HELP! MIXED IMPEDANCE CABS

[r0ger9]

Hi Guys,

I've stupidly found out recently that my set up might be dangerous?

I originally had a Little Mark 111 hooked to a Mark Bass 8ohm 2x10 Cab, I recently came across the chance to buy another Mark Bass 2x10 cab and a Little Mark 250 head for a decent price 2nd hand and I'd been looking for another cab so I'd have the option of running 2x10 or 4x10 so I bought them.

I've been running the LM111 outputting to the original MB 102p 2x10 and then daisying that to the other MB 102p 2x10... Only today learning that this could be very wrong and possibly dangerous? As the first cab is 8ohm and the second 4ohm. Is there a way I can run this set up? 

Any and all advice gratefully accepted, all insults grudgingly tolerated  

[BassBunny]

A 4 ohm and an 8 ohm cab together in parallel will produce 2.67 ohms resistance. The LM3 has a minimum output impedance of 4 ohms, so surprised the protection cicuitry hasn't kicked in.

The other thing is that as you are saying it "works", the 4ohm cab will have twice the output of the 8 ohm cab.

[r0ger9]

Thanks for the reply BassBunny, is parallel when both cabs are connected to the amp and is what you're suggesting?

& series is how I've got them - amp to cab and then onto next cab?the protection circuitry probably hasn't kicked in yet as I've not played it out of the house yet (currently just what next door can stand re: volume).

Would it be better to run one cab from the speakon output on the amp and the other from the jack output on the amp or should I run the output to the 4ohm cab first and then daisy that to the 8ohm cab.... or is all of this a big no no?

Edited March 8, 2018 by r0ger9

[BassBunny]

Although you have the rig wired Amp - Cab - Cab that is still a parallel arrangement. It makes no difference if you wired both back to the amp and used the speakon and jack, the result is exactly the same and a potentially damaging load on the amp.

I would just use the 4 Ohm cab until yo decide a way forward. If you want to run 2 2 x 10's, you need to sell the 4 Ohm and replace it with another 8 Ohm.

A friend of mine tried a couple of EA cabs on his Mark Bass amp not knowing they were actually 6 Ohm impedance and thus 3 Ohms when in parallel. It was a costly mistake.

[xgsjx]

You could run the 2 amps, putting the 4 ohm cab on the LM250. 

You could even take the fx send from the LMIII to the LM250 (maybe straight into the fx return on it).

[r0ger9]

6 hours ago, BassBunny said:

Although you have the rig wired Amp - Cab - Cab that is still a parallel arrangement. It makes no difference if you wired both back to the amp and used the speakon and jack, the result is exactly the same and a potentially damaging load on the amp.

I would just use the 4 Ohm cab until yo decide a way forward. If you want to run 2 2 x 10's, you need to sell the 4 Ohm and replace it with another 8 Ohm.

A friend of mine tried a couple of EA cabs on his Mark Bass amp not knowing they were actually 6 Ohm impedance and thus 3 Ohms when in parallel. It was a costly mistake.

Thanks BB, I'll take your advice...  when I've got some free time I'll take some photo's and put up on here and use to cash to finance a new 102p @ 8ohm.

[r0ger9]

2 hours ago, xgsjx said:

You could run the 2 amps, putting the 4 ohm cab on the LM250. 

You could even take the fx send from the LMIII to the LM250 (maybe straight into the fx return on it).

Cheers xgsjx, I'll try that while I'm waiting to sell the 4ohm one

[chris_b]

How often have you run both cabs together? Was it at low volume?

You don't have to sell anything. Just run 2 rigs and daisy chain them. Run an instrument lead from the send on one to the return on the other. So you'll be running the preamp in the amp your bass is plugged into and both power amp sections into their respective cabs. That will get you your extra volume from the second cab without risking any damage.

[r0ger9]

On 09/03/2018 at 07:54, chris_b said:

How often have you run both cabs together? Was it at low volume?

Yeah it was at home Chris_b, so fairly low volume (still filled the whole of downstairs with a wall of sound) - a good thing though as it it probably stopped me from causing the kind of damage that BassBunny was eluding to.

On 09/03/2018 at 07:54, chris_b said:

Run an instrument lead from the send on one to the return on the other. So you'll be running the preamp in the amp your bass is plugged into and both power amp sections into their respective cabs. That will get you your extra volume from the second cab without risking any damage.

 So I'm assuming that this is what xgsjx was suggesting but with more explanation & detail?  

Thanks for the replies fellas, appreciate it