Puritan Audio PSM156 Review (AC Filter)

[pma]

I think if they did not claim that it 'Enhances clarity and dynamics' then they would get a pass.

That's a necessary marketing claim. Separate it from the objective parameters. This forum calls itself "scientific" so please let's stay on the ground of science and engineering and not on the ground of subjective feelings and populism.

 

[KSTR]

It's not immediately clear if Amir's insertion loss measurement used the industry standard input and output termination impedance of 50Ohms? If not, it is not really useful.
EDIT: and actually, it should be two measurements, one differential-mode and one common-mode (wrt L and N).

 

[MC_RME]

Well, the 50 Ohm standard isn't useful at all - it's complete bollocks, especially when applied to the small filters everyone uses (230V loaded with 50 Ohms equals 4.6 A and 1058 Watts - highly unrealistic). Yet knowing how input and output impedance have been set when measuring such a filter array is very important, as it will change the frequency response curve. Output impedance should be as low as possible (power grid equals near 0 Ohm). The AP's 600 Ohm input choice equals 88 Watt load, much better suited than 50 Ohm, IMHO.

 

[KSTR]

Yeah of course 50Ohm isn't really appropriate but it happens to be the standard, to allow for comparisons and to check against filter manufacturer claims.

 

[pma]

Output impedance should be as low as possible (power grid equals near 0 Ohm).

Yes and then you need a buffering with a power amplifier added behind a signal generator, or to use a specialized signal generator.

 

[sq225917]

Why?

Because inductors.

 

[sq225917]

If I was testing I'd load my entire hifi onto it and the AP, then test. That'd shut up the detractors, and still show nothing.

 

[pma]

If I was testing I'd load my entire hifi onto it and the AP, then test. That'd shut up the detractors, and still show nothing.

So do it, instead of talking. Too much talking here, too many opinions and little real results. Results count, opinions do not.

 

[sarumbear]

With respect, it makes no sense to talk about an FFT frequency spectrum by referring to a single signal frequency. It’s meaningless, as it tells you nothing about the FFT.

I'm confused with your post. It makes perfect sense to talk about the FFT of a single frequency. In fact that is often the only reason for an FFT analysis. That is how you see the distortion elements in that single frequency signal.

 

[sq225917]

So do it, instead of talking. Too much talking here, too many opinions and little real results. Results count, opinions do not.

Oh, the irony...

 

[Bob from Florida]

No, the bloody FFT as I showed you. Why is this so hard to understand?


The only thing shaky is your arguments. People said in the last power filter review that tube amps with AC filaments could benefit. Well, this one is supposed to use that as well. Now you are complaining about this as well? It is not like I have 50 broken audio devices to pick from.

Amir,

I was one of the people suggesting that "maybe" a difference could be seen with a tube amp utilizing a directly heated triode. This preamp uses a 6922 dual triode which uses the more advanced heater separate from the cathode. The minor descriptions I could find on this preamp indicated the AC filament option has been suspended so it may have DC filaments as well. If you ever have a 2A3, 45, or 300B SET amplifier handy that uses AC filaments at the same time as one of these power conditioners that would be a good test. This is assuming the power transformer passes all that noise to the filament winding that would then show up as distortion at the output. A lot of "what ifs" for sure.

 

[pkane]

I'm confused with your post. It makes perfect sense to talk about the FFT of a single frequency. In fact that is often the only reason for an FFT analysis. That is how you see the distortion elements in that single frequency signal.

The original poster point was that Amir’s measurement should be repeated with a 10KHz FFT. My point was the FFT includes a range of audible frequencies. Any effects of AC noise would be visible in this range, whether or not the test signal is at 1KHz or 10k. What seems to be missed is that the real test signal here is not 1KHz or 10KHz but 60Hz mains frequency with its noise and its harmonics.

 

[LTig]

If you ever have a 2A3, 45, or 300B SET amplifier handy that uses AC filaments at the same time as one of these power conditioners that would be a good test. This is assuming the power transformer passes all that noise to the filament winding that would then show up as distortion at the output.

That would be a truly bad design, and I'd rather replace such a bad amp by a better one than "fix" it with such an expensive power line filter.

 

[Ajax]

Thanks for another insightful review into another nonsense product.

I bought a Furman 6 outlet power conditioner on sale 3 years ago and for lots of reasons (renovations etc) never opened the box. I can now sell it and get some better speakers that will actually make a difference to my listening pleasure.

This site is invaluable and will always be my first port of call prior to making a purchase.

 

[Snoopy]

Just considering that this £1500 does absolutely nothing worth mentioning I wondering what people expect from the low cost solutions from ifi , dynavox etc

 

[MrPeabody]

This thing works quite well and is exactly doing what we expect from the mains filter. The meaningful test would be with several audio components connected to its plugs and mutually interconnected to make an audio chain. Especially if some of them use SMPS power supplies. This would show if there is an effect to reduce switching frequency intermodulations. The test with single component like DAC or preamp is meaningless.

