Building a Balanced Power System

[DiminishingReturnsOfficer]

Its been a long time since I've posted on here. I originally started this post as a reference to anyone interested in building a balanced power unit. A few of you were discussing problems that I felt could be helped by balanced power. Anyway, some CA members challenged my understanding of what goes into a well designed and executed power line conditioner. I took into account some of their suggestions as well as some ideas of my own to produce what I feel is a much better unit.

The first thing I wanted to address was the mechanical buzzing present in my existing transformer. The Plitron 8575-X0-02 was loud enough to be heard from the listening position thus mitigating most of the filtering attributes. After extensive in home testing, I decided that the transformer was defective. I took it to 4 different locations, powered it through another isolation transformer, and even a portable generator, and noted the same buzzing in each instance. It cost me $75 to ship the unit back to the manufacturer. Needless to say, I was pretty sure it was defective. Unfortunately, the good folks at Plitron did not agree with me. They ignored several request for information regarding the exact nature of the tests conducted and thier findings. All they were able to tell me was that it was "not a warranty item" and I would be charged a 30% restocking fee if I wished to return it. After much prodding, I got them to reduce the restocking fee to 15%. It was a gamble for me because if they were saying that the old unit was functioning properly, then what assurance did I have that the replacement would not do the same thing? Well, I gambled and won because the new toroid is one of their LoNo designs which is supposed to operate quietly even with moderate amounts of DC offset and overvoltage. It also features NBT technology which offers additional mains "filtering". I can't say much for their customer service, but they do make a good product. The new transformer is quiet as the catacombs. It can only be heard with an ear pressed to the case when its completely quiet.

 

You'll also notice the small transformer I have mounted in a Hoffman 6x6x4" box. It is a 12V 225 VA model that I'm using as a Buck and Boost autotransformer to reduce the line voltage to 113V. My residence runs somewhat hot at 125V. Due to the regulation of the big toroid, I would have 132V on the receptacles with no load. Since it will only be loaded at a small percentage of it's capacity, I decided to buck the voltage down in order to protect sensitive electronics. My calculations were nearly exactly correct, and I have 119V on the receptacles with no load and 118V with the entire system playing at a moderate volume.

Some improvments I made are as follows: I got a 3/8" thick 7075 Aluminum plate underneath the chassis. This is more than adequate to support the heavy (20 Kg.) transformer. As suggested by a CA member, I eliminated the wire nuts and made all connections on a terminal strip, directly to the switch, and the secondary (balanced conductors) land on the first receptacle. I replaced 3 ATL receptacles with 2 15A Furutech copper, and a 20A Furutech gold plated. I feel that a 15A receptacle grips a 15 plug better than a 20A, though, the 20A pretty well has the amp and pre-amp plugs in a death grip. I used #12AWG Furutech POCC wiring to connect the receptacles; paralleling the 15A's off the 20A. I also elected to use a stainless steel bolt to mount the transformer because of it's non-ferrous composition. The inside of the cover is lined with Stilltech ERS fabric to reduce the magnetic field rediated by the power unit.

I had been listening to unfiltered power for months, so I feel I can make an informed evaluation of the merits of balanced power in this application: The "noise floor" has been lowered throughout the system. Instruments emerge from a stark black background. A measure of upper mid range "haze" has been eliminated and the sound is much more focused. Video is much cleaner with no grain present on a DVD, or Bluray disc. The most startling effect is in the bass region; tight, impactful, punchy bass. Musical dynamics have improved as well. This is something you might not expect from a conditioner, most people report a constriction of dynamics with a conditioner especially those using inductive devices. The large 2400 VA transformer has no problem supplying the amp with all the peak current it needs; this is evident.

 

I elected not to use any additional filtering capacitors as I've heard mixed reviews about their effectivness. The NBT transformers have capacitive properties and offer a good bit of high frequency attenuation on their own. Possibly, later on, I may experiment with some X caps in another enclosure.

 

I would like to take this opportunity to encourage anyone looking to make an improvement in their system for a minumal investment, to do so. I'd be glad to answer any questions you might have. Don't skimp on material quality, take time to plan out the unit thoroughly, and experiment with different configurations. I believe that you can make a conditioner that will hold it's own with any commercially available models.

 

 

 

[wgscott]

Ultimately, how much did this cost (apart from the shipping/exchange/restocking of the defective transformer)?

 

How much would this drive up my electric bill, and how likely would it be to burn my house down?

 

 

 

[One and a half]

the transformer was too noisy, it's surprising from a toroid design. I guess it's a trade off for completely potted (with epoxy) designs versus wrapped, the heat dissipated starts to come into its own. I have seen potted reactors to 1500A, but they are water cooled, I think the pump would make more noise!

 

Kudos on getting rid of the wire nuts, the crimps look good with extra earth wire, this is important to keep the impedance low.

