The ACUPWR Papers

ACUPWR featured in

ACUPWR is proud beyond belief, the premier website and forum for musicians, music enthusiasts, home recording geeks, and anyone and everyone involved in music and sound, has hosted an article written by ACUPWR’s Mike Bieber titled, Transformers, Not the Movie: “When touring in a land of unfamiliar voltages, make sure you choose the right kind of transformer.” The article addresses international voltage conversion as it relates to touring musicians. The article can be found at

We’ve blogged before about ACUPWR being the safest and most reliable transformer for musicians relocating or touring overseas with “fixed-voltage” amps or instruments (see our blog article Shut Up and Play Yer Guitar in Denmark. By fixed-voltage, we’re referring to equipment with a power transformer that can accept only a particular line voltage—say 110-120 volts or 220-240 volts. So, let’s say you have an ‘50s era Fender Deluxe that requires 117 volts, and you’ll be taking it to, hmmm, Cologne, Germany where the line voltage is 220-240. In this case, an ACUPWR AD-500 step down transformer will convert voltage for the amp. And voilà.

Mike’s article also discusses how cheap, low-budget transformer—those black-box types made in Asia with cheap parts—are fraught with problems that’ll have your amp literally smoking in the middle of your allegedly smoking guitar solo. Using a solid, American-made transformer, one that has a thermal protection sensor for overload protection rather than a glass fuse, will save your amp and everything else—perhaps even your life.

Below is the the article in its entirety.


Transformers: Not the Movie: When touring in a land of unfamiliar voltages, make sure you choose the right kind of transformer

By Mike Bieber, ACUPWR

Musicians travel and that’s the way it’s been for thousands of years. So, all hail the roving troubadour, the travelling minstrelsy, the road dogs in the Ford Econoline, and the New Jersey hair bands in their steel horses. And let’s not forget the Travelling Wilburys.

Seriously, touring internationally should be an exciting adventure for any performer or musician. Yet the prospect of jet lag, getting treated like royalty by a tiny two-person label, and performing in an exotic place like Sheffield can obfuscate important logistical factors—like AC voltage differences. Granted, you often don’t need to think about this; power supplies in most newer electronics and electrical equipment can accommodate a line (household) voltage range of 100-240 volts. This range encompasses the international voltage standards used throughout the world, and most modern guitar amps have power transformers that accept world-wide voltages as well.   

Still, plenty of touring musicians are tone obsessives who can’t part with their vintage tweed Deluxe amp or vintage keyboard or pedal or whatever, and lots of old gear accepts only a single voltage standard (particularly export gear). For example, the backline of Fender amps seen in the Beatles’ “Let it Be” rooftop concert were export models fitted with power transformers to accommodate England’s 220-volt, 50 Hz AC power. Most older amps were built to operate on the voltage standards of the countries from which they originated; for years, Marshall shipped amps to the US with fixed-voltage power transformers designed to handle only the US’s 110-120-volt, 60 Hz voltage standard. Meanwhile, today many boutique amp builders use single-voltage power transformer to match the voltage standard in a distributor’s country, so an amp shipped to a European distributor likely has a power transformer that accepts the European voltage standard of 220-240 volts and 50 Hz. (Fun fact: two thirds of the world rely on 220-240-volt, 50 Hz electricity.)  

Needless to say, amps with single-voltage power trannies have hardly stopped dedicated musicians from bringing them all over the world. That said, what’s the workaround for using your fixed-voltage amps and instruments in a country with incompatible voltage? Let’s consider the options.

  • Rent your equipment overseas. Most touring musicians bring only their instruments, and rely on equipment rental houses or the club’s backline for gear like amps and drums.
  • With fixed-voltage amps, convert the power transformer to one that will accommodate 220-240 volts, 100 volts (as used in Japan), or whatever the voltage standard is in the country you’ll be using it in. Amp-friendly power transformers are available from Mojotone, Hammond, Mercury Magnetics, Tube Depot, and other sources.
  • Use an external step up/step down voltage transformer that converts the line voltage in a particular country or region to match the voltage requirement of your amplifier or instrument. This route eliminates the hassle of modifying your amp for a situation that might be only temporary (such as touring).

Each of these options has its own merits, and you can decide which of them is most convenient for your needs. But we’ll limit this discussion to the third option: using an external step up/step down voltage transformer to convert international voltages.

This option lets you leave the power transformer in your amps, keyboards, and other equipment completely stock—something appreciated by vintage amp collectors—and instead, use a “plug-and-play” solution between the power source and your equipment. Guitar technicians and live sound contractors rely on step-ups and step-downs for all kinds of line voltage conversions; with a high-quality, American-made transformer you can play the heart out of your old ’67 Deluxe Reverb (the one with a power requirement of 117 volts) somewhere in Norway (where everything runs on 220 to 240 volts).



