Converting 8Ohm Cab to 2Ohm

[awilkie84]

Ok...before anyone says this can't be done...YES IT CAN.
I have confirmation from Ampeg that my specific cab CAN be wired to 2Ohm, but they don't support it.

Here's what I want to do. I have an Ampeg PF-410HLF cab. 4 10" 8Ohm speakers wired in Series/Parallel. My head is a Traynor YBA-300 that runs at 4Ohm or 2Ohm output. I'd like to wire the 8Ohm cab so it matches 1 of the 2 output options. Given that the 4Ohm load can't be done without changing drivers, 2Ohm is the only way to go.

I'm not trying to "get the most" out of my head. I'm simply trying to run my Tube amp at a setting that it's built for.

Does anyone have a wiring diagram I could use?

 

[CL400Peavey]

Wire them all in parallel.

 

[will33]

Wire them all in parallel.

Yup. Start at the jack and run the positive from there to one driver, then the next, then the next, then the next. Same with the negative. No oddball connecting + to - or anything, just string them all along. Plug it into the 2ohm tap on the amp.

Remember you wired it this way if you ever use a different amp.

 

[will33]

 

[awilkie84]

Thanks

 

[Hoochie Coochie Man]

After you have wired it, and before you close up the cab, you should confirm that all the drivers are wired the same polarity by briefly connecting a nine volt battery to the input, while observing that all the cones move the same direction. Also, apply a label near the input connector that identifies the cabinet as two Ohm impedance.

 

[BassmanPaul]

Will, your wiring diagram looks a little sketchy!

 

[bassmeknik]

Sketchy but accurate, this is an easy mod just remember you did this in the future so you don't blow up an amp not designed to run 2 ohms with it. I fully support the idea of marking the cab as 2 ohms as this is an uncommon cab impedance, it is the best option in your application however...

 

[awilkie84]

Sketchy but accurate, this is an easy mod just remember you did this in the future so you don't blow up an amp not designed to run 2 ohms with it. I fully support the idea of marking the cab as 2 ohms as this is an uncommon cab impedance, it is the best option in your application however...

That's what I was thinking. The other option was to split it into 2 4Ohm cabs & run it using the stereo outputs on my head.

 

[bassmeknik]

It is my opinion that Ampeg "doesn't support it" because it makes the cab an potential amp killer for many amps where a 4 ohm cab can be hooked to almost any amp without issue a 2 ohm cab is kind of specialized and they don't want customers blowing up there new rig cause they didn't pay attention to impedance. Believe it or not many people are clueless to tech stuff and Ampeg wants to shield that group from catastrophe. How many 2 ohm cabs have you seen before? There is nothing wrong with the idea just pay attention to the impedance limits when using it, IE don't connect it to a 4 ohm amp ever.

It is the amp killer possibility that prompts the recommendation to mark the cab "2 ohms" so as to lessen the likelihood of catastrophe in the future.

 

[awilkie84]

No, they don't support it because it voids the warranty. lol
And, I will be marking the cab as 2Ohm.

I wonder what kind of switch work I'd need to make it so the cab could run at 8 OR 2 Ohm loads. lol

 

[bassmeknik]

A switch is possible, let me think about it a minute...


Anybody know this?

 

[bassmeknik]

It appears a DPDT switch will do the trick; https://www.google.com/search?q=ser...ads%2Fampeg-v4-cab-for-bass.529540%2F;800;524

 

[bassinflorida]

Probably have to be (2) four pole switches or (1) eight pole switch. Preferably a manual switches rather than relay(s) as they would require external power.
And hope 'the force is with you'

 

[bassmeknik]

Here is a suitable switch:


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A similar scheme is used for split pick-up guitars where the user can switch from series to parallel wiring with a DPDT switch...

 

[awilkie84]

It appears a DPDT switch will do the trick;

Awesome! Now, which position is which? lol I can't follow that to save my life.

 

[awilkie84]

Here is a suitable switch:


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A similar scheme is used for split pick-up guitars where the user can switch from series to parallel wiring with a DPDT switch...

But that's usually switching 2 pick-ups, not 4 speakers, though. I guess to go to 8Ohm, I'd need 2 parallel wired pairs of 10s wired together in series, right?

 

[bassmeknik]

But that's usually switching 2 pick-ups, not 4 speakers, though. I guess to go to 8Ohm, I'd need 2 parallel wired pairs of 10s wired together in series, right?

Yes, the speakers are treated as 2 parallel pairs when wiring and a DPDT switch will do it.

 

[bassmeknik]

A little knowledge of switch diagrams helps here. The diagram shows the contacts on the back of the switch but not the lever. The lever (obviously) has 2 positions one way or the other. When the lever is in the down position the switch is wired for parallel operation (relative to the drawing) and the up position corresponds with series. Since you want series parallel for 4 drivers just think of it as 2 sets of 2 drivers each set wired in parallel, now the switch just connects these 2 sets in parallel (2 ohms) or series (8 ohms).

 

[bassmeknik]

When you buy your first DPDT switch sit down with it and your ohm meter/continuity tester and figure it out. One way I remember its operation is that the set of contacts not in use (for any switch position) are the side the lever faces in all toggle/lever switches I am familiar with. (Another way to say this is the lever faces away from the set of contacts in use.) The center set of contacts alternate connection from one set of outer contacts to the other, if that makes sense. You will understand this better when you "test" the switch in your hands...