 

I found the bass did tighten up as well, and I agree with the noise floor dissapearing leaving room for other instruments to make themselves known. Add to that the satisfaction of doing it yourself and making such an improvement makes the hassle with the transformer long forgotton.

 

Congratulations on a fine job!

 

[DiminishingReturnsOfficer]

to wsgott: Hello, and glad you're still around. I've caught some of your postings about the Optical cable. Thinking back on it, you may have been the one who inspired to me talk about the benefits of Balanced Power.

OK, in terms of cost: without a doubt the most expensive piece is going to be the transformer. There are many options there and I'm not going to tout any particular brand or design over any other. Toroidal transformers make a lot of sense in this application, but they are not necessarily the final word. One weakness of this configuration is that the primary and secondary are wound on top of one another separated only by insullation and perhaps an electrostatic (Faraday) shield. Greater line isolation can be achieved with a C or R core design, but you may have difficulty finding one of adequate size. Another option that I haven't discussed is to use separate transformers sized for the particular components or one for digial components and one for analoug. Since your question was specific to the unit I built, I will pass along prices relative to my particular build:

Plitron 2400VA toroidal transformer: $350

Hammond enclosure: $50

3 Furutech audio grade receptacles: $200 (2) 15A / (1) 20A

approx 12"x12" 7075 Aluminum plate: $80

Power Strip: $100 (mine was free thanks to Lee @ Cryo Parts)

Eaton 20A SPST switch: $10

Square D ground bar: $8

Ideal terminal strip: $5

feet: $8

6' entry cord: $60 ($10/ft. Cryo 3)

6' 3/8" tinned copper braid (for shielding): $12

10' Kevlar fabric (covers cord): $20

Hubbell 20A Hospital Grade plug: $25

T&B cord grip connector: $15

terminals: $4

heat shrink: $10

Stilltech ERS fabric: $50 (2 pieces of the adhesive type)

internal wiring: $12 (1 meter of Furutech 12AWG hook up wire)

misc. hardware: $10

total: $779 without shipping costs

Wow, that's more than I thought I spent! That being said, I had a good many of these parts on hand, and the final iteration of my unit was spread out over several months. You could get started for much less and upgrade as you go. If you look at the largest of the BPT products and compare; it comes in at close to $2300. I just mention BPT because it is the product to which this one is most similar. Chris makes a very nice product that employs additional filtering and surge protection. I can't compete with his overall "fit and finish", although I think my unit has a character that you would not get from a commercial product. For those looking for something of better quality than my unit, you might want to check out the Equi=Tech toroids, but be prepared to fork out some serious cabbage, and find a much larger enclosure. For anyone looking to bring the project in much cheaper, you could consider Avel, Air Link, or Hammond (just to name a few) transformers, or scrap one out of an old power amp or commercial line conditioner. You could wind your own transformer which would add even more of a DIY feel to your project. Audio grade receptacles are not mandatory, in fact, you'll see that most commercial products offer hospital or "spec. grade" receptacles. Also check out Par Metal for enclosures. Their cases look very sturdy and more closely approximate an audiophile product.

The one requirement you must adhere to if you want Balanced Power as opposed to just an isolation transformer is a Center Tapped secondary. This will appear on manufacturer's spec sheets as "60-0-60". Establishing the ground reference at the symmetrical center point of the secondary winding is what makes balanced power balanced. Cancellation of "common mode" noise follows from this configuration, and is not offered by a simple 1:1 isolation transformer.

Sorry to have gone on for so long. Your second question spoke to the safety of such a unit. I can tell you that I have complete confidence in MY power conditioner. Without a doubt, the most valuable thing in my residence is my stereo system. I don't have insurance, and as you can see from the photos, it sits on the same rack as the rest of the gear; meaning if there was a fire, the stereo would be the first to go. I would not, however, give an unconditional endorsement to any other DIY project without having the opportunity to look inside and test it. Something as simple as a loose termination could cause a shock hazzard. If you're taking about generating the kind of heat that would start a fire: that would most likely happen due to an undersized component in the current path. This can be avoided by properly sizing your unit to the system requirements and following the NEC requirements for conductor ampacity (article 310.16) and overcurrent protection. I am a licensed Journeyman electrician, so I'm very familiar with these requirements. I will be glad to answer any questions you might have.

 

[DiminishingReturnsOfficer]

to wsgott: Hello, and glad you're still around. I've caught some of your postings about the Optical cable. Thinking back on it, you may have been the one who inspired to me talk about the benefits of Balanced Power.

