Vox AC15C1 extension cab question?

[mindtwist07]

Hi! I have a 1 year old Vox AC15C1 which I have been using a lot sounds great btw and I have a speaker lying around which is a 8 ohm celestion custom speaker rated at 75 watts. Can I use this for an extension cab? I see a switch with 8ohm and 16ohm values at the back of the amp with the extension speaker output. Can I just plug the 8ohm speaker with cab on the extension spkr out put and switch it to 8ohms? together with the stock 16ohm stock greenback? Am I doing it wrong? Please enlighten me. Thanks a lot!

 

[dragonfly66]

No you canNOT plug in an 8ohm extension cab. The manual, which you can get online, explains all of the scenarios on page 10 under Power Output Jacks and Impendence Select Switch.

http://www.voxshowroom.com/ct/manuals/AC30C2-AC15C1_Manual.pdf

The only scenario is doesn't clarify is if you put an 8 Ohm speaker in the amp and select 8 Ohms on the switch. I read a post by someone who said this was ok and someone who said it wasn't. Both said they asked VOX. So if you want to use an 8 Ohm speaker in the AC15C1 I would call VOX to verify this scenario will work.

 

[HappyHwy1owner]

Switching the cabinet to 8ohms disconnects the internal speaker, and you would use the external speaker jack. To run an extension cabinet, it specifies to use a 16ohm speaker and the external cabinet jack.

 

[mindtwist07]

I see. I saw some opinions on other forums and I just can't find a definite answer to that extension cabinet thing. I'm not sure whether to go with it and I'm afraid I might damage the amp. I other case I have another speaker for which is a 8ohm 75 watt fender speaker. If I combine the two 8 ohm speakers both at 75 watts in series can I get it to work with the internal speaker at 16ohms? correct? Series 8 ohms + 8 ohms =16ohms and for parellel 2 8ohms is just 8ohms ? correct?

 

[losergeek]

I see. I saw some opinions on other forums and I just can't find a definite answer to that extension cabinet thing. I'm not sure whether to go with it and I'm afraid I might damage the amp. I other case I have another speaker for which is a 8ohm 75 watt fender speaker. If I combine the two 8 ohm speakers both at 75 watts in series can I get it to work with the internal speaker at 16ohms? correct? Series 8 ohms + 8 ohms =16ohms and for parellel 2 8ohms is just 8ohms ? correct?

Parrallel for 2x8ohms is actually 4 ohms (http://www.bcae1.com/spkrmlti.htm), but you're correct on serial, if the 2 speakers are the same wattage and both are 8ohms then you can wire them in serial at 16ohms and use this as an extension cabinet.

 

[Ragtime Dan]

mindtwist07,

There are two output jacks, correct?

One is marked "EXTERNAL SP"

The other is marked "EXTENSION SP"

When you plug into the "EXTERNAL SP" jack, The internal speaker is disconnected. And you must set the impedance switch to match the external speaker cabinet. The jack it's self is switched to disconnect the internal speaker when you use it.

When you plug into the "EXTENSION SP" jack. The internal speaker is put in parallel with the external speaker cabinet.
The external cabinet must be 16 Ohms.
And the impedance switch must be set to 8 ohms.
This is because the 16 Ohms of the extension cabinet in parallel with the 16 Ohms of the internal speaker, equals 8 Ohms.

Do not plug an 8 Ohm load into the "EXTENSION SP" jack under any circumstances.

So in my roundabout way, I am agreeing with "Losergeek". Yes, you can wire two 8 Ohm speakers in series, to make 16 Ohms, and use it as an extension cabinet.

 

[Ragtime Dan]

The impedance switch sets the amplifier output transformers to accept either a total 16 Ohm load, or a total 8 Ohm load. Don't make the mistake of thinking it only effects the jack it is next to.

 

[mindtwist07]

Thanks guys for the replies, Ragtime dan, losergeek, dragonfly66, HappyHwyOneowne.

I think i get it now. Correct me if i'm wrong..again

I'll use 2 8ohm speakers both at 75 watts, wire it in series so I can get that 16ohm load and when I connect that to the ''extension'' output at the back of the amp, I'll switch it to 8ohms, because it runs parallel to the internal 16ohm green back speaker.

16ohm (extension cab (In series) )+ 16ohm (internal speaker) in parallel is 8ohms (switch at back of cab).

Correct?

Thanks again guys, sorry for the noob thing about extension cabs. I'm used to using just one combo with one speaker, for almost 10 years. I'm trying to do this so I can have more clean headroom. The 35watt greenback breaks up easily, even at low volume.

 

[losergeek]

Thanks guys for the replies, Ragtime dan, losergeek, dragonfly66, HappyHwyOneowne.

I think i get it now. Correct me if i'm wrong..again

I'll use 2 8ohm speakers both at 75 watts, wire it in series so I can get that 16ohm load and when I connect that to the ''extension'' output at the back of the amp, I'll switch it to 8ohms, because it runs parallel to the internal 16ohm green back speaker.

16ohm (extension cab (In series) )+ 16ohm (internal speaker) in parallel is 8ohms (switch at back of cab).

Correct?

Correct on the setup.

I'll be interested to see if this gives you the headroom you need though - obviously it'll help a little but it seems when people are trying to make the AC15 do something other than what it does best (ie. nice natural overdrive) they usually don't find satisfaction with that particular amp. An AC30 is probably more along the lines of what you need.

 

[jefrs]

This AC15 has output taps of 8 ohm and 16ohm
Its internal speaker is 16ohm
The external 75W speaker is 8ohm

This permits another 16ohm to be added in parallel into the ext cab socket, but the output must now be switched to 8ohm because that is what the load is now.

