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Parasound Zphono Phono Preamplifier Review

amirm

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#1
This is a review and detailed measurements of the Parasound Zphono phono stage. It is on kind loan from a member and costs US $200. There are also versions with USB and ADC (for ripping Vinyl) and higher-end version with more control.

The look is unmistakably Parasound which is to say somewhat industrial and plain:

Parasound Zphono Phono Preamplifier stage MC M stereo review.jpg


The back panel shows the included, voltage selectable AC mains which I appreciate:

Parasound Zphono Phono Preamplifier stage MC M back panel input RCA ground AC Polarity stereo ...jpg


As you see the input gain can be changed from moving magnet (MM) to moving coil (MC).

Interesting to see an AC mains polarity switch. Not sure of the safety of that but I guess if you have a hum, it is worth having a switch like this to at least troubleshoot the problem.

Overall, the Zphono is a business-line phono amplifier with solid construction.

Phono Stage Audio Measurements
Let's start with our usual 1 kHz dashboard view with moving magnet setting:

Parasound Zphono Phono Preamplifier stage MM audio measurements.png


As with all good phono stages, there is no visible distortion. So what sets SINAD is simply noise which in this case rises enough to set it to 75 dB. This puts the Zphono in the middle of the pack:

best phono stage review 2020.png


Moving Coil setting with input changed to 0.8 millivolts naturally degrades performance due to increased noise that goes with increased gain:

Parasound Zphono Phono Preamplifier stage MC audio measurements.png


Since LP grove noise is likely to be higher than the preamp, the next test becomes more important which is the RIAA equalization:
Parasound Zphono Phono Preamplifier stage Frequency Response RIAA Equalization audio measureme...png


We see nearly flat response which is what we want to have (i.e. no tonality imparted on behalf of the phono stage). A rumble filter would be nice but that is reserved for their higher end unit.

Let's sweep the input voltage and see where hard clipping occurs as this will impact how bad LP pops and clicks will sound:

Parasound Zphono Phono Preamplifier stage headroom THD+N vs Input Level audio measurements.png


This is better than a lot of budget phono preamps. But let's see if that is frequency dependend:

Parasound Zphono Phono Preamplifier stage headroom THD+N vs Frequency vs Level audio measureme...png


So no concern there.

We can see the same when we sweep the frequency fully:

Parasound Zphono Phono Preamplifier stage headroom THD+N vs Frequency audio measurements.png



Conclusions
The Parasound Zphono is not sexy but solidly delivers on basic functionality of a budget phono stage. Not much fault can be found in the measurements other than perhaps level of noise.

Overall I am happy to recommend the Parasound Zphono.


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As always, questions, comments, recommendations, etc. are welcome.

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restorer-john

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#4
@amirm Do you have other choices for generator output impedances (you used 20R) closer to a typical MM and MC cartridge respectively?
 

Hayabusa

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#5
The RIAA curve is defined with two RC constants with a typical phase curve at the recording side in such a way that an analog filter with playback RC constants would correct the phase response back to 'flat' for the whole audio chain.
Now we see some phone preamps that have a DSP for RIAA.
Now the phase response could be quite different depending on how the RIAA is implemented digitaly.

So it would be interesting to see also a phase response.
 

Rja4000

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#7
@amirm
Hi Amir
About your ranking for phono preamps:
Shouldn't you compensate somehow for the gain difference ?

This one has 75dB SINAD for 46dB gain.
If you compare with the Cambridge Solo, that's 86dB SINAD for 39dB gain.

That means that, anyway, you'll have to push the Cambridge up by 7dB to achieve the same level. So another gain stage will be required, with its own noise contribution.
As SINAD is directly linked to noise, if I'm not wrong, the gap may actually be significantly lower than RAW SINAD indicates.
Is that right ?
 

MC_RME

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#8
I don't think so. SINAD without distortion (here...) is Signal to Noise. If you change the Parasound's circuit to have 7 dB less gain the noise floor will be 7 dB lower - but the signal too, so SNR (here SINAD) will not change at all. So the Cambridge still deserves the first place for being the most noiseless preamp tested so far.
 

MC_RME

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#9
@amirm Do you have other choices for generator output impedances (you used 20R) closer to a typical MM and MC cartridge respectively?
That's an interesting point. 20 Ohms basically short the phono preamps input, for max SNR. What impedance do typical MM and MC systems have - you have some numbers at hand?
 

restorer-john

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#10
That's an interesting point. 20 Ohms basically short the phono preamps input, for max SNR. What impedance do typical MM and MC systems have - you have some numbers at hand?
MC is very low, the loading (matching) on MC front ends usually is switched or suitable for 3 Ohms to 40 Ohms, whereas the loading for MM is typically 47K Ohms. The cartridge impedance itself with MCs and MMs* is around 1/10th-1/100th of the load value.

In my opinion, the source impedance for the MC is perhaps too high and for the MM is way too low. It will give artificially high numbers for the MM I would expect. @SIY may have some comments. It should be shorted or typical R IMO.