OK, in terms of cost: without a doubt the most expensive piece is going to be the transformer. There are many options there and I'm not going to tout any particular brand or design over any other. Toroidal transformers make a lot of sense in this application, but they are not necessarily the final word. One weakness of this configuration is that the primary and secondary are wound on top of one another separated only by insullation and perhaps an electrostatic (Faraday) shield. Greater line isolation can be achieved with a C or R core design, but you may have difficulty finding one of adequate size. Another option that I haven't discussed is to use separate transformers sized for the particular components or one for digial components and one for analoug. Since your question was specific to the unit I built, I will pass along prices relative to my particular build:

Plitron 2400VA toroidal transformer: $350

Hammond enclosure: $50

3 Furutech audio grade receptacles: $200 (2) 15A / (1) 20A

approx 12"x12" 7075 Aluminum plate: $80

Power Strip: $100 (mine was free thanks to Lee @ Cryo Parts)

Eaton 20A SPST switch: $10

Square D ground bar: $8

Ideal terminal strip: $5

feet: $8

6' entry cord: $60 ($10/ft. Cryo 3)

6' 3/8" tinned copper braid (for shielding): $12

10' Kevlar fabric (covers cord): $20

Hubbell 20A Hospital Grade plug: $25

T&B cord grip connector: $15

terminals: $4

heat shrink: $10

Stilltech ERS fabric: $50 (2 pieces of the adhesive type)

internal wiring: $12 (1 meter of Furutech 12AWG hook up wire)

misc. hardware: $10

total: $779 without shipping costs

Wow, that's more than I thought I spent! That being said, I had a good many of these parts on hand, and the final iteration of my unit was spread out over several months. You could get started for much less and upgrade as you go. If you look at the largest of the BPT products and compare; it comes in at close to $2300. I just mention BPT because it is the product to which this one is most similar. Chris makes a very nice product that employs additional filtering and surge protection. I can't compete with his overall "fit and finish", although I think my unit has a character that you would not get from a commercial product. For those looking for something of better quality than my unit, you might want to check out the Equi=Tech toroids, but be prepared to fork out some serious cabbage, and find a much larger enclosure. For anyone looking to bring the project in much cheaper, you could consider Avel, Air Link, or Hammond (just to name a few) transformers, or scrap one out of an old power amp or commercial line conditioner. You could wind your own transformer which would add even more of a DIY feel to your project. Audio grade receptacles are not mandatory, in fact, you'll see that most commercial products offer hospital or "spec. grade" receptacles. Also check out Par Metal for enclosures. Their cases look very sturdy and more closely approximate an audiophile product.

The one requirement you must adhere to if you want Balanced Power as opposed to just an isolation transformer is a Center Tapped secondary. This will appear on manufacturer's spec sheets as "60-0-60". Establishing the ground reference at the symmetrical center point of the secondary winding is what makes balanced power balanced. Cancellation of "common mode" noise follows from this configuration, and is not offered by a simple 1:1 isolation transformer.

Sorry to have gone on for so long. Your second question spoke to the safety of such a unit. I can tell you that I have complete confidence in MY power conditioner. Without a doubt, the most valuable thing in my residence is my stereo system. I don't have insurance, and as you can see from the photos, it sits on the same rack as the rest of the gear; meaning if there was a fire, the stereo would be the first to go. I would not, however, give an unconditional endorsement to any other DIY project without having the opportunity to look inside and test it. Something as simple as a loose termination could cause a shock hazzard. If you're taking about generating the kind of heat that would start a fire: that would most likely happen due to an undersized component in the current path. This can be avoided by properly sizing your unit to the system requirements and following the NEC requirements for conductor ampacity (article 310.16) and overcurrent protection. I am a licensed Journeyman electrician, so I'm very familiar with these requirements. I will be glad to answer any questions you might have.

 

[DiminishingReturnsOfficer]

I neglected to answer one question regarding how much it would cost to run this kind of unit. That question relates to the efficiency of the transformer. Here is a link to the spec. sheet for the model I used in the latest version of my power conditioner: http://shop.plitron.com/specs/877001.pdf As you can see, the efficiency is rated at 93%. The simplest way I know to relate this figure is to say that you would pay 7% more to run whatever you have connected to the secondary of the tranny (assuming Unity power factor). Please don't confuse this unit with something like the PS Audio Power Plant that converts AC to DC and back to AC again. This strategy may be quite effective, but its known to be less than 50% efficient. Another thing to note is the temperature rise, 79*C. This is much higher than any of the other toroids in this category, and as a result, this one is equipped with class F insullation (155*C). This might make it necessary to provide some ventillation if you're going to be running close to maximum capacity. Temperature rise is inversely proportional to load current. If there are no additional questions, I'm willing to let this thread die. It was satisfying for me to write and I learned a lot in doing so. Hopefully, it will serve as a reference for someone interested in building one. I don't know how long CA keeps threads on file. I was encouraged to see it come up in a Google search for key words "Balanced Power Conditioning".

 

[Fife]

What now just get a APC S15?

 

http://www.apc.com/resource/include/techspec_index.cfm?base_sku=S15

 

Filthy cheap from Vann.com or through Amazon.com at only $300.

 

Can even disconnect the S15 PC and run your gear off its internal battery.

