Orange TH30 & Speaker Cab & Ohms

[Legend]

Im new to Orange and I gotta say they are incredible amps............Ok I got 2 Mesa 2x12 cabs running 8 ohms each. The back of the TH30 has 8ohms input and 16ohms. How would I want to plug both 8ohms cabs into the TH30?

[a.hun]

Hi Legend. Unfortunately you can't simply hook them both up. The back of the amp has speaker outputs optimised for one or two 16 ohm cabs, but for only a single 8 ohm cab. (The outputs on the back of a Mesa amp are optimised for one or two 8 ohm cabs or a single 4 ohm one! American amps very often use 8 ohm cabs, British ones 16 ohm cabs!)

I've literally just sent a PM explaining this stuff to another member, so I hope they won't object to my copying (most of) it here:

Hi TyQ. Impedances and speaker hookups are pretty confusing, but with valve amps they are also important and you do want to get them right. They aren't daft questions at all - this stuff isn't very obvious. Read this through a couple of times though and hopefully it'll (start to) make some sort of sense.

Okay, for starters you should be thinking about amp OUTPUTS, not inputs. (The input is where you plug your guitar in! ) And the way they work is something like this...

After the power valves, between them and the amp's speaker output sockets, is the amps output transformer. (Often just called the 'OT'.) This converts the high impedance signal (from the power valves) to a low impedance one to correctly match the speakers impedance.

Orange use 16 ohm transformers and using the full transformer coil you'll be able to correctly impedance match a 16 ohm speaker load (like your PPC212OB cab). So yeah, that output coil is simply connected to the 16 ohm output on the back of the amp. To run a 16 ohm cab from it you simply run a single speaker cable from the amps 16 ohm output to the cab.

There is also a so called 'partial tap' of that OT coil, which lets you use not the full output coil but only a part of it. This 'tap' will let you match the amp with an 8 ohm speaker load. And yes while there are two 8 ohm output sockets, these are both identical and simply connected to each other.

However (electrically speaking) there are two possible ways of connecting them together, called either 'series' or 'parallel' connections. And if you connect each output to a separate speaker load, those loads would also be connected to each other, again either in series or in parallel.

The difference between series and parallel electrical connections is this simple: Having them in series means one speaker would be connected (electrically speaking) 'after the other'. With parallel connections though both speakers would be connected 'side by side'.

The way these two 8 ohm outputs are connected to each other is in parallel, which is totally standard for amps with double outputs. So connecting speakers to both means they are also always being connected in parallel.

If they were being connected in series (which they aren't!) than the two speaker impedances would simply be added together to give the total impedance load. So two 16 ohm speakers in series would make a total load of 32 ohms. Adding loads in series always gives a higher total impedance.

With parallel connections though the overall impedance load is always lower than the separate individual loads. Two 16 ohm loads if linked in parallel will give you a total load of 8 ohms. So by plugging two 16 ohm loads into those two (parallel linked) amp outputs they are themselves linked in parallel, and become an effective 8 ohm total load. Which is connected to the 8 ohm tap from the OT = perfect.
Looks like this:

A (8 ohm output) --> cab 1
M
P (8 ohm output) --> cab 2

There is also another way of doing it, called 'daisy-chaining'. This makes use of the double sockets on the back of the speaker cabs themselves, which just like those twin amp outputs, are also normally connected to each other in parallel. They are identical and if you only use one of them no problem, it just works as a simple input. But (if you want) you can then use the second one as an output to run to a second cab. Though it looks like one cab is physically 'after the other' the wiring connection is in parallel, so electrically they are 'beside each other'. The total load the amp sees is exactly the same as before though, two 16 ohm loads in parallel = 8 ohms total. Only the place where the parallel connection is made is different. In this case at the backplate of the first speaker cab rather than at the back of the amp.

Basically when daisy-chaining you run a single speaker cable from the amp to the first cab, (use either of the amps 8 ohm outputs, doesn't matter which), and another from the first to the second cab.
Daisy chaining looks like this:

AMP (either 8 ohms out) --> Cab 1 --> cab 2.

If running 2 speakers you can do it equally well either way, it really doen't matter much at all. The actual load the amp 'sees' is identical either way - an 8 ohm (total) speaker load on the 8 ohm tap of the amps output transformer coil.

So you have 3 basic cab hookup options with these amp outputs:
1 x 16 ohm cab from the 16 ohm amp output.
2 x 16 ohm cabs either using both 8 ohm amp outputs or b daisy chaining the cabs from one single amp 8 ohm output.
1 x 8 ohm cab from an 8 ohm output.

You can't run more than one 8 ohm cab with those outputs though. (Two 8 ohm cabs in parallel would be 4 ohms total but the amp has no 4 ohm output coil tap. So if you want to correctly run two cabs at once they MUST both be 16 ohm cabs!


PS. The amp is strictly mono by the way, no stereo possible. That isn't what the multiple speaker outputs are for.

Hope that helps more than it confuses.


Best,
Andy.

What you could do though Legend is to buy or make a 'series' box. This will let you run the two 8 ohm cabs in series for a total load of 16 ohms. You could then run them together from the amps 16 ohm output.

See here for a series box design:
http://forum.orangeamps.com/viewtopic.php?t=13774" onclick="window.open(this.href);return false;


Andy.