Voltage

[James Clausen]

I recently bought a Brown Box voltage attenuater. I have been playing a lot of jams and noticed that my tube amp sounded different in different places. After hearing techs talk about rigs pluged into Brown Box attenuators due to voltage variations in different venues I thought that one might be good insurance for a $1200 amp. Sure enough it has proven a very useful tool in keeping a consistant sound. The varience in power from one place to another surprised me.

[WRGKMC]

Vintage amps many were built to run on 110V. The power companies supply 120V and the fluctuation may be +5 to -5V either way. You can use one to bring the voltage down to 100 or 100V and get a brown sound if you want. I never saw much sense in it myself. Both tube amps and SS amps can usually run on a line with + or -10 volts without a hiccup. Its mainly the high voltage spikes you're worried about.

 

The thing is, its not the voltage that's the problem, its the current in back of it. What typically happens is a sea saw effect. Voltage and current are inversely proportional. If there is a big current draw, the voltage goes up automatically to compensate and vice versa. That's just how transformer work including the ones on the street that supply buildings.

 

A line attenuator is only good for cranking tubes down to run cooler. I used them in a shop for years repairing gear and bringing up the voltages slowly so you don't fry the components you just changed if something else is wrong. They don't provide any extra protection against surges besides the attenuation and the added inductance. There are much simpler ways of getting that protection if that's what you're looking for.

 

Some people like the brown sound of under powered tubes. Others like myself see no need for it. I can re-bias my tubes or simply tweak the EQ to get those tones.

 

I'm not worried about blowing the power transformer on a tube amp. The SS stuff usually has cheaper and weaker power supply components. If anything I'd tend to protect them over a tube amp which is super durable. The one fender has lasted me 50 years unprotected. It will likely last another 50. Its got a fuse to protect it from the outside line. The transformers inductance acts like a shock absorber to most surges. Once its converted to DC the large caps smooth all the spikes out. You just need to replace the caps every 5~10 years and replace the tubes before they fail.

 

If I were to use a AC filter it would be an isolation transformer with surge protection. I have several of those I've acquired over the years because I deal with them every day on the day job. My company sells them and anything they take in on trade from another company gets thrown out because we use different surge protector manufacturers. I collected enough of them for my own needs. I even have a large UPS battery backup unit designed to run a huge server room that can handle enough amps to run a tube amp for a couple of hours.

 

Surge protectors protect against voltage overs and spikes. Nothing besides a battery backup can protect against a brown out or complete drop out. You're not worried about that too much with analog gear because little damage can be done by voltage loss. Its just the surges that do damage popping weak components that cant handle the spikes.

 

I'd say if the unit makes you happy and you like having a brown sound, go ahead and use it. I sure wouldn't want to be busting a gut hauling one around. It helps isolate you from the outside line, but most attenuators have no surge protection, so don't expect it to protect your gear against surges. its a fast change that can cause weak components to blow more then the actual voltage itself. Ever notice how bulbs blow when you first turn them on? Attenuators attenuate, that's it. Surges can still pass through them. A good 15A surge protector power strip that cost maybe $15 will do more to protect your gear then an attenuator will. If that's what you're looking for that's what you should get.

[onelife]

...

 

The thing is, its not the voltage that's the problem, its the current in back of it. What typically happens is a sea saw effect. Voltage and current are inversely proportional. If there is a big current draw, the voltage goes up automatically to compensate and vice versa. That's just how transformer work including the ones on the street that supply buildings...

 

That seems like a contradictory statement.

 

I don't understand ??? please elaborate.

 

 

 

 

[Mr.Grumpy]

If there is a big current draw, the voltage goes up automatically to compensate and vice versa. That's just how transformer work including the ones on the street that supply buildings.

 

That's not correct. A transformer's voltage will decrease with increasing load. If transformers were self-regulating, the OP wouldn't NEED a $350 outboard gizmo to regulate his amp's AC supply voltage.

 

Utility transformers have various taps on the secondary windings so the utility can 'fine tune' the output voltage to both the primary supply voltage and the load on the secondary. The voltage coming out of your outlet is not "regulated" but should fall within a certain range.

 

Voltage and current are inversely proportional.

This is also incorrect, or at least incomplete. For a regular "linear" ohms load, if voltage rises, current rises too.

[Cyborg]

I... I thought that one might be good insurance for a $1200 amp. Sure enough it has proven a very useful tool

in keeping a consistant sound. The varience in power from one place to another surprised me.

Hello James. The price of the amplifier has no bearing on supplied inconsistent voltage levels. If you're concerned about this, I suggest investing a few $$$ in a good Furman power regulator/conditioner strip, such as a Furman PL-Plus Series.

 

I wish I had a nickel for every venue I gigged at where the voltage fluctuation was no less than remarkable.

 

Get yourself a Furman of your choice with SMP and rest well.

 

Good luck.

 

 

[MacFangus]

The Brown Box is what's called a "bucking transformer". It will not regulate. Output voltage is predicated upon line input voltage + BB setting. If you're using digital effects, you may want to avoid using a regulator. The best way to determine the optimal operating voltage for your amp, is to take a tube heater voltage reading. Vintage amps tend to reach maximum heater supply voltage at the lower end of the scale... 110VAC to 115VAC.

[WRGKMC]

According to P=VI…or…I=P/V….or …V=P/I,….. It says that Current inversely proportional to the voltage if power remain same. In a Transformer, If power remain same, and voltage increase, then current decreases

 

If the Voltage input and the Current Input remain unchanged, as Voltage output increases, Current output MUST decrease proportionally…. otherwise you’d be creating power in the transformer

 

This applies when local power companies are supplying constant power to the local step down transformers in the neighborhood. They have a pretty good system of self regulating power up to that transformer. Many of your spikes and over/under voltages occur on the drop side if the street where AC, Heating, refrigeration, Motors etc draw heavy current within a localized area. Voltage can fluctuate up when heavy current is being consumed but the overall power being supplied to that local step down transformer remains the same.

