NAD PP 2e Phono Stage Review

[CleanSound]

It seems that every time I read a NAD review, the results are never flattering.

When I was in my late teens and twenties, NAD had the reputation for being a premium manufacturer with state of the art products.

Was I (we) snookered all along or have they completely lost their way?

Their new amps licenses out Purifi technologies are good amps. But since they licensed out Purifi technologies, they didn't design it themselves.

Back in the "old days," no reviewer had an audio analyzer and since most manufacturers at that time weren't engineering for ultra low distortions, most manufacturers are generally at about THD+N between .05% to .07%. And manufacturer did not have a standard for THD+N measurements, so it was never apple vs. apple, for example, what bandwidth was used, what impedance, which frequency, at what power was the THD+N measurements done at, it was never ever specified looking at the specs.

And also at that level of THD+N, I don't think reviewers were able to tell the difference. At least, I don't have confidence to tell the difference at that level of THD+N at the normal level of volume I listen to. Unless I mute the source crank it up and put my ears next to the tweeter to listen for hissing.

I share your same sentiment that the NAD brand aura was indeed high end. But was it? The only way to find out if NAD was making good performing equipment is to go back and measure their old equipment with a measurement standard.

This is part of the reason why I no longer buy into brand recognition/history/aura, I need to see measured performance and wait to see how it performs with real world reliability.

 

[SMc]

Interesting perception. Mine was that their products were intended as 'value propositions'--> decent value for the dollar, but nothing special. However it was/is, market perceptions don't necessarily correlate with either value or electronic goodness. We all know that.

Shame that a cheap wall wart is the problem. If it's typical of QC, it shows how much NAD cares.

A quick search shows that everyone and his brother sells 'em. And they all use the same blurb:

The PP 2e Phono Preamplifier offers superb performance in a clean and simple package...

Well, at least the box it comes in is clean and simple. If packaging is important then they've got that covered.

Mine has remained unopened in the box for years now. If I ever get the turntable working again I don't see it offers an advantage over the phono section of my even more ancient integrated amp unless it has an older model power supply that isn't as noisy.

 

[anmpr1]

As I recall, the claim to fame for NAD was that the gear was 'designed' in the US and outsourced to Asia for manufacture. Giving it a cost to quality spread advantage over both gear designed in Asia and made in Asia, and gear designed and made in the US. I never understood that sort of geographical logic, but it was a time when gear was still being made in the USA, and US gear had a certain (not always deserved) quality reputation, and was almost always more expensive than Asian product.

In the analog department NAD once marketed an unusual record player with a flat tonearm. Again, as I recall, its claim to fame was that being flexible along the longitudinal axis it somehow better 'absorbed' warps, or provided damping, or something or another. One feature was (again, doing it from memory) that you could lift the entire arm off its pivot, making cartridge changes easier. I don't think it was very successful in the marketplace, though. I never encountered one so have no personal experience with it.

 

[SMc]

In the analog department NAD once marketed an unusual record player with a flat tonearm. Again, as I recall, its claim to fame was that being flexible along the longitudinal axis it somehow better 'absorbed' warps, or provided damping, or something or another. One feature was (again, doing it from memory) that you could lift the entire arm off its pivot, making cartridge changes easier. I don't think it was very successful in the marketplace, though. I never encountered one so have no personal experience with it.

I saw that turntable and arm in a system with a McIntosh receiver and DIY speakers. I have no memory of problems with warps or damping!

 

[AuricGoldfinger]

Interesting perception. Mine was that their products were intended as 'value propositions'--> decent value for the dollar, but nothing special.

The thing with NAD was no money or effort was put into “rack appeal” aesthetics, luxury features or performance. They were very budget level. I was loaned one of their integrates and it was pulled out of my system in less than 20 minutes - nothing special sums it nicely.

Their integrates had a bad tendency to blow essentially every component on the board all at once. The term “carpet bombing” was coined to describe NAD failures.

 

[Postlan]

This amp is too quiet for vinyl.

 

[amirm]

This amp is too quiet for vinyl.

Not if it buzzes before you put on the LP on some sensitive speaker.

 

[Zapper]

I recall NAD's reputation from the mid 1980's as "budget audiophile"; two steps up from the Technics and Pioneer receivers and amps one bought at a box store; a step up from brands like Yamaha and Onkyo that were sold in HiFi stores, but well below the luxury brands like McIntosh. In retrospect I wonder how much those perceptions correlated with reality.

 

[Zapper]

@amirm, does the power supply noise you observe on this and several other phono amps become less if the connections to the phono inputs are removed and the inputs shorted? This might suggest that loading from the signal source plays a role in converting PS noise to audio signal.

I am wondering if the conversion of ground noise to audio signal might be very different when a floating cartridge is connected (low capacitance to ground) compared to an audio analyzer (grounded, or if floating, higher capacitance to ground than a cartidge). If so, the observed PS noise might be less than measured in actual use.

