Trying to convert my amp's 4 ohm jack to 8 ohms

[Audiokill]

I have two 16 ohm cabs that I'd like to run into my C+ as a full stack. There is only one 8 ohm jack and two 4 ohm jacks on the amp, so running two 16 ohm cabs is not quite compatible - doable but not ideal. What I need to make this work is two 8 ohm jacks on the amp.

Now, looking at the inside of the amp, the first 4 ohm jack is wired in parallel to the second 4 ohm jack (the second 4 ohm jack is the one directly wired to the rest of the amp). The first 4 ohm jack only has the one lead wire connected to it, conjoining it to the second jack. If I were to disconnect that lead wire between the two 4 ohm jacks, then solder a wire between the first 4 ohm jack and the 8 ohm jack, would I then have two 8 ohm jacks?

 

[MrMarkIII]

I believe if you hook both 16 ohm cabs up to those two 4 ohm jacks, that will parallel the cabs, giving you a total load of 8 ohms.

 

[thunda1216]

If I were to disconnect that lead wire between the two 4 ohm jacks, then solder a wire between the first 4 ohm jack and the 8 ohm jack, would I then have two 8 ohm jacks?

you would have two jacks that the total load if one or both jacks are used would be 8 ohms. Do your speaker cabs only have one input jack on each? Are you not able to daisy chain one cab to the next? This would accomplish the same end result without modifying your amp.

 

[Markedman]

I don't see a problem. You can run 2 16 ohm cabs off of the 2 4 ohm outputs. Rewiring the cabs is a better option if you're concerned about it, but I wouldn't fuss. 2 4 ohm cabs would be bad news.

 

[firmani99]

If I were to disconnect that lead wire between the two 4 ohm jacks, then solder a wire between the first 4 ohm jack and the 8 ohm jack, would I then have two 8 ohm jacks?

you would have two jacks that the total load if one or both jacks are used would be 8 ohms. Do your speaker cabs only have one input jack on each? Are you not able to daisy chain one cab to the next? This would accomplish the same end result without modifying your amp.

That's what I would do is try to daisy chain the cabs. If you can't do that then maybe make a y adaptor out of some jacks and speaker wire. I wouldn't mess around with the amp.

 

[morgan138]

I don't see a problem. You can run 2 16 ohm cabs off of the 2 4 ohm outputs. Rewiring the cabs is a better option if you're concerned about it, but I wouldn't fuss. 2 4 ohm cabs would be bad news.

If you do this you're running an 8 ohm load off the amp's 4 ohm tap. I've tried it and it seems to work fine, but I don't think it's great for the tubes/amp in the long run?

I'm actually dealing with the same issue, but I'm just gonna add a parallel jack to the top cab and daisy chain them into the 8 ohm output. Seems a lot easier than messing with the amp.

 

[Audiokill]

Turns out I was right from the get go. Easiest mod in the world. Totally reversible, took only a few minutes, and cost nothing. As previously stated, one of the 4 ohm jacks (middle jack) is wired in parallel to the other (main) 4 ohm jack with a single wire. I just unsoldered it from the main 4 ohm jack and connected that end to the 8 ohm jack, effectively making two 8 ohm jacks. Relabeled the middle jack with some electrical tape to read 8 ohms. Tested everything with a voltmeter and the ohm readings are as they should be. My Mark II can safely run a Marshall full stack now. Not so scary once you know what you're doing.

Making an external Y adapter would have worked as well, but I accomplished the exact same thing, only inside the amp and without having to buy parts.

 

[morgan138]

Making an external Y adapter would have worked as well, but I accomplished the exact same thing, only inside the amp and without having to buy parts.

Nice! I fixed the same problem by adding a parallel jack to my top 2x12. It cost me one 1/4" jack I had lying around, and a couple of 2" pieces of wire, so you're JUST BARELY ahead there...

 

[kippiejr]

You can safely run 2 16 ohm cabinets out of the two 4 ohm jacks without changing anything. Or just get 2 Recto cabs and go out of the 4ohm jacks. That is what that C++ is begging for anyway.. :lol: :lol:

 

[Audiokill]

You can safely run 2 16 ohm cabinets out of the two 4 ohm jacks without changing anything. Or just get 2 Recto cabs and go out of the 4ohm jacks. That is what that C++ is begging for anyway.. :lol: :lol:

:roll: Yes, yes. As I, myself, mentioned in the original post, though it is technically safe to run two 16 ohm cabs in the amp's 4 ohm jacks, it is not ideal. The tone does indeed suffer when the impedance on the speaker load is double what it should be. No bueno.

Haven't had the pleasure of playing the ++ through recto cabs, though. Someday. However, the Marshall cabs sound better to me than anything else I've tried so far, including the Mesa Traditional and Mesa Halfback. Those Marshall Vintage speakers are tough to beat.

 

[dodger916]

I built a serial/parallel box using Radio Shack parts which will accommodate almost any combination of speaker cab impedances and amp speaker outputs. The box has two independent halves, each half with three female jacks. Two jacks are for the speaker cabs while the third jack runs from the box to the speaker out on the amp. One half of the box is wired in series, the other half in parallel. So if I need to increase impedance, I plug the speaker jacks into the series side of the box. If I need to decrease impedance, I use the parallel side. I use different amps: Mesa, Orange, Laney, Peavey, and who knows what will be next! All my speakers are 8 ohms. So if I'm using the Laney combo (Cub 12R) with one 16 ohm speaker out, I plug two 8 ohm speaker cabs into the series side of the box for 16 ohms.

It probably cost under $20 and took about an 30 minutes to solder/assemble.

 

[psychodave]

I simply move the solid wire joining the two 4 ohm jacks to the 8 ohm jack this making TWO 8 ohm output jacks. I prefer the sound of the 8 ohm jacks with no mismatch. I find using the two 4 ohm jacks a little dark and tiny bit looser.