Mark V speaker hookup question

[alamakluke]

Hi All,

I own a Mark V combo and right now that's all I have, the one speaker so it's plugged into the 8 OHM (Combo) 1/4 jack. I would like to add 1 2x12 Mesa Rectifier Guitar cab. This cab is 8 OHM as well right? Can I just plug the Rectifier cab into the other 8 OHM jack (right underneath) the speaker jack that I am using right now for my 1 single 12" 8 OHM speaker?

Thanks in advance
Luc

 

[Authorized Boogie]

As shown in your User Manual, 2 8ohm cabs will use the 2 4ohm jacks on the amp. Move the combo speaker to one of the 4ohm jacks, and plug the ext cab into the other 4ohm jack. Thanks!

 

[alamakluke]

Thanks for the reply. I just wanted to be clear. I should not use any of the 8ohm jacks anymore? I just want clarification don't want to damage the amp.

Thanks

 

[bandit2013]

Only if you are using two 8 ohm loads, yes you are correct.

I converted my Mark V head to a combo recently for more than just practical reasons. I can drive two 412 cabs (both being 8 ohms) but need to use the two 4 ohm jacks (combo speaker remains unplugged). When running more than one cabinet or speaker load, they will be run in parallel so divide the impedance by number of cabinets. You do not want to drive less than 4 ohms. Also, do not use the other output jacks as this will overload the OT. For simplicity, if you had two 16 ohm cabs, connect both to the 8 ohm jacks and use nothing else. Two 8 ohm loads use the 4 ohm jacks and nothing else (this would include an 8 ohm 1x12, 2x12, or 4x12 with another 8 ohm load such as the combo speaker or other). If your extension cab is 4 ohms, use only the extension cab by itself plugged into the 4 ohm jack (do not attempt to use the combo speaker in the 8 ohm jack with a 4 ohm load in the 4 ohm jack, there is one exception to this if your extension cab is 16 ohms, a safe mismatch would be to use the 8 ohm jack for the 16ohm load and the 8 ohm load in the 4 ohm jack). All of this is in the manual on speaker schemes. I typically run my Mark V combo speaker with an 8 ohm extension cab both in the 4 ohm jacks).

 

[alamakluke]

Ah yes I see the different speaker schemes now in the manual. :? Thanks to both of you for the info "When running more than one cabinet or speaker load, they will be run in parallel so divide the impedance by number of cabinets" is what made it clear for me, I understand more now. I will use both my 4ohm output jacks.

 

[dodger916]

Ah yes I see the different speaker schemes now in the manual. :? Thanks to both of you for the info "When running more than one cabinet or speaker load, they will be run in parallel so divide the impedance by number of cabinets" is what made it clear for me, I understand more now. I will use both my 4ohm output jacks.

That only works when both speakers are the same impedance. The formula is:

S1 x S2
S1 + S2

Where S1 is the impedance of Speaker 1 and S2 is the Impedance of Speaker 2. So if both are 8 ohms, it's 64 divided by 16, or 4 ohms. When running in series, simply add the impedances, or 16 ohms in the same example.

 

[alamakluke]

it's a little confusing right because both my cabinets are 8ohms. The original 12' speaker that comes with the Mark V combo amp is 8ohms so I've been using 1 8ohm speaker jack for that. Now I bought 2x12 rectifer cab, and again the cabinet is 8ohm, so i was thinking that I would just plug my cabinet into the other 8ohm jack that i have free but that's not what the manual and other are saying on the forums.

I just got my new cab and it sounds good but i thought it would be louder then that. My combo speaker sounds dead when i use 4ohm jack compared to the 8ohm jack.

 

[dodger916]

it's a little confusing right because both my cabinets are 8ohms. The original 12' speaker that comes with the Mark V combo amp is 8ohms so I've been using 1 8ohm speaker jack for that. Now I bought 2x12 rectifer cab, and again the cabinet is 8ohm, so i was thinking that I would just plug my cabinet into the other 8ohm jack that i have free but that's not what the manual and other are saying on the forums.

I just got my new cab and it sounds good but i thought it would be louder then that. My combo speaker sounds dead when i use 4ohm jack compared to the 8ohm jack.

Simple answer: plug each of the 8 ohm loads into the 4 ohm speaker outputs.

Reason: The 4 ohm speaker outputs on the amp are wired in parallel, meaning the speakers are running in parallel. To calculate the total load, use the parallel formula above, which for two 8 ohm loads results in a 4 ohm total load. So, you'll need to plug each 8 ohm load into the 4 ohm speaker outputs. I agree, I was a bit confused to first too, but when you know how the total load is calculated, it begins to make sense.

 

[alamakluke]

Thanks all for the info... I am using both 4ohm speaker jacks... let the playing begin.