*I dug out a box of random average MMs to measure the DCR of them (both channels) and put in a spreadsheet. (the things we do)

1599556172780.jpeg
 
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#11
What impedance do typical MM and MC systems have - you have some numbers at hand?
MM: 500 … 1000 Ohm, 0.5 … 1H
MC: 3 … 30 Ohm, < 100µH

Testing SNR of a MM input with <100 Ohm source impedance doesn't make sense, because the Johnson noise of the MM cartridge and the input current noise of the amplifier (which is converted into voltage noise by the impedance of the cartridge) is not taken into account.
 

MC_RME

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#13
MM: 500 … 1000 Ohm, 0.5 … 1H
MC: 3 … 30 Ohm, < 100µH

Testing SNR of a MM input with <100 Ohm source impedance doesn't make sense, because the Johnson noise of the MM cartridge and the input current noise of the amplifier (which is converted into voltage noise by the impedance of the cartridge) is not taken into account.
If you use a higher impedance you will raise the noise - but that only averages the result(s). It might be useful to use a lower impedance to better show the difference in excellence of engineering. You could also say lets measure with the needle dropped - more realistic again, but then noise would swamp away any difference...

For line inputs SNR is usually tested with shorted inputs. It is the task of the source to be as low impedance as possible. In real world using 150 Ohms instead of 0 Ohms does not make much difference with line. With high gain mic inputs the difference between 150 Ohms and 0 Ohms is about 3 dB.

For an MM input it is easy to test what happens as the AP can switch between 20 Ohm, 100 Ohm and 600 Ohm. The question is if such an impedance change just gives the expected small difference in noise, or some more artefacts like even more noise and THD due to specific properties of the circuitry under test.

Maybe SIY knows the answer already, and testing at those impedances won't change the outcome in a significant way.
 

restorer-john

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#14
Here are the results of 24 MM cartridges as pictured above. Left and Right channels.

1599559301529.png


at = Audio Technica (twin 90 degree magnets)
at vm = Audio Technica vertical magnet
piezo = The Japanese manufacturer named Piezo.
 
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restorer-john

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#16
I'd love to see a "dashboard" of actual vinyl playback SINAD
It would be a fight for the poor AP to give a stable number.

It's much easier to just listen to those records you love and marvel in the knowledge that a rock, dragged along a groove, and has its movements which induce a tiny voltage then amplified by 60dB, sounds so awesome.
 
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#17
If you use a higher impedance you will raise the noise - but that only averages the result(s). It might be useful to use a lower impedance to better show the difference in excellence of engineering. You could also say lets measure with the needle dropped - more realistic again, but then noise would swamp away any difference...
Sorry, but this is wrong.

1.) For high frequencies the source impedance for the input approaches 47kOhm (input resistor). One way of "excellence of engineering" is to replace the 47k input resistor with a higher resistor (e.g. 1 Meg) which is not connected to ground but to an inverted and amplified "copy" of the input signal. Yamaha did this in the seventies in their top models. You can gain approx. 1.5dB of SNR with this "trick" with real life cartridges. This real life advantage would be hidden by the use of a low source impedance. See for example Self, Small Signal Audio Design, 2nd ed., p. 321ff.

2.) Input noise current is very real with bipolar transistor inputs. With a low source impedance you simply ignore the input noise current—with a real MM cartridge you can't. NE5534A with typ. 0.4pA/sqrt(Hz) is a good example for a very low input noise current with bipolar inputs, AD797 in contrast with 2pA is quite high. With 10k Source impedance (remember the inductance!) these values translate into 4nV/sqrt(Hz) (NE5534) and 20nV/Sqrt(Hz) (AD797). Compare this to the noise voltage densities of these OP amps (3.5nV/sqrt(Hz) for NE5534, 0.9nV/sqrt(Hz) for AD797).
 
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SIY

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#18
MC is very low, the loading (matching) on MC front ends usually is switched or suitable for 3 Ohms to 40 Ohms, whereas the loading for MM is typically 47K Ohms. The cartridge impedance itself with MCs and MMs* is around 1/10th-1/100th of the load value.

In my opinion, the source impedance for the MC is perhaps too high and for the MM is way too low. It will give artificially high numbers for the MM I would expect. @SIY may have some comments. It should be shorted or typical R IMO.
The MC source impedance for units that are not transformer coupled is pretty noncritical as long as it's in the dozens of ohms or lower. Current noise is generally not enough of a factor to make much of a difference.

MM is a different matter- higher DCR and (most importantly) higher L mean that any input current noise will translate to a higher overall noise as the cartridge impedance rises with frequency (and thus shunts the 47k input resistance less).

Keep in mind that once you go beyond 70dB or so signal to noise, you've already hit the cartridge Johnson noise limit, so the preamp will have almost no noise contribution.

edit: @paschulke2 and I cross-posted.
 
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PuX

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#20
seeing these measurements, I have a question:

could vinyl be better that cd audio in any way?

all I can think of is that for example there are vinyl rips with wider frequency range (with sound over 22khz).

are there any other vinyl benefits considering most phono preamps seem to have worse performance that an average DACs (in terms of SINAD at least)?
 
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