The Power Quality FAQs

Q: Is there a difference between the PS Audio Power Plant AC regenerator and the  Pure Power AVPS?
Q. What about current limiting?
Q. Does PurePower offer variable frequency control?
Q. Will balanced power technology do what PurePower does?
Q: Will an isolated receptacle provide clean AC power?
Q. Won’t an isolation transformer make a new clean power supply?
Q. Why aren’t the PurePower receptacles isolated from each other?
Q: Can a dimmer switch be placed in the same circuit as my PurePower? 

Q: Is there a difference between the PS Audio Power Plant AC regenerator and the  Pure Power AVPS? 
A:  PurePower’s “transformer-less”  Off-Grid Power Supply uses solid-state components and proprietary software, with an unsurpassed efficiency of over 90%. The efficiency and intelligence are both crucial to the optimum operation of high power amplifiers, and HDTV’s.  Power Plant uses a class AB power amplifier design that incorporates a large toroidal transformer to maintain output voltage, lowering its efficiency to 50%.

The primary difference between the two is PurePower’s auxiliary battery that allows PurePower units to be 100% Off-Grid from all utility based power. PurePower produces 120 volts, 60 cycle output no matter what the input – even if the input is zero volts. Power Plant is unable to be completely isolated from the incoming power quality – so when the incoming power drops below certain values or the load is high, or both, Power Plants output follows the utility voltage drop and its distortion reflects the input distortion. Simply put, when the utility sags, the Power Plant  sags too. When the input power is below 95 V or above 135V the Power Plant simply shuts down.

Q. What about current limiting?
A: The logic of current limiting is simple. If the wall outlet of a typical 15-amp circuit is capable of delivering 1750 watts, and your AC regenerator is 50% efficient – obviously the RMS current is limited by 50% . The PurePower AVPS is 90% efficient. The PurePower 1050 keeps delivering its full rated output of 1050 watts continuously even when the inbound utility voltage drops to 60 volts – and keeps on delivering it even if the utility voltage drops to 0 thanks to its integral high energy battery backup system.

Long term, short term and instantaneous power.
Power amplifiers require different amounts of current under different conditions. They have an RMS requirement that draws a steady wattage over time. They have short term start up requirements for as much as 150% of the rms value that may last from 5 to 30 seconds and they may have an instantaneous requirement for 200 to 300% of the rms value for milliseconds when they have to drive the speakers during a sharp peak (think cannons in the 1812 overture).

The PurePower is designed to support the start up inrush by delivering 150% of capacity for up to 30 seconds and 110% for 2 minutes. The PurePower design is capable of delivering instantaneous power up to 300% of its rated output, even when utility voltage drops. For our PurePower 1050, that means instantaneous current of over 37 Amps.

Voltage drop and circuit “intelligence”
Supplying the current an amplifier wants when it wants it is a demanding task because the amplifier can change its power needs very dramatically very quickly – in fact in a fraction of a cycle. The PurePower AC Regenerator circuit is designed to be “smart” about maintaining voltage no matter what, and maintaining voltage during high current draw is exactly what allows the amplifier to meet its wattage needs and provide the best dynamic range without clipping. By contrast, a normal wall outlet actually experiences a voltage drop that reduces an amplifier’s current draw under the same conditions. The performance improvement provided by the PurePower design can be impressive in terms of amplifier performance as illustrated on our technology page and attested to by our customer and reviewer comments.

Q. Does PurePower offer variable frequency control?
A: The PurePower AVPS matches the frequency of the new regenerated sine wave to the utility power frequency automatically. PurePower maintains an exact 50 or 60 Hz frequency +- .1Hz%. PurePower does not allow operation of components at any frequency other than the frequency for which they were designed.

