15w tube amp through 400w 4x12 cab... bad idea?

[sfusiondj]

Dear all

I'm hoping to get my first tube amp combo tomorrow - the stellar Vox AC15C1. I know for a fact, however, that an amp that small won't be able to keep up with the full band I'm in.

So the obvious solution is to plug a cab into the external speaker jack on the amp to try get some bigger volume.

I just so happen to have a Marshall MF400A cabinet and was wondering if this could do the trick? It's listed as a 400w cab loaded with four Celestion G12K100 speakers. Are the power ratings of amp and cab simply too far apart? I can match the impedance using a switch on the amp, so at least that isn't a problem.

Many thanks!

 

[gypsymoth]

it's not a issue - the power ratings are basically an indication of how much heat the speakers can withstand.

 

[jhundt]

it will work. Sometimes high power speakers don't sound their best without some muscle behind them, but there is no danger in this set-up and it might sound great.

 

[middy]

It will work fine, and may give you the volume you need. You may need to roll off some bass with a closed-back 4x12.

 

[Tony474]

The G12K-100 is one of my personal favourites. A pretty efficient speaker, with very good bottom-end response, so whatever power you're putting into four of them, they'll certainly make the most of it. Anyway, you're getting the amp, you've got the cab, so what's to lose? It must be worth a try before considering further expense.

 

[telex76]

It doesn't matter as long as the OT sees the correct load.

 

[sax4blues]

I played my Orange Tiny Terror through a 4x12 and oh my what a glorious sound Look at your amp and speaker for impedance selection options, and make sure you understand clearly how your combo amp outputs are used. Some amps are made for only one output, they aren't set up to run the internal speaker and the extension.

 

[sfusiondj]

Look at your amp and speaker for impedance selection options, and make sure you understand clearly how your combo amp outputs are used. Some amps are made for only one output, they aren't set up to run the internal speaker and the extension.

Apparently the Vox AC15C1 has two output functions - one for an extension cab (restricted to 16ohms in addition to the 16ohms of the internal speaker, giving a total load of 8ohms) and one for an external speaker which is selectable to either 8 or 16ohms. The latter bypasses the internal speaker, which I guess isn't that much of a loss considering it's being replaced by four others

Thanks for the advice everybody - I can't wait to try it out. I'll report back tomorrow!

 

[sfusiondj]

Tried the hook-up today and it works great. Nice smooth sound and marked increase in volume. Good to know I have some extra muscle when I need it. (I also need more muscle to carry my new AC15C1 around... Weighs the same as my Peavey Special 130, if not more )

Thanks again folks.

 

[Stewart Ward]

Tried the hook-up today and it works great. Nice smooth sound and marked increase in volume. Good to know I have some extra muscle when I need it. (I also need more muscle to carry my new AC15C1 around... Weighs the same as my Peavey Special 130, if not more )

Thanks again folks.

Don't make the mistake of assuming this will increase the power. Any volume increase will be limited to the effects of the speakers' higher efficiency only.

An open back cabinet will have a bass resonance of about 80Hz (open E - 6th string). Almost any closed back cab will have a higher bass resonance of 110Hz approx (open A - 5th string).

 

[jefrs]

Don't assume a 15W amp cannot keep up with a full band, an AC15 at full chat is a pretty raucous beast.

I use a variety of amps with a full band, from a very loud 30W 2x12 to an old 17W 1x12 that can cut clean through the mix no problemo.

A 15W can sound pretty good plugged into an ext cab. The extra speakers make it sound bigger, but you still only have 15 watts max power. It may shift a little more air (more speakers is more efficient, honest, but don't make me do the maths again), however it all very much depends on the actual speaker efficiencies.

The stock AC15C1 should have a 98dB Celestion G12M-25 Greenback
but a 400W "Marshall" 4x12 might have a set of 97dB G12T-100 (the T-series being a "high-power Greenback" type) but usual choice for an ext cab are 98dB 80W Seventy80 (cheaper).

The AC15 option G12-15 Alnico Blue is 100dB but only 15W and really, really does not like being thrashed.

 

[Tony474]

The stock AC15C1 should have a 98dB Celestion G12M-25 Greenback but a 400W "Marshall" 4x12 might have a set of 97dB G12T-100 (the T-series being a "high-power Greenback" type) but usual choice for an ext cab are 98dB 80W Seventy80 (cheaper).

The OP told us up front that his Marshall 4x12 has Celestion G12K-100s in it. That model's rated at 99dB/1W/1m - and in my experience Celestion sensitivity ratings are quite conservative compared with those of some other manufacturers - down to testing methodology, I'd assume. So, as I said before, even with only limited power available, those efficient speakers will be making the most of the 15 watts going into them.

