AC Power Conditioning Clarity

I tried various transformers before settling on what I now have. Its larger core size brings a number of benefits - maintains voltage under load, does not saturate as quickly, high immunity to DC, has low inrush current therefore no need for soft-start, etc. I use a couple of smaller transformers side-mounted in the same chassis, to feed preamp and digital player separately.

You need to match your transformer size to the load. If you are using multiple big amps with high current draw, you either need to go up in transformer capacity or use multiple units. Toroid capacities above 2.4KVA for DIY use are hard to find. I don't see much benefit to running a sub amp on balanced power. The smaller gear can be run off a small transformer of a few hundred VA capacity.



In this Equi=Tech factory made unit, they use EMI/RFI block filters to isolate two outlets:

Those tiny inductors in the author's "suitable" mains noise filter will probably cause current limiting. Balanced power is a proven technology with sound theory behind it. So many people in commercial and home audio report similar benefits from the use of balanced power. If you want to go simple, just get one of the popular line conditioners (Panamax, Furman, Belkin PureAV, etc.) and call it a day. They all employ similar noise filters, employing common-mode chokes and noise suppression caps. I use the Belkin PF-60 pictured below in my home theater system.

Furman:


Panamax:


Belkin:


APC:

I am certain the transformer in that Furman unit accounts for the largest portion of the cost, followed by the enclosure. It looks like a Plitron LO-NO transformer in that Furman unit. Plitron is an OEM supplier to a number of manufacturers. I have around $2K invested in my DIY unit. The transformers alone account for about 50 percent of that cost.

I don't need soft-start. My main transformer, with its massive oversized core has low inrush current. You could probably get away without the thermistor if you are plugging into a 20A circuit. Even if you trip a househohold breaker the first time you power up the transformer, chances are it won't happen on the second or third try. It all depends on where AC cycle is at the moment you energize the transformer. Its not like you will be turning it on and off frequently. With 2KVA or 2.4KVA transformer I suggest a breaker such as this, to serve as both your overcurrent protection and power switch: http://www.digikey.com/product-detail/en/T11-2-20.0A-01-11AL-V/723-1273-ND/2781062

Glen, that's an eye-popping unit you got there

Johnny, I built this one for a pair of Class A amps with a *lot* of capacitance (0.5F), and they work a treat:



I had to add more capacitance over the 470nF present to get the relay coil to reliably operate. The relay voltage and coil resistance needs to be factored into the circuit, which is not something you read where these simple 'lifted' schematics are printed.

You can use Thermistor/s instead of resistors just fine. I mistakenly connected resistors in parallel and I've to fix that before I commission the amps, or I may just dispose the whole thing and redo it with thermistors.

Anyhow, to calculate the thermistor values needed you need to choose an NTC with a maximum current limit capability that is lower than the lowest breaker in the circuit you do not want to trip. The initial resistance should be sized to prevent excessive voltage drop to connected equipment or circuitry for the time the thermistor operates.

If the running resistance is too high for you, then the softstart is a good idea, but it will be fine without if you study the datasheet and work out what you need for the running value (again, this depends on connected equipment and how much resistance is appropriate). Since we have 230V mains, for large projects where the softstart is needed it usually manifests as a 2-5 ohm unit with a current rating of 2A-4A. My last largish was finished without a thermistor and I regret it because the unit kept blowing fuses and needed to be fitted with a 6A fuse for a 1A draw!! The cap bank was much smaller and I used an EI transformer, but a 2.5A slo-blo fuse wasn't holding up. I shall be refitting it with a 5 ohm thermistor soon.

Edit: here's a short paper describing the calculations involved. http://www.ametherm.com/inrush-current/transformer-inrush-current.html

Glen,

I can tell you that your assumptions about the CMC's are correct and incorrect.

First, using one sized at the specs for your entire expected load would be a terrible idea. But some of your pictures show one that may be for the entire unit, part of a filter, and others that are for separate sockets.

Properly sized CMC's will never, and I mean never, limit dynamics. However there are other factors that may be perceivable from incorrect usage that would lead one to criticize it with any term; meaning that the one definitive notion is it's wrong.

I'll make a simple case, no one has ever claimed an Audience Adept unit limits dynamics. BUT every socket has a CMC on it. That's because they're sized for an ampere rating no single device could in the slightest way begin to tax. There's more resistance in the average IEC inlet (not copper) than the CMC's.

Basically everywhere you look people love to point fingers at "coils" and "capacitors" at power conditioners as if they're some sorta bad voodoo. It's ridiculous, and we wouldn't even listen to music without both. Just because someone's design doesn't use them, doesn't invalidate them. Yet at the same time just because someone uses them, doesn't mean it validates them. It's all marketing.

My point is to belittle a myth. I'll point this out, a 2.4mh CMC at 60hz has the reactance of .9ohm, and typically .008ohm DC resistance. In other words, essentially nothing. If you were worried then you'd get rid of the average fuse found in most equipment that increases resistance as it uses more power. This is the same value or less than the ones used in Audience Adept units, per socket, with no report ever of limited dynamics.

But what happens if you run say 13a worth of gear through it? Then they spike, peak, here and there? Now you might be seeing the issue that happens often. It's not good either, it can melt the insulation.

My rule of thumb is to use CMC's at no less than double the ampere rating required for most devices. When it comes to large transistor operated amplifiers it's best to go higher because despite that perhaps they shouldn't, they tend to tugg on the transformer harder than many amps (the size of the transformer despite exceeding the necessity tends to improve sound quality as size increases to at least 2x needs). However digital on the other hand is circuits basically entirely fed by capacitors no where near their power supply, and can easily be run with CMC's even a little bit less than double the ampere rating required.

I've been at the power conditioning thing for awhile. :nerd: