How to connect 3x 8 ohms

[LPJunky]

You have to excuse me, that aspect has been covered more than once but...

I bought 2 single 12" cabs and I have a 2x12" already. All of them 8 ohms. I read the manual of course and could connect all of them if I used a series box for 2 of those and connecting in parallel with the remaining 8 omh. It would give 5.3 ohms and would be a SAFE MISMATCH in the 4 ohms output.

But I figures there's 4 connectors at the back. By looking at the schematics it's obvious that the 2 labeled 8 ohms are in parallel. Same for the 2 outputs labeled 4 ohms in parallel. The two sets come from what looks like a different tap wire from the output transformer. If I assume they are totally independent I could connect say my 2x12" in one of the 8ohms output and connect the two remaining 8 ohms single 12 "cab in both 4 ohms outputs. That is tempting is'nt it?

If it sounds acceptable then at low level I would be comfortable to run it like that but as you increase the level at which you play is there a chance to go above the transformer's rating by feeding 2 loops? As in melting the wax or something as horrifying

 

[mejoshee]

You have to excuse me, that aspect has been covered more than once but...

I bought 2 single 12" cabs and I have a 2x12" already. All of them 8 ohms. I read the manual of course and could connect all of them if I used a series box for 2 of those and connecting in parallel with the remaining 8 omh. It would give 5.3 ohms and would be a SAFE MISMATCH in the 4 ohms output.

But I figures there's 4 connectors at the back. By looking at the schematics it's obvious that the 2 labeled 8 ohms are in parallel. Same for the 2 outputs labeled 4 ohms in parallel. The two sets come from what looks like a different tap wire from the output transformer. If I assume they are totally independent I could connect say my 2x12" in one of the 8ohms output and connect the two remaining 8 ohms single 12 "cab in both 4 ohms outputs. That is tempting is'nt it?

If it sounds acceptable then at low level I would be comfortable to run it like that but as you increase the level at which you play is there a chance to go above the transformer's rating by feeding 2 loops? As in melting the wax or something as horrifying

do you need to use all 3 cabs? maybe you want more power...

the 2x12 can be rewired for series operation when you put another cab in extension, thus obviating the series box. at least if it has one of those extra jacks on it (i think every 2x12 has that from mesa?). does that make sense? then you could go on to the wiring of the #10 picture in the manual (2 in series to 8ohm output, 1 in 4ohm output). or, you could just use 2 1x12 and get more spreadable phasing for a stereo setup (the mark v does not have stereo output though).

oh and you're not feeding "loops" they're just different output taps of the output transformer secondary winding. with a safe mismatch, they should balance alright.

 

[MrMarkIII]

You should end up with a total load of 2.67 ohms.
(Three 8 ohms in parallel).

Here's a calculator for speaker impedance matching:

http://colomar.com/Shavano/impedance_proc.php

Values entered horizontally are for series connections.
Parallel connections are entered vertically.
Be sure to show all your work. This will be on the final.

 

[LPJunky]

Thanks ! The 2x12" cab is loaded in parallel with 2x16ohms so series is out.

The 5.3 ohms I quoted was the only way to get a safe mismatch from my three cabs. 2 x 8 ohms in series = 16 ohms plugged say in the top 4 ohms output and the third 8 ohms in parallel in the bottom output.

 

[thunda1216]

:roll: my head hurts...

 

[LPJunky]

Starts to look more and more like a surprise quizz. Sorry about that May be in the morning it's easier.

 

[spawnofthesith]

Soo... for the slow folks hear like myself, in simple English, is it possible to run 3x 8 ohm cabs as described in the OP with one going out of the 8 ohm, and the other two going from the 4 ohms?

 

[MrMarkIII]

Soo... for the slow folks hear like myself, in simple English, is it possible to run 3x 8 ohm cabs as described in the OP with one going out of the 8 ohm, and the other two going from the 4 ohms?

Yes.
Once again, three 8 ohm loads in parallel = 2.67 ohms, approaching the limit of "safe".
It's a bit safer to do the 5.33 ohm option as stated above. Just don't go below 2 ohms.
For example, don't run two four ohm cabs from the two four ohm jacks. That's two ohms total load.
*Danger* Will Robinson!
Any mis-match will wear out the power tubes faster, but Tweed Power will mitigate that.
Mis-matching also changes the tone. It's squishier, more compressed, less punchy, darker sounding. YMMV.

