Audio Technology

Furman Power Elite 15i Impressions


Although the house has full-house surge protection in the panel, I elect to use a second line of defense for the computers, network electronics, and audio and video systems. In the past, I had used APC power conditioners for this task but another 5 years had passed and it was time for battery replacement. Being tired of messing with lead acid gel cell batteries, I looked around and settled on Furman Power conditioners. After all, something robust enough to protect a $40,000 church PA should be good enough for home, right? Turns out, it was more than good enough. Product impressions and listening impressions follow plus a bit of EE tech.


  5.  Live From Here “Saturday” Playlist


Who is the audience for this article? As I was shopping for power conditioning, I read a lot of marketing material and catalog blurbs. I quickly concluded that most of what appeared at point of sale was garden fertilizer. The Amazon and enthusiast reviews were not much better. In this article, I’ll attempt to shoot the rapids between the Furman Power papers listed in the references and the catalog blurbs which are completely stupid.

Furman Power Technologies

Furman power conditioners have 5 key technologies, AC voltage regulation (very expensive), power factor correction (somewhat expensive), extreme voltage shutdown, series multistage protection, and linear filtration. The Elite 15i that I purchased provides 3 of these key protections: extreme voltage shutdown, series multistage protection, and linear filtering of the mains. In the 15i, the linear filtering is organized into 3 stages for analog electronics, digital supporting electronics, and video electronics. It also offers protection for cable and telephone connections to your AV components.

Voltage Regulation

Voltage regulation maintains the 120 V output voltage while the input voltage varies over a typical range. Most devices implement voltage regulation using an autotransformer and tap changer. The autotransformer is designed for a specific input range. A control circuit measures the input and output and adjusts the autotransformer tap to maintain the output voltage in limits.

Voltage regulation is of interest to gigging musician who may be using power from improvised sources for a live event or out of spec power in a large venue. It will probably not be of benefit in a home audio environment or home studio environment.

Extreme Voltage Shutdown

Extreme voltage shutdown trips the power supply to the output when line input over voltage is detected. This feature primarily protects gigging musicians who are changing venues and use house power connections (company panel connections) that may be miss-wired or miss-labeled. The intent is to prevent a fire or complete loss of equipment should improper power be present at the mains connection.

In a home environment, this feature will probably be of limited benefit but would protect your equipment if a power repair were miss-wired say 220 where 120 should be present.

Series Multistage Protection

Furman’s series multistage protection feature protects equipment against lightning and other transient over voltage events. The intent is to protect the equipment from strikes on the high voltage transmission lines that are reflected through the transformers to the retail distribution and to the customer distribution. This feature will protect against electromagnetic pulses from nearby strikes but will probably not protect against direct exposure to lightning. That’s the job of homeowner’s insurance. SMP stays out of the way during normal operation, but steps in to clamp line transients in voltage and to pass the excess energy to the grounded neutral.

Furman Power makes one important point about the SMP implementation. It is not sacrificial. When an over-voltage protective response is required, it happens without degradation of the protective devices. They retain their ability to protect your equipment during future events. This is in contrast to department store power strips that are good for one insult.

Linear Filtering

Linear filtering removes audio frequency noise and RF noise that hitch hikes on the AC power. This noise energy interacts with the electronics in the amplifier to be detected and introduced into the audio signal. How it presents depends on the amount and nature of the specific contamination present. If you see a ferrite bead clamped around a power cord, it is an attempt to keep RF contamination out or in as the case may be. The effect of linear filtering is to maintain your equipment’s noise floor as low as possible.

Power Factor Correction

Power Factor Correction is technical stuff with its roots in AC power theory. Power factor is the cosine of the phase angle between the voltage (taken as reference) and the current in an AC power line.

Most load circuits are lagging (current behind the voltage) because most composite loads are inductive. Inductors act to resist current change. When voltage is increasing, they resist the increase in current by absorbing energy into the magnetic field in the device. When voltage is decreasing, they release energy from the magnetic field to sustain the current.

Power Factor is the cosine of the phase angle between the current and the voltage. It is a measure of the extent to which the current and voltage are in phase. The real power delivered by the circuit is voltage magnitude times current magnitude times the power factor. Think of real power as the beer in the glass.

