Sounds too good to be true

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I've been singing the praises of switching power supplies in power amplifiers for a few days, explaining why they have many advantages over a traditional supply: those advantages pretty much unobtainable by classic power supplies.

It's important to note that what I have written does NOT apply to MOST SMPS and only a small handful of these supplies actually provides these specs - so be aware that what I've written probably does not apply to most.

As with any technology we want to apply to designing a high-end audio product with, certain precautions have to be taken to maximize their benefit. For example, even the best SMPS don't have much energy storage on their outputs. This is because they are designed by engineers unconcerned with what we, in the high-end, would consider important.

I have seen this trait again and again and it's instructive to note that it is many times folly for audio designers to blindly believe what they're taught in school without challenging that knowledge as it applies to what we hear. Output capacitance of a SMPS is, as I mentioned, a great example.

Because of the tight regulation these supplies provide, most engineers would be fine leaving off any additional energy storage, but they'd be leaving sonic advantages on the table if they did. By treating the SMPS as one would a traditional supply, adding just the right amount of low ESR capacitance to the output, the designer can nail exactly the tonal balance they are looking for in an amp.

I know this raises the hair on the back of many folks' neck and that's ok - I've been doing that most of my life.

In point of fact, the final tuning of a power supply needs to be done by ear. Too much capacitance can actually harm the regulation of the supply and cause the sound to be too "fat" and "sluggish" sounding - too little and it gets "thin" and "reedy" sounding.

I have never known anyone that could design a world class sounding audio product 100% on paper - and I know plenty that have tried and stick to their guns with arms folded over the audible tuning process necessary to really make something sing - but they'd be in the minority of successful designers.

Tomorrow let's spend a little time on classic supplies.

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Paul McGowan

Founder & CEO

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