calculate volts and amps from 1000 watt head into 4 ohms

Discussion in 'Amps and Cabs [BG]' started by GGman, Dec 24, 2016.

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1. GGman

Oct 17, 2008
I have an SVT7 Pro amp that produces 1000 watts into 4 ohms. I would like to know the max voltage and amperage from the speaker outputs.

Last edited: Dec 24, 2016
2. agedhorseSupporting MemberCommercial User

Feb 12, 2006
Davis, CA (USA)
Development Engineer-Mesa, Product Support-Genz Benz
Review Ohm's law... specifically the formula P = V^2/R, solve for V and you have the voltage. For the current, P = I^2 x R, solve for I and you have current. (V^2 is V squared, I^2 is I squared)

Solving for V: V = sqrt(P x R)

Solving for I: I = sqrt(I/R)

(sqrt is square root)

Since the power is based on RMS units, the results will be RMS voltage and RMS current. For peak voltage and peak current, multiply the RMS values by 1.414. Peak values would be used to calculate peak power, or to look at current density at a contact surface (such as a jack) or for insulation breakdown in the case of peak voltage.

3. GGman

Oct 17, 2008
thanx guys

Last edited: Dec 24, 2016
4. agedhorseSupporting MemberCommercial User

Feb 12, 2006
Davis, CA (USA)
Development Engineer-Mesa, Product Support-Genz Benz
14 gauge is plenty fine, hope you are using SpeakOn for this connection.

5. GGman

Oct 17, 2008
the speaker cabs are only 1/4".

Last edited: Dec 24, 2016
6. beans-on-toastSupporting Member

Aug 7, 2008
The problem is, your amp is capable of producing peaks that are well above the RMS values. You asked about maximum, the RMS is not that.

The maximum peak output that an amp in the real world is capable of putting out is not so easy to predict based on the available RMS numbers.

I = Sqrt(1000W/4) = 15.8A

V = P / I = 1000W / 15.8A = 63.3 V

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7. GGman

Oct 17, 2008
I am trying to determine the best speaker wire gauge and if 1/4" jacks will be ok. The cabs only have 1/4".

Last edited: Dec 24, 2016
8. Killed_by_DeathSnaggletooth

The amount of money you'll spend to do it right vs. penny-pinching will be negligent.
Do it right the first time & then you don't have to second guess if you did it right the first time.

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9. GGman

Oct 17, 2008
Killer by Death, what do you think the correct wire gauge is for my rig?

Last edited: Dec 24, 2016
10. MrLenny1

Jan 17, 2009
N.H.
Twist lock is it. For safety. 1000 W is a lot of power
and your best protection from a loose connector is a Speakon conn.
Save up, it's worth it.

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11. GGman

Oct 17, 2008
I NEVER plug in a speaker cable with an amp turned on.

Last edited: Dec 24, 2016
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12. agedhorseSupporting MemberCommercial User

Feb 12, 2006
Davis, CA (USA)
Development Engineer-Mesa, Product Support-Genz Benz
Good questions.

The reason I mentioned peak current is because the connector contact surface area has limits due to current density. Only so many amperes of current per square inch is safe, as contact area decreases the allowable current also decreases. A 1/4" connection has a very small area, therefore a proportionally small current for a given current density. SpeakOn connections gave a larger contact area (with higher contact forces also), thus higher allowable current.

Other important factors include the problem that when the 1/4" plug comes out of the jack on the speaker end, the tip shorts to the sleeve (inside the jack's barrel) and has the potential to damage the amp due to short circuit.

The third issue is that on a bridged amplifier (such as this), the shell of the 1/4" plug is not at ground but may swing as much as ~80 volts peak, and even more attention getting, the voltage between tip and sleeve would be ~160 volts peak if you happened to grab the connector while playing (or somebody else is playing)

Best solution is to have your cabinets updated to SpeakOn as well, and be done with it.

13. bumperbassSupporting Member

Jun 19, 2012
Do Speakon. Trust the agedhorse! 1/4" was only designed for a low signal level input/output. I just got done updating all of our PA speakers to Speakon. Can you imagine a Peavey Subcompact 18" sub with 1/4" jacks? All that low frequency energy and power was going through perhaps a tiny 1/32" tip of a skimpy-in-the-first-place jack. Now, our CS800S's do not go into DDT any longer and you can hear the difference.

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14. hondo4life

Feb 29, 2016
SC
There is such a thing as a locking 1/4" jack. I used one on a cabinet I built. No amp explosions so far.

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15. Raf Seibert

Dec 16, 2013
Texas
So far as I know, none of these guys work for Neutrik (makers of Speakon). Their advice is purely in the interest of making it safe for you.

Raf

16. BogeyBass

Sep 14, 2010
best way get free speaker cables is steal the guitar players at a gig.
play stupid and they usually think they just forgot the cable at the venue.

I'm kidding lol don't do that.

so what year was the 1/4 inch telephone patch connector invented anyways. I think it's getting close to being or maybe more than 100 years now

17. Nev375

Nov 2, 2010
Missouri
You can get speakon cables for under 10 bucks these days.

A pair is less than a set of strings. Why mess with 1/4?

18. GGman

Oct 17, 2008
Ampeg only uses 1/4" jacks on these cabs.

Last edited: Dec 24, 2016
19. Downunderwonder

Aug 26, 2009
New Zealand
Buy parts and wire and make the cable. Far cheaper. I hope you have good earplugs with all those watts flying about, lest you finish your days saying ''what?'' all the time.

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20. BogeyBass

Sep 14, 2010
cause the other end is going to a
1/4 and he has no interest or budget to convert.

y'all must be rich lol.

cause like he stated some people literally don't have the money.

I've been broke for like 2 weeks too.
literally zip zero...nothing.
so I wouldn't spend money to convert a cabinet that already had a working jack. for a newer standard.
knowing it won't handle a 1000 watts anyways. probably any cabinet with a 1/4 inch won't do more than 300 watts before fart city. even if it's rated at 800 or whatever bs rating the manufacturer gives it.

like he mentioned it is easier cheaper and more fun to make your own anyways. cause you can use super heavy gauge wire and not pay a bundle
of money for premade cables which are more expensive in heavier gauges. I never really buy wire you can find that laying around. just have to buy the 1/4 inch plugs and they have them with enlarged covers and screw terminals for solid connection.

Last edited: Dec 24, 2016
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