Need help with my MK IV

Pre Recto days. Boogie modified Fenders, Mark I-IV, Dual Calibers, etc

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Lonewolve
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Need help with my MK IV

Post by Lonewolve » Wed May 06, 2020 7:43 pm

Hello, I really need some help connecting my MK IV to two Marshall JCM 900 1960 4x12 stereo cabinets.
The MK IV has
https://drive.google.com/file/d/1gUL1u3 ... p=drivesdk

The Marshall 4x12 JCM 900 has
https://drive.google.com/file/d/1gV5nfn ... p=drivesdk

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Markedman
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Re: Need help with my MK IV

Post by Markedman » Fri May 08, 2020 8:10 am

I can't view the pictures so I'm assuming you're using 16 ohm cabinets. Use the 4 ohm outputs, one to each cabinet. Your amp will handle the slight mismatch of ohms which is not hard on your tubes. A mismatch the other way (16 ohms into 8 ohms) would still be alright but will wear out the tubes quicker.
JP2C, Mark llC++ DG, Mark IV-A/B.

Lonewolve
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Re: Need help with my MK IV

Post by Lonewolve » Fri May 08, 2020 7:01 pm

Markedman, sorry I am having a bit of trouble trying to figure out how to post pics.
The Marshall JCM 900 1960 A&B 4x12 Stereo cabinets have a switch on back , the inputs are marked 4 ohm or 16 ohm when switch is in mono.
As you already know the MK IV head has one 8 ohm jack and two 4 ohm jacks .
Question I need an answer to is can I run 4 ohm ( MK IV) TO 4 ohm ( Marshall JCM 900 ) and be ok? Or do I have to use the 16 ohm jack?

stephen sawall
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Re: Need help with my MK IV

Post by stephen sawall » Sat May 09, 2020 5:30 pm

You don't want to run into the speaker cab 4 ohms input. Two 4 ohms speakers makes a 2 ohm load. This wouldn't be good for the amp.

You want to hook the two 4 ohm Jack's on the amp to the 16 ohm connection on each speaker cab.

Two 16 ohm cabs connected this way is 8 ohm load. This is a safe mismatch. I've done it with my Mark IV for thirty years.
The fact that Stephen appears from nowhere, is sentenced to death in an emotional public trial without anyone interfering at all and is then altogether forgotten as if nothing happened, is already suspicious.

Lonewolve
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Re: Need help with my MK IV

Post by Lonewolve » Thu May 28, 2020 8:40 pm

Stephen,
My Marshall cabinets have a selector for mono / stereo and two input jacks , one input jack on the left of the selector switch ( 4 ohm ) and one input jack on the right of the selector switch ( 16 ohm ) the cabinet on mono selected runs at 300w RMS you may only use one jack in mono, with a choice of either input jack.
On the back of my Mesa/Boogie MK IV ( revA ) there are three speaker output jacks , one 8 ohm output jack , two separate 4 ohm output jacks.

stephen sawall
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Re: Need help with my MK IV

Post by stephen sawall » Sat May 30, 2020 9:25 am

I've already explained what to do.
But to make it clear....
1) Use the mono switch on both cabs
2) Use the 16 ohm jacks on both cabs
3) Use the two 4 ohm speaker outputs on the amp.


I own a Mark IV and several Marshall speaker cabs with the stereo / mono switch. I have been doing exactly this for thirty years.
Last edited by stephen sawall on Sat May 30, 2020 9:48 am, edited 1 time in total.
The fact that Stephen appears from nowhere, is sentenced to death in an emotional public trial without anyone interfering at all and is then altogether forgotten as if nothing happened, is already suspicious.

stephen sawall
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Re: Need help with my MK IV

Post by stephen sawall » Sat May 30, 2020 9:43 am

Never connect the two 4 ohm jacks on the amp to each of the 4 ohm on the speaker cabs.
When running two cabs this way it makes a 2 ohm load. The Mark IV isn't designed to run at 2 ohms.
.......................


If you want to hear the effects of a mismatch do this.

1)Use one cab only for both examples.
2)Use the mono switch on the cab.

Correct match (first example)
3)Use either 4 ohm jack on the amp.
4)Use 4 ohm jack on one cab.

Safe mismatch (second example)
3)Use 8 ohm jack on amp.
4)Use 16 ohm jack on one cab.
The fact that Stephen appears from nowhere, is sentenced to death in an emotional public trial without anyone interfering at all and is then altogether forgotten as if nothing happened, is already suspicious.

jsullivan2112
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Re: Need help with my MK IV

Post by jsullivan2112 » Mon Jun 22, 2020 5:11 pm

Won’t a bad mismatch also cause flyback voltages inside the transformer and burn it out? I’ve read and been told that it does more than just melt your tubes.
Finally a Mesa Mark owner. Noob, on here to learn as much as I can.

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Markedman
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Re: Need help with my MK IV

Post by Markedman » Mon Jun 29, 2020 10:40 pm

Set the switch on both of the Marshall cabinets to 16 ohm mono.

Plug a cable from one Mk.4 4 ohm output jack into one cabinet.

Plug another, separate cable, from the other Mk.4 4 ohm jack to your second Marshall cabinet.

2 - 4 ohm outputs from a MESA/Boogie tube amplifier, 2 speaker cables, 2 16 ohm inputs = a good, almost immeasurable mismatch that will cause no harm or excessive tube wear, for at least 30 years or more.
JP2C, Mark llC++ DG, Mark IV-A/B.

JJ Walker
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Re: Need help with my MK IV

Post by JJ Walker » Thu Jul 02, 2020 9:45 am

You could run the cabs at 4 ohms together in series and plug into 8 Ohms to get the perfect match. I run my IVa into two Peavey 2x12s sometimes, and that's how I manage it.
I have built my own series cable to do just that, but you can buy a product which does it, google: Radial CabLink Speaker Cabinet Merger.
Mesas are supposed to have overbuilt their transformers, so don't react as poorly to impedance mismatching as other amps do. As such you should not incur the same level of volume loss you would incur with a safe impedance mismatch of plugging an 8 ohms load into a 4 ohm jack, so it may not be as big of a deal as you might otherwise think.

But if you looking for a perfect match, a series cable would be the way to go.
Just be careful; if one of the cables is unplugged, the whole rig is unplugged, meaning your amp head will be running with no load (bad JooJoo). Parallel is safer; if one of the ends becomes open for some reason, the other will still provide a load.

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