 

[Michael Fidler]

Voted fine. The RIAA accuracy is pretty good, and the THD seems better than many. You can see the zero in the RIAA network feedback peaking the response up at the top of the HF range, which may not be great for overload behaviour... A big plus for a proper active RIAA network and those nice equal clipping lines!

The power supply noise is disconcerting though. This appears to be a single supply rail design. My bet would be that this is coming in through the input biasing. Or probably if the outboard SMPS is noisy, you'll see those higher order harmonics peaking up as the rejection ratio of the regulator and op-amps isn't too good at higher frequencies.

The clipping point depends on the power supply rails and the gain. In this case, it is about 5V RMS output maximum, due to sub-regulation of the 24V input (probably down to 18V or so), which gives you about 7V either way once you subtract the rail distance most op-amps manage. In this case we get over 20dB of overload margin, but with 37dB of gain the nominal output might be a bit low in comparison to modern digital sources. If I had these limitations, though, I would choose a similar gain...

 

[Michael Fidler]

@amirm, does the power supply noise you observe on this and several other phono amps become less if the connections to the phono inputs are removed and the inputs shorted? This might suggest that loading from the signal source plays a role in converting PS noise to audio signal.

I am wondering if the conversion of ground noise to audio signal might be very different when a floating cartridge is connected (low capacitance to ground) compared to an audio analyzer (grounded, or if floating, higher capacitance to ground than a cartidge). If so, the observed PS noise might be less than measured in actual use.

Some discrete circuits are especially prone to this, as the power supply can modulate their input currents (even when the loop is closed), but many op-amps are much more immune. It is possible to see changes in PSRR depending on input impedance, although a typical cartridge will have an impedance of around 800 ohms or so at the power line frequency, so the effect is not great. Usually the input coupling capacitor is the biggest culprit for doing this, as it is calculated relative to the high-impedance 47k load and has a very significant impedance.

This preamp shows signs of much higher order power supply harmonics, so if this mechanism was significant (as it might be - we see discrete transistors around the input), then it might be much worse with an MM cartridge, whose impedance may rise up to 30k or so towards the top of the audio band.

 

[anmpr1]

I recall NAD's reputation from the mid 1980's as "budget audiophile"; two steps up from the Technics and Pioneer receivers and amps one bought at a box store...

For whatever reason, I associated them with brand like Adcom. I think both were about at the same price point. I don't know if either was generally better than anything else for the dollar. If you still have one from the '80s that works well then you are ahead of the game.

Domestically (US) I don't know of anyone making 'popularly priced' gear, other than the full of Schiit guys. Slumming, I checked Crutchfield--NAD has a decent line of reasonably priced gear, along with a few items in the more expensive (but not crazy expensive) category. They sell a four thousand dollar class D stereo amplifier, but once you get in three + territory you're competing with Benchmark, and I don't see the appeal of a NAD product at those prices. Everyone's MMV.

 

[Zapper]

Some discrete circuits are especially prone to this, as the power supply can modulate their input currents (even when the loop is closed), but many op-amps are much more immune. It is possible to see changes in PSRR depending on input impedance, although a typical cartridge will have an impedance of around 800 ohms or so at the power line frequency, so the effect is not great. Usually the input coupling capacitor is the biggest culprit for doing this, as it is calculated relative to the high-impedance 47k load and has a very significant impedance.

This preamp shows signs of much higher order power supply harmonics, so if this mechanism was significant (as it might be - we see discrete transistors around the input), then it might be much worse with an MM cartridge, whose impedance may rise up to 30k or so towards the top of the audio band.

What I have in mind is this: the charging currents from the power supply create a ripple in the local ground of the amplifier input. However, the 1st stage is properly designed and its input reference is Kelvined to the input return. This makes the ripple common mode, which the amplifier rejects. If this is true, if the inputs are shorted (or better yet, tied to gnd with 800 ohms), the ps noise should go away. Hence my first question to Amir.

Now if this amp is connected to a cartridge via a phono cable, the cable and cartridge ride on this common mode ripple, so the signal from the cartridge has the same ripple as the gnd node, which is rejected by the amp. So all is good and little ps noise while playing records.

However, when Amir connects his audio analyzer to the inputs, now an external ground connects to the amp ground. The signal no longer rides on top of the amp's gnd ripple, but is tied to earth gnd in the analyzer. Now the ripple shows up as differential signal and is not rejected by the CMRR of the amp. If Amir tries to float the analyzer by disconnecting earth ground, or using an isolation transformer, it's not entirely successful in removing the PS noise, because the analyzer is a big metal box with a lot of capacitance to the environment, and the environment is filled with EM energy at the PS frequency and its harmonics.

I've struggled with issues like this in the lab, not specifically for audio but similar issues. Solutions/work-arounds have included small signal transformers to isolate the input, galvanically isolated digital and power links with local ADC/DAC conversion, or driving large amplitude signals through a high impedance attenuator to resistively isolate the input. In each case the goal is to allow the input to float on the local return voltage.

Of course, eliminating PS noise is the correct solution, so I'm not excusing the designer nor am I faulting Amir's measurements.

