20/20 in Mono

[JonStradling]

I have two marshall 4x12's that are each 8 ohm mono. My usual set up is the two cabinets hooked up to the 8 ohm outs on each side. I am wondering if there is a way to hook up just one 8 ohm cabinet while still utilizing both sides of the 20/20? Would I have to wire a switch into the cab or just make a special Y-Cable?

 

[disassembled]

You cannot put two sides of the 20/20 into 1 8ohm input because that would be like plugging a cable from the 8ohm on channel A into the 8 Ohm on channel B. The result would not be pretty and I doubt the amp would survive very long. You will have to split the cab into two different sections. I am not sure how the cab you have is wired but assuming all 4 speakers are 8ohms you could wire each side to be 4 ohms and run the cab like that. Or you can run 1 channel of the amp only to the 8ohm input of the cab but make sure you do not plug a signal into the unused side.

 

[ned]

Using 1 cab with a 20/20 is no problem. I use a Marshall 1965A (4x10) with mine. The channel you are not using you turn the volume all the way down and the presence all the way up - not sure why but this is what the manual says to do.

 

[JonStradling]

I know how to do it with one side, but then i'm not utilizing the full power of the amp. I've been researching rewiring one cabinet for mono/stereo operation but with four 8 ohm speakers the only combination I can think of is two wired in parallel on each side making a four ohm load for each side of the cabinet and plugging the mesa into each side of that via the four ohm outs, and then making a switch or cable to bring it back to mono 8 ohms, like a y cable that has a mono plug going into the mesa's 8 ohm jack and two plugs to go into each of the cab's four ohm inputs and the cable wired to series. I'm just wondering if there was an easier way

 

[spikenet]

Hi, I did a similar thing of running the 20/20 in to a "supposed" stereo quadbox. I ran it this way for a while then thought it sounded weird so checked the wiring and discovered it wasnt stero at all, both inputs were in parrallel! yikes.

So I rewired it so I have 2 x 8 ohm speakers in series for each side giving me 2x16ohm. this allows me to run the 20/20 in full stereo out of the 8 ohm outputs. I also made a small resistor pack thats 16ohm also and put that in parrallel to the speaker so its looks like 8 ohms to the amp when running at home, it reduces the volume slightly. But running 16ohm is no problems either way.

You could wire it this way and have the 2nd socket that only separates it stereo when the 2nd plug is inserted thus being 8 ohm mono or 16 ohm stereo. Depends if your happy running in series or parallel.

cheers.

 

[disassembled]

Hi, I did a similar thing of running the 20/20 in to a "supposed" stereo quadbox. I ran it this way for a while then thought it sounded weird so checked the wiring and discovered it wasnt stero at all, both inputs were in parrallel! yikes.

So I rewired it so I have 2 x 8 ohm speakers in series for each side giving me 2x16ohm. this allows me to run the 20/20 in full stereo out of the 8 ohm outputs. I also made a small resistor pack thats 16ohm also and put that in parrallel to the speaker so its looks like 8 ohms to the amp when running at home, it reduces the volume slightly. But running 16ohm is no problems either way.

You could wire it this way and have the 2nd socket that only separates it stereo when the 2nd plug is inserted thus being 8 ohm mono or 16 ohm stereo. Depends if your happy running in series or parallel.

cheers.

Take that resistor out before you destroy the resistor and then hurt the amp from not having a load. You do not need an 8ohm load in the 8 ohm jack. The manual states you can run a 16 ohm or 8 ohm load on the 8 ohm jack.

Adding resistance to speakers is not how you get proper impedance.

 

[spikenet]

disassembled, the resistor is in parrallel so even if it burnt out (which it wont) the speakers are still connected. I had a few words with Ted Webber and its the same idea as one of the products he sells used for removing speakers out of a quadbox yet maintaining the load.
cheers

 

[disassembled]

disassembled, the resistor is in parrallel so even if it burnt out (which it wont) the speakers are still connected. I had a few words with Ted Webber and its the same idea as one of the products he sells used for removing speakers out of a quadbox yet maintaining the load.
cheers

What is the wattage rating of that resistor?

 

[spikenet]

its a nest of 12x5watt resistors giving 16ohm load. so its in effect 60watt. the things dont even get warm with the amp at full tilt. Also its not taking the full power of them amp only a small portion, if it was in series then that would be different . cheers.

 

[disassembled]

Yeah well in that case it's ok. I just don't want you to confuse others in turn having someone blow up their amp by using a 1/4 watt resistor as part of the load.