need strategies for dealing with extension cabs

[tone4days]

my brother wants to buy a new fender twin amp that has two 8-ohm speakers in it, wired in parallel, for a total load of 4 ohms ... he expects that he will want to use an extension cabinet with it ... the amp has an external speaker output that is wired in parallel with the main speaker output ... the manual indicates that the amp wants to see a total of 4 ohms and states that the only way to use both outputs at the same time is to use two external cabinets, each at 8 ohms ... this seems to say that you wont be using the two speakers in the amp at all, which seems like a tremendous waste ...

so, is there a way he can use an 2x12" external speaker cab such that he can use the 4 ohm load of the 2x12" internal speakers in parallel with the external cabinet? what impedance speakers in what configuration would work best ?

thanks
t4d

 

[jeremy]

Re: need strategies for dealing with extension cabs

not really. if you swapped the two 8 ohm speakers for 16 ohm speakers itll work, but im not sure you can run any cab with those two internal speakers and get 4 ohms.

why does he want to use a cab? for a closed back?

 

[tone4days]

Re: need strategies for dealing with extension cabs

thanks .. yeah he is joining a band with a guy that has a marshall with a 4x12" .. so he wants to use the 2X12" open back with a 2x12" closed back to be able to keep up volume-wise, but retain a different overall sound

he might have to pull the (2) 8 ohm speakers out and replace them with two 16 ohm speakers in parallel or two 4 ohm speakers in series .. and do the same for the extension cab

if he ran two 16 ohm speakers in the extension cab in series (total impedance = 32 ohms), then ran that cab in parallel with the 4 ohms of the internal speakers, it'd be a bit less than 4 ohms (32/9 ohms to be exact) ... what would the sonic effect be of that? is that doable? is it adviseable?

 

[suislidE03]

Re: need strategies for dealing with extension cabs

I have a similar scenario with my Laney.. interested in what compromise you guys come up with.

 

[tone4days]

Re: need strategies for dealing with extension cabs

bump .. any of you A.M. guys able to weigh in with some pointers?

thanks
t4d

 

[telenoiz]

Re: need strategies for dealing with extension cabs

I'm assuming the Fender Twin is like mine and has an impedence selector switch of 4,8,or 16 ohm.

What I've discovered but haven't done is to wire your 'internal' 2 (8 ohm) speakers in series. This will equate to a 16 ohms for the 'internal' 2x12.

With an external 2x12 cab also with 2 (8 ohm) speakers , wire them in series also, equating to a 16 ohm cab. Since the external output is wired parallel with the main speaker output, you will now have 8 ohms total. Set the impendence switch at 8 ohms on the amp.

If you wish to disconnect the external cab, you should switch the impendence switch to 16 ohm as your 'internal' is 16 ohm.

Here is a link for you
http://colomar.com/Shavano/2x12wiring.html

 

[Hellion]

Re: need strategies for dealing with extension cabs

I don't have a lot of experience with the Twin, but I HAVE played through them. Tubes will handle the stress of lower impedence a lot better than SS. I routinely ran my 1978 Fender 75 (kind of Fender's answer to Mesa Boogie) with a 4-5 ohm load when it clearly states that it shouldn't be less than 8 ohms. The amp just sat back and smiled. Didn't bother it at all. I don't recommend this type of experimentation, but you can find things out!

 

[tone4days]

Re: need strategies for dealing with extension cabs

thanks guys

the whole thing was overcome by events - he didnt join that band because they play too damn loud ... but interesting ideas all around

cheers
t4d