 

Weighs a good 60 pounds!

 

Perfect for digital gear and some amps.

 

[DiminishingReturnsOfficer]

Fife,

Certainly this would be an option for power conditioning. There are literally hundreds of power filtering products available. This thread, however, was intended for people interested in building their own version of a specific kind of conditioner. The APC unit does not provide balanced AC, and is a fully assembled product requiring no intervention on the part of the consumer. From checking the link you provided, it seems that the primary function of this unit is to provide emergency back up power (UPS). It also offers surge protection for phone, fax, and cable lines. Personally, I would not want this type of potential interference to pass through a line conditioner. I also noticed that it has a fan which is less than ideal for critical audio applications. I use a UPS with surge protection on my computer which is on a different circuit from my stereo. Nonetheless, if you are happy with the results of the APC device, that's great. Its just not particularly relevant to this discussion.

 

[davidR]

UPS units are known to inject their own noise into the power system starting at 6dB per unit. Just throwing it out there. Seems to defeat the purpose but then you would need to filter the device that's supposed to filter in the first place. Seems redundant. This noise isn't a buzz or hum but like most EMI buries itself into your music.

 

[One and a half]

If you want to use a UPS, then by all means, have it far away from Audio gear, and install a transformer to isolate the common mode noise.

UPS manufacturer's usually show how clean their power is on the output, but you should see the horrendous rubbish on the front end, which ultimately comes back via ground to audio equipment.

 

[Benie]

Certain APC units are known to be good in audio systems.

 

MOST UPS devices are not as they produce a square wave. This APC item is different as it produce a Sine wave.

Much different then 98% of UPS devices out there.

 

But is does not have the benefits of Balanced Power.

For the Most part Balance Power is better, although some have reported that some components don't respond to Balanced power as they hoped it would. But these reports a far and few.

 

Another way to get the Benefits of Balanced Power, is to get ahold of some of the better Isolation transformers , such as , Xentek, Elgar, Topaz.

 

But you have to get the bigger ones, they have the different taps that allow you to run it as just a reg. isolation transformer or change the taps on the primary + secondary to run in Balanced mode. The 3 Brands I mentioned are top quality brands for these devises.

 

Here is a link just for reference, I have nothing to do with them. http://www.surplussales.com/Transformers/IsolationXmers-2.html

 

I myself use 3 Isolation transformer in my system, 2 are in Balanced mode and 1 on my amps is just acting as a Reg. isolation transformer, it is a 2.5 Kv Elgar running my 2 Acoustat Direct Drive Servo Tube Amps. I have not tried this in Balanced mode as amps usually need alot of headroom. If I go into Balanced mode the 2.5 Kv rating is said to be halved to 1.25 Kv, but with more headroom because of the bigger Core.

But after reading this thread, I may just try my amps from the Balanced mode and see.

 

Most of the rest of my system is on a 2.5 Kv Elgar Isolation transformer that is run in Balanced mode.

 

With another Daltec 1Kv in Balanced mode.

 

The Elgar ones are not your run of the mill isolation transformers, here is some info on Elgar products.

http://www.programmablepower.com/products/Discontinued/Downloads/HIT%20Series%20-%20High%20Isolation%20Transformers.pdf

 

A buddy of mine uses the Plitron setup as the OP and has very good results as well.

 

I have some DIY Power strips hard wired to the secondary of the Transformers, with Furutech outlets and filters in the Power Strips

 

Balanced Power is the way to go, but there's more than one way to skin a cat. )

 

 

[1audio]

If you are building your own balanced power device you should (must per NEC) use a GFI on the output for safety. Since there are several power paths a single fuse or breaker in a load device won't necessarily protect you if a fault develops in the load. Also with 2KVA capability you should have a fuse or circuit breaker on the load side scaled to your load. That is a lot of energy so be very careful.

 

On the Monster Power centers with balanced power we determined that the option of switching between balanced and isolated was important since every situation is different. Many loads are imbalanced with different capacitances between the chassis and ground. A balanced drive will force additional current down the ground and create more hum and noise than an isolated drive will. But in other applications balanced drive worked better.

 

I'm also concerned about the less than thorough safety aspects of some audiophile power distribution products. UL certification is an expensive, and involved process. For a surge protector they require at least 50 pieces for destructive testing so its not a cheap effort either. But, after attending several fire investigations I better understand its importance and why these anti-audiophile aspects are required (like X-Caps that don't burn up and UL rated circuit breakers and fuses that can disconnect with over 1KV across them).

