Bad bar electrical systems: Use a variable transformer on the supply?

[byacey]

The "bad power" is more likely poor AC grounding, or electrostatic noise picked up on low level signal lines. Most audio gear isn't overly sensitive to voltage variations +/- 10 volts.

 

[Nevada Pete]

We play a lot of outdoor festivals, that will likely not help you.

Educated guess........when the refrigeration or ac compressors kick in, voltage goes low.

That won't help.

Conditioning cleans ups noisy power.

We decided to ask for a dedicated circuit.

This is the problem I had on Broadway in San Francisco, both at the Off Broadway where Charlie Button was mainlining their sound and at the former Stone nightclub I put in a few doors down. Stage power was an after thought at both these venues when they were built and came from the three phase feeds employed to run the giant walk in freezers and refrigerators. When those big motors on the compressors kick in, the in rush current is massive and plays havoc with line voltage. Then, when the in rush is done and the motor wingdings are saturated you have a huge spike not dissimilar to a water hammer slamming you electronic gear. It takes its toll. I had PG&E do a voltage recorder test over two days for us at the Stone, and that's when we learned that running stage power from those kinds of circuits is not a good idea. We had a 100 amp single phase 220 V feed from a center tapped pole transformer that served the rest of the club, and when we had an electrician take the stage power from that, all our problems went away.

You will also run into problems taking 120 V from 208 legs / three phase when its running air conditioning motors. Yes, you will get 120 V from one of the 208 legs of the star if you know how, but you run the risk of overloading the circuit. Then the air conditioning motors draw too much current on account of the low voltage and heat up excessively. In Santa Cruz one night smoke from an over heated air conditioning motor started coming down through the ceiling mounted air conditioning registers in a room crammed full of 800 to 1000 people. Not good. The owner of that facility said, "Oh, it always does that!"

For my money, I just wouldn't play at a joint that had bad AC on stage. Inform the club owner of the problem and the possible consequences, and wait for them to fix it before you play there again. You might be waiting a long time. Maybe even until the joint burns down.

 

[gelinas666]

Tripp-Power Conditioner LC1200

.. I use it for all my shows and for studio work.. Keeps it 120volts...I use many All Tube Bass heads and they run as they should.. My Ampegs use to go into "Fault" mode when the voltage dropped below 110 at some over used and under powered shows.. This was my fix and have been using them for years..

 

[joebeadg]

just what a venue needs, a non master electrician going in their circuit breaker panels connecting some hokey ass ext cord. You should really just plug into their outlets, if they have power problems, don't play there. Our equipment operates fine in occupancies that have flour. lighting and air conditioning.

 

[TakeABreak]

Yes. PM me.

I have a veriac but I wouldn’t want to be carrying that thing around it really belongs on the scientific bench

Thanks - it was more of a hypothetical inquiry. Unless you can get a variac in pedal form.

 

[44me]

Speaking from more than 30 years power electronics design experience (amplifiers, motor drives, power supplies, inverters), I can tell you with certainty that a variac is not going to help, and may actually make damage more likely. When you can hear the effect of bad building wiring, it's usually related to grounding and noise. A good quality line filter and over-voltage protector will address most risks. Equipment is designed to work over a reasonable line voltage tolerance. Newer, high quality gear is likely to be more tolerant than older gear although tubes are generally forgiving of moderate voltage variations.

 

[TheDirtyLowDown]

We have a couple of Furman voltage regulators which help with varying AC voltage. Here is an
example of one Merit Series 15 Amp Voltage Regulator | Furman Power | Purifying power for over 40 years.
When the AC power sags, the regulator's autotransformer switches taps and maintains line voltage. It's amazing to see how often this happens in bars, parks, festivals, and anywhere with sketchy AC power -- the indicator lights on the front show you the actual line voltage and the voltage coming out of the regulator.

I think that is what you want: a voltage regulator.

Regarding the original post: I have an old Variac similar to what you posted, which I use for electronics projects -- it is a variable autotransformer, but the key difference is that you manually adjust it to set the voltage output you want. That's not something you'd want to use in a live band setting, because you'd have to manually monitor it and change it. But it's great for the workbench, where you want to vary the AC voltage in a controlled way and see how your circuit behaves.

I hope this helps. Good luck!

 

[Wasnex]

We have a couple of Furman voltage regulators which help with varying AC voltage. Here is an
example of one Merit Series 15 Amp Voltage Regulator | Furman Power | Purifying power for over 40 years.
When the AC power sags, the regulator's autotransformer switches taps and maintains line voltage. It's amazing to see how often this happens in bars, parks, festivals, and anywhere with sketchy AC power -- the indicator lights on the front show you the actual line voltage and the voltage coming out of the regulator.

Regarding the original post: I have an old Variac similar to what you posted, which I use for electronics projects -- it is a variable autotransformer, but the key difference is that you manually adjust it to set the voltage output you want. That's not something you'd want to use in a live band setting. But it's great for the workbench, where you want to vary the AC voltage in a controlled way and see how your circuit behaves.

I hope this helps. Good luck!

The only way I would us a variac for live work is if I intentionally wanted to brown out the voltage. For example, I have an early Vox AC30 that really needs 110V instead of 120V. The transformers were supposedly tapped for 115V per the control panel, but on 60hz the plate voltage runs a bit high. The amp biases perfectly on 110V and the heaters read 6.25V, which is well within spec.

 

[edbass]

So many misunderstood concept in this thread. May marketing dominate everybody's thoughts...

In an attempt to put a positive spin on this thread;

It's somewhat entertaining, but regretfully in the perverse/guilty way that it can be hard to look away from a horrific accident.
It illustrates why arbitrarily taking technical advice verbatim from an un-vetted enthusiast forum can be a risky proposition at best.
It quantifies why companies invest so much of their corporate budgets into marketing as compared to R&D.

