Puritan Audio PSM156 Review (AC Filter)

[sarumbear]

Hi Amir, the filtering of such devices depends on the load.

Why?

 

[ShinMolina]

So, the bottom line is that the Puritan box indeed does what they say it does, but what it does doesn’t matter.

It does something, which is a plus when comparing it to other similar devices. But what it does has little to none relation to what they say it does.

 

[amirm]

On top of it, the noise could be balanced (on both F and N wires) and unbalanced (for example F + GND).

A lot of stars have to line up for that noise to occur and to matter audibly. Your speakers for example are differential. They sit there in air with no connection to earth. Should there be common noise on both lines feeding it, it won't be converted to sound. Your equipment also has many dBs of common mode rejection on its own. Regulatory certification routinely calls for chokes on power input to get rid of such noise generated internally. Granted, those filters tend to work at hundreds of Kilohertz and higher but that is the likely source of noise, not down this low.

But sure, if you are hearing audible noise and you can identify it as being common mode, and this device has good filtering there, then there may be a solution here. In this broad category of audible noise being there in your equipment, I supported what this box does. But this is not how it is marketed to the audiophiles and why they buy them. They all buy them without any indication of pops and ticks. And what they report is independent of such. Here is the feedback from one such review:

"Once the Puritan was ‘in the wall’, as it where, I stopped and paused. I couldn’t quite believe what I was hearing and stopped in my tracks when the music played again. There was a distinct difference in sound quality. It seemed that the Puritan’s mere presence within the mains was having an effect because it started to clean up the mains, adding a slice of focus and reducing noise right there and then. I fact, I could hear a low level bass rhythm for the first time. "

He never heard the low level bass rhythm before it!!!

On company's website there is this testimonial:

"Now to my review; the volume increased 1 notch very obvious no placebo. The instruments are more fixed in the soundstage and they sound more like they should. The vocals are clearer and harmonies are more separated. The piano sounds more like a piano and the bass is deeper. Minute background detail can now be heard. "

Miraculous stuff that can't possibly be explained by the measurements I showed and certainly not by any common mode noise.

 

[David_M]

A quick immediate test - there is a line amplifier with 30dB gain (called Amp 30dB) on my workbench. Its input is shorted and its SE output is connected via shielded twist-pair cable RCA-XLR to the balanced measuring input. There is no other connection than USB from the soundcard to the PC notebook that is class II instrument.
Now, to the same 230V/50Hz mains line there is a SMPS 24V/5A power supply connected which I switch on and off. The DC output of this power supply goes to AIYIMA A07 amplifier which I also switch on and off. This A07 amplifier is neither connected to the 30dB amp, nor to the soundcard. The only interaction is via mains 230Vac power, which is used to supply the Amp30dB, PC and SMPS.

1) output noise of Amp30dB, SMPS off, A07 off
View attachment 150116

2) output noise of Amp30dB, SMPS on, A07off
View attachment 150117
see the spike above 500Hz

3) output noise of Amp30dB, SMPS on, A07 on
View attachment 150118
Again additional spikes

These interfering spikes are very low in level, however in the audio band. The only coupling is via 230V mains network. The line above 500 Hz is most probably an intermodulation product reflected in the audio band. Additional filter at the SMPS mains line would with highest probability change the measured plots.
Only 50 cm of pseudobalanced RCA-XLR cable was used at the Amp30dB output. Longer cable or 2-wire SE cable would for almost sure worsen the results. The additional spikes have origin in mains interference voltage and also result in cable shield capacitive currents.

Thank you for taking this data. It is telling, in this case, that increasing current loads from the mains, can inject unrelated(?) noise into the audio spectrum. Though, it's interesting that all spurious products are multiples of your 50Hz mains frequency. Would this translate if used on 60Hz mains? I wonder...

 

[David_M]

In your posts in this thread, you seem to systematically confuse completely different things:

- the signal fed, in these test cases usually a simple waveform oscillating with a single frequency
(e.g.1000 times the same pattern per second = with a parameter of 1 kHz)

- the FFT, a which is not a signal but an operation, not characterised by a frequency. Its maths will convert the data from the time domain to the frequency domain, revealing the frequencies of the input , signal.

Before criticizing Amir, one should at least understand the very basics ...
The famous philosopher Wittgenstein said something like:
Wovon man nicht weiss, darüber soll man schweigen...
.