 

[DiminishingReturnsOfficer]

Thanks to 1audio for concerns and input. You are absolutely correct about both the need for overcurrent protection on the primary side of the transformer (NEC 450.3 C), and GFCI protection for receptacles on the secondary(647.7 A (1)). Both requirements are addressed further back in the text, but it is certainly important enough to state again. It is the intent of the NEC to limit the use of balanced power to "commerical or industrial occupancies" (647.3(1)), and conditions where "The system's use is restricted to areas under close supervision by qualified personnel" (647.3(2)). Article 647 is intended for professoinal audio, video production studios, and other such areas where "Technical Power" for "Sensitive Electronic Equipment" is installed as premisis wiring with it's own distribution panel, and clearly marked junction boxes, and receptacle outlets. I do not belive that it is particularly relevant to a cord and plug connected, completely self contained unit such as what is discussed in this thread. A DIY balanced power system can, however, be considered a "separately derived system" as there is "no direct electrical connection, including a solidly connected grounded circuit conductor" [neutral]. Only the GROUNDING conductor is continuous. It is certainly not my intent to encourage anyone to do anything unsafe or illegal. I made the choice to omit primary overcurrent protection and secondary GFCI protection because I felt it would hinder the performance of the unit. As an experienced electrician, I am aware of the risks involved and I am willing to accept the consequences of my decision.

 

 

[bmckenney]

This is a great subject, but more suitable for diyaudio.com if you ask me. But it is great to see some balanced power enthusiasm on any audio board. There have been quite a few posts on this board about balanced power benefits for audio. I recommend balanced power and rank it as high as room acoustics and treatment, speaker quality/performance, speaker to room matching and integration. Balanced power is well ahead of the electronics such as amp, dac, music server, software etc in importance for good sound, but it doesn't get the coverage on audio boards for what ever reason. Electronics and software are handicapped by poor power. But then again, good power is handicapped by poor acoustic setups. I have a 240V balanced Torus and it is one of my must haves right up there with my speakers.

 

[One and a half]

Finally having some time over the holidays to pour over some theory and put that into practice into improving SQ from my rig. Best to clean up the power supply then at least that's done, so that should provide a great foundation for good sound.

 

Power wise, the current system consists of a 2KVA 240/240 Isolation transformer with Faraday shield. The secondary of this transformer feeds a pair of 240/60-0-60 1kVA transformers. They are connected in parallel to provide 2kVA for audio and computing use via GFI. Since purchasing the integrated amp, it is factory fitted to run from 240V only, same with the DAC. For about 12 months +, the amp has run raw from the mains, with a simple power board filter and over/under voltage protection. This means the DAC is also connected to the same network. There aren't that many spikes and pops that come through the system that are audible, but the other issue was worrying is that noise from the Tuner, Mac Mini, Oppo and any switch mode power supply on an unbalanced power supply system (TN Earthing system) will just propagate that noise wherever it likes. This means feeding into the amplifier where the filter caps need to filter this rubbish of varying quantity, rather than supply pure power to the output stages. The TN system is used in the USA, UK, Australia, NZ, Europe.

 

I have understood that a balanced power supply with the centre taps grounded cancels out any common mode noise, much like the OP made an analogy with balanced interconnects which is correct. Common mode noise being asymmetrical to the power supply's lines is ignored by the load, since the noise is not part of the balanced equation, it ends up on the ground. If there are EMC filters placed in circuit to reflect common mode noise, for a balanced supply the reflection is perfect, since noise is asymmetric, the effectiveness of the filter increases, so the noise to the load is reduced to the muck in the mire. It means then you can have any number of noise producing audio components on the one power board, and they won't interfere with each other through the power network. Different story though on the USB side to the DAC, where the computer still can create emitted (and then conducted) noise to a DAC, so devices like the ifiUSB are a good idea, where the shield of the USB cable is electrically removed.

 

In a TN system, to limit the noise, you can use an EMC filter for each piece of audio equipment, which is included in PowerCenters from Monster, Furman, Equi-tech and many others. Filters are tricky to get the right results, since you are guessing that a certain piece of equipment such as a computer has a certain signature of nose, and is different to say an AVR. The Monster designs split up the outlets protected by filters for different categories, such as Amps, DVRs and so on. The filters allow 50/60Hz to pass (so they are LPF) and block freq above 150kHz something to the MHz.

 

You just let the balanced power do the work with elegance, but that comes at a cost, but worth the investment. In a 'moment of clarity', I read this excerpt and hey, duh, noise as well as harmonics are also cancelled out by a balanced power supply. This page is worth its weight in gold from Equi-tech as it explains the theory and application of balanced power supplies used from a recording studio installation perspective. If the recording studio benefit from balanced power, then, our humble playback system most certainly can.