 

[OogieWaWa]

Well . . . we got there last night, and lo and behold, there's six shiny new 4-outlet covers/boxes in the band area on three separate circuits, and the owner said that the utility re-analyzed their system and upgraded the transformer on the pole!

Apparently a couple of camp site were added over the years, and the permanent ones were having issues with burning out A/C units, so the bands were a secondary concern but will all benefit.

 

[rocu]

Well . . . we got there last night, and lo and behold, there's six shiny new 4-outlet covers/boxes in the band area on three separate circuits, and the owner said that the utility re-analyzed their system and upgraded the transformer on the pole!

Apparently a couple of camp site were added over the years, and the permanent ones were having issues with burning out A/C units, so the bands were a secondary concern but will all benefit.

Win!

 

[bbh]

That’s great. A lot of owners can’t afford the upgrade.

 

[Slevage]

that is a “voltage regulator” which would indeed totally fit the bill. it’s a variac that self-adjusts to keep its output voltage constant.

computer UPS things don’t have the current to run big bass amps and power amps; they’re for stuff like computers and digital mixers and keyboards, things that get messed up if they lose power.

UPS ‘s come in all sizes if you want to pay the price. I’ve installed some with a 60amp, 3 phase main disconnect switch.

They are not self adjusting variac’s ( auto transformers). They take the incoming AC, change it into DC, then back to clean AC with constant amplitude.

 

[agedhorse]

There are different kinds of UPS devices, those that transfer upon loss of AC or serious drop of voltage, and those that are always rectifying and inverting.

Only the latter can maintain AC quality.

 

[Jim C]

Hey Andy, Paul, Wasnex,
Am I wrong thinking that most modern amps have gone to great lengths for a propper filtered power supply?

Assuming grounding, neutral, and L1 are all propperly supplied, isn't the issue folks really have is not having a steady 120 VAC supply? (assuming that there isn't some ridiculous amount of nosie on the line that no consumer product would fix anyway).

Wouldn't a voltage regulator be the correct tool to draw more current from the outlet in order to maintain a steady voltage?

 

[agedhorse]

Hey Andy, Paul, Wasnex,
Am I wrong thinking that most modern amps have gone to great lengths for a propper filtered power supply?

Assuming grounding, neutral, and L1 are all propperly supplied, isn't the issue folks really have is not having a steady 120 VAC supply? (assuming that there isn't some ridiculous amount of nosie on the line that no consumer product would fix anyway).

Wouldn't a voltage regulator be the correct tool to draw more current from the outlet in order to maintain a steady voltage?

It depends very much WHAT the real problems are with the AC supply.

For example, large amounts of noise can be generated simply by a neutral and ground being connected together or reversed anywhere in the feeder or branch circuits that are common to that feeding the supply. Not an uncommon fault where somebody forgets to remove a ground to neutral bonding screw from a sub-panel. This can cause circulating currents within the grounding system and induce noise.

The amps I have designed recently won't benefit from external voltage regulation anyway, it's already included and built into the power supply (including the main amp rails).

 

[Slevage]

It depends very much WHAT the real problems are with the AC supply.

For example, large amounts of noise can be generated simply by a neutral and ground being connected together or reversed anywhere in the feeder or branch circuits that are common to that feeding the supply. Not an uncommon fault where somebody forgets to remove a ground to neutral bonding screw from a sub-panel. This can cause circulating currents within the grounding system and induce noise.

The amps I have designed recently won't benefit from external voltage regulation anyway, it's already included and built into the power supply (including the main amp rails).

Sub panels with bonded N to G is a pretty good indication that a permit was not pulled for the job and done by a hobbyist.
On a sub panel install, the first two things the AHJ looks at is the size and type out the feeder and over current device and separate, unbounded N and G busses.

 

[Jim C]

...right
I'm talking legal power and suggesting that older / other very good amps could work with with a voltage regulator assuming low or variable voltage problems.

 

[agedhorse]

...right
I'm talking legal power and suggesting that older / other very good amps could work with with a voltage regulator assuming low or variable voltage problems.

If there's voltage problems significant enough to cause problems with any even basically reasonable quality modern amp (within the last 30+ years), that by itself defines am NEC 210 & 215 non-complying installation. It is generally required that the engineering calculations for an electrical installation show a voltage drop of less than 3% for a feeder and less than 5% for a branch circuit at rated feeder/circuit current. For sensitive load circuits the voltage drop can't be greater that 2-1/2%.

There is a potential problem with voltage regulating devices on AC supplies that can cause issues with dynamic loads and large supply voltage drops...

As the current increase, the voltage drops and the regulator boosts which causes an increase in current which further decreases the voltage and so on. Now, when the load is reduced, the current quickly drops which causes the regulator the buck which decreases the further current, which raises the voltage which needs more buck. If the control loop governing this doesn't have adequate damping, or the loop gain is too high (these variables are different for every combination of scenario) then the system can hunt or oscillate and hopefully only shut down the regulator. This is one of the principle causes of tap commutating regulator failures.

 

[Slevage]

If there's voltage problems significant enough to cause problems with any even basically reasonable quality modern amp (within the last 30+ years), that by itself defines am NEC 210 & 215 non-complying installation. It is generally required that the engineering calculations for an electrical installation show a voltage drop of less than 3% for a feeder and less than 5% for a branch circuit at rated feeder/circuit current. For sensitive load circuits the voltage drop can't be greater that 2-1/2%.

Good point here— just to clarify— total voltage drop allowed at end of branch circuit is 5%. 3% max from feeder, 2% max from branch circuit for a total allowable drop of 5%.