DIY Balanced AC Power Conditioner

[Glen B]

I've read a Topaz Isolation transformer with a 0.0005 pf rating can have a common mode noise reduction of -146 db. The pf rating seems to determine the noise reduction. How low can you go with common mode noise reduction to reach the noise floor or until it is inaudible to the human ear? Can you get -300 common mode noise reduction? I don't know if it has any differential mode noise reduction. I think what people need to look for is the curve on a graph of the common mode and differential mode noise reduction within a range of frequencies if possible. The problem is I don't know how these frequency ranges affect digital and analog gear separately. Also how do these transformers affect the sine wave?

The pf rating appears to be the capacitance figure between primary and secondary. You would want capacitance to be as low as possible so as not to couple differential HF noise, which can pass from primary to secondary, and may need to be filtered if this occurs. This can be accomplished before or after the transformer. Many of the audiophile isolation transformer products employ some additional form of noise filtration.

I like to use caps across the primary line and secondaries for this purpose. I’ve tried several of the popular box filters and did not like their effects on the sound. Although on paper, these products operate outside the human hearing range, to my ears, when in the circuit, they imparted an undesirable veiling and loss of detail, like if a blanket was thrown over the speakers.

How your system sounds with a particular transformer may be more important than raw noise reduction specs. Also, there is only so much noise reduction that can be achieved. For one thing, an isolation transformer (or any kind of line conditioner/filter) will not remove thermal noise (a.k.a. Johnson-Nyquist noise). It is interesting to note that the audiophile products have noise reduction figures in the range of -80dB. An isolation transformer should not affect the sinewave, after all it is just a transformer.

[Dual-500]

There have been a number of threads on AK and other places on balanced power conditioners, and the benefits they can bring in reducing the noise floor in an A/V setup. So, I started building one and wanted to share some of the details. It is not complete yet, but I will wire it all up hopefully over the next couple of weeks.

What can balanced power do for you? It can be a little, a lot or nothing at all. It depends on how clean the ac input is to begin with. A good isolation transformer can bring much of the same benefits that a balanced power conditioner can bring – namely, reduction in the common mode noise that might be riding on the power lines. But I suppose a balanced power conditioner can be used to extract the last bit of performance from your system.

I use a 220v to 110v step down isolation transformer with it's own #8 awg copper ground. Keep it simple.

[lag0a]

Has anyone been able to compare the performance of the Avel Y236905 to an Equitech 1kva? How come the Avel weighs about 14 lbs. while the Equitech Son of Q Jr. 1kva weighs 48 lbs. (not sure what % is not the transformer? Does the Avel Y236905 produce any hum or audible noise, and how efficient is it because Equitech claims 97% efficiency?

[Glen B]

Has anyone been able to compare the performance of the Avel Y236905 to an Equitech 1kva? How come the Avel weighs about 14 lbs. while the Equitech Son of Q Jr. 1kva weighs 48 lbs. (not sure what % is not the transformer? Does the Avel Y236905 produce any hum or audible noise, and how efficient is it because Equitech claims 97% efficiency?

The transformer in the Equi=Tech Son of Q should be around 30lbs, which is about 1/3 larger than other manufacturers' toroids of similar VA rating. The cores of all Q type transformers are oversized, which helps to maintain power factor, regardless of the load, and also helps them be resistant to saturation by DC on the power line. In the case of the Son of Q, that massive core is responsible for the vast difference in weight between it and the Avel. Following is a link to a thread on cheap DIY balanced power that employs the same 800VA Avel unit. The builder shares his impressions near the end of the thread.

HTGuide Forum - Cheap DIY balanced power device

[ursus262]

Hello, Glen

I use Balanced Power on my system using an off the shelf transformer with pleasing results. I bought mine from Airlink Transformers in the UK. I would like to ask a couple of questions if I may:

1. I notice that noise filtering components operate across both legs, instead of down to earth. I assume that this is to prevent filtered noise polluting the earth and, hence, finding its way back into the balanced system. Am I correct in this assumption?

2. I notice from the schematic that the centre tap of the secondary winding is referenced to ground (earth). Whilst this is inherently a wise thing to do, is there not a risk that earth noise could find its way into the secondary winding, or up into the audio system through the earth pin?

Many thanks

Dave

[Glen B]

1. I notice that noise filtering components operate across both legs, instead of down to earth. I assume that this is to prevent filtered noise polluting the earth and, hence, finding its way back into the balanced system. Am I correct in this assumption?
Dave

The caps across the two hot legs are differential filters.

2. I notice from the schematic that the centre tap of the secondary winding is referenced to ground (earth). Whilst this is inherently a wise thing to do, is there not a risk that earth noise could find its way into the secondary winding, or up into the audio system through the earth pin?

No, the center-tap is at "0V" potential, and the balanced configuration is inherently noise-cancelling in its design. The following article will give you an idea of how noise currents flow in unbalanced and balanced AC systems.

Balanced Power: The Next Generation

[ursus262]

That was a really good read. Thank you so much for that. I does help to be reminded of basic AC theory from time to time as I hadn't dealt with it since my days as an engineering apprentice.

The other thing worthy of note, is the presence of DC on the mains supply. When using a balanced transformer, this manifests itself as a rattling noise coming from the transformer housing as the cores saturate in the transformer itself. This can also degrade sound quality and is also filtered out by the isolation that the transformer can provide.

With my system, this noise comes and goes - as if someone in our neighbourhood is using an appliance which causes this to happen. In fact, our washing machine and dishwasher both do this when they are switched on

[Glen B]

I've tried a number of different isolation transformer brands and had experience with DC on the mains. The 2,000VA transformer in my first post in this thread buzzed like a gas powered chainsaw in time with the agitation of the household washing machine anytime it was running. Equi=Tech Q type and Plitron LO-NO transformers are designed to be quite immune to DC. Simple DC blocking circuitry will solve that core saturation issue and noise. I've built a number of DC blockers for people that either totally eliminated transformer buzzing or reduced it to a tolerable level (see post dated 8/4/09 at link below). PM me if interested in circuit details.

AudiogoN Forums: Do all toroidal transformers hum?