Four Jack cab stereo plate re-wriring question

[merkaba22]

I have a MB four jack stereo cab plate that I want to use with my vintage 2x12 vertical thiele MB cab -- in this instance I ant to be able to tap either 8 ohm speaker or see the normal mono output of the cab of 4 ohms.

When I check the resistance of the each "8 ohm" output I get the correct 4.7 ~ 5.0 readings for each EV -- however, when I check the resistance for the 4 ohm "In", I get 9.7 ~ 9.9 ohms.

Correct me if I am wrong, but I believe this jack plate may have been mis-wired to create a 16 ohm rather that 4 ohm input, and, if so, I would like to switch the appropriate wires to get the intended 4 ohms at the "In".

Any suggestions on how to remedy will be greatly appreciated

 

[94Tremoverb]

Yes, that does appear to be the case. It's a little tricky to follow, but it looks to me like the signal path goes:

The + (lower terminal in the 6 o'clock position) of the 4-ohm jack goes to the + of the top speaker connection (in the top pic, the bottom one if you look at it from the outside in the other pic); - of that speaker to one contact of the switch on the 4-ohm jack (the two contacts in the 8 o'clock position), then from the other contact of the switch to the + of the bottom speaker connection; the - of that speaker back to the - of the jack (upper terminal in the 6 o'clock position): this is a series connection. The Out jack is correctly wired in parallel with the 4-ohm jack.

Also make sure that none of the bare wires are touching each other - ideally they should have insulating sleeves on them to prevent that.

If that was factory wired like that, it's very bad practice and could cause a major problem.

How to wire it for 4 ohms: first connect the - terminals of all four jacks together. Then connect the + connections of the 4-ohm jack, the Out jack and *one* of the 8-ohm jacks together. Finally, connect this common + connection to the jack switch, then to the + of the remaining 8-ohm jack.

Hope that helps and you can follow it!

 

[merkaba22]

Yes, that does appear to be the case. It's a little tricky to follow, but it looks to me like the signal path goes:

The + (lower terminal in the 6 o'clock position) of the 4-ohm jack goes to the + of the top speaker connection (in the top pic, the bottom one if you look at it from the outside in the other pic); - of that speaker to one contact of the switch on the 4-ohm jack (the two contacts in the 8 o'clock position), then from the other contact of the switch to the + of the bottom speaker connection; the - of that speaker back to the - of the jack (upper terminal in the 6 o'clock position): this is a series connection. The Out jack is correctly wired in parallel with the 4-ohm jack.

Also make sure that none of the bare wires are touching each other - ideally they should have insulating sleeves on them to prevent that.

If that was factory wired like that, it's very bad practice and could cause a major problem.

How to wire it for 4 ohms: first connect the - terminals of all four jacks together. Then connect the + connections of the 4-ohm jack, the Out jack and *one* of the 8-ohm jacks together. Finally, connect this common + connection to the jack switch, then to the + of the remaining 8-ohm jack.

Hope that helps and you can follow it!

Hey thanks, I appreciate it but I was not clear about what you were indicating -- I added a new pic with numbers associated to each of the lugs -- maybe "paint by number" -- lol?

 

[94Tremoverb]

OK - what they are/do:

1 - which is actually two contacts, a/b, it doesn't matter which way round these are
2 - 4-ohm jack + connection
3 - 4-ohm jack - connection
4 - 8-ohm jack #1 + connection
5 - 8-ohm jack #1 - connection
6 - 8-ohm jack #2 - connection
7 - 8-ohm jack #2 + connection
8 - out jack - connection
9 - out jack + connection

Currently the signal path goes: 2 > 4 > speaker > 5 > 1a > 1b > 7 > speaker > 6 > 3. (Hence the '4-ohm' jack is actually a 16-ohm jack.)

What you need is to connect 3, 5, 6 and 8 all together; connect 2, 9, 7 and 1a together; and connect 1b to 4.

 

[merkaba22]

OK - what they are/do:

1 - which is actually two contacts, a/b, it doesn't matter which way round these are
2 - 4-ohm jack + connection
3 - 4-ohm jack - connection
4 - 8-ohm jack #1 + connection
5 - 8-ohm jack #1 - connection
6 - 8-ohm jack #2 - connection
7 - 8-ohm jack #2 + connection
8 - out jack - connection
9 - out jack + connection

Currently the signal path goes: 2 > 4 > speaker > 5 > 1a > 1b > 7 > speaker > 6 > 3. (Hence the '4-ohm' jack is actually a 16-ohm jack.)

What you need is to connect 3, 5, 6 and 8 all together; connect 2, 9, 7 and 1a together; and connect 1b to 4.

wow, thanks -- this looks good, may be until the weekend that I can try this out -- thanks again

 

[merkaba22]

OK - what they are/do:

1 - which is actually two contacts, a/b, it doesn't matter which way round these are
2 - 4-ohm jack + connection
3 - 4-ohm jack - connection
4 - 8-ohm jack #1 + connection
5 - 8-ohm jack #1 - connection
6 - 8-ohm jack #2 - connection
7 - 8-ohm jack #2 + connection
8 - out jack - connection
9 - out jack + connection

Currently the signal path goes: 2 > 4 > speaker > 5 > 1a > 1b > 7 > speaker > 6 > 3. (Hence the '4-ohm' jack is actually a 16-ohm jack.)

What you need is to connect 3, 5, 6 and 8 all together; connect 2, 9, 7 and 1a together; and connect 1b to 4.

Finally, had a break in things and worked on it today -- happy and grateful to say that your recommendations were right on the money -- thank you again