Two 4 ohm speaker and one amp

Len Amaral · Post by **Len Amaral** » 2 Apr 2021 3:40 pm

I have two separate cabs with a JBL K-130 speaker. Each speaker is 4 ohms. I can't run both speakers with one amp as that will result in a 2 ohm load.

Is there a way or a device that I can plug the speakers into then the amp to increase the ohms to operate the amp safely?

Post by **Dave Mudgett** » 2 Apr 2021 4:21 pm

That depends on what impedance the amp is looking for. What kind of amp, is it tube or solid-state, and what is the recommended impedance?

If you run the speakers in series, you'll get 8 Ohms, if that helps. With two separate cabinets, that is a little more involved than running them in parallel, and depends on how the cabs are configured. Are there two input jacks on each cab?

Len Amaral · Post by **Len Amaral** » 2 Apr 2021 5:36 pm

Hi Dave, the amp is a DV Mark 250 and 4 ohms is the lowest load you can run. Each cab has a single input. The amp has two speaker outputs so if my speakers were 8 ohms there would be no problem.

John Ducsai · Post by **John Ducsai** » 3 Apr 2021 3:43 am

Series wiring:

Post by **Dave Mudgett** » 3 Apr 2021 5:26 am

As you can see from John's diagram, you need a wire going from speaker 1 negative terminal to speaker 2 positive terminal. That is easy if the speakers are in the same cabinet - just run the wire from one terminal to the other.

But since these speakers are in different cabinets, it's a bit of a PITA, and more convenient if you have a second input jack on each cabinet. Then you can wire up a cable with a single conductor to go from the tip of the first amp output jack to the + terminal of speaker 1, and a second cable with a single conductor to go from the sleeve of the second amp output jack to the - terminal of speaker 2. Then to complete the circuit, wire up a 3rd cable to connect the - terminal of speaker 1 to the tip of the plug one one end via its 2nd input jack, and the + terminal of speaker 2 to the tip of the other via its 2nd input jack. This gives 3 separate cables you can just wire up - but you need to make sure you wire them up correctly!

Of course, this can be done without the second speaker jacks. I guess one way would be to kludge some type of hard-wire connection from one cab to the other. Blecch!

To do this with 1/4" plugs, wire a single conductor from the tip of the amp output jack to the tip of the plug going into the speaker 1 jack, and then wire the tip end of the speaker 1 jack to the + terminal of speaker 1. Now wire a second single conductor from the the - terminal of speaker 1 to the sleeve end of the speaker 1 jack. Now wire a single conductor from the sleeve of the speaker 1 plug to the tip of the speaker 2 plug, and wire the tip end of the speaker 2 jack to the + terminal of speaker 2. Finally, wire a single conductor from the - terminal of speaker 2 to the sleeve terminal of the speaker 2 jack, and then wire the sleeve of the speaker 2 plug to the sleeve of the amp output jack. This gives a single harness with 4 jacks. Blecch! I've seen people do this, but I hate it.

If I was really hell-bent to do this, I'd add a second jack to each cab - I assume they're not valuable vintage cabs. This gives 3 separate cables to run, and not a single harness. If I trusted female-to-female 1/4" connectors, one could separate the harness into 3 cables. But I don't trust them with speaker cables - I've had them fail, and this can be a showstopper.

The other thing with the DV Mark amps (I have a Ciro Manna 50 Watt head) is that you lose significant power at 8 Ohms. All the 250 Watt heads I'm familiar with give 250 Watts at 4 Ohms and 150 Watts at 8 Ohms. I guess that's not an issue with JBL K-130s, because I suspect that even 150 real Watts into the pair could blow them!

Personally, I tend to use real robust speakers for something like a 250 Watt amp. I think even 150 real Watts is pushing it for 2 JBL K-130s. These speakers are valuable and getting harder and harder to get in nice shape.

Jon Light (deceased) · Post by **Jon Light (deceased)** » 3 Apr 2021 5:39 am

Here is an patch box idea you could play with if you feel like DIY'ing it. And you can ditch the switch and hardwire it for series if you just want this single purpose use.

I haven't built this but it seems like a good idea. Remember that you want to use speaker cables, not guitar cables, for your hookups.

http://www.generalguitargadgets.com/eff ... patch-box/

Tony Prior · Post by **Tony Prior** » 3 Apr 2021 6:48 am

I use a DV Mark 50 watt Jazz and/or a 50 Watt head now and then. I spoke with DV about this exact question they replied, don't worry , the speaker outs have a protection circuit for overload and will shut the amp down if there is a problem.

I run both of mine with 8 ohm speakers along with another 8 ohm cab, bringing it all to 4 ohms. I also have 2X speaker jacks on each ext spkr cab ( parallel) should I need to run them in parallel with another amp head. Ya never know .

Plus I have not experienced any noticeable volume drop going from 4 to 8 ohms. The math says 1/2 power, my ears say, nope.

Pete Burak · Post by **Pete Burak** » 3 Apr 2021 6:52 am

I would either grab a second amphead and run the speakers in stereo, or buy a 2x12 cab with the two speakers wired in series.
Or just let it rip with one speaker cab.