 

"(Excerpt) The Digital Domain

 

In the digital domain, balanced power creates a more subtle change in noise characteristics but an equally dramatic improvement in performance. The major issue in digital signal processing is high frequency noise -- noise that approximates the frequency of various digital operations. For example, the sampling rate of digital recordings is 44.1kHz. That times the bit rate equals the rate of the data stream (approximately 700kHz in 16 bit audio.) It has been found that digital jitter is reduced by approximately 1/3 to 1/2 in equipment that has been tested first without and then with balanced AC. High frequency interference (caused primarily by switching power supplies and other half-current-pulse semiconductor devices) is eliminated by balanced AC architecture in a manner analogous to removing the carrier frequency from an FM broadcast. In the case of balanced power, nulling low frequency harmonic current is in essence "knocking the legs out from under" the high frequency harmonics in the AC system. Everything collapses. "

 

Screwdriver in hand, the 60-0-60 transformers were changed to be connected in series, so that the outer rails provide 240V for audio and the inner secondaries 120V to run the computers, routers and network gear in the garage, in a dual GFI & voltage balanced system. The dedicated line from the transformer to the audio system run across the house had to have a different receptacle (dang the switch on that needs to be double pole...). Added shielded cable from the new receptacle to an existing Monster PowerCenter where all audio components are plugged into.

 

So any noise, harmonics generated by any component is shunted to ground, and no outside noise can get in via the primary transformer. The results speak for themselves, bass is tightened, overall a cleaner result, and the change to a balanced supply is much the same as any major change to a hi-fi system such as buying a better set of speakers, intercoonects or a DAC. Even albums like Cross Words from Christopher Cross, a very commercial album, has a sound stage, wide open, with accurate placement of people and instruments. Can't wait to play a 'real' recording!!

 

Once again, thanks for Equi-tech to provide some very enlightening papers on a simple, yet very effective 'noise filter'.

 

If you don't have a balanced power supply, you're just listening to noise and this is very relevant for computer audio. I see lately there are solutions with batteries that minimise connection to the grid, in an effort to reduce or eliminate noise that comes form there,and having more headaches in the process in workarounds. I think it's wise to understand the nature of where the noise comes from, how it can propagate, and find solutions already existing that can cure noise problems (from a power supply perspective). Building one's own balanced supply needs some very careful construction with legal and regulatory requirements in many countries, so building one is not for every audio enthusiast to undertake. However, several companies produce equipment that will work out of the (heavy) box, and they don't need to have any fancy lights and dials either, they are nice to have but not essential. Here's a quick guide on what I found in researching for this post.

 

Power Conditioner

Simply, this is a choke and capacitor that when interact provide some decent regulation from a mains network. It can still propagate common mode noise.

 

UPS - Regenerator

UPS create an AC sine wave from a DC supply inside the UPS. You can on some models run the UPS without batteries, so it behaves like a super regulator, ideal for sites where the voltage swings are very bad an you can dispense with the batteries. The downside is the distortion on the sinewave output is typically 5%, and there are a RF emissions and harmonics to deal with at the front end. None of the smaller UPS I came across from Powerware for example do not have a balanced output. Ideally you could use a UPS feeding a balanced power supply, so it would provide tight voltage regulation, but you still have the distortion to contend with. Measured at my house, the raw mains voltage distortion is 2%.

 

Balanced Power Supply

These are modest looking devices but contain some very nice noise hammering circuitry. They are often heavy as the transformer to do the work is no lightweight. Adding shields causes the heat to be managed, not a trivial task. Efficiency is about 96-98% and are normally very quiet and do not require a fan. As a guide, you can use a 1000VA transformer for a 100-250W/ch amp, and work down from there. Computers (Mac mini, CAPS, Sonore) and DACs consume very little power, typically 20-100W. Transformers can take a fair bit of overload so they can with a bit of effort have plenty in reserve for those cannon shots in the 1812.

Companies that produce balanced power supplies or components

Equi-Tech

Monster Cable

Furman Sound

 

Hundreds of other transformer manufacturers, like BLOCK in Germany, Plitron are more for the systems integrators, or those who have a qualified electrical background.

 

As far as protection is concerned, often included in audio power supplies, I see that a lot of numbers are touting joules this and that...if you are going to be hit by lightning in an impending storm, pull out the plugs, lightning is a law unto itself, if it wants to destroy your TV, it will find a way, don't worry. Surges do happen, but sustained ones will hopefully just destroy the protective device and leave the equipment alone, so count on replacing a unit one day. Under and over voltage protection are must haves, over can kill transformers, under can make digital circuits behave very badly. Under voltage for fridges can burn the motors out quick smart. One other benefit of using a balanced power supply is that the voltage to earth is 1/2 the mains voltage. If a live wire does come to the frame, the GFI/RCD will trip, but the voltage reduction reduces the current by half as well.

 

The main issue for audio use is to eliminate common mode noises and interference between connected components. Protection is an important secondary measure, but it's not what we listen to.

 

For the OP, I came across a method to stop the noise in your transformer by blocking DC components on the primary, have a look here. Hope this can help you.

[One and a half]

Using the standard house power supply, I could barely get to 11 o'clock on the volume of the amp (no signal) and be plagued with SMPS noises from computers and just about the whole neighbourhood's rubbish, even with filters.