 

[jebbo]

I use a 15w fender blues junior, and it keeps up just fine. You shouldn't have to use a 412 cab IMHO. 15w of tube is actualy a lot of power. I used my blues jr at an outdoor gig just so I could crank it up, and it sounded awesome. The other guitarist was using a hot rod deville with 410's and a 412 extension cab. My little jr was just as loud, but not only that. It sounded a lot better. I cranked it up and just used my guitars volume knob to switch between rythym and solos. It was one of the best tones I've ever got. Don't under estimate 15w of power.

 

[jefrs]

The OP told us up front that his Marshall 4x12 has Celestion G12K-100s in it. That model's rated at 99dB/1W/1m - and in my experience Celestion sensitivity ratings are quite conservative compared with those of some other manufacturers - down to testing methodology, I'd assume. So, as I said before, even with only limited power available, those efficient speakers will be making the most of the 15 watts going into them.

That will teach me to read properly.
However Marshall 4x12 have and do get fitted with a variety of speakers. The (yes 99dB) G12K-100 are more expensive than the G12T-100. And the characteristic Celestion "thump" from a Marshall 4x12 is usually modelled on a G12T-75 load.

 

[jefrs]

I use a 15w fender blues junior, and it keeps up just fine. You shouldn't have to use a 412 cab IMHO. 15w of tube is actualy a lot of power. I used my blues jr at an outdoor gig just so I could crank it up, and it sounded awesome. The other guitarist was using a hot rod deville with 410's and a 412 extension cab. My little jr was just as loud, but not only that. It sounded a lot better. I cranked it up and just used my guitars volume knob to switch between rythym and solos. It was one of the best tones I've ever got. Don't under estimate 15w of power.

I have noticed that the Fender BJ is not as loud as other 15W amps, I have often seen them struggle with a full band. I believe the problem is their small box and hence poor projection. Fifteen watts is loud but we must play a lot louder than you do
The AC15 does not suffer from this, it was designed as a stage amp and it has a long history of doing its job well.

 

[twfnm]

Cabinet select settup

Tried the hook-up today and it works great. Nice smooth sound and marked increase in volume. Good to know I have some extra muscle when I need it. (I also need more muscle to carry my new AC15C1 around... Weighs the same as my Peavey Special 130, if not more )

Thanks again folks.

Hello wanted to know how you hooked it up. I am using a Marshall 1960A and can only get 2 speakers to work. Can you tell me how its supposed to be connected? I know the Vox has the 2 outs for external speakers then the Marshall has:

2) Right* input
When switch (1) is set to:
i) Stereo, this provides connection to the right* side pair of speakers.
Rated at 8 Ohms.
ii) Mono, this provides connection to all four speakers. Rated at 4 Ohms.
3) Left* Input
When switch (1) is set to:
i) Stereo, this provides connection to the left* side pair of speakers. Rated at 8 Ohms.
ii) Mono, this provides connection to all four speakers. Rated at 16 Ohms.


So am i running 2 cables from the vox out to the marshall? And do i leave the switch to MONO and plug one into the right input and one into the left?
Little confusing.
Thanks!
Greg

 

[JD0x0]

No it'll open up a black hole and swallow the universe if anyone uses more than 2x the power of the amp. Everyone knows you gotta have those speakers on the verge of catching fire, to sound good.

 

[Ringo]

On a slightly different topic, I had a SF Champ that I ran into 2 different 4-12 cabs,a cheap Marshall and a old Peavey with Scorpion speakers.
it sounded great, better through the Peavey, and very loud.
it was just an experiment, but fun.

 

[TelekineticBoss]

Hello wanted to know how you hooked it up. I am using a Marshall 1960A and can only get 2 speakers to work. Can you tell me how its supposed to be connected? I know the Vox has the 2 outs for external speakers then the Marshall has: 2) Right* input When switch (1) is set to: i) Stereo, this provides connection to the right* side pair of speakers. Rated at 8 Ohms. ii) Mono, this provides connection to all four speakers. Rated at 4 Ohms. 3) Left* Input When switch (1) is set to: i) Stereo, this provides connection to the left* side pair of speakers. Rated at 8 Ohms. ii) Mono, this provides connection to all four speakers. Rated at 16 Ohms. So am i running 2 cables from the vox out to the marshall? And do i leave the switch to MONO and plug one into the right input and one into the left? Little confusing. Thanks! Greg

If I'm reading this correctly, what you want is the switch to mono and plug into the 16 ohm option (left?). You want to then run one cable from the jack that isn't switchable. This should in theory keep you internal speaker on and all four of the cab speakers on. If you don't want the internal speaker you'll have to run the cable from the switchable jack set to 16.

EDIT
I looked at it closer. You want to flip the switch to mono and use the right input for 16 ohms. Then run a 16 ohm out from the vox. One cable. That's all you need.