Series or Parallel? Total impedance?

[congerz83]

Hello all..

 

I have a new EVH 5150 50W el34 arriving today.

 

I plan to use it with an old Crate 4x12 cabinet I have laying around (for now).

 

Can someone please help me to determine if my amp is wired SERIES or PARALLEL and what my total impedance is?

 

I don't want to destroy my new amp.

[daddymack]

its not the amp, but the cabinet that would be wired series or parallel. IIRC the 5150 has selectable impedance from 4 to 16 ohms; your 4x12 cabinet is likely 16ohms, which can be easily verified with an ohm-meter.

[DeepEnd]

Based on your pic, the answer is both. The speakers are all 8 Ohm. Four 8 Ohm speakers wired in parallel would give 2 Ohms and there aren't any 2 Ohm cabs because most amps can't handle a load that low. Four 8 Ohm speakers wired in series would be 32 Ohms and 32 Ohm cabs are also rare. Assuming the cab hasn't been rewired for some reason, what you most likely have are two pairs of 8 Ohm speakers wired in series for 16 Ohms and then those are wired in parallel for 8 Ohms total. You can buy a Volt/Ohm meter cheap from Walmart if you want to check. Is your EVH a head or a combo? If it's a head, it will handle 8 Ohms just fine. If it's a combo, the external cab will run in parallel with the internal speaker(s); if it's a head, make sure the impedance selector is set for 8 Ohms, plug and go. If it's a combo, I can't find the impedance of the internal speaker(s) and I'd want to call EVH to be sure but assuming it's 8 Ohms the total impedance will be 4 Ohms and you'd set the impedance selector accordingly.

[WRGKMC]

If the cab has 4 X 8 ohm speakers its likely wired series parallel for 8 ohms.

 

If the cab is untouched from the manufacturer you can likely trust what the manufacturer publishes for impedance. If this is a used cab you are better off checking the impedance either by cracking it open and seeing what kind of speakers it has or by using an ohm meter.

 

An ohm meter wont be exact because you're measuring DC resistance not AC Impedance but you can usually get a reading that's within 2 ohms of the nearest standard impedance ie a 7 ohm reading will make the cab 8 ohms. A 14 ohm reading will make it 16 ohms. a 3.5 ohm reading will be 4 ohms.

 

Note, there is no way of knowing if the impedance is improperly set by simply listening. What an impedance miss match on a tube amp typically does is drastically reduce the tube life when the cab impedance is too high for the head which in turn can lead to blowing other components. If the cab is too low for the head you can risk blowing a transformer, especially one that has different impedance settings.

 

 

If it was a transistor amp, a matched setting transfers maximum wattage from amp to speaker. If the impedance is higher it doesn't normally hurt the head but there is reduced power/sound. An impedance too low overheats the output transistors and you risk a full meltdown of the output transistors.