Q. Will balanced power technology do what PurePower does?
A: No, balanced power is an ingenious technique that uses transformer technology to cancel noise and distortion in the AC sine wave.  However balanced power transformers are notoriously inefficient, can crush system dynamics and they have no effect on voltage drops, brownouts or blackouts. (See our comparison chart.) Balanced power systems in which the normal 120 volt line and grounded common wire are replaced with a 2 wire +/- 60 volt scheme. They are non-standard compared to house wiring and must be isolated to make sure they do not cause dangerous voltages in other household power systems. We do not have a professional opinion on their safety, but tend to think that it is always preferable to operate electrical equipment in the simplest way possible that fully meets local standards.

Q: Will an isolated receptacle provide clean AC power?
A: An isolated ground receptacle has no effect on AC power. There is a great deal of confusion about the term “isolated receptacle” and the term is often misapplied. An isolated outlet is better described as an “isolated ground” outlet. Its purpose is to make sure the safety ground wire has the best direct connection to the supply ground at the service entrance. This is critical to prevent unwanted currents or noise from being carried between the common and ground wires. Ideally there is zero potential between them, and therefore no unwanted signal, but bad connections can create an opportunity for “common mode noise” to exist.

Q. Won’t an isolation transformer make a new clean power supply?
A: Expensive isolation transformers can be used to create a new “clean” ground at the point of use and this will fix a common mode noise problem – but at a high cost and a risk of dampening audio system dynamics. It will not correct voltage sags or spikes. It is better, and cheaper, to run new, uninterrupted wiring from the service entrance to a single “isolated ground” receptacle. This simple step will almost always be effective at cleaning up common mode noise that can cause hum.

Q. Why aren’t the PurePower receptacles isolated from each other?
A: All AC circuits in a single residence are connected together, and a power problem that exists at one outlet will be experienced at all outlets served by the same distribution transformer. This often means you are sharing power problems with several of your neighbors. The only way to truly isolate one receptacle from another is to provide separate power sources for them. This can be done by individual isolation transformers, or by separate AC Regenerators.

When you see the term “isolated outlets” in receptacles in the same enclosure or on the same power bar you should take the term with a grain of salt. Many power conditioners  have an added low pass filter – basically a small coil and capacitor – attached to each receptacle. The theory is that this will filter high frequency noise generated by a device plugged into one receptacle and prevent “cross contamination” to other devices.

These inexpensive filters may have some efficacy, but there are 10 different “power gremlins” that can reduce AC power quality, and a filter can only affect 1 of the 10, so perhaps “1/10 isolated receptacle” might be a better descriptor. If you plugged your amplifier into one outlet, and a light dimmer switch into the other, some of the high frequency noise from the dimmer switch could be attenuated by the filter. If you own a CD player or preamp that makes noise like a dimmer switch, it could likewise attenuate that noise. (Our advice to all audiophiles is to not let a dimmer switch come anywhere near your house, and if you bought a piece of high quality audio gear that radiates noise like a dimmer switch, send it back.)

There are two flaws in the filter plan. 1: most audio system component power supplies either do not radiate such noise into the AC line, or they are so small a contributor as to be negligible. 2: The distortion they do tend to generate is harmonic distortion. This distortion is completely unaffected by a low pass filter.

PurePower’s engineers considered adding low pass filters to our output receptacles, but discarded the idea. We believe it is just as likely for the filters to reduce current flow and diminish sonic performance as it is to remove harmful high frequency noise. We think they are of small benefit – other than to use as a marketing point.

Q: Can a dimmer switch be placed in the same circuit as my PurePower? 
A: Dimmer switches are one of the worst offenders in adding noise to household electrical circuits. They can generate low frequency noise in the wiring and radio frequency noise by radiation and conduction. They should definitely not be placed near sensitive audio and video components and certainly not in the same circuit. Solid State dimmer switches operate by chopping current into very fine steps. This can interact with audio equipment in unpredictable ways.  If you insist on using a dimmer, make sure it is on a completely separate circuit from your audio and home theatre equipment. For more info on dimmer behavior see: http://www.lutron.com/product_technical/FAQ.asp 

The PurePower AVPS will completely remove all dimmer switch noise from the ac line supply to your system.