Converting a Cab to Stereo

[BigBazz]

The other guitarist in my band just bought a Marshall Jmp-1 Preamp and a Marshall EL84 20/20 Poweramp.

The poweramp is stereo and only stereo so we have come accross a problem, dispite the shop saying that it was fine to run just one side (left or right) without damaging the amp, the online manual said that both sides must be plugged in, if my guitarist had known this he would have gotten a mono poweramp.

His cabinet is a Peavey 5150 cabinet, 16ohm mono, single jack.

i was wondering how hard it was to convert this into stereo, to have the poweramp powering 2 speakers for each side of the poweramp (like it does through my marshall stereo cab).

I have looked for parts to do this and for guides but i dont really know what im looking for, i assume it needs a new back plate for the cab to make this work?

all i really need to achieve is to make sure that his poweramp isnt gonna blow up on him.

Edit: The cab is rated at 300w, 16ohm mono, has 1 jack input and also what looks like a cannon input, like mic-pa input, i dont know what its for.

The poweramp has a Left and Right outputs (stereo) each with a 16ohm and 8ohm output, stated that only one of them are to be used at once (either 8ohm or 16ohm)

[mammoth guitars]

Re: Converting a Cab to Stereo

I rewired a Carvin cab back in the 80's for stereo. Just added a second 1/4 inch jack in the same back plate (removed the fuse in this case but you could also drill a hole). Then wired each two speakers to each jack. Whether to wire in parallel or serial depends on the speakers. There is a simple rule:
Wiring serial adds the resistance together, ie 8ohm+8ohm=16
Wiring parallel divides by four, ie 16+16=8 (only applies when there are 2 speakers)
Match the resitance at or higher than what the power amp is rated. ie if the power amp output is 8 ohm, match it at 8 ohms or greater.

[BigBazz]

Re: Converting a Cab to Stereo

Bump!!

anyone else can help please?

[The Golden Boy]

Re: Converting a Cab to Stereo

Drill a hole large enough to install a 1/4" female jack.

Wire 2 speakers in parallel, (red wire to + connection of each speaker to the + terminal of one jack and the black wire to the - connection of each) Then do the same to the other jack and speakers.

So when you look at it, red wire to + of one speaker and + of other speaker; black wire to the - of one speaker to - of the other speaker.

That'll give you two seperate "channels" at 8 ohms a piece.

It might get goofy with some internal phase cancellation without a wall seperating each "side" of speakers.

[BigBazz]

Re: Converting a Cab to Stereo

thanks , just what i needed to know.

[ErikH]

Re: Converting a Cab to Stereo

Better yet, get a Marshall type jack plate and wire it so you can run it in stereo or mono.

[The Golden Boy]

Re: Converting a Cab to Stereo

Better yet, get a Marshall type jack plate and wire it so you can run it in stereo or mono.

Those have a slide switch or something?

[ErikH]

Re: Converting a Cab to Stereo

Those have a slide switch or something?

I think so. You get 16 ohms mono or 8 ohms stereo, split vertically. It would require cutting a square out of the back of the cab for it but worth it. The 5150 cab should've come with that panel in the first place.

EDIT: Here's an excerpt from the Extension Cabs Handbook.

"To ensure maximum flexibility, four of our 4 x 12 cabinets boast a Mono/Stereo switching system on the back. When ‘Stereo’ mode is selected, the cabinet is split into two 8 Ohm ‘halves’ for use with a stereo power amp (e.g.: EL34 100/100, EL34 50/50, EL84 20/20, 8008 or VS 120/120) such as used in a rack system. When ‘Mono’ is selected you are offered two different impedance inputs (4 Ohms or 16 Ohms) from which to choose. Always ensure you select the correct one to match the impedance of your amplifier and NEVER use both inputs at the same time when the cabinet is in ‘Mono’ mode."

[BigBazz]

Re: Converting a Cab to Stereo

I have one of those Marshall cabinets myself so i know about it, i dont know where to obtain such a back plate like on the marshall, i have looked and found nothing. Anyway thanks for the help.

[muttonchopsrule]

Re: Converting a Cab to Stereo

Those have a slide switch or something?

yes. you can run it in 8 ohms stereo, or either 16 or 4 ohms mono.

there are two inputs...when stereo is selected they're both 8 ohm inputs. when it's on mono, one input is for 4 ohms and the other is for 16 ohms.

[ErikH]

Re: Converting a Cab to Stereo

http://www.ampwares.com/ - carries them but appear to be out of stock.

http://www.mojomusicalsupply.com/cgi...e/9131210.html - looks to have it.

http://www.tubesandmore.com/ - might have them or know where to get them.

It would be worth hunting one down instead of just adding another jack, which will limit the cabinet's use. It couldn't run all 4 speakers at a 16 or 4 ohm load, it'd be stuck with two 8 ohm inputs with 2 speakers on each.

[BigBazz]

Re: Converting a Cab to Stereo

Thanks , i like it when people spoon feed me , but i honestly could not find any sites with it on :S