# How to use an extension cab with combo amp



## mrfiftyfour (Jun 29, 2008)

Hey y'all,

I've got a Traynor YCS90 2-12 combo amp.
The speakers are wired for 8 ohms.
There is an extension cabinet jack with a 4/8 ohm switch.
What I want to do is run the speakers in the amp (open-backed 2-12) and a Marshall 1965A (closed back 4-10) cab as well.
The Marshall has been wired for 16 ohm.
Should the selector be set at 4 or 8 ohms?
Can I leave the Marshall at 16 ohms or should I change it to 8. BTW, I believe the cab came stock @ 8 ohms. Don't know why it was changed.
Can I put a Boss GE-7 between the amp jack and the Marshall cab? 
And finally, is this a good idea at all?
Anyone with experience with the 1965A, please chime in


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## GTmaker (Apr 24, 2006)

first of all you should be able to run both (open back and closed back ) cabinets.
I would first rewire the Marshall for 8 ohms...
Then the only other question realy is the 4/8 ohm switch.
You have to figure out if that switch applies to the extention cab only or the total load on the amp.
Stating the obvious, if its the extention cab then you set it to 8 ohms.
IF its the total load, then you'll have to assume that its a parallel connection and you would set it at 4 ohms.
I dont know the switch answer so someone much smarter then me will have to chime in.

What I do know is that if you have a 8 ohm cabinet and you play it with a 4 ohm cabinet, the tow cabinets see much different power distributions and to me thats not a good ballance thing. One cabinet will be much louder then the other .
HAve some fun and look at this cool interactive web page.
PLug in the parallell/series connection and the ohms ratings for cabinets and make note of the power distribution going to each cabinet.

http://www.speakerimpedance.co.uk/?act=two_parallel&page=calculator

hope this works for you

G.


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## greco (Jul 15, 2007)

mrfiftyfour said:


> Can I *put a Boss GE-7 between the amp jack and the Marshall cab? *


*I wouldn't do this!!!!!*

I would also wire the Marshall cab to 8 ohms...as GTmaker suggests.

Cheers

Dave


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## mrfiftyfour (Jun 29, 2008)

I don't know why the seller changed it to 16 ohm, perhaps he swapped out the original speakers.
I'll know more when I have a look at it


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## greco (Jul 15, 2007)

If you end up with 2 speakers at 8 ohms each, you can wire them in parallel for 4 ohms total and then use the 4 ohm switch at the amp. Correct?

Cheers

Dave


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## GTmaker (Apr 24, 2006)

greco said:


> Can I put a Boss GE-7 between the amp jack and the Marshall cab? *I wouldn't do this!!!!!*
> 
> Cheers
> Dave


hey Dave
Why are you so opposed to a little puff of smoke and a small fire...

G.


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## mrfiftyfour (Jun 29, 2008)

GTmaker said:


> hey Dave
> Why are you so opposed to a little puff of smoke and a small fire...
> 
> G.


Ok, not my brightest moment. 

"If you end up with 2 speakers at 8 ohms each, you can wire them in parallel for 4 ohms total and then use the 4 ohm switch at the amp. Correct?"

This I don't understand. The 2-12 amp is wired @ 8 ohms. The 4-10 cab is wired @ 16ohms.
How do I wire the cab for 8ohms?


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## GTmaker (Apr 24, 2006)

mrfiftyfour said:


> Ok, not my brightest moment.
> "If you end up with 2 speakers at 8 ohms each, you can wire them in parallel for 4 ohms total and then use the 4 ohm switch at the amp. Correct?"
> This I don't understand. The 2-12 amp is wired @ 8 ohms. The 4-10 cab is wired @ 16ohms.
> How do I wire the cab for 8ohms?


please understand that sometimes I just want to have a little fun.....

OK...back to business...

your #1 point is to fugure out what ohm ratings the 4/10 speakers .( I'm talking each speaker )
Lets assume they are all 8 ohms each.
simple reply is 
2 speakers in parallel = 4 ohms
the other 2 speakers in parallel = another 4 ohms...

take these 2 bundles and wire them up in series for a total of 8 ohms..

sounds complicated but its realy not...
plenty of web sites to whow you the exact wireing...
copy it down, and just follow the wires...

G.


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## greco (Jul 15, 2007)

mrfiftyfour said:


> This I don't understand. The 2-12 amp is wired @ 8 ohms. The 4-10 cab is wired @ 16ohms.
> How do I wire the cab for 8ohms?


Sorry, I didn't read carefully that you were talking about a 4 x 10 cab...my error.

You still might be able to wire the 4 x 10 cab for 4 or 8 ohms depending on the ohms/impedance ratings of *each* speaker in the cab.

Cheers

Dave


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## jb welder (Sep 14, 2010)

If the 4x10 is a 16ohm cab, then it either has 4ohm or 16ohm speakers in it. And it can only be wired to be either a 4ohm or 16ohm cab.
Check to make sure it is a 16ohm cab, it would be better if it was 8ohm, with 8ohm speakers in it.
Right now, if it's 16ohms and you run it along with the YCS speakers, the YCS speakers will get more power than the 4x10.
And you would set the switch on the amp to 4ohms. The amp switch is for the total load of all speakers connected.
In this case, the 8ohm ycs and the 16ohm 4x10 in parallel works out to about 5.3ohms, so you would set the switch on the amp to 4ohms.


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## allthumbs56 (Jul 24, 2006)

I thought the 1965A was 4 - 12s, wired 16 ohms mono and 8 ohms stereo - or is that just the newer ones?


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## jb welder (Sep 14, 2010)

You may be right, but for stereo you need 2 amps. In stereo the cab is really two 2x12 cabs at 8ohm each, with 2 separate input jacks.
So he could disconnect 2 of his speakers in the 4x12 cab and have an 8ohm 2x12.
But the new cabs with stereo option have a divider between the 2 sides.
Without the divider, a 4x12 with 2 speakers disconnected would probably not sound so good.


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