Amp Power Usage

[ddezz]

This Summer I saw a friends band play at an outdoor town concert. It became obvious that the outlets did not have enough power as when he played his bass through an Agulair tube bass head the lights dimmed. They blew the circuit breakers twice. They then used a class D bass head and no longer had the problem.

 

[somebrains]

It's be a worthwhile winter project to combine power alerting to a mobile device or set of alerting LEDs.

Most of the code you'd need is open sourced student projects.

Pi's are cheap.

 

[sawzalot]

Yep. When my band brings the PA we always have to weigh our current draw against the available power at the venue. Sometimes there’s enough and sometimes not, and if there’s not we have to adjust.

 

[dBChad]

Was this an outdoor pavilion?

If so, it should be equipped with a ground fault circuit interrupter. If one of those has any moisture in it (or any other number of other possible bits of debris) it can cause the outlet to cut out well below what the breaker will trip at.

GFCIs are good, because they keep people from being electrocuted, but one constantly exposed to the elements can eventually become contaminated by something (bugs, grass, moisture) that triggers the safety mechanism and cuts power to the outlet.

 

[Jaygetsreal]

Assuming the 121p uses Class D power amplification (I have no experience with MarkBass) I am wondering if something I have observed is connected.

I built a custom 2X200w class D power amp with an analogue +/- 70V power supply. I noticed that the Class D boards would sometimes shut down if the supply voltage drifted outside their specified range. It was quite amusing - I could make the amp go off and on from downstairs in the kitchen by turning the electric oven off and on LOL! Maybe (someone correct me if I am off track) the voltage in the pavilion was having that same effect?

I subsequently replaced the power supply with a robust switched mode supply and it's bullet-proof now.

 

[agedhorse]

Assuming the 121p uses Class D power amplification (I have no experience with MarkBass) I am wondering if something I have observed is connected.

I built a custom 2X200w class D power amp with an analogue +/- 70V power supply. I noticed that the Class D boards would sometimes shut down if the supply voltage drifted outside their specified range. It was quite amusing - I could make the amp go off and on from downstairs in the kitchen by turning the electric oven off and on LOL! Maybe (someone correct me if I am off track) the voltage in the pavilion was having that same effect?

I subsequently replaced the power supply with a robust switched mode supply and it's bullet-proof now.

I already mentioned this earlier.

The under-voltage protection is an important part of most class D and some class AB amps for reliability reasons.

 

[brianrost]

I've had amp protection circuits kick in and blown circuit breakers playing outdoors a few times.

If you plan on doing lots of outdoor gigs, especially on generator power, get yourself a voltage regulator to guarantee a steady voltage. A "power conditioner" like you see in many racks does not do this. Furman makes one that is about $500 and handles 15 amp loads.

 

[JimChjones]

The question is, is there any way to tell how much power an amp uses? I'm thinking of getting one that may use less power as a back up, if that is even possible. Any ideas are useful.

I have a Markbass Blackline head, which sometimes doubles as a power amp for a small PA. I had to set up a little PA for my partner outdoors, and was proposing to use a 300W battery pack/inverter she has. Fortunately I tested beforehand, and the Markbass simply refused to turn on. Being naive in these things I was expecting not to be able to turn it up. I had to use a 1W guitar amp to drive my PA speakers! Funnily enough they survived being so grossly underpowered [grin].

I've since been looking around for a little PA amp which will run off the power pack, and its surprising how many don't seem to mention power consumption, so I've just ordered something very low powered and hope it will work. Although, all else being equal, one would hope the lower the amp power the lower the power requirement, in fact my understanding is that different amp designs have wildly different power requirements. Modern Class D are I understand by far the most efficient in terms of power in against power out, and Class A the least efficient. I don't know if one can construct a vague rule of thumb for max required power for different styles of amplifier, or whether tubes are inherently more or less efficient than solid state. I vaguely gather that many or most class D amps are based on a limited range of power modules, in which case one might suspect they will all be much the same. Cue @agedhorse ?

Jim C

 

[Wasnex]

I have a Markbass Blackline head, which sometimes doubles as a power amp for a small PA. I had to set up a little PA for my partner outdoors, and was proposing to use a 300W battery pack/inverter she has. Fortunately I tested beforehand, and the Markbass simply refused to turn on. Being naive in these things I was expecting not to be able to turn it up. I had to use a 1W guitar amp to drive my PA speakers! Funnily enough they survived being so grossly underpowered [grin].