Jim Kennedy · Post by **Jim Kennedy** » 3 Apr 2021 9:06 am

Webber speakers sells a 100 watt passive impedance matcher that matches any amp impedance to any speaker impedance from 2 to 16 ohms. Choose amp impedance, choose speaker impedance, and you are good to go. I have one and it works great. Currently $166 on the Webber speakers web site.

John Ducsai · Post by **John Ducsai** » 3 Apr 2021 11:38 am

Series with 2-cabs

John Ducsai · Post by **John Ducsai** » 3 Apr 2021 11:42 am

The patch box Jon Light mentions is the easiest way with what equipment you probably already own - without any modifications.

Len Amaral · Post by **Len Amaral** » 3 Apr 2021 3:28 pm

Thanks for all the recommendations and insight. I think Jon's patch box idea is the easiest way to go to use the two 4 ohm cabs with one amp to create an 8 ohm load.

Len Amaral · Post by **Len Amaral** » 4 Apr 2021 10:54 am

My cabs are Walker Stereo Steel cabs with a single input jack. I came across this duel jack plate in my parts bin and if I add a 3rd jack from the speaker out of the amp I can wire it and fit it into one cab so when I use the two cabs it will be an 8 ohm load.

John Ducsai · Post by **John Ducsai** » 4 Apr 2021 12:50 pm

Len,

If you use the jack plate you've pictured, you need to remember to isolate the 1/4" jacks with insulating washers so no metal touches the body of the jacks (including the threaded shaft) - otherwise you'll have a short. This needs to be done because of the "series" config - not needed with "parallel" wiring.
John

John Ducsai · Post by **John Ducsai** » 4 Apr 2021 12:57 pm

These will do the trick:
https://www.amazon.com/Switchcraft-Shou ... B07CS5B2W1

Ken Fox · Post by **Ken Fox** » 4 Apr 2021 3:26 pm

Switchcraft N111 jacks work well. The threaded portion is plastic thus isolating it
https://www.mouser.com/ProductDetail/Sw ... qUOA%3D%3D

Len Amaral · Post by **Len Amaral** » 4 Apr 2021 4:27 pm

John & Ken, good points on isolating the jacks. I would not have thought of that.

George Biner · Post by **George Biner** » 5 Apr 2021 7:17 am

Seems like a lot of unnecessary work. Sell the cabs and buy normal 8 ohm cabs -- you have no flexibility with 4 ohm cabs. Or buy a bruiser power amp that can operate down to 2 ohms.

Len Amaral · Post by **Len Amaral** » 5 Apr 2021 4:47 pm

George, really? Sell the 4 ohm cabs and get 8 ohm cabs or get a bruiser power amp to handle 2 ohms when for less than $10.00 and an hour or so labor I can have what will be effective and work.

Dennis Detweiler · Post by **Dennis Detweiler** » 5 Apr 2021 7:26 pm

Use a small plastic project box and add an amp input speaker jack and two speaker output jacks wired in series. It would be a permanent series box to plug into. Not switchable. Cheap fix.

Ron Pruter · Post by **Ron Pruter** » 6 Apr 2021 11:46 am

I'm thinking maybe you'll get a disappointing less output??? RP

Dennis Detweiler · Post by **Dennis Detweiler** » 6 Apr 2021 12:25 pm

I have a Quilter 201 amp. 200w rms at 4 or 8 ohm. I can run two 4ohm spkrs in series (8ohm) or a single 4 ohm.

Old amps have to have their specific ohm rating to maintain their power output. Some had switching transformers that allowed to step down and gain power (heavy amp). Years ago, I used two 8ohm 1505 BW speakers with my 1974 Session 400 and had no problem with power.

Len Amaral · Post by **Len Amaral** » 6 Apr 2021 5:05 pm

My plan is to use one 4 ohm cab for 90% of the few times I play out and two 4 ohm cabs with the splitter series box for a larger gig. I'll post a pic when I get the splitter box made with the amp/speakers hooked up.
The insulating washers are on order and due in a week. the aluminum project box was delivered today.

George Biner · Post by **George Biner** » 6 Apr 2021 6:21 pm

Len: I am older than I used to be and I just blurt my opinions out.

Dennis' external jack box is great since you already own the cabinets -- but I just think manufacturing a 4 ohm cabinet is not a good idea and is out of the mainstream simply because most stage amps can't drive 2 ohms and, unless I'm wrong, don't have series connection option to extra cabs -- I'm not a speaker designer, but most companies seem to have no trouble making 8 ohm cabinets -- and modifying the cabinets might someday lead to someone plugging into the wrong jack with hilarious consequences.

That's my take and I know that somehow your rig is gonna sing no matter what!

Dennis Detweiler · Post by **Dennis Detweiler** » 6 Apr 2021 7:08 pm

I threw together the series plastic box (size:2X3X1) tonight. It tested 7 ohms ohms with two 4 ohms in series. Plugged it into the amp and sounds great. Since the Quilter will handle a 4 and 8 ohm load and get full power, I would assume anything in between 4 and 8 ohms is sufficient.

The Steel Guitar Forum

Two 4 ohm speaker and one amp

Two 4 ohm speaker and one amp

Jacks