This is a review and detailed measurements of the Cambridge Audio Alva Duo Phono Pre-amplifier. It is on kind loan from a member who purchased it and drop shipped it to me. The Duo costs USD $299 and includes Amazon Prime or free shipping from the company itself.
Despite its budget price, first impressions are positive as far as look at the unit:
A momentary switch turns power on/off and controls whether it is amplifying the movie magnet or moving coil input.
The volume control is only there to vary the level of the 1/4 inch headphone jack. It has no effect on the pre-out in the back.
Oddly, the unit came with two identical IEC cords. There is even dedicate space for each in the packaging. Wonder if someone is getting paid by how many power cords they move every day.
Yes, there is a Solo version of it with just moving magnet input and no headphone jack. Wonder if that one comes with two power cords two!
Rear panel connectivity is as you suspect plus a balance control which you don't:
Note how thoughtful someone was to put a set of labels upside down so that you could read them when leaning over the unit!
The overall packaging left a positive impression. Let's get into measurements and see if that feeling fades out or gets stronger.
EDIT: Click for updated review and measurements of Cambridge Audio Duo Phono Stage.
Measurements
This is my first attempt at standardizing my phono preamp measurements and making them more comprehensive. So please provide feedback on them as once there, it should make it easier to compare products from different companies/models.
Here is the dashboard view using MM input:
I am standardizing on 1 volt output since one of the specs for Duo was stated as such. But also because it reduces the effect of hum which is the main limiting factor in phono pre-amplifiers. Even with that high output (requiring 11.3 mvolts of input) THD+N is limited by the 60 Hz mains leakage. Initially the level of hum was much higher with the floating inputs of Audio Precision analyzer. I grounded the input to the Duo and it made a 10+ dB improvement. Grounding to the chassis screw on the Duo made things worse so I left that alone. Using this configuration, my measurements agree more or less with company's THD+N spec of 0.002%. We will analyze this performance more in later measurements.
Frequency sweep shows a rumble/subsonic filter permanently engaged:
This measurement is with the Audio Precision generator EQ for inverse RIAA engaged. As such, it shows the accuracy of RIAA implementation in Duo which seems very good. No coloration from this unit.
Using the same 1 volt output, we get 90 dB signal to noise ratio which confirms our finding in the dashboard:
Once again, we have measurements which match the spec which is reassuring.
Running a 1 kHz FFT with high resolution shows the spectrum of any distortion or noise:
As with the dashboard we see the mains/power supply harmonics and an odd peak at about 19 kHz. The latter is strange in an analog unit we read that it has a switching power supply. I wonder if that is the switching frequency???
Note that there appears to be no harmonic distortion of any kind! All the spikes are mains driven. We can confirm this by turning off the generator and just examining the spectrum of what is there:
I have shown the noise spectrum using log display now to show more detail in low frequencies. And also included that of moving coil input (in blue). We clearly see the 60 Hz mains noise plus other harmonics going on and on. And our 19 kHz or so spurious tones.
In an attempt to make the graph easier to relate to audibility, I have overlaid the threshold of hearing assuming a peak playback of 120 dB SPL. Research shows that live concerts can reach such levels in typical seating position. Using that as the baseline, then we can properly overlay the hearing threshold (in pink) over our graph. Once there we see that none of the measured noise components reach audibility.
Of course this is with my setup. Yours will vary and may very well have far higher hum. If you are into LP playback, you are probably used to this challenge.
Here is the intermodulation distortion (SMPTE signals) versus output level which levels the playing field between the two inputs (and other products measured in the future):
The MC input (blue) has more gain so it gets pushed into clipping with 20 millivolt input level. Note that I had to lower the input level for MC to get the full graph (was too lazy to document it in the graph). Bottom line, you have to use a lot more gain with MC input and that translates into nearly 20 dB higher noise level.
We get the same view if we measure THD+N versus level:
You have to push the Duo to more than 6 volts output to generate any distortion. Since most power amplifiers need less 2 volts (or even 1 volt), you can compute your headroom using this figure.
Switching to headphone amplifier, the outcome is disappointing. Here it is with 300 Ohm load:
Even when you force the unit with far higher levels than any cartridge provides, you only get 10 milliwatts of power. My standard is 100 milliwatts here. With typical cartridges, you are likely to get single digit output power in milliwatts. Better have a sensitive headphone to get much value here.