I've since been looking around for a little PA amp which will run off the power pack, and its surprising how many don't seem to mention power consumption, so I've just ordered something very low powered and hope it will work. Although, all else being equal, one would hope the lower the amp power the lower the power requirement, in fact my understanding is that different amp designs have wildly different power requirements. Modern Class D are I understand by far the most efficient in terms of power in against power out, and Class A the least efficient. I don't know if one can construct a vague rule of thumb for max required power for different styles of amplifier, or whether tubes are inherently more or less efficient than solid state. I vaguely gather that many or most class D amps are based on a limited range of power modules, in which case one might suspect they will all be much the same. Cue @agedhorse ?

Jim C

A tube amp will generally work to some degree as long as the voltage is high enough for the heaters to work. I think the amps I have tested will begin to pass signal with about 70VAC or so, however it won't sound great at this voltage. Unfortunately tubes amps pull quite a bit of current on idle and are also inefficient at making power, so I would say they are not a good choice for running off a battery. Some of my bigger tubes amps pull close to 4A at idle. I have several tube amps with four output tubes, and they all pull between around 1.2.-1.3 at idle on 120VAC.

I think where Class D really comes into it's efficiency is when it's making full power. I don't think they are particularly efficient when they are idling or being used at low power. So perhaps it would be a good idea to chose a class D amp that is the right size for the job if you running on battery power.

 

[agedhorse]

I have a Markbass Blackline head, which sometimes doubles as a power amp for a small PA. I had to set up a little PA for my partner outdoors, and was proposing to use a 300W battery pack/inverter she has. Fortunately I tested beforehand, and the Markbass simply refused to turn on. Being naive in these things I was expecting not to be able to turn it up. I had to use a 1W guitar amp to drive my PA speakers! Funnily enough they survived being so grossly underpowered [grin].

I've since been looking around for a little PA amp which will run off the power pack, and its surprising how many don't seem to mention power consumption, so I've just ordered something very low powered and hope it will work. Although, all else being equal, one would hope the lower the amp power the lower the power requirement, in fact my understanding is that different amp designs have wildly different power requirements. Modern Class D are I understand by far the most efficient in terms of power in against power out, and Class A the least efficient. I don't know if one can construct a vague rule of thumb for max required power for different styles of amplifier, or whether tubes are inherently more or less efficient than solid state. I vaguely gather that many or most class D amps are based on a limited range of power modules, in which case one might suspect they will all be much the same. Cue @agedhorse ?

Jim C

Every PA amp that carries a safety agency certification is required to state the average power consumption (usually 1/8 rated continuous power duty cycle).

The reason the amp wouldn't turn on is likely due to the inrush current, which trips the inverter's protection. Quality battery/inverters do not have as much trouble with inrush currents.

Class D amps are WAY more efficient than a tube amp. It's not the class d amp that's responsible for the inrush current, it's the power supply that powers it. They are all different.

 

[brianrost]

Modern Class D are I understand by far the most efficient in terms of power in against power out, and Class A the least efficient. I don't know if one can construct a vague rule of thumb for max required power for different styles of amplifier, or whether tubes are inherently more or less efficient than solid state.

Rough rule of thumb based on power consumption ratings listed on the back of the many amps I've used over the years:

Tubes -- draws about 4x the rated output wattage (~400W draw for 100W RMS output)

Solid State Class A -- draws about 2x the rated output wattage (~200W draw for 100W RMS output)

Class D -- draws only a small amount above the rated output wattage (~100W draw for 100W RMS output)

Tube amps have the most power wasted because they need to heat the tubes, class D is by far the most efficient in terms of power in vs. power out.

 

[rufus.K]

I cant say this will work everywhere, but ive seen folks cary small UPSs to these type of gigs, where they plug them in to the supplied recepticles and power their personal gear thru it. Theoretically to smooth out the dips.
Im not saying it works that way, but these were folks who play street fairs and such all the time.

 

[agedhorse]

Rough rule of thumb based on power consumption ratings listed on the back of the many amps I've used over the years:

Tubes -- draws about 4x the rated output wattage (~400W draw for 100W RMS output)

Solid State Class A -- draws about 2x the rated output wattage (~200W draw for 100W RMS output)

Class D -- draws only a small amount above the rated output wattage (~100W draw for 100W RMS output)

Tube amps have the most power wasted because they need to heat the tubes, class D is by far the most efficient in terms of power in vs. power out.

This might be roughly close for maximum power, but not for average power as defined by the international safety regulation community (which most manufacturers choose to adhere to).

I cant say this will work everywhere, but ive seen folks cary small UPSs to these type of gigs, where they plug them in to the supplied recepticles and power their personal gear thru it. Theoretically to smooth out the dips.
Im not saying it works that way, but these were folks who play street fairs and such all the time.

Yes, a quality double-conversion UPS with a pure sine wave output will work well, but beware that many are not rated the way you think until you get into the more commercial/industrial duty units.