But why wouldn't you contact the manufacturer and ask them if they have any documentation of this kind of capability, from the testing they have done? Shouldn't the burden of proof be primarily on the manufacturer to prove whatever they claim in their marketing stuff, and burden placed upon independent testers be limited to claims they have made that refute claims that had first been made by the manufacturer?

The thing is, it ought to sufficient for audio consumers to simply point out, when a manufacturer has not provided compelling evidence that the product actually does whatever it is explicitly or implicitly supposed to do, that the evidence that is required of them has not been provided. The job of someone like Amir should only be to validate the claims and evidence given by the manufacturer. Manufacturers often leave it for audiophiles to decide for themselves what a given product actually does, thus creating a situation where someone like Amir needs to come along and inform audiophiles that the thing doesn't actually do that. Then the audiophiles who believed something that drawn into question by Amir's tests get all up in arms. This is NOT the way it ought to be. Manufacturers should be expected to state their claims clearly and back up their claims by publishing their test results. And when Amir tests something and finds that it doesn't do what the manufacturer claims, audiophiles should expect the manufacturer to either admit that their testing was flawed or else point out the flaw in Amir's testing.

Thus, it seems to me that you ought to contact the manufacturer and ask for proof or evidence of the device's ability to isolate each output from the switching noise fed back into the box by other devices with switching power supplies.

 

[MrPeabody]

Completely agree, measurements featuring multiple types of interferences and such could be interesting.

Many people living in apartments face elevator noise issues as I do while other may encounter air conditioner noise and many other existing sources of RFI/EMI.

I understand that this measurements are mostly focused on checking the claims of the manufacturer. Nothing wrong with it, my main complaint is directed towards the marketing of these kind of devices, but the measurements could also be focused on noise mitigation as previous one have been.

I don't agree at all. I think that people who challenge Amir's findings should stop nitpicking and do tests of their own. If you think that there is a different type of noise+distortion that will affect typical audio equipment and that a power conditioner such as this one will have the superior ability to cope with that type of noise+distortion, then it seems to me that the onus is on you to (1.) identify exactly what that type of noise+distortion is, then (2.) demonstrate via testing that typical audio gear really is unable to cope with that type of noise+distortion, then (3.) demonstrate that when a power conditioner such as this one is used, the problematic noise+distortion is eliminated such that it no longer presents a problem with which the typical audio gear can't cope.

The thing is, when it is thought appropriate for complaints of this sort to be registered at all, i.e., "you didn't test with the right kind of noise and distortion", it can go on forever, with no end in sight. Surely this is apparent to everyone, and as such, everyone ought to understand that if they want to assert that the test wasn't done with the right kind of noise and distortion, that they need to do what I explained in the previous paragraph.

 

[MrPeabody]

If the intention of these companies is good, they should start marketing their products as tools that help removing unwanted noise from electric motors and such, not as audio performance enhancing devices.

In my case, the controller of the elevator from the building I live in adds some 8 kHz noise when in operation. This noise leaks as EMI when I put interconnect cables near AC power ones.

Using a device like the one in this review should easily solve this problem because it has an attenuation of around 35 dB at 8 kHz which should mask the spike completely. For the price, I prefer to keep my cables tidy, but some people may like the idea.

In the great majority of cases the signal conveyed from a power cable to nearby interconnect will be the fundamental AC frequency. If you are truly having a problem of this nature, it is surely going to be the case that the interconnects pick up the fundamental (60 Hz or 50 Hz) to a considerably stronger level vs. noise at 8 kHz. And no power conditioner is going to fix this, for obvious reasons. It would be interesting and informative to see a spectral analysis of the leaked signal picked up by the interconnects, to reveal the relative strength of the fundamental mains frequency vs. the noise at 8 kHz.

 

[MrPeabody]

Is this an opportunity to suggest a measurement setup with schematic so that Amir, or someone else, can measure these devices in the situation where they have the best possible chance of proving their worth? Then there can be no more doubt.

The "Amir or someone else" should be the manufacturer. Amir should only be asked to validate claims made by the manufacturer. In this case, the claims the manufacturer has made are not conditioned on any specific level or type of noise+distortion on the mains, nor on any limitation within the audio components for dealing with the noise+distortion. As such, all that Amir needed to do, to refute the manufacturer's claims, was to show that when using typical audio gear connected to the mains supply at his home, the device had no benefit. There are people here who obviously don't understand this, and the reason they don't is because from the beginning, manufacturers of audio equipment were not held to an appropriately high standard with respect to the claims and their testing to back up the claims. This has been the status quo for so long (from the start) that most audiophiles take for granted, unthinkingly, that it is appropriate for manufacturers to make various claims, both explicitly and implicitly, without providing a shred of supporting evidence, and that when someone like Amir comes along and does what he does, that it is reasonable for everyone to pile on and find ways to criticize his testing. This is 180-degrees opposite of how it ought to be.

 

[pma]

You are writing long posts with philosophical content, @MrPeabody . I would rather appreciate facts and test results.