 

[Michael Fidler]

What I have in mind is this: the charging currents from the power supply create a ripple in the local ground of the amplifier input. However, the 1st stage is properly designed and its input reference is Kelvined to the input return. This makes the ripple common mode, which the amplifier rejects. If this is true, if the inputs are shorted (or better yet, tied to gnd with 800 ohms), the ps noise should go away. Hence my first question to Amir.

Now if this amp is connected to a cartridge via a phono cable, the cable and cartridge ride on this common mode ripple, so the signal from the cartridge has the same ripple as the gnd node, which is rejected by the amp. So all is good and little ps noise while playing records.

However, when Amir connects his audio analyzer to the inputs, now an external ground connects to the amp ground. The signal no longer rides on top of the amp's gnd ripple, but is tied to earth gnd in the analyzer. Now the ripple shows up as differential signal and is not rejected by the CMRR of the amp. If Amir tries to float the analyzer by disconnecting earth ground, or using an isolation transformer, it's not entirely successful in removing the PS noise, because the analyzer is a big metal box with a lot of capacitance to the environment, and the environment is filled with EM energy at the PS frequency and its harmonics.

I've struggled with issues like this in the lab, not specifically for audio but similar issues. Solutions/work-arounds have included small signal transformers to isolate the input, galvanically isolated digital and power links with local ADC/DAC conversion, or driving large amplitude signals through a high impedance attenuator to resistively isolate the input. In each case the goal is to allow the input to float on the local return voltage.

Of course, eliminating PS noise is the correct solution, so I'm not excusing the designer nor am I faulting Amir's measurements.

I think there's a lot of mileage in your theory. SMPS (double insulated) like this one can lead to higher frequency currents in the ground path.

One thing worth saying might be that the gain is only 17dB at 20kHz, so to my eye they look a bit more pronounced than they should be. There could be a loop current, like you say, through the input node, although I'm not sure what kind of isolation AP uses if any.

In any case it could be possible that this is reduced with a floating load, although I've seen this effect with SMPS class 2 supplies at a much lower level in other designs. Perhaps the reference ground is connected at a funny point, within the power supply section of the circuitry. Similar effects can be seen when the reference is taken ahead of a filter cap, which results in a lot of noise current going into the reference.

 

[amirm]

If Amir tries to float the analyzer by disconnecting earth ground, or using an isolation transformer, it's not entirely successful in removing the PS noise, because the analyzer is a big metal box with a lot of capacitance to the environment, and the environment is filled with EM energy at the PS frequency and its harmonics.

AP's inputs by default are floating in unbalanced configuration. I attempted to ground it in various ways and it made no difference at all. So I think the issue is independent of this.

 

[AuricGoldfinger]

I recall NAD's reputation from the mid 1980's as "budget audiophile"; two steps up from the Technics and Pioneer receivers and amps one bought at a box store; a step up from brands like Yamaha and Onkyo that were sold in HiFi stores, but well below the luxury brands like McIntosh. In retrospect I wonder how much those perceptions correlated with reality.

McIntosh definitely had that reputation, and they do last. Higher line Yamaha separates did as well. Reputations become marred to some extend by their box store grade gear. About ten years ago, a professor friend did a thorough bench test of one of their two top amplifiers and it resulted in 125dB SNR, with 0.00018% THD. If they still made them I’d be in the market for one.

 

[beefkabob]

McIntosh definitely had that reputation, and they do last. Higher line Yamaha separates did as well. Reputations become marred to some extend by their box store grade gear. About ten years ago, a professor friend did a thorough bench test of one of their two top amplifiers and it resulted in 125dB SNR, with 0.00018% THD. If they still made them I’d be in the market for one.

I'm feeling like calling BS on these measurements.

 

[AuricGoldfinger]

Based on what, exactly? I have nothing gain either way. We have Benchmark today anyway.

 

[zoink]

Do not buy, will die. C-tier capacitors.

These things can only be reliably reviewed if the example is less than 2-3 years old at max.

Since I generally purchase gear to last more than 2-3 years, arguably that would mean a review of an item older than that will be a more accurate review of how the item will perform over time than brand new. Plus, you often don’t know how long an item has been sitting on a shelf before you buy it.

As an aside, I believe I purchased the reviewed item new in 2015, so it is about 9 years old.

 

[Angsty]

Some discrete circuits are especially prone to this, as the power supply can modulate their input currents (even when the loop is closed), but many op-amps are much more immune. It is possible to see changes in PSRR depending on input impedance, although a typical cartridge will have an impedance of around 800 ohms or so at the power line frequency, so the effect is not great. Usually the input coupling capacitor is the biggest culprit for doing this, as it is calculated relative to the high-impedance 47k load and has a very significant impedance.

This preamp shows signs of much higher order power supply harmonics, so if this mechanism was significant (as it might be - we see discrete transistors around the input), then it might be much worse with an MM cartridge, whose impedance may rise up to 30k or so towards the top of the audio band.

Of course, I’d love to see how the Spartan 5 would compare!