Speaker ohms question.

[Duffy]

Simple question that I always want to get right before I hook up an amp to a multiple speaker cabinet.

I have a Crate V32 212 Palomino that I want to use as an extension speaker cabinet for a couple of my fender eight ohm amps. The V32 has a jack on the back labelled "8 ohm speaker" into which a quarter inch plug from the twin 16 ohms each Celestion speakers is plugged in.

Because the stock/factory jack is labelled "8 ohms" I am thinking that the two sixteen ohm speakers are wired to equal an 8 ohm load, and, therefore I should be able to unplug the quarter inch jack coming from the speakers and plug it into a coupler, and then plug a speaker cable between the coupler and one of my Fender tube amps (HRDX, SCXD) that recommend connecting 8 ohm extension speakers.

This will, I think, allow me to use the Crate V32 212 Palomino as an extension speaker cabinet. The Crate amp, obviously, would be turned off and not connected to the speakers in its cabinet. To be safe I will put a piece of duct tape over the on switch on the Crate.

Am I correct in thinking that this extension speaker wiring scheme will be appropriate for use with the Fender amp?

The simple answer seems to be, "yes". Therefore, wiring two sixteen ohm speakers "in series" divides the ohm value in half?

I'm just making sure Crate did it right in the first place.

By the way, I really like the V32 212 Palomino. It could use some deoxit on the pots and jacks, as well as possibly some new power tubes because I sometimes get intermittent volume drops. Hitting the pots and switches and jacks with some deoxit might correct that problem though. I have not been using the amp enough to estimate where the problem may be. It could just be a half way dead spot on one of the pots.

[olddawg]

You are correct. Series would be 32 ohms and that is the only other permutation. However, it isn't a good idea. Most couplers are made for instrument/line level signal. I would suggest making your own coupler out of two Switchcraft jacks, speaker wire, and a plastic project box. And... I would recommend pulling the main fuse out of the Crate first so someone doesn't accidentally switch it on and ruin your amp with a no load condition.

[soundguruman]

Two 16 ohm speakers in series is 32 ohms. R1 + R2 = load (in series)
Two 16 ohm speakers in parallel is 8 ohms:
R1 X R2 divided by R1 + R2 = load in parallel
You cannot add an 8 ohm load to an 8 ohm amplifier that already has an 8 ohm internal speaker, that makes 4 ohms total load.
If the amp says "8 ohms" don't hook it up to a 4 ohm load. It can overheat.
Do not add speaker loads, unless you are absolutely sure that the speakers are wired correctly, and that the amp is specifically rated for the load. Don't even take the chance, unless you are absolutely sure, and you KNOW, by verification, (not guessing) that the amp is rated to power a 4 ohm load.
I see amps blown out all the time, by people who guess and assume, without verifying. This is the most common mistake made by owners of amplifiers, and it costs them plenty in repair bills.

Another big mistake: the speaker cable. Don't use a guitar cable to hook up speakers. Use ONLY a two wire speaker cable, and MAKE SURE that the connections and plugs are solidly connected.

A customer of mine said the tubes in his Marshall were turning RED. This turned out to be a defective speaker cable, purchased from e bay. The rivets holding the plugs together were coming apart and producing an intermittent connection. Just because you buy a speaker cable, does NOT mean it's a GOOD speaker cable.
Never assume anything. Stop guessing.
If you have ANY doubt about impedance or condition of speaker and cables, get a tech to test it for you. It will save you $$$ in the long run to know FOR SURE.

[Duffy]

Thanks for the feedback. I like the project box idea, and screw it to the bottom of the inside of the amp. I wonder if the extra jack connection will introduce noise? Am I correct in thinking that the typical guitar cord "couplers" are shielded? What is the reason that one would not work well coupling the speaker cable?

The speakers are definitely wired in "parallel" to the plug.

[jmaf]

Thanks for the feedback. I like the project box idea, and screw it to the bottom of the inside of the amp. I wonder if the extra jack connection will introduce noise? Am I correct in thinking that the typical guitar cord "couplers" are shielded? What is the reason that one would not work well coupling the speaker cable?

The speakers are definitely wired in "parallel" to the plug.

Instrument cables are made to carry small signals, tiny voltages and negligible current. Instrument cable focus is on quietness, good shielding, flexibility, low capacitance, etc, not on being able to carry power. The most common thing around is to see musicians use signal cables for power. Even experienced guitar players I've met had instrument cables from head to cabinet, that's a big mistake. Same thing with the coupler: its wiring and structure is made for microamperes current, signal level voltages...

Lead dress near where you place the jack on the amplifier is important. If any preamp grid wires are near it could induce noise or oscillation. In between speaker cables the noise induction risk is for practical purposes zero. So if you have an 8 ohm output lead near where you place the other jack, you could wrap those wires around each other for what it's worth and not get any noise anywhere. The problem is passing those power leads near the preamp grid sections(which I don't think is the case.).

[g1]

Sounds like you checked and both your Fender amps are able to run 8 ohm ext. cabs in addition to their internal speakers. Your Crate cab is 8 ohms so everything is good there. You will be disconnecting the speaker plug from the crate amp and connecting it to your junction box screwed to the bottom of the cab so noise will not be an issue as we are dealing with speaker level signals. Just to be sure, you did mean the box would be at the bottom of the cab. ?
JMAF explained why couplers designed for instrument level are not suitable for speaker level signals. As olddawg mentioned, be sure you use speaker gauge wire in your junction box, and fuse removal from the crate is a wise precaution.

[Duffy]

I wonder if a speaker cable can be purchased with a female end and a male end, quarter inch jack size?

Another option could be to use a ten foot length of speaker cable and attach a quarter inch speaker cable plug onto one end and secure the other end to the tabs on the speaker in the cabinet. The cable could be clamped to the inside of the cabinet with a screw in cable clamp about a foot from the connections to the speaker. This would prevent pulling the speaker cable off of the speaker tabs accidentally. The ten foot cable could be coiled into the base of the amp and the plug inserted into the jack on the amp for combo use, and unplugged from the combo amp and plugged into the head unit or extension speaker eight ohm output on a Fender amp for use as an extension cabinet. Would this extra speaker cable laying in the bottom of the combo amp affect the sound of the amp?

[Enzo]

That would be called an extender cable. You might find such a thing, but it wouldn;t be common. Grab a solder iron and some wire and make up whatever special cable you desire.

Even with the cable clamp, I don;t like the idea of 10 foot cable wired directly to the speaker terminals. Just asking for the speaker terminals to get yanked of one day.


Here is an idea for you. Mount a right angle bracket on the sidewall of the Crate cab facing out back. Nice and sturdy. Now mount a Cliff type jack there and wire tip and sleeve contacts to your speaker. Then connect the wires from the amp to the tip cutout contact and the sleeve cutout contact. Now with nothing plugged into the new jack, the Crate works as it always did, the jack just passes the amp output to the speaker. Plugging a speaker cord into the jack lifts those cutout contacts, neatly disconnecting the Crate amp chassis from the speaker. The other end of the speaker cord is then plugged into the Fender or whatever. Now the Crate acts as a speaker box.

Neat and simple. It allows the Crate to go anywhere by itself and not act strange. And to use the Crate as a speaker only, just plug into the jack like you would ANY speaker cab.

[Duffy]

Very nice idea. Either that or the project box screwed to the bottom would be better ideas. I'm good with my soldering irons and can make either of those mods with no problem.

Who is a good source for the parts? Stew-Mac? I usually stay away from GFS.