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Discussion in 'Amps and Cabs [BG]' started by DrumsAndBass, Oct 11, 2013.
If a bass head is also rated for 2 ohms does that mean that it will have reserve power at 4 ohms ?
Not at all. In the case of SS and hybrid heads, it will make available whatever wattage the company says at whatever impedance you use. And reliability isn't affected by 2-ohm capability at all.
If you run a 4 ohm cab on an amp capable of driving 2 ohms, then there's less power and less heat than if you were running a 2 ohm cab and the power supply doesn't have to work as hard.
So, yes it's likely to be more reliable driving a 4 ohm load than a 2 ohm load.
It is when driving a 2 ohm load...
If heads that allow for a 2 ohm load weren't reliable with 2 ohm loads, nobody would buy them.
This is true. I don't know that anyone could dispute this.
Although it doesn't mean that it necessarily has any more 'reliability' or 'reserve power' at 4ohms than an amp that is listed as being safe at 4ohms.
I definitely (and possibly incorrectly) feel more secure with heads that can handle 2 ohms.
A four, or eight Ohm load on a two Ohm capable solid state amp does cause less current flow in the output devices, and the power supply. But, there are failures that are not related to how close to the maximum current capability of components the amp is operating, so there is an increased reliability for failures that are caused by running the amp near its maximum output rating, but no improved reliability for other failure modes. The MOSFETs commonly found in then output sections of most ss amps can be damaged by voltage spikes, that could occur under operating conditions of a four, or eight Ohm load. Inductive components subjected to rapid rising, or falling waveforms can generate high voltage spikes that cause a failure known as Cdv/dt shoot-through that will cause the device to short out. It is a voltage/time dependent, not a current dependent failure.
Other failure modes will be just as likely either way, but reduced risk of thermal failures means increased reliability overall. Ohm's law and common sense.
One would hope that a manufacturer that states that their amp is safe and capable of functioning at 4ohms would mean just that...operating at 4ohms will not cause thermal shutdown or failure based upon the responsible use of any cab that has been given an accurate nominal impedance rating of 4ohms. After all, that is well within the spec of the amp.