 

[LPJunky]

If you find that boring please skip...

Ok! Finally! I checked the outputs and noticed the tips (signals out) from the outputs ( 4ohms and 8ohms) were electrically connected. So we have an output transformer with a secondary winding with a tap for a 4 ohms cab, whereas the complete winding is for an 8ohms cabs. If you workout the numbers you get 3 times as much power coming out of the output winding if you connect a 4ohms load from the 4ohms output AND a 8ohms load from the 8ohms output. It would be ok only if the OT specs would permit it....

I sent a message to MESA and got an answer a week back. Fired an other and got more or less the same. It basically says that the example 7, 10 and 14 from Mesa's owner guide p-55-58 that those are the minimum loads you can have if you use both 4ohms and 8ohms outputs at the same time. So the story makes sense at last.

So I need a series box.

Here are the emails

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Hello again Stephane,
Just to reiterate: the set up in the manual is definitely the way to go. It is the safest, most effective way to run multiple cabs. The amp was not designed to run any other way. I am not sure what schematic you are looking at, since we do not make them available for current production amplifiers.

Please use the diagram from the manual to safely run your cabs.

Thanks again!


michael taylor :: product specialist

M E S A E N G I N E E R I N G

7 0 7 . 7 7 8 . 6 5 6 5 x. 3 3 2


-----Original Message-----
From: Stéphane Pilotte [mailto:[email protected]]
Sent: Thursday, May 06, 2010 12:48
To: Michael Taylor
Subject: RE: Mark V question

Thanks Michael!

I don't want you to loose time over this but I find it quite interesting to clarify this issue since it would offer even more flexibility.

>From the schematic we can see that both 4 ohms share the grounds
>(rings) and they share the tip (signals) so connecting two cabs (one in
>each 4ohms
output) is like connecting them in parallel. Same comment for the two 8ohms outputs.

The way I wish I could connect my cabs (3x 8ohms) is equivalent as if you'd connect a 4ohms cab in the 4ohms output and an 8 ohms cab in the 8ohms output. The situations most similar that are described in the manual cases 7, 10 and 14 present 3 cases of safe mismatch. Is it possible to get a CORRECT MATCH using both 4ohms and 8ohms output?

I have a technical background so any ugly details would help. What are the ratings of the output transformer?

Sorry to get back at ya!

Love the amp! Wouldn't want to hurt it!

Regards,

Stéphane


-----Message d'origine-----
De : Michael Taylor [mailto:[email protected]] Envoyé : mai 04 2010 20:52 À : [email protected] Objet : RE: Mark V question

Hello there,
thanks for your email.
You want to run it the way the manual says to do (series box) Running them the other way will result in damage to your Power tubes & your transformer, which will not be covered under warranty.

Hope this helps.
If you have any further questions, please call us here at the factory at
707-778-6565 Monday - Thursday 9-5 PST.

Thanks for your interest in MESA!



michael taylor :: product specialist

M E S A E N G I N E E R I N G

7 0 7 . 7 7 8 . 6 5 6 5 x. 3 3 2



-----Original Message-----
From: Stéphane Pilotte [mailto:[email protected]]
Sent: Tuesday, April 20, 2010 8:41 AM
To: info
Subject: Mark V question

Need help with Mark V speaker outputs!

I bought 2 single 12" cabs and I have a 2x12" already. All of them 8 ohms. I read the manual of course and could connect all of them if I used a series box for 2 of those and connecting in parallel with the remaining 8 omh. It would give 5.3 ohms and would be a SAFE MISMATCH in the 4 ohms output.

But I figures there's 4 connectors at the back. By looking at the schematics it's obvious that the 2 labeled 8 ohms are in parallel. Same for the 2 outputs labeled 4 ohms in parallel. The two sets come from what looks like a different tap wire from the output transformer. If I assume they are totally independent I could connect say my 2x12" in one of the 8ohms output and connect the two remaining 8 ohms single 12 "cab in both 4 ohms outputs. That is tempting is'nt it? Is it safe to run this at full power?

Thank you,

Stéphane


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