If you enter the search term “step-down voltage transformer” in, you’ll see dozens of similar-looking black boxes with a slew of different brand names, among them PowerBright, SevenStar, Simran, Rockstone, etc. Now, because I’m with an American company (ACUPWR) that makes step-up/step-down transformers, the following may seem self-serving—but I’ve also accumulated a lot of experience regarding what does and does not work. The bottom line is playing through something like an amp involves high power, high voltages, and high current drain, which places significant constraints on what you can use. It’s not like you’re trying to power a radio or electric razor.

The visual similarity of the black boxes referenced above is due to their being manufactured inexpensively in China, usually under the same roof (regardless of brand name). These types of transformers are ill-suited to serious use, for reasons we’ll discuss later.

In the other corner there’s quality. Scroll a few pages in on the “step-down voltage transformer” search and you’ll find some American-made models by ACUPWR. This brand costs more ($159 for a 500-watt step-down model compared to a 500-watt Chinese model that sells for $32.95) but there’s a reason for this kind of price difference. Ideally, a transformer is reliable, energy efficient, and have a long useful life. Even more importantly, when you’re dealing with all things electro-magnetic, safety is first and foremost. 

At a $32.95 price point, the corner-cutting involves using aluminum wiring and coils, cheap steel for the transformer core, and an ordinary glass fuse that often doesn’t blow until there’s been an overload for a period of time. These differences are important. For example not only does aluminum have lower current carrying capacity than copper, if a product mixes aluminum wiring and copper (e.g., in connectors), corrosion becomes a factor because aluminum will react electrochemically with copper when moisture is introduced into the system (e.g., humid environments). As to glass cartridge fuses, although they’re supposed to blow when the circuit is overloaded to protect the transformer and your amp, the response time can be sufficiently slow that they may not blow until after the transformer has caught on fire due to overheating.

Professional units that can handle the kind of current needed by amps are hand-built with premium-grade electrical steel, copper core wiring, heat resistant enamel coating, and a thermal protection sensor instead of glass fuses. These sensors react to the heat caused by an overload condition instead of reacting solely to the amount of current. This is important because if the fuse thinks the amount of current is okay, it will keep supplying current and continue heating up the transformer. A sensor will shut the unit off automatically if it becomes too hot due to an overload condition, but also restart the transformer when it cools down (unlike a blown fuse, which you have to replace) and also unlike a fuse, will work beyond the stated wattage if there’s no danger over overheating.

Remember, parts aren’t just simply parts. Using cheap steel for a transformer’s core and aluminum wire makes the transformer susceptible to overheating, power loss, and inefficiency. The cheap core can also lead to a very audible AC hum (a principle known as hysteresis), and not enough magnetic flux to move the electrons along. To compare, a recent bench test between an ACUPWR transformer and a Chinese PowerBright model showed the ACUPWR model to have 95% energy efficiency compared with the Chinese model’s 85% energy efficiency. Tested at their fully stated wattage load capability of 500 watts, the ACUPWR model converted 220-volt input to the desired 110-volt output, while the PowerBright model converted 220 volts to an undesirable 95 volts—the equivalent of running your amp during a brownout.



There’s more to the subject than just converting voltage, because of the AC line frequency differences that exist with different line voltage standards. 60 Hz, or cycles per second, is common with 110-120-volt electricity and 50 Hz is typical with 220-240-volt electricity. Voltage transformers don’t convert AC frequency. Does this matter? It’s a complicated question with many opinions for answers. A solid, ruggedly built voltage transformer has enough iron in its core to allow for safe operation of 60 Hz equipment in a 50 Hz country. The general rule is that any electronic device with a high-power motor will be affected and not crank at the proper torque. Also, devices that depend on the AC voltage frequency for timing (e.g., many analog tape decks) will be affected. Low-power “servo” motors are not impacted, nor are electronics. However, this answer doesn’t always satisfy audiophiles and tone purists who insist that there’s a difference. Whether their observations stand up to double-blind testing is another matter altogether, so we’ll just leave it at that. 

“Golden ears” questions aside, the most important point is that step-up or step-down voltage transformers are not just about getting a job done reliably, but getting it done safely. If you have a few low-current consumer gadgets, the $32 transformer might do the job. But when you want something that won’t damage either your gear or yourself, or turn your smokin’ solo into a literally smokin’ solo, it’s crucial to do your research and choose transformers that prioritize reliability and safety.

Mike Bieber is the Marketing Director for ACUPWR transformers. He is not related to Justin.

Leave a comment