How to wire a 4x12 cabinet for 2 set of speakers??? (different ohm)

[g0ldr4k3]

Hello, I would like to make a mixed 4x12 but I just discovered that my greenbacks are 16 and the v30 are 8ohm....
how can I rewire the cabinet to ise them all?
thank you

 

[cooljuk]

You can run the two 8 ohm speakers in a series pair to make 16 Ohms, then run them in parallel with ONE of the 16 Ohm speakers so you end up with a series / parallel arrangement totaling 8 Ohms.

You could also do the opposite, running the two 16 Ohm speakers in parallel for an 8 Ohm load and run that load in series with ONE of the 8 Ohm speakers for a parallel / series arrangement totaling 16 Ohms.

In either case, you use only 3 speakers.

You can't do what you are asking using all four speakers and end up with a typical impedance load to match the OT on most amps. You can do it and end up with a weird impedance load with four speakers and deal with some other issues. Any amp manufacturer is unlikely to sanction this stuff.

You will also have to consider efficiency and volume differences of the various speakers.

Whether or not these issues and risks matter to you is highly personal.

Some may also say, if you have to ask this question - it's beyond the scope of something you should be trying. The BEST solution is likely to sell two of the speakers and buy two others that better match up.

 

[Big John]

Parallel the GB's to make an 8 ohm load for the pair.
Series the V30's to make a 16 ohm load for the pair.
Parallel the GB pair with the V30 pair to make a 5.33 ohm load.
Set the amp to 4 ohms.

 

[NotScott]

Parallel the GB's to make an 8 ohm load for the pair.
Series the V30's to make a 16 ohm load for the pair.
Parallel the GB pair with the V30 pair to make a 5.33 ohm load.
Set the amp to 4 ohms.

The other advantage to this wiring method is that it accounts for the increased efficiency of the V30s, so wiring as John suggests will also even out the levels from the different loudspeakers.

 

[cooljuk]

Parallel the GB's to make an 8 ohm load for the pair.
Series the V30's to make a 16 ohm load for the pair.
Parallel the GB pair with the V30 pair to make a 5.33 ohm load.
Set the amp to 4 ohms.

That's how I did two D120s and two T1221s in a cab, only I think I set the amp to 8 Ohms under the premise that the OT would prefer lower, rather than, higher mismatch.

I was also willing to smoke something in the name of tone and trust old Dagnal iron more than I do modern stuff.

 

[Big John]

...it accounts for the increased efficiency of the V30s...

Somebody get this man a beer.

 

[g0ldr4k3]

Parallel the GB's to make an 8 ohm load for the pair.
Series the V30's to make a 16 ohm load for the pair.
Parallel the GB pair with the V30 pair to make a 5.33 ohm load.
Set the amp to 4 ohms.

Can I use in some way at least the mono OR the stereo input in the back? do you have a diagram to follow? and....really.....thank you!

ps. consider that I run them at very low volume..now I am using a lpad attenuator to use the 4x12 at home....

 

[Big John]

I can draw it up, but what kind of mono/stereo jack plate are you talking about? Post a pic of it.

 

[Big John]

Also, let me know how you plan to configure the speakers (vertical pairs, horizontal pairs, x-pattern).

 

[g0ldr4k3]

I think to use a connector from this panel, and I would like an X pattern but I don't really know why....just a tought and I don't know a real difference other than maybe v30 lower to enhace some low frequency,....but I don't really know.
to illuminate my ignorance: why can I use a 4ohm setting to a 5.33 total impedance of the speakers? can I assume that if I use greater impedance of the speakers works ok for the amp (like 16ohm speakers with a 8ohm amp)??

thanks a lot

 

[Big John]

I was taught years ago to run the amp as close to the cab as you can, and to keep any mismatch with the amp being the smaller ohms of the two. I'll draw up a diagram for you in a bit.

IMO, you might like having the GB's across the top and the V30's across the bottom better. But there's no rules here. Experiment!

 

[Big John]

 

[NotScott]

I was taught years ago to run the amp as close to the cab as you can, and to keep any mismatch with the amp being the smaller ohms of the two. I'll draw up a diagram for you in a bit.

IMO, you might like having the GB's across the top and the V30's across the bottom better. But there's no rules here. Experiment!

Again, listen to this man!

The failure mode for mismatches is usually as follow:

Load < Amp rating - Can cause overheating of the OPT coil and failure of the OPT.

Load > Amp rating - Can cause high voltage spikes that arc across tube sockets and cause further damage.

Since you are not running a 3:1 mismatch and don't intend to dime your amp, you will be fine running it as John says.

As for speaker patterns, I hate the sound of V30s in my face. I think they can get strident. My preference would be to go with the warmer GBs on top and the brighter V30s on the bottom.

 

[Big John]

Here's with the GB's on top....

 

[g0ldr4k3]

what can I say..... THANK YOU!!!! really!
another things...I keep readying that there is no point mixing those two...why?
If I wanted to use just the 4 v30...can I use the same stock wiring? ohms?
more I learn...more I'm changing my mind!

 

[strayedstrater]

what can I say..... THANK YOU!!!! really!
another things...I keep readying that there is no point mixing those two...why?
If I wanted to use just the 4 v30...can I use the same stock wiring? ohms?
more I learn...more I'm changing my mind!

V30's are louder than greenbacks and some people assume you wouldn't really hear the greenbacks. (You will hear them to some degree but the V30's will ne most of the tone -- many people suggest putting the greenbacks at the top instead of an X pattern so you'll hear them better.)
-------------------------
You can run four 8 ohm speakers with the stock wiring, but the impedance at all the jacks will change. The "16 ohm" jack will be 8 ohms, the "4 ohm" jack will be 2 ohms, and the "8 ohm" stereo inputs will be 4 ohms each.

(There's no way to modify the wiring to give normal impedances with four 8 ohm speakers.)

 

[g0ldr4k3]

thanks for the explanation, but the original cab where I will took the v30 has [email protected] and 4 or 16 in mono....how is it cabled?

 

[strayedstrater]

thanks for the explanation, but the original cab where I will took the v30 has [email protected] and 4 or 16 in mono....how is it cabeled?

Someone must have swapped the stock 16 ohm speakers with 8 ohm speakers.

The only way a 412 can have 4/16 mono and 8 ohm stereo is with four 16 ohm speakers or four 4 ohm speakers. Cannot be done with four 8 ohm speakers.

Check that cab with a multimeter. If it has four 8 ohm speakers the jacks are 8 or 2 in mono, 4 in stereo. (Or 8 or 32 in mono and 16 in stereo if the speaker pairs are wired series instead of parallel.)

 

[Big John]

....how is it cabled?

Borrowed this from the Marshall forum....