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adding an extension speaker to a combo amp
Old 17th October 2013
Here for the gear

adding an extension speaker to a combo amp

Hi. I have an old StudioMaster VLM 1x12" combo amp and a speaker cabinet I built using a couple of 12" JBLs (@ 8 ohms ea).

I have blown my transformer before, so I have to believe my load is wrong. If the original speaker (Fane) is an 8 ohm, and my cabinet is showing 8 ohms, and the amp has two speaker out plugs (1/4 female)...

the question - when I plug in the ext cab (8 ohm load) and have the internal speaker plugged in also (8 ohm load) - is the amp seeing an 8 ohm load?

Is that how they wire those things?

Oh yeah, the VLM also has a switchable load (4 or 8) ohms... I've been leaving it at 4 even with the ext cab plugged in.

Okay, are there any amp guys out there? Thanks for any light you can shed.
Old 17th October 2013
Lives for gear
2 -8 ohms = 4 ohm.

However your 212 jbl cab if wired parallel is 4 ohm. If it's wired series it's 16 ohm.

Three 8 ohm speakers paralleled
8\3=2.66 ohms.

=not good for an amp designed for minimum 4 ohm load.
Old 15th February 2014
Here for the gear

Thank you VERY much - sorry to be so long getting back - it's been an... odd... couple of months.

You information is very helpful and I'll be correcting the JBL cabinet shortly.

Have a great time!
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