 

As a test today on a balanced power supply, I plugged in a Sony Vaio SMPS which is the worst noise offender into the same circuit as the amp, and wound the volume control to 11 o'clock....silence. Then all the way full gain..had to remove the speaker grille, and hold my ear about 1in away from the cone, close windows and doors, before I could just hear a faint hiss from the amp. Theory holds its own, the noise is vanquished, and with that a great gift for the New Year!!

[musimarine]

Thank you.mark and study.

[liquidsmoke]

Firstly thank you DiminishingReturnsOfficer and OneAndAHalf Great read and very good links to help an electrical noob understand how a balanced power supply works. After reading everything and reading everything again. I still have 1 question in my mind which is stopping me pulling the trigger on an AirLink 1500 or 2000va transformer to power my kit.

Standard Balanced Power Supplies

 

The question I have is would a balanced transformer prevent ground loops and interference if all equipment were connected to the transformer? Or would it prevent the ground loops and interference only if 1 of two devices that were involved in a ground loop were connected to the transformer, and the other device operated directly from the mains?

 

I suppose what I’m wondering is can I connect all equipment (DAC, Mac Mini, USB interface, 2x Power Amps, AV Receiver, TV, Bluray player, media streamer) to the transformer and expect the system to operate without ground loops and mitigating the nasty switch mode psu noise? Or do I need to experiment with some devices connected and some not?

 

I seem to see conflicting information. Some people are saying they split digital and analog devices over 2 different balanced supplies, and some like the equitech article seem to suggest to me that due to the nature of the balanced supplies, that anything connected to it will not interfere with one another...?

The Origin of Balanced Power

 

The answer to this question decides whether I can just buy 1 big balanced PSU (2000va) or if I need to buy 2 separate ones; and spend more money

 

Thanks!

[One and a half]

Firstly thank you DiminishingReturnsOfficer and OneAndAHalf Great read and very good links to help an electrical noob understand how a balanced power supply works. After reading everything and reading everything again. I still have 1 question in my mind which is stopping me pulling the trigger on an AirLink 1500 or 2000va transformer to power my kit.

Standard Balanced Power Supplies

 

The question I have is would a balanced transformer prevent ground loops and interference if all equipment were connected to the transformer? Or would it prevent the ground loops and interference only if 1 of two devices that were involved in a ground loop were connected to the transformer, and the other device operated directly from the mains?

 

I suppose what I’m wondering is can I connect all equipment (DAC, Mac Mini, USB interface, 2x Power Amps, AV Receiver, TV, Bluray player, media streamer) to the transformer and expect the system to operate without ground loops and mitigating the nasty switch mode psu noise? Or do I need to experiment with some devices connected and some not?

 

I seem to see conflicting information. Some people are saying they split digital and analog devices over 2 different balanced supplies, and some like the equitech article seem to suggest to me that due to the nature of the balanced supplies, that anything connected to it will not interfere with one another...?

The Origin of Balanced Power

 

The answer to this question decides whether I can just buy 1 big balanced PSU (2000va) or if I need to buy 2 separate ones; and spend more money

 

Thanks!

 

Ground loop prevention - If all your AC devices terminate from the one distribution device, the chances of ground loops reduce, but won't be eliminated. If the intention is to use a balanced supply, the reference ground to the AC lines is much the same value throughout the system, so the chance of a ground loop diminishes, especially if the AC cables are shielded and grounded at both ends.

 

There are balanced transformers and then some. Initially tried off the shelf toroid transformers with I guess 3-5% regulation with the centre tap earthed. The sound wasn't bad, but not what I really expected and certainly not up to the hype.

 

Still encouraged by what could be a potential night and day, I purchased an Equitech Model Q, and the background noise just vanished to nothing, ti was awesome (and still is). The technique of the balanced supply is to maintain the symmetry of the two outer lines as close as possible to one another in voltage.

 

For a transformer to do this, the build, materials, and how the core interacts with the winding are all quite critical. The transformer then requires it to be a very low number regulation (I suspect 1-2% or less), and then the size and weight increase markedly, so does the cost and the advantages.

 

Currently I throw everything on the Equitech, amps, DACs, even a HP Z800 workstation. The beauty of the system is, the noise (line harmonics and conducted RF) on the system is assymetric (with reference to earth and the two AC lines), and as such, does not propagate to the other audio components, since, it mathematically, doesn't belong along the two AC lines.

 

Further tips:

The output of the balanced transformer must be protected with a GFCI/ELCB.

 

Use a standard 1:1 isolation transformer on the input to the balanced supply to absorb the rapid di/dt caused by 'absorbing' the pulse currents from SMPS.

 

Never use a Furman or Monster commercial line conditioner in front of the balanced transformer, the sound will be awful, thin and no dynamics. A conditioner on the output will fault, since the conditioner is expecting an earthed neutral and doesn't receive one.

