[HumanMedia]

In my time I've tried quite a few power filters including 1:1 Transformers, ferrites, chokes, commercial capacitor networks, DIY resistor-capacitor networks, Bybee filters and numerous commercial filtration strips. From all these trials a clear pattern has emerged - active, current limiting filtration such as generic surge suppressor strips is almost always detrimental to the sound of audio equipment.  1:1 Transformers are great for front ends like CD players and digital equipment, but terrible for pre-amps and amps.  RF suppressors like ferrite clamps on AC power are always detrimental to the sound of audio devices, even when placed on only the earth wire.  However they do have a place on video equipment and on non-AV equipment on located on different circuits to the audio system.  Usually the very mechanism used for filtering the power has an audible side effect which far outweighs any filtering effect.

Devices that I have found which are generally positive for audio systems are 'passive' filters. These don't suppress current surges, but rather use capacitor networks whose most basic function is to shunt high frequency noise away from the active lead of the AC power supply to stop it from entering your equipment.  This high frequency noise, or Radio Frequency Interference (RFI) is becoming worse in its prevalence due to computer use, wireless networks and radio communications. Even worse is the prevalence of radio frequency noisy 'switching power supplies' found in almost all household appliances.  All of these sources radiate RFI directly though the power line, or through the air and are picked up by power cables just like antennae.  Some components are not noticeably affected by this noise, but others, such as digital audio players, preamps, phono preamps etc can be quite profoundly affected and then amplified through the audio reproduction chain.  The audible results are not usually directly noticeable as white noise or gross signal breakup, but fatiguing, edgy treble or an unnatural murkiness to the sound.  Often you can't consciously hear the background noise, until it is taken away, making backgrounds sound 'blacker' and the audible signal is 'brought into focus' and made clearer.

After trying my own hand at a couple of DIY passive filters, I thought I would try some of the Alan Maher Designs "Power Enhancer" filters. I liked what I heard, which was a cleaner purer sound where I could hear more resolution in the midrange and higher frequencies. It was clearly better than my DIY attempts and other commercial passive filters I have tried.  Since then I have tried almost the entire range of "Power Enhancer" filters, and now the subject of this review, the "Reference II" filter. 

Soundwise the Reference II seems to combine the sound qualities of the Power Enhancer I, III and IV and roll them up in a single general product - highs and midrange are cleaner and bass is more defined. It seems as though I can 'see into' and enjoy the midrange more.  The Reference II also seems more neutral tonally compared to other Power Enhancers.  As with all of these passive filters the Reference II seems to interact with different components in different ways, and synergizes with some components more than others.  So trial and error is highly recommended which for which component it works with best and where on your audio circuit find its most effective location. In my system the Reference IIs have settled into the adjoining socket to each of the duplexes feeding each of my Channel Islands monoblock power amplifiers.  I cycled through this configuration without any filter and also with other filters in their place.  The result was that the Reference IIs always sounded better than anything else in this position.

Some other information about the Reference II filters.  In my experience the effect the filter has on the sound does not stabilize until they are 'burned-in' which takes about 5 weeks.  So don't judge them until they have been in circuit for a while. These filters come packaged in 'wall-wart' style cases with a USA plug without a ground pin.  The way they plug in is very important, in fact integral to the way they function, and must be positioned the correct way around, so that the active and neutral prong goes into the correct hole in the socket.  This usually means that the hanging end of the case must face ground, or be oriented towards the where the ground pin in the socket is.  They should not be plugged in 'upside down'.  International users must use a reasonable quality plug adapter which preserves absolute polarity. Note that European and Australian plugs swap active and neutral positions so if there is a one to one correspondence in your adapter plug then the Reference II will need to be plugged into the adapter upside down compared to a USA socket, in order to preserve the AC polarity.  Since the filter is a 'wall-wart' with quite a wide case, users may also find that this becomes cramped or physically impossible to plug it into some power boards or double duplex sockets.  In this case a short IEC power cable ('jug-plug') can be used with a PC burn in adapter to plug the filter into tight spots.  Also note that the Reference II uses X-rated capacitors which are safety compliant for 110-240V applications.

