some reason the one speaker jack was not working. Removed the amp chassis and used an speaker cable and found I could not get contact from the jack connections to the tip. That was because it was covered in spider guts after I smashed it when I inserted the speaker cable. I had a bug in the circuit literally.

 

[user 41014]

Hello everyone,

I am having a minor issue with my Mesa 4x12 three-quarter back cabinet. It is one of the cabs with an 8 ohm input but also two 4 ohm inputs for "split stereo or bi-amp." There seems to be some strange volume drop outs when I'm plugged into either 4 ohm input. I wonder if this is some kind of wiring problem that could be easily fixed? It does NOT sound like a blown speaker or distortion, more like a quick fade/drop out in the volume...

Any advice would be appreciated!

I have to agree with bandit if deoxit on a T/S inserted in the jacks several times doesn't help. I hope by now you figured it out.

My advice is to pass the cab over to me! I need more of these cabs after converting 1 to blues, wanting a full stack to handle a D or H Marks, while a full stack stock would be incredible for a coli.

A MS-12 loaded one would be great too.

 

[guitarsawicki]

I would check the connectors on the cab. Remove the 4 screws and pull the jack plate out. The 8 ohm jack has a bump switch in it. When a speaker cable is plugged into that jack, it disconnects the ground on one of the pair of speakers and connects them in series for the 8 ohm load. When the speaker plug is removed, the series connection gets broken, and the bump switch reconnects the ground to the one pair of speakers. Why I call it a bump switch, there is a inner connection on the 8 ohm jack that connects to the sleeve of the TS plug, this forces the finger to move which has a rubber bump on it to separate the contacts that maintain the ground or series connection. If there is any intermittency of the switch parts, the speaker may cut out on the one 4 ohm circuit. Not sure about the other side. Also the 4 ohm jacks use an isolation form, so the sleeve or threaded part is made of plastic. Same type of jacks you find on the amp itself. I would look inside those jacks for signs of life with a flashlight. Spiders often like to use them for some reason if they did not have the plastic plug caps. I had that issue with an amp, for some reason the one speaker jack was not working. Removed the amp chassis and used an speaker cable and found I could not get contact from the jack connections to the tip. That was because it was covered in spider guts after I smashed it when I inserted the speaker cable. I had a bug in the circuit literally.

I do not want to use the split mode again. Sounds like it could damage the Mark V output transformer.

 

[bandit2013]

I would send Mesa customer service an email and see what they respond with. There may be a fix we are not aware of. Perhaps a new jack assembly with new parts would be needed. Not sure if they have those as a replacement item.