[liquidsmoke]

My amps power consumption are 'rated' at a max of 800VA according to the manual, which I presume is because they each have 1 800VA rated toroidial transformer inside them. I'm having trouble deciding how much power I need the balanced transformer to supply. I have been reading around and it seems that a typical amp like mine will only draw a max of 200W electrical power at high volume. And the OP mentioned that he thought that a 2000VA balanced transformer would be more than enough for a mid-high end system with 2x 500w monoblocks. If so then that is a good sign for my wallet!

[liquidsmoke]

I'm wondering if anyone has used or built a DC blocker for use between the wall and the balanced PSU toroid?

 

I received my airlink balanced supply and am really happy with the results. I have my whole hifi setup connected to it as well as a plasma TV. The only problem I have is that when the plasma TV is on, I get an intermittent loud buzzing noise coming from the airlink. Now I've heard that DC voltage on the mains feeding the airlink can cause issues like this, however if the plasma is connected to the balanced supply then would any DC voltage that the plasma drops into the mains cause this too?

 

I'm thinking to try to put one of these inline from the airlink to the plasma:

avahifi - AVA HumDinger

 

Perhaps I need one between the mains wall socket and the airlink too?

 

I would appreciate any informed opinion or help as my knowledge of power circuitry is very limited.

[One and a half]

I'm wondering if anyone has used or built a DC blocker for use between the wall and the balanced PSU toroid?

 

I received my airlink balanced supply and am really happy with the results. I have my whole hifi setup connected to it as well as a plasma TV. The only problem I have is that when the plasma TV is on, I get an intermittent loud buzzing noise coming from the airlink. Now I've heard that DC voltage on the mains feeding the airlink can cause issues like this, however if the plasma is connected to the balanced supply then would any DC voltage that the plasma drops into the mains cause this too?

 

I'm thinking to try to put one of these inline from the airlink to the plasma:

avahifi - AVA HumDinger

 

Perhaps I need one between the mains wall socket and the airlink too?

 

I would appreciate any informed opinion or help as my knowledge of power circuitry is very limited.

 

What happens is the plasma draws quite nasty current lumps from the airlink. These lumps have a 'high' di/dt (change in current versus change in time) and these tend to rattle the windings in a balanced transformer design. The rattle is on the AC Line side, since the balanced side rejects the out of balance currents on the secondary. They have to go somewhere, so it's back to the main power supply.

 

I don't think the Humdinger will fix this problem, since the humdinger will look for crossover at the zero point anomalies only. Three choices:

 

a) Install a standard 1:1 isolation transformer ahead of the Airlink. Size at least 2 x the airlink in VA. The isolation transformer will provide an inductive reactance, so that current peaks are tamed somewhat, and you end up with quiet operation. It also serves as an further common mode rejection, which is always handy. I used this approach in my installation and it works very well.

 

b) Plug the plasma into the wall bypassing the airlink, and use a optical fiber cable to your audio system.

 

c) Find out the slope and shape of the current peaks, and design an inductor to smooth or filter out. This method is beyond the hobbyist though, and any change in the plasma's switching pattern may bypass the action of the inductor and you're back to where you started

[liquidsmoke]

Thanks for your reply. Thats interesting info. I guess if I got hold of/borrowed a DC blocker to put between the airlink and the plasma, then it would rule out DC as the problem?

 

Regarding the solutions you have offered:

a) sounds like a fair idea. Would this isolation transformer go between the Wall and the airlink? Is there a reasonably priced off the shelf unit that would do for my application? Otherwise my problem is that without detailed idiot proof step by step guide to making one, I would be out of my depth.

 

b) This isn't really practical as with this method I get horrible ground loop problems throughout my system due to the HDMI connection between my AVR and TV. This is actually one of the reasons which got my looking at balanced supplies in the first place. And thankfully the balanced supply has worked at curing this problem. I suppose I could remove the ground pin on the TV, but I would be wary of doing this for obvious reasons.

 

c) I wouldn't know where to start!

 

I'm sure I am completely stupid in thinking so, but couldn't I use some kind of capacitor arrangement between the airlink and the plasma to smooth out the current draw? As a kind of buffer? Or does this approach only work with DC?

[Speedskater]

.....................................

I have my whole hifi setup connected to it as well as a plasma TV. The only problem I have is that when the plasma TV is on, I get an intermittent loud buzzing noise coming from the airlink. Now I've heard that DC voltage on the mains feeding the airlink can cause issues like this, however if the plasma is connected to the balanced supply then would any DC voltage that the plasma drops into the mains cause this too?

..................................................

I would appreciate any informed opinion or help as my knowledge of power circuitry is very limited.

Plasma TVs are notorious RFI interference generators. HAM radio operators often complane about the interference from their neighbors plasma TV.

[liquidsmoke]

I wasn't aware RFI would cause a buzz in a balanced power transformer?