Series / Parallel / Mono / Stereo cabinet wiring

[Jaga]

Hello everyone!

There is a possibility to wire a cabinet with 2 speakers so that either one of the speakers can be used separately, or both or them can be used in series or parallel. Some examples can be found on this resource: www.colomar.com/Shavano/2x12wiring.html

There's a disclaimer:

WARNING: The Left and Right jacks cannot be mounted on the same metal plate (serious damage to some power amps will occur if you do this). Use a seperate jack plate for each channel, mounted on a non-conductive surface

Could someone explain what will happen if Left and Right jacks are mounted on the same plate?

Also, there is already prewired solution for the same purpose, and they use one plate for all the jacks. They have schematics like this: www.amplifiedparts.com/sites/default/files/associated_files/s-h700_plug_drawing.pdf

Am I right that their version don't have the issue which could cause damage to some amps?

[thetragichero]

so you probably *can* but that doesn't mean that you *should*
one more point of failure, one more switch position you have to check while setting up for a gig, have to get high enough wattage speakers so that you're not blowing them since you're not distributing the list, and frankly two speakers right tf next to each other aren't going to give you enough separation for stereo effects to sound good (to the audience member they sound as if they're coming from the same speaker). in situations with a mic in front of each (recording of foh support) you'll get some bleed anyway

[newey]

Nov 25, 2020 11:22:06 GMT -5 Jaga said:

Could someone explain what will happen if Left and Right jacks are mounted on the same plate?

thetragichero makes several valid points, but let me answer your question. The colomar website's scheme uses two jacks, one of which is a switched jack- the ground on the switched jack is lifted when the second plug is inserted for stereo operation. If the two jacks are mounted to the same metallic plate, the grounds may not remain properly separated, because the sleeve of the non-switched jack is not isolated, and will contact the switched jacks's frame through contact with the metal mounting plate. Once you plug the second jack fully in, the ground is switched, and so is separate from the other jack, but there is a moment before that contact is made and the jack is switched when the impedance will be wrong. Doing it once or twice probably isn't going to damage the amp, but repeatedly, over time, you could cause a problem. By using separate plates, or a non-metallic plate, the problem is alleviated as the two jacks stay fully isolated.

They advise using two separate plates and that both plates be mounted on a non-conductive surface, that way, the grounds always stay isolated.

Not sure about the other website you linked to, they just give general instructions. But using two switched jacks as opposed to one switched/one unswitched (if appropriately wired) would also solve the issue, so that may be what they're doing.

[reTrEaD]

Nov 25, 2020 11:22:06 GMT -5 Jaga said:

There's a disclaimer:

WARNING: The Left and Right jacks cannot be mounted on the same metal plate (serious damage to some power amps will occur if you do this). Use a seperate jack plate for each channel, mounted on a non-conductive surface

Could someone explain what will happen if Left and Right jacks are mounted on the same plate?

Many solid state amplifiers have outputs where neither (+) nor (-) connections are connected directly to ground. Each of the two connections has its own circuit driving it such that when one connection goes positive, the other goes negative in an equal but opposite amount.

If the (-) outputs of each channel is connected to the sleeve of a phone jack, there will be a serious problem if both sleeves are mounted on the same metal plate. Both sleeves (and in turn the (-) connection of both channels) will be tied together.

If the output for one channel isn't exactly the same as what's on the other channel, those circuits driving the two (-) connections will fight each other HARD, resulting in high current in the driving circuits and likely damage which will occur in just a moment or two.

[Jaga]

Actually I have a reason in such a setup because I'd like to use both bass and guitar speaker simultaneously but independently in home application

thetragichero, newey, reTrEaD, thanks for the explanation. So we don't want to connect grounds of several amps together.

The other website has the following schematics: www.amplifiedparts.com/sites/default/files/associated_files/s-h700_plug_drawing.pdf

And their plate looks like this

So I'm curious if it would be safe to use this jack in stereo mode considering the fact they are using metal jack sockets and the plate is metal as well. However, they specify that L+ AND L- ARE SEPARATED FROM R+ AND R- in stereo mode. Not sure how it is possible.

[thetragichero]

by using isolation washers. use em in amp builds all the time so i can control my grounding points
(note that the picture is of both a flat and shoulder but you have to buy em separately)
tubedepot.com/products/isolation-washers-for-1-4-input-jack-flat-shoulder?gclid=CjwKCAiAnvj9BRA4EiwAuUMDf96qatCrLMhO_P9a5exotdCQ6m68IgdBOzqdDCAXUl4epEIjk4K4sRoCCHoQAvD_BwE