The external 8ohm (75W) speaker may be connected to the amp provided the internal speaker is disconnected and the output set to 8ohm..

However 8ohm + 16 ohm in parallel is (16/3) 5.33333ohm which is too low for the 8ohm output tap (but would be acceptable on a 4ohm tap, should you have one).

 

[losergeek]

This AC15 has output taps of 8 ohm and 16ohm
Its internal speaker is 16ohm
The external 75W speaker is 8ohm

This permits another 16ohm to be added in parallel into the ext cab socket, but the output must now be switched to 8ohm because that is what the load is now.

The external 8ohm (75W) speaker may be connected to the amp provided the internal speaker is disconnected and the output set to 8ohm..

However 8ohm + 16 ohm in parallel is (16/3) 5.33333ohm which is too low for the 8ohm output tap (but would be acceptable on a 4ohm tap, should you have one).

All of these issues were already brought up in the thread. He has it right, probably best not to confuse the issue at this point.

 

[mindtwist07]

thanks losergeek,

I use the amp though only for cleans, I get my dirt from my pedals. Problem is I need a little more headroom at loud volumes and can handle being clean without breaking up. If i do use it at a loud volume without any extension cab, it tends to breakup easily and I dont want that since the AC15c1 doesnt have an effects loop so everytime I added a delay or modulation or something I dont want it to go through the preamp section with the natural overdrive of the amp. I use the amp for everything even for bigger gymnasiums with or without PA. So I thought the extension cab will bring more headroom for cleans without breaking up at loud volumes.

btw I dont use the natural overdrive of the amp since it still has its stock tubes in it, when the topboost is all the way up, it sounded muddy and less defined so I use it only for cleans and it does pretty well with my pedalboard.

 

[Ragtime Dan]

I think you might get more cleans by selling your spare speakers (saving the original in the amp in case you want to put it back) and getting a couple of 16 Ohm Weber Californias. Or JBLs if you can find them. One for in the amp, and one for and extension cabinet. Even just one characteristically cleaner driver in your amp might surprise you. I love the clean JBL sound. And I think the Weber California is designed for that clean sound too.

 

[b2187101]

I have an Avatar 112 with a Celestion Greenback hooked up to my AC15C1. Sounds nice

 

[Wayne Alexander]

You haven't said what speaker you have in the amp now. If it's a Greenback, you'll get a significant volume and clarity boost by changing to a single Celestion Blue or Gold and forgetting about extension speakers. The Blue and the Gold are much more efficient than a Greenback, and will make the amp louder, with more clean volume before breakup, and a chimier, sweeter tone, both clean and dirty.

Changing to a JBL or Weber California would also give you more volume, but those speakers are not the normal voice of the amp, I don't like Voxes through American -voiced speakers, though it's possible that you would.

 

[mindtwist07]

hmm.. what I have Is a 1x12 cab with a fender special design speaker 8 ohms and 75 watts..I'm planning to change that to a 2 x 12 and also by removing the speaker from my line 6 spider 3 which is a celestion custom design also 8ohms and also 75 watts i can make that into a 2x12 cab two 8 ohms in series is 16 ohms right? with 150 watts in all.It can be loud. I was thinking it will make it harder for the amp to make the speakers breakup easily because of its higher wattage and it will add more volume.

Thanks for the suggestions for the jbl/weber, celestion gold and blue speakers I don't think we have those in our country.

and yes I forgot the stock speaker in my amp is a 35 watt greenback and I also think after using it for a long time its not breaking in.

 

[Wayne Alexander]

By the way, the wattage rating of a speaker has nothing at all to do with the volume it will put out. What matters is the "sensitivity" or "efficiency" rating. A Greenback is about 97 dB sensitivity, a Blue is about 100dB, the Blue is MUCH louder with the same signal. A 75 watt rated speaker is not louder than a 30 watt rated speaker - what matters for volume is how efficient the speaker is.

 

[Ragtime Dan]

I think Weber would respond to you. But due to shipping costs you might pay about double.

 

[mindtwist07]

I see. hmm I should check the db's of those speakers to find out how loud they can be. Thanks for clearing it out wayne. I mean Its a waste if I haven't use those stock speakers I have. I like the sound of them btw when they were installed on my ss amps. Since my line 6 is already broken, I have no further use for it. The speaker might be of some use, the same with the fender speaker and a 2 x 12 cab is what i'm thinking about.

Hey there dan, I have no intention of buying another speaker. Eminence,weber Celestion gold or blue etc, yeah they all sound pretty good but with this economy and a very minimal salary, paying double is going to be the last thing in my mind.

 

[jefrs]

thanks losergeek,

I use the amp though only for cleans, I get my dirt from my pedals. Problem is I need a little more headroom at loud volumes and can handle being clean without breaking up. If i do use it at a loud volume without any extension cab, it tends to breakup easily and I dont want that since the AC15c1 doesnt have an effects loop so everytime I added a delay or modulation or something I dont want it to go through the preamp section with the natural overdrive of the amp. I use the amp for everything even for bigger gymnasiums with or without PA. So I thought the extension cab will bring more headroom for cleans without breaking up at loud volumes.

btw I dont use the natural overdrive of the amp since it still has its stock tubes in it, when the topboost is all the way up, it sounded muddy and less defined so I use it only for cleans and it does pretty well with my pedalboard.

This is one of the olde problems with the AC15 - cranked up for larger venues it is not a clean amp, it turns into a nasty little hooligan. And I don't think it matters what speaker, just the nature of the beast.