Question: Is a 30-watt amp head going into a 2x12 cab good enough for medium-sized gigs?

Old Music Guy said:
I really don't want to start an argument, I really don't.
Firstly, what do you mean by "physical description" ? Fit, form, and function?
Secondly, how would someone go about measuring the "inductance" of a transformer i.e. inductor?
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Strictly speaking a transformer, when correctly terminated is not an inductor. This is how audio transformers 'can' give a flat, extended frequency response but beware! They are rarely perfectly driven or loaded and so are not totally' flat'.

Transformers all have losses of course and one test is to measure the impedance of say the primary with all the other windings shorted. In theory the primary should be just the DC winding resistance but in practice there will be a small inductance. This is termed "leakage inductance".

Dave.
 
ecc83 said:
Strictly speaking a transformer, when correctly terminated is not an inductor.
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I'm sorry, but that is totally incorrect. Properly terminated or not, a voltage across a primary winding of a transformer, wrapped around a common core, induces a voltage on the secondary, that is directly proportional to the ratio of the primary winding to the secondary winding.
How can it possibly NOT be an inductor?
 
Old Music Guy said:
Firstly, what do you mean by "physical description" ? Fit, form, and function?
Secondly, how would someone go about measuring the "inductance" of a transformer i.e. inductor?
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Diameter and height.
It will narrow down who I bug for a transformer. Because certain people only deal with certain core sizes.
 
Old Music Guy said:
I'm sorry, but that is totally incorrect. Properly terminated or not, a voltage across a primary winding of a transformer, wrapped around a common core, induces a voltage on the secondary, that is directly proportional to the ratio of the primary winding to the secondary winding.
How can it possibly NOT be an inductor?
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OK, LAST thing I wan ti is a cow with YOU friend but consider a "perfect" 1:1 ratio transformer in the OP stage of a mixer say? We expect and find, to a first approximation, the the frequency response is decently flat from say 40Hz to well beyond human hearing. Were the transformer behaving as an inductor that could not be! Of course, if you put a winding on an LCR bridge you can measure its inductance...WITH the coils O/C.

If there are any Power engineers here they would tell you that line transformers have to be "balanced" so as to present a reasonably resistive load otherwise the power Co gets very miffed and you can have terrifying voltage spikes. The same applies with large capacitive loads but in that case you get huge out of phase currents.

Transformers are not perfect of course, they have resistance, leakage inductance and Iron losses. These failings can be minimized of course but Sod's Law states that "better" is always more "expensive"! Traffs are also made in a range of ratios and it is a fact that the further you go from one to one the harder it is to keep high performance

All sorts of electronic "devices" LOOK like one thing but behave differently in circuit. EQs often use "Gyrators" these are a collection of just Cs and Rs round op amps but BEHAVE like inductors.

A single loudspeaker in a cabinet is a small inductor but over its operating range the complex impedance caused by the cone movement and the air load can make it "look" like a capacitor at some frequencies.

IF this stuff was easy anyone could do it and I would be a freaking sight better off!


Dave.
 
ecc83 said:
That is a solid state amplifier and will therefore equate to about 15, maybe only 10 watts from a good valve amp. Vox AC30s are extremely loud! Maybe if the 2X12 contains some really sensitive speakers such as the Celestion V30s it might cope but I doubt it. The main problem is that sstate amps do not sound nice if you push them into distortion.

As others have said, go through the local PA. You could still use the amp as a personal monitor and then have the cab micc'ed up or run a line to the desk from the FX send, probably need a passive DI box for that but the sound "person" should have a few of those. Mention was also made about the impedance of the cab? Check that the amp is happy with whatever it is. Very few 2X12s are as low as 4 Ohms but some sstate amps are only safe down to eight. Check it.

Dave.
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It sounds like snake oil and 1 watt on a factory spec scale should equal another and maybe they do but I’ll say this in support of above…the loudness (maybe just perceived) is different in both SS vs Valve, but I’ll even suggest vintage vs new. Buddy has a newer Yamaha power plant stereo with tuner for his modular home sound system. Nothing fancy but decent Bose speakers. I have a ‘76 Marantz 2275 75 watt power plant (also with tuner though the glide wheel not digital). We’ve never put them side by side but I would wager my Marantz, at a minimum, produces the same ‘loudness’ as his Yamaha. I may be wrong but that’s my perception.

As for guitar amps, I’ll add this:
First ‘real’ amp after a Sears thing with a 6” speaker) was a Peavey Bandit 50 watt with 12” speaker. Second amp was a Peavey Musician head with a Oeavey 4x 12 oversized (and unnecessarily HUGE cab. That was a cool amp, SS. Third was a 1982 Marshall 2204 50 watt head and 4X12” cab bought used 1985. Then a JC-120 Jazz chorus 120w (60 x 2 in stereo) SS beast, Fender tube Suoer Reverb 40 watt and Orange TT combo 15 watt tube. Marshall Fender and Orange I still own.

I’ll argue all day long my Marshall at 50 watts is WAY louder by loudness than the Bandit 50. The Jazz Chorus? Never really opened it up enough to say for sure, but (like the Marshall), it was loud on 2. The Fender also loud on 2. The Orange 15w is sweet but on 2 you’ve got plenty of room to increase volume before you start laboring your ears.
Just wanted to respond to a fellow tuber in here
 
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And regarding mic’ing the amp,!yes that is an absolute reality and a standard for even medium-sized bars/venues. Most will have a house PA system and smaller ones come with a sound man to run it. Any sound man will tell you first thing at soundcheck to turn your amp down. And it’s annoying. But they want to be able to give you that practice place live sound through on stage monitors and be able to mix front of house without physically walking up on stage and adjusting you aml’s volume if too loud and fucking up the mix.

Personally, I love some good volume on my amps live and hate to rely on monitor mixes…I like everything to sound like rehearsal in a (usually) small basement room. Only way to get that in a bigger space is to mic and mix it.

Is 30w 2x12 cab enough for a 350 seat venue. I could do it with my 15watt Orange.
 
There was a time decades ago where PA’s weren’t that advanced and audience volume was needed from each instrument. Those years are long past. Big rock/punk/whatever style bands you see with stacks of speakers behind them? Most are void of heavy speakers because they’re unnecessary.

UNLESS (and I’m assuming you are not) putting a mic through your guitar amp with the guitar and maybe you are) then you’re good with 30w 2x12 and will only use a fraction of that when mic’d up.
 
Seeker of Rock said:
Then a JC-120 Jazz chorus 120w (60 x 2 in stereo) SS beast,
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Got one! Early 80s from Japan. I would be hard pressed to pick another "all around" on stage amp. Used it for my Rhodes. Used it for my bass. Use it for my edrums.
Maybe I should jam out on the porch with that?
They would definitely find me then.
 
I’ve always had a simple formula.

If at rehearsals your amp isn’t drowned out by the drummer you’re golden. Usually at your rehearsal space the only PA gear is for vocals.

Small bar gigs, club gigs are pretty much the same.

You get to a bigger venue, usually you have bigger PA, and things besides vocals get miced up.

So the key is if you can keep up with your drummer, you’re good.
 
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