In conclusion, my opinion is that the Reference II is the best low cost passive filter product on the market.  It is the culmination of many iterations of passive filter design based on empirical testing of how the unit sounds and not just how it measures.  I recommend it as great standalone filter or for use in concert with other power treatment devices.

[alanmaher]

Carl

WOW great review....thank-you! 

[denjo]

They should not be plugged in 'upside down'.  International users must use a reasonable quality plug adapter which preserves absolute polarity. Note that European and Australian plugs swap active and neutral positions so if there is a one to one correspondence in your adapter plug then the Reference II will need to be plugged into the adapter upside down compared to a USA socket, in order to preserve the AC polarity. 

Looks like I have been using the PE II in the 'upside down' position all this while!!  Looks like I will need to correct the polarity. Thanks for your post and great review!

[denjo]

I have reversed the PE II and observed an improvement within 15 to 20 minutes! Will continue to monitor progress in the days and weeks ahead.

Alan: you might want to add a note in your FAQ to advise users in Europe, Australia and Asia to use the PE with the short side facing Earth.

[denjo]

Alan

You may have missed my earlier post!

[alanmaher]

denjo

Good to see everything worked out.  How is the filter sounding a couple days into the switch?

[denjo]

Alan
I think I have finally got my PE II to come to life!  How does the standard PE II compare with the Reference II?

Best Regards
Dennis

[alanmaher]

The Reference II is a more harmonic, rich, organic, neutral kind of filter compared to the PE II.  The new series of filter designs is a good step forward in sound quality without giving up the exacting precision of the original design.

[Paul_Bui]

Hi Dennis,

I know you asked Alan the question, but I thought you might want to know the answer from a different angle:  from me as a customer/audio enthusiast/music lover just like you.  If you OK with it, please read on.




You see, I am currently beta-testing the Ref II, and having had it for only 3 days in my room, I am not qualified to post a definite and credible review of the product.  Anyway, I just can't help breaking the silence.  For the last few days I skipped sleeps more often, played more tracks than I had played during the last several months; before the Ref II arrived, that is.

So, after some minor and primary fine tuning (I have had a number of Ref I's, PE's, PE II's, PE III's, a PE IV and PE V in my house), I plugged the new Ref II into an AC outlet adjacent to the main AC outlet where I have the PE V Pro Custom and the Power Center which feeds AC juice to a tube pre and a chip amp.  Transport and DAC being battery-powered.

Let's cut to the chase.  Adding the Ref II to an already highly AC tuned system such as mine proves a very positive improvement.  Alan's description of the Ref II's benefits is absolutely spot on.  After a little roller-coaster ride during the 1st few hours, and especially now when it's been 3 days with the Ref II helping my system, I have to resist myself not to make a phone to Alan asking for more Ref II's.

I am listening to Diana Krall at this moment.  More so than ever, her voice is so warm, intimate yet clear and deep in my room.  There's a bigness in her throaty breathy voice that's in contrast to her swift fingers on the piano.  It's like I had just upgraded my speakers to a higher efficient driver.  "How Deep Is The Ocean" is one of those tracks.

The same can be said about tracks in Il Divo and Celtic Woman CD's.  The vocal performers take on a bigger image, warmer not muddy but richer texture, more lifelike overall impression.  And it sounds wonderfully like that no matter it's day or night.     

Since there're already a variety of PE's in my house and my room, YMMV.  But I know the Ref II is just my poison.  Oh, to answer your question:  I think the Ref II is a more like a turn-key no-brainer filter than the PE II; the latter seems to take you some time and effort to fine tune.  After all, they both (and all other PE's) seem to work together very well.

I'm still shaking my head, wondering how just by tuning the AC you can improve the sound and picture quality that much (yes, video is clearly sharper and higher resolution looking than elsewhere even with standard HDMI cable).

[denjo]

Hi Paul

Really good to hear from you and thanks for sharing your experiences with the Reference II! Wow, what am I waiting for? I might try the Ref II once I move some gear to free some funds. I have been trying to rationalise and downscale my audio system. Not sure if the Reference II is helping me do that!

