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Joined:
June 2005
Posts: 274
Location: Maryland, USA | Everyone, I need some help understanding how exactly cabs and heads work, when compared to a combo amp.
Of course I know the head is basically the pre-amp, and the cabinet is a speaker, and you hook them up to play.
I also know that a combo is essentially the combined of these two.
However:
When I bought a 50watt Vox Valvetronix combo amp about a year and a half ago, I figured that would be good for practicing with a band, and gigs by myself. Because it included an out volume, I thought I could purchase a 100 or 200 watt cab and basically use the combo as a head if needed when playing with a band live at a show that needed such volume.
However, now I'm confused now, as it appears heads are paired with the same cab that have the same wattage output.
Does this mean my sound will suffer if I do happen to buy a 200watt cab for my combo to output through?
Or will it not be loud when compared to a 200 watt head and a 200 watt cab?
Can someone help me understand this?
Thank you very much, and sorry about asking probably an obvious question like this. |
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Joined:
December 2001
Posts: 10583
Location: NJ | amplification is divided into 3 parts.
preamp boost the signal from high or lo z to be amplified and controls the overall vol.
amplifier amplifies the preamped signal. This is always running full up it just depends on where your pre amp is set for the vol
speakers changes the electrical signal into something we can hear.
your amp will always be 50 watts you cannot change that.
what you are looking at is wattage ratings of speaker cabs. that is basically how much the speakers can handle before they blow out. IF you don't boost the signal with another amp then you don't get any more sound.
here is where it gets tricky. the more efficient your speakers are and the more of them means the more headroom you can have and therefore have more sound and perciece it as being louder.
Back when I was a kid I remember auditioning for bands and being told if you don't have a 100 watt amp don't bother coming to the audition. Well depending on the efficiency of the system you can have a 20 watt amp that can compete.
so what you need to do is this. look at the manual for your vox amp on line and see what load the external speaker cab should be. If you use the recommended load it will make the amp more efficient and sound louder. if you mis max the impedence loads then you can either wind up with significantly less power and/or blow up the amp.
I hope some of this made sense, if not ask another question and I will try to answer it. |
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Joined:
January 2004
Posts: 1225
Location: Lake Hiawatha, New Jersey | "he hooked up our stereo, eh..."
- Bob McKenzie |
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Joined:
December 2003
Posts: 1071
Location: Carle Place, NY | Stephen:
I checked the stats on your amp and it does NOT have a speaker out. It has only a line out. That means that you cannnot add an extension/speaker cab. The only Valvetronix with a speaker out is the 100 watt model.
The line out on your amp is the signal from the pre-amp, not the powered signal that you need to drive speakers. If you tried to connect the line out on your amp to a speaker cab, it won't produce sound.
Keep in mind that on lower power (under 100 watts) solid state amps (your Vox is solid state even though it uses a small tube in the circuitry) an extension cab doesn't improve the sound as much as it would with a low power tube amp. A 15 watt tube amp, or even a 5 watt, can be used to power a 2 X 12" cab with good results. A 50 watt solid state amp can't do the same thing. Extension cabs really are made for tube amps. I'm not an electronics guy and I can't explain why but it has something to do with a tube amp being designed to be operated under "load" or with the resistance of a speaker.
If you need more sound, mike the amp through the PA. |
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Joined:
January 2006
Posts: 5881
Location: Colorado Rocky Mountains | Thanks, Al, for the explanation on speaker efficiency. I have, among others, two very large Yamaha concert speaker cabinets (I believe an 18" and a large horn) driven by a Yamaha stereo PA head. Although I was disappointed when I learned the speakers were rated only at 50 watts (the head being 100 watts), the things can blast way into pain. I've used them in a 3,000 seat performance hall and still had to keep the volume down. Wattage ratings don't necessarily seem to equate to quality loudness. The efficiency of the speakers, as you put it, means a lot. |
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Joined:
February 2002
Posts: 5750
Location: Scotland | A lot of high powered guitar amps use relatively low wattage inefficient speakers, as speaker distortion is an integral part of some guitar sounds, unless of course you need an ultra clean sound. When Fender started putting JBL's in Twins just about everbody except pedal steel players prefered the earlier versions with the supposedly inferior speakers. That and the fact that the JBL's damn near doubled the weight of what was already a ball-breaker.
As Al said, the most important aspect to adding extension speakers to tube amps is making sure you get the impedances matched, or you may end up with a fried amp and an expensive repair. Solid state amps are more tolerant to impedance mis-matches, but you still should not load under the stated minimum Ohmage |
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Joined:
October 2005
Posts: 803
Location: Avondale, AZ | Wow I thought the difference was stage presences. Heads and cabinets make you able to play bigger venues. |
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Joined:
May 2003
Posts: 4389
Location: Capital District, NY, USA Minor Outlying Islands | Another factor to consider is whether the cab is wired in series or parallel. And as above beware the ohms, worry about the ohms ... |
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Joined:
July 2006
Posts: 171
Location: Oregon | So much to consider when buying amps....*head explodes* |
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Joined:
March 2005
Posts: 1421
Location: Orange County, California | Let me see if I can make some sense of this for you. most "guitar amps" are combo's. They have an amplifier and a speaker in the same box. Some of them have the ability to drive an external cabinet. A "head" is just the amp, no speaker attached, and it doesn't matter whether you drive a single, 2x12 or 4x12 cab as long as the impedence is rated the same as what's on the back of the amp. The power rating of the amp SHOULD NOT exceed the power rating of the speaker you are diving with it, whether it's the internal speaker of a combo, or an external cab. It won't hurt to run a 15w amp into a cab rated at 100w. In fact, if the cabinet is a little inefficient, you'll be able to turn up the amp more, getting more into the distortion of the amp, at a slightly lower overall volume. Don't worry, running your 50W Valvetronix into an 4x12 will be plenty loud. If it doesn't have a external speaker out, a trip to the electrincs store or an amp shop for a switching 1/4 jack on the back fixes that. |
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Joined:
June 2005
Posts: 274
Location: Maryland, USA | Thanks guys, I understand the concept much better now.
and MitchRX,
maybe the specs for Vox has changed in the last year, but right on the back of my amp I have the red jack that says "External Speaker Out", but thanks for looking for me.
This makes me feel a lot better, thanks guys! |
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Combo amps or head with cab?