Kind of odd is how quickly the graph flattens. Seems to be high level of noise there to dominate that way.
The situation is not much better with 33 ohm load:
You will be lucky to get 10 milliwatt output with any real cartridge.
There is good news however in the form of low output impedance:
Conclusions
The Cambridge Audio Duo phono preamp comes in an attractive package despite its budget price and branded label. Its amplifier is essentially distortion-free and performance is mainly limited by power supply hum/mains leakage using MM input. MC incurs a penalty of 20 dB so you may hear some hiss there that would not with MM.
Sadly the headphone stage is a throw-away design. You can use it in a bind but don't be surprised if it has too little power/too high of a noise floor.
The Duo seems to be competently designed and attractively priced so I am happy to put it on my recommended list.
------------
As always, questions, comments, recommendations, etc. are welcome.
Have craving for some good Dim Sum. Nearest place is 35 miles away so I need gas money for that. Please consider donating money using:
Patreon: https://www.patreon.com/audiosciencereview), or
upgrading your membership here though Paypal (https://audiosciencereview.com/foru...eview-and-measurements.2164/page-3#post-59054).
Despite its budget price, first impressions are positive as far as look at the unit:
A momentary switch turns power on/off and controls whether it is amplifying the movie magnet or moving coil input.
The volume control is only there to vary the level of the 1/4 inch headphone jack. It has no effect on the pre-out in the back.
Oddly, the unit came with two identical IEC cords. There is even dedicate space for each in the packaging. Wonder if someone is getting paid by how many power cords they move every day.
Yes, there is a Solo version of it with just moving magnet input and no headphone jack. Wonder if that one comes with two power cords two!
Rear panel connectivity is as you suspect plus a balance control which you don't:
The overall packaging left a positive impression. Let's get into measurements and see if that feeling fades out or gets stronger.
EDIT: Click for updated review and measurements of Cambridge Audio Duo Phono Stage.
Measurements
This is my first attempt at standardizing my phono preamp measurements and making them more comprehensive. So please provide feedback on them as once there, it should make it easier to compare products from different companies/models.
Here is the dashboard view using MM input:
I am standardizing on 1 volt output since one of the specs for Duo was stated as such. But also because it reduces the effect of hum which is the main limiting factor in phono pre-amplifiers. Even with that high output (requiring 11.3 mvolts of input) THD+N is limited by the 60 Hz mains leakage. Initially the level of hum was much higher with the floating inputs of Audio Precision analyzer. I grounded the input to the Duo and it made a 10+ dB improvement. Grounding to the chassis screw on the Duo made things worse so I left that alone. Using this configuration, my measurements agree more or less with company's THD+N spec of 0.002%. We will analyze this performance more in later measurements.
Frequency sweep shows a rumble/subsonic filter permanently engaged:
This measurement is with the Audio Precision generator EQ for inverse RIAA engaged. As such, it shows the accuracy of RIAA implementation in Duo which seems very good. No coloration from this unit.
Using the same 1 volt output, we get 90 dB signal to noise ratio which confirms our finding in the dashboard:
Once again, we have measurements which match the spec which is reassuring.
Running a 1 kHz FFT with high resolution shows the spectrum of any distortion or noise:
As with the dashboard we see the mains/power supply harmonics and an odd peak at about 19 kHz. The latter is strange in an analog unit we read that it has a switching power supply. I wonder if that is the switching frequency???
Note that there appears to be no harmonic distortion of any kind! All the spikes are mains driven. We can confirm this by turning off the generator and just examining the spectrum of what is there:
I have shown the noise spectrum using log display now to show more detail in low frequencies. And also included that of moving coil input (in blue). We clearly see the 60 Hz mains noise plus other harmonics going on and on. And our 19 kHz or so spurious tones.
In an attempt to make the graph easier to relate to audibility, I have overlaid the threshold of hearing assuming a peak playback of 120 dB SPL. Research shows that live concerts can reach such levels in typical seating position. Using that as the baseline, then we can properly overlay the hearing threshold (in pink) over our graph. Once there we see that none of the measured noise components reach audibility.
Of course this is with my setup. Yours will vary and may very well have far higher hum. If you are into LP playback, you are probably used to this challenge.
Here is the intermodulation distortion (SMPTE signals) versus output level which levels the playing field between the two inputs (and other products measured in the future):
The MC input (blue) has more gain