ohms scare me

[Big_Stu]

[quote name='obbm' post='1242156' date='May 23 2011, 08:03 PM']Looped inputs is a term used in electronics where an input has 2 sockets, passively conected that allows a signal to loop out and onto another piece of equipment. Most [b]recent[/b] speaker cabs have this. When you connect the 2 cabs together you are putting both sets of speakers in parallel.[/quote]
Fixed it for you



.... and thanks for the info.

[umph]

[quote name='alexclaber' post='1241870' date='May 23 2011, 04:57 PM']The AD200 is a valve amp so the rules are totally different to the solidstate amp ones. It looks like it has both an 8 ohm tap and a 4 ohm tap on the output transformer and you can use either one but not both. You could safely run three 8 ohm cabs on the 4 ohm tap, that won't bother it at all as valve amps are sensitive to overly HIGH not low impedances. Likewise I wouldn't envisage a problem running all those cabs you describe off the 4 ohm tap.[/quote]

true, as long as its not reading to near an open circuit. it's not like speaker provide a uniform impedence at all frequencys anyway

[Phil Starr]

[quote name='therose789' post='1241787' date='May 23 2011, 04:01 PM']can i run a 4ohm cab and two 8 ohm cabs at the same time from my ad200? i dont have that amount of cabs, im just wondering?

if so what will it do? kill people?[/quote]

Since your 4ohm seems to be an 8x10 that plus two more cabs is more likely to kill your back. You surely don't need extra volume?


[quote name='obbm' post='1241902' date='May 23 2011, 05:15 PM']From Adrian Emsley - Tecnical Director at Orange Music Electronic Ltd - 24 April 2008 in answe to my question.

It confirms what has been previously said.

1 x 8 ohm cab = 8 ohm socket

2 x 8 ohm cabs = both 4 ohm sockets

1 x 4 ohm cab = either 4 ohm socket


Regarding the original post

Run the 2 x 8-ohm cabs in parallel

Put these in series with the 4-ohm cab to make 8-ohms.

Run the lot from the 8-ohm output.[/quote]
This is the spot on technical answer if you want to go ahead. It would be the sort of thing that would be fun to try if you have the cabs sitting around and an hour to kill and you know how to wire cabs in series. The 'mismatched' 4.something arrangement wont give you more power as you have a valve amp. It may be quieter as it distributes the power between the speakers in an odd way. Who knows if the tone from either arrangement will 'work', there is more to matching multiple speakers than just worrying about ohms.

[MB1]

MB1.
That Dr Watsons no oil painting either!

...Sorry! I'll get me coat!

[ZMech]

To the OP, just think of each cab as a resistor, and think back to your physics lessons. If adding two resistors in parralel, you use the equation 1/Rtotal = 1/R1 + 1/R2. So in this case, combining a 4ohm and 8ohm cab in parralel gives a total resistance of 2.7ohms. Then the equation P = I x R^2 tells you that having lower makes the current higher for the equivalent power, which is presumably bad for the amp. For two 8ohms in parallel this gives 4ohms, your minimum value

putting them in series would add the resistances normally (Rtotal = R1 + R2) but for some reason this isn't common when combining cabs, possibly due to some quirk of AC and phase changes.

p.s. think I'll stick to my 1x12"

Edited May 24, 2011 by ZMech

[aldude]

To the OP:

If you want a smaller rig for practise, and a larger rig for gig, I would personally get two 8 ohm cabs, and use one of them for practise, and both for the gig.

So, for example, two 8 ohm 15" cabs would do it. Or a 15" plus 2x10", use the 2x10 for practise. Or a 2x12 plus 1x12. Or.... etc. In other words, get a big one and a small one, both 8 ohm.

[alexclaber]

It's a valve amp with an output transformer, not a solid-state amp! All the posts talking about increased current flow at low impedances are wrong - valves and output transformers do not behave like that. This is quite informative: [url="http://www.metaltronix.net/metaltronix-amp-basics.htm"]http://www.metaltronix.net/metaltronix-amp-basics.htm[/url]

4 ohm cab on an 8 ohm tap and you'll get about half the 8 ohm power. 16 ohm cab on an 8 ohm tap and you'll get about half the rated power. Go lower than 4 ohms and the power decreases further but the amp doesn't care. Go higher than 16 ohms and the power decreases further AND you risk killing your amp. (The reasons are complicated but explained in that link).

I'll say it again - valve amps do not behave like transistor amps!

[razze06]

[quote name='alexclaber' post='1242844' date='May 24 2011, 12:47 PM']It's a valve amp with an output transformer, not a solid-state amp! All the posts talking about increased current flow at low impedances are wrong - valves and output transformers do not behave like that. This is quite informative: [url="http://www.metaltronix.net/metaltronix-amp-basics.htm"]http://www.metaltronix.net/metaltronix-amp-basics.htm[/url]

4 ohm cab on an 8 ohm tap and you'll get about half the 8 ohm power. 16 ohm cab on an 8 ohm tap and you'll get about half the rated power. Go lower than 4 ohms and the power decreases further but the amp doesn't care. Go higher than 16 ohms and the power decreases further AND you risk killing your amp. (The reasons are complicated but explained in that link).

I'll say it again - valve amps do not behave like transistor amps![/quote]

I stand rightly corrected!

I did a little reasearch, and i think i now understand more about impedance matching on output transformers, cheers!

[nomis]

[quote name='Musicman20' post='1242049' date='May 23 2011, 07:06 PM']Just get one 4 ohm cab or two 8 ohm cabs..thats about it

Personally, I can see exactly why you would want to spend time thinking about....but please give things a try to see if you like them. Sometimes we get swallowed up in specs and it turns out to be nothing like we expected.[/quote]

mate its confusing the hell out of me! i just started look out of interest thinking about maiing my rig more ''transportable'' with doing a few tours etc... later on in the year and now im so confused, i really fancy some ocrange cabs to match my amp (and it will look cool!)

sounds live is quite local to me and they are selling some ex display ones but not much of a discount! i migh wait to see if any second hand ones show up on here! i know one went recently and i just missed it.