[WRGKMC]

 

That's not correct. A transformer's voltage will decrease with increasing load. If transformers were self-regulating, the OP wouldn't NEED a $350 outboard gizmo to regulate his amp's AC supply voltage.

 

Utility transformers have various taps on the secondary windings so the utility can 'fine tune' the output voltage to both the primary supply voltage and the load on the secondary. The voltage coming out of your outlet is not "regulated" but should fall within a certain range.

 

This is also incorrect, or at least incomplete. For a regular "linear" ohms load, if voltage rises, current rises too.

 

We're dealing with AC power. According to P=VI…or…I=P/V….or …V=P/I,….. It says that Current inversely proportional to the voltage if power remain same. The power companies regulate power up to your street transformer very well. Most fluctuations occur at a localized level and over/under voltage fluctuations are the result of current fluctuations after the local step down transformer on a block by block level.

When transformers decrease the voltage, the transformers increase the current that is available if a circuit is formed. Before a circuit is formed, there is no current.

 

Energy is conserved. Transformers are generally very efficient, having little losses, so the power into the transformer is going to be substantially equal to the power out of the transformer. If the voltage changes (i.e., if it is a step up or step down transformer) then the current will also have to change. Of course, if it is just an isolation transformer, and the voltage out is equal to the voltage in, then the current will be substantially the same (just a little less than the input current, to reflect the minor losses in the transformer)

In DC circuits, power is the product of current and voltage (P=IE), and so current is directly inversely related to the voltage. But this is an AC circuit (transformers don’t work with DC…..), Power is the product of current, voltage and the Power Factor (PF) of the circuit. PF = cos φ and φ = power factor angle (phase angle) between voltage and amperage. Assuming the power factor doesn’t change… then we get:

Pin = Pout

Vin x Iin x cos φ = Vout x Iout x cos φ

Vin x Iin = Vout x Iout

If the Voltage input and the Current Input remain unchanged, as Voltage output increases, Current output MUST decrease proportionally…. otherwise you’d be creating power in the transformer… violating the rule of Conservation of Energy.

Similarly, if the Voltage input and the Current Input remain unchanged, as Voltage output decreases, Current output MUST increase proportionally…. otherwise you’d be destroying power in the transformer… violating the rule of Conservation of Energy. (okay, this actually happens, a little bit, because of losses in the transformer, but if we assume that the losses are a constant percentage of the power input, and that the losses are so insignificant that we can set them equal to zero, we can ignore them).

So you see, with constant power input into the transformer, current output MUST vary proportionally to voltage output or you violate basic laws of nature, the law of Conservation of Energy… at least as far as simple non-relativistic constructs go. I have no idea of what happens when you start considering n-Dimensional Gravity, Black Holes, Dark Matter, or multiverse cosmology.

 

I should add the power companies regulate the power. When the secondary at street level increases the power company will (should) increase the power needed. They of course can only compensate for the draw so much before safety devices kick in. You have various types of breakers on the lines as well as breakers in local homes.

 

But the reason you don't see voltages changing much when current is drawn from the street transformers is because the power to the transformers are regulated.

It might make more intuitive sense if you think of mechanical power, instead of electrical power. Power is also the product of force and velocity:

P=Fv P=Fv

You can lift something heavy with a lever, but you will have to move the lever faster if you want to accomplish the same amount of lifting in the same amount of time. Or, you can move something far with a lever, but you will have to push harder.

Ohm's law is not violated because a transformer also transforms impedance, like a lever can transform the apparent weight of something. The transformers used in the AC distribution system are electrical levers, with a net effect like this:

By adjusting the turns ratio of the transformers between the power plant and the electrical load, we can move the fulcrum of this lever in either direction. Insulation is cheaper than conductors, so we put the fulcrum close to the power plant to minimize cost.

 

The local voltage can fluctuate quite a bit before its seen at the power plant, most of which is automated. As the fulcrum shows a large change on a local level makes only small changes at the power plant and vice versa. I know there are all kinds of computerized sub stations that regulate power on a local level to end users. If users are drawing allot more current (hot days where all the AC is cranked up) power company maintains the power needed by the local users by leveraging the supply. This way you don't see the huge voltage/current fluctuations caused by a transformers inversely proportional laws involving power.

 

I'm not an AC distribution expert but I do know the basics. In the cases where you see high voltages, a localized high current draw is usually the cause. Its high enough to effect the street transformers output but not great enough to make the power company compensate for that draw. There can be a number of factors, the kinds of businesses in that localized area, how far away the local sub station is, how complex that local network is etc.

 

Of course it can be other things like a crappy breaker box, bad outlets, bad ground causing voltage losses too but by description of why voltages fluctuate is mainly focused on the power company side, the meter to street and beyond.

 

In my business we regularly use line monitors when we suspect power problems at various companies having electronics failures. We run the monitor for a week or so to capture a history of the voltage and current fluctuations. Sometimes those fluctuations correspond to what that company does inside the building. Other times we get the power company involved and its up to them to find out who on the local network is affecting they're business and take corrective action. I can say power companies are fairly good at taking action to regulate things so one business isn't taxing others on the street. All they may be seeing on they're grid is what occurs up to that local transformer, not what's beyond. They need to hear from local users when diagnosing local line issues and when you have a monitor running they know they're distribution must change.

 

Again, this assumes the business isn't exceeding its local demands, building wiring issues, inadequate breaker box, line drops to the street etc. Those all need to be diagnosed by an experienced electrician who can determine is the issue is inside or street level. What you see at an outlet can be either.