The sine of the phase angle is a measure of the stored energy flopping around in the system. Power engineers call this reactive power. Think of it as the foam in your beer mug. It is there and takes up room in your beer mug but it does not supply but contains no beer. The higher the power factor (0 to 1) the more dense the beer or the more real power being delivered for the current present in the circuit. Maximizing load power factor minimizes circuit current.

Correcting power factor reduces the angle between voltage and current; it reduces the foam in the beer being drawn. By reducing the foam, a given current can supply more useful power to a load. Power factor correction is most useful to live sound contractors using generator power in a  park or operating a large multiple amplifier array off of line power.

To get such a rig going requires inrush current limiting and power factor management to prevent breaker tripping on startup and during operation and load sequencing to avoid tripping the panel feeder breaker or stalling the generator. Pro audio amplifiers have soft start and power factor correction built into the power supplies but load sequencing is external. Furman Power makes load sequencers also.

Most older amplifiers like my Great American Sound Ampzilla, do not have soft start (inrush current management) or power factor correction. Power factor correction is not commonly needed in a home audio environment but it may be beneficial in smoothing out the line draw following transients. Think the massive tympani beats in the Rite of Spring, the 1812 cannon shots, or Micky Hart’s mother of all bass drums.

The Elite 15i Soft-Starts!

When I installed the Furman Power Elite 15i, I popped the cover off to take a look inside. There are 2 primary circuit boards, one with a large ASIC on it that is the brains of the device. It operates the front panel voltage display. The second board is the protection and filtering board that is the back end of all Furman Elite products. This board contains the SMP and Linear Filtering components. It is the board appearing in the featured image (from Reference 1, thank you Furman Power).

I tucked the Elite 15i under my Parasound P5 preamp and cabled Ampzilla, the P5, and 2 power strips to it, one from Monster and a second from Furman Power (6 outlet stage distribution set). I powered up the Elite 15i. The first surprise is that it required about 5 seconds for the meter on the front panel to stabilize. The power switch is a robust circuit breaker.

Then I started my preamp and finally Ampzilla. Ampzilla has a 60 pound power transformer feeding a bridge rectifier assembly going straight into two 40,000 micro-Farad power capacitors connected in a stacked configuration to provide +70 and -70 VCC for a fully balanced amplifier. The inrush would drag the mains down to 90 volts  for a second or so until the power capacitors charged. This inrush would actually modulate the room lights and Ampzilla’s meter lights would blink on. This inrush transient was as dramatic as starting a circular saw or an old washer going on spin (but quicker). Sorry if my age is showing. Modern washing machines have variable frequency inverter drives and no inrush current drama going on spin.

Starting Ampzilla was the second surprise. It just started without drama! This was totally unexpected. Pre-sales, I asked Furman Power which Elite series products would be appropriate for Ampzilla and they listed the lot as OK.

The third surprise came later in the evening when a thunderstorm tripped the street power for fifteen or so seconds. When power restored, the Elite 15i soft started with Ampzilla on. No drama. All the digital source devices had to be restarted manually but the Elite 15I and Ampzilla started without fuss. No blinky drama.

Put another way, the Elite 15i exhibits low voltage restart (LVR) behavior as opposed to low voltage protect (LVP) behavior where the load remains de-energized when power is restored.

Listening Impressions

The fourth surprise came some evenings later when I sat down to listen to the Live from Hear Saturday playlist. Oh my god, the sound was awesome. I suspect a couple of things. First, Gabe has taught staff how to mix. Second, the Elite 15i does some things unexpected. The following things struck me.

  • Stereo image was focused and deep as the Scarlettown Well.
  • Sticks could be heard hitting skin
  • Cymbals were clean with extended ride
  • Fiddle and bass strings were clean when plucked and complex when bowed
  • I played Joey Alexander’s Countdown record and observed the same. Joey’s playing was distinctly muscular yet defined and articulate.
  • Thile-Mehldau mandolin plucking was focused and Brad Mehldau’s piano notes danced on stage.
  • No power supply breathing was observed (seen in meter back light fluctuations)

I was not expecting a significant change in sound character. Part of me says this was placebo effect but it was long after the initial change (5 days of NPR and PBS news and I had forgotten — that evening was my first listening session in a while).



By davehamby

A modern Merlin, hell bent for glory, he shot the works and nothing worked.