I'm really puzzled by your comments. I'm not criticizing Amir on the measurements he took but suggested that maybe a more involved test methodology (injection of AM/FM noise into the AC mains and having multiple loads as others have suggested) would reveal whether this line filter (and all others for that matter) would be useful at blocking their potential effects in the audio spectrum.

And yes, in my signal processing world that I've been a part of for more than 20+ years now (first starting with my Master's thesis on Spatial and Frequency domain processing of Images), when one says "I've got the 1 MHz FFT data you asked for", we all know what it means....that an FFT operation was performed on the 1MHz signal in question. So, please, with respect, it's not necessary to treat and be lectured to as an infant in one of my areas of expertise.

 

[tmtomh]

Look at the graphs to the right. SINAD is worse by 0.2dB *with* the filter. But if you ONLY looked at 3 kHz, you'd expect the THD% from 1-5k for example to be much higher?

View attachment 150156

The results in the graphs you’ve copied here are identical with vs without the AC filter in the chain. These are measurements of the output of an audio device - a DAC.

The other graphs are measurements of the actual AC feed, with vs without the filter - no audio device is in the chain in that case. The discrepancy is because the DAC itself - like 99+% of audio devices - already filters the incoming AC, making the $1500 AC filter irrelevant. I don’t know how else to explain this; what are you not understanding?

 

[Alice of Old Vincennes]

I want to say
I'm very embarrassed that ASR makes completely wrong measurements for such products every time.
To evaluate such a product, create a situation that actually causes disturbance such as noise and affects the audio equipment, and measure how the target product is attached and how it works at that time. If you don't, it doesn't mean anything.
It is natural that measuring it in a normal state without any obstacles has no effect. "No effect" is the correct answer. If there is any change in the audio signal, it means a defective product.
Such products are similar to car seat belts and lightning arresters, and only show their effects in the event of an accident. It usually looks like a useless and disturbing entity.
Do not measure such products in the same way as audio equipment. Evaluation of these products requires a completely different and advanced measurement environment.

Bull. You must have a really expensive one.

 

[tmtomh]

I want to say
I'm very embarrassed that ASR makes completely wrong measurements for such products every time.
To evaluate such a product, create a situation that actually causes disturbance such as noise and affects the audio equipment, and measure how the target product is attached and how it works at that time. If you don't, it doesn't mean anything.
It is natural that measuring it in a normal state without any obstacles has no effect. "No effect" is the correct answer. If there is any change in the audio signal, it means a defective product.
Such products are similar to car seat belts and lightning arresters, and only show their effects in the event of an accident. It usually looks like a useless and disturbing entity.
Do not measure such products in the same way as audio equipment. Evaluation of these products requires a completely different and advanced measurement environment.

This is nonsense.

 

[Alice of Old Vincennes]

No. Typical use is that you connect more components to the filter outlets and you interconnect them with signal cables. So you get loops when especially SE cables are sensitive to shield currents and add the voltage drop into the signal. Depending on EMI emitted by the components to the power net the filter may reduce the shield circulating currents and thus improve S/N. This is the goal with AC filter. Not to measure single component in a clinical laboratory AP setup with balanced l/0, possibly with floating outputs.

Sounds like marketing nonsense.

 

[pkane]

I'm really puzzled by your comments. I'm not criticizing Amir on the measurements he took but suggested that maybe a more involved test methodology (injection of AM/FM noise into the AC mains and having multiple loads as others have suggested) would reveal whether this line filter (and all others for that matter) would be useful at blocking their potential effects in the audio spectrum.

And yes, in my signal processing world that I've been a part of for more than 20+ years now (first starting with my Master's thesis on Spatial and Frequency domain processing of Images), when one says "I've got the 1 MHz FFT data you asked for", we all know what it means....that an FFT operation was performed on the 1MHz signal in question. So, please, with respect, it's not necessary to treat and be lectured to as an infant in one of my areas of expertise.

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.

 

[DualTriode]

In the 1990’s I worked at a large teaching hospital with many buildings across a 100 acre plus site. There were several industrial facilities nearby.

Daily the electric utility would switch in large banks of capacitors for power factor correction. When the capacitors were switched on line there were several finicky pieces of equipment across campus that would trip off line as a result.

There were many 3 phase power filters much like the one reviewed here that were installed to keep mission critical equipment operating.