Best Regards
Dennis

[alanmaher]

Marketing hype aside the Reference II has become a valuable asset in my set up.  Right now I have 4 installed on non-A/V circuit (final version installed about 6 months) to test the strength and I love the performance.  The Reference II melts into the PE perfectly to extend the PE filtering frequency.  During the development stage I tried very hard to combine the musical truthfulness of the original PE with the definition of the II, the warmth and extension of the III, and the detail of the IV....I think we struck a nice balance, the Reference II provides 85% to 90% of the performance of the other three filters rolled into one.    During design stages I try to keep a tight lip about things, but as you may be aware, we retired the II, III, and IV last year because of the positive results we experienced during the various design stages of the Reference II. 

[turkey]

These filters come packaged in 'wall-wart' style cases

So they're good for removing warts too?

[sherod]

Very interesting, this new Reference II. I have two of Alan's original PE walwarts that I bought about a year or so ago. They are wonderful and I'm wondering if a Ref. II would add that icing on the cake for me. I currently have a PE on the subpanel and one in the same outlet of my two monoblock amps. I wonder what location the Reference II would be best for me? Decisions, decisions...   

[alanmaher]

The Reference II can be installed on the same circuit as the audio in concert with the PE, or it can be installed on any non-A/V circuit and still enjoy the enhanced benefit.  Check out the review for non-A/V enhancement: http://www.audiocircle.com/index.php?topic=67000.0

[denjo]

Alan

I wrote earlier but you seemed to have overlooked my post and that of Carl (Human Media). It is an important question which I think deserves a full reply. In Asia, the live and neutral are reversed as compared with US which means that the orientation of the plug should be downwards instead of upwards. Is this correct? Can you please confirm and if so, perhaps an addendum in your FAQ would help.

Best regards
Dennis

[alanmaher]

Correct.

How does the filter sound since it was flipped around?

[denjo]

Correct.

How does the filter sound since it was flipped around?

Alan, it seems to sound better when flipped around. Let me give it more time as I am expecting a "roller-coaster" ride as cautioned.

Best Regards
Dennis

[sherod]

Well, I had to order this new Reference II and it came in yesterday. Apparently it was Alan's last one available until he gets back from his tour to make some more. I have had it plugged in for about 24 hours now. I can hear a much quieter background with this in the outlet, but the bass seems a little reserved and a little bloated. The mids are a little reticent and have lost their palpable presence. The highs are also a bit reserved. I'm assuming that this is normal until they finish their break in. I can sense an overall better tonality to instruments, though. When you say they take at least 5 weeks to fully settle in, can you tell me when they at least dissappear enough to allow the full frequency spectrum to open up and bring back that nice presence? I have had two of the original PE walwarts in series in my system for over a year now and they have become a major part of my system. As I recall, they took at least a week to settle down and open up the sound. I wasn't certain if this new Ref II had similar break-in characteristics.

[alanmaher]

The Reference II needs a good week before the bloat starts to give way.  At 2 weeks the filter will start to show the resolution in the tonal hues.  Between week 2 and 5 the filter smooths a bit and refines in the upper mids and treble.  Give the bass thickness about 4 to 5 days, if it doesn't give way in that time try playing with the filter position/circuit until it snaps together.

I will have more II's available next week.  The Quantum's are out of stock until I return from Motley the beginning of July.

[tenantman]

I have to admit that in the beginning I was a non believer of Alan's Wal-wart Power Enhancer. Loved what it did for my Video but for my Hi-end Audio, no way. 3 years later I have added a PE V S/AC, PE IV, Alan's Power Center and the PE REference II. Folks, the Reference II is a serious design that makes the previous designs seem outdated but not obsolete. In the order of money spent these days for cables or other tweeks that are overpriced, this AC filter is a real steal especially if you are lucky enough to have a speaker that tends to throw a seemless image in all three planes. You owe it to yourself or better yet your ears, to grab this one and be prepared to get addicted.  You have been warned.

Currently using battery powered electronics and music PC server, both have replaced a fine tube based system.

Enjoy