Thanks DT

 

[David_M]

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.

It's the output of the DUT and the distortions it makes to the original single test signal (e.g 10 KHz) that comprises the phrase "Get me that 10kHz FFT" spectrum.

We can also choose to examine the purity of a 'single frequency' in the real world via its FFT spectrum. It's never a pure tone since its generator is not perfect but has harmonic distortions and noise as impairments. It's not 'meaningless' as you indicated above.

Determining the FFT of this pure tone (e.g by performing a back-to-back measurement with DUT bypassed) is a VALID statement to make as one determines tone purity by measuring the distortions of its generator. For example, the more expensive AP systems would have the cleanest FFT spectra of its single tone (~ -140dB THD+N spec or better) than a more affordable PC card system with a THD+N of ~120dB or worse).

Your assertion that "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" is not valid in the real world. One of the figures of merit of a commercial signal analyzer is the FFT-based THD+N spec, a measure of the purity of its sine wave generator as measured by its own input circuitry. It tells me a lot about the sophistication of the design of the signal analyzer.

 

[IVX]

No surprise that a few cheap common-mode coils do not help but the thing still surprises me is the price. Why do not they ask for a reasonable price for 100.0% useless product, let's say $20? Maybe $2000 helps to believe that so expensive a cord extension couldn't be so simple?

 

[Frank Dernie]

but the thing still surprises me is the price

It needs to be expensive for its target audience to show any interest.
Placebos work more powerfully when the subject believes them to be expensive.
If cheap the sort of person taken in by such devices would look elsewhere for an expensive model since the whole hifi world has been assuming more expensive = better for many years, maybe even decades.
Price is the one measurements high end audiophiles "understand"

Edit:
Mind you for a nicely made unit it isn't that expensive compared to a lot of such devices

 

[restorer-john]

The only noise I’ve had was mechanical hum from the toroidal transformer in one of those power amps - precisely because my AC is dirty and has DC in the line. That problem was solved by a $150 DC blocker (a different, more specific tech that, unlike these alleged power cleaners, actually works).

This Puritan unit also has a DC blocker in it. The designer speaks of it in the linked video at the point linked below. You can see the heatsinked bridge rectifier and the bank of electros for that purpose.

A noisy transformer from DC offset in an otherwise excellent amp or preamp can be infuriating.

 

[MC_RME]

No surprise that a few cheap common-mode coils do not help but the thing still surprises me is the price. Why do not they ask for a reasonable price for 100.0% useless product, let's say $20? Maybe $2000 helps to believe that so expensive a cord extension couldn't be so simple?
View attachment 150201View attachment 150202

The 'coils' used here aren't cheap. Have a look at the photo again. Such a low corner filter frequency isn't possible with the 'coils' that you referred to. This is most probably done with the two very large inductors on the right side. As such the earlier reference to a cheaper Dynavox unit is invalid - it can not do that and indeed uses the 'cheap coils' only.

 

[restorer-john]

To me it's a well built distribution unit. Very nicely constructed, common mode filters with large inductors, extensive DC blocking, HF filtering and surge/MOV protection followed by individual filtering on each outlet. And very cool spring loaded flaps over each outlet. I like those.

Sure, it's expensive and won't offer a night and day audible improvement, but nobody can deny the good it is doing behind the scenes.

It disappoints me that some of the power conditioning products get tarred with the same ASR pile-on brush as the snake oil products. This one is clearly not from the latter category.

 

[IVX]

MC_RME the best of what they could use is a nanocrystalline core and it is inexpensive too.

 

[pma]

To get this attenuation
https://www.audiosciencereview.com/...6-measureemnts-frequency-response-png.150007/
at mains power supply level needs LC with quite high inductance and low resistance on the core that would not saturate at higher current that is needed to supply the audio components connected. Such coil would not be small and would not be cheap. There is a high level of ignorance displayed by some.

 

[Mart68]

To me it's a well built distribution unit. Very nicely constructed, common mode filters with large inductors, extensive DC blocking, HF filtering and surge/MOV protection followed by individual filtering on each outlet. And very cool spring loaded flaps over each outlet. I like those.

Sure, it's expensive and won't offer a night and day audible improvement, but nobody can deny the good it is doing behind the scenes.

It disappoints me that some of the power conditioning products get tarred with the same ASR pile-on brush as the snake oil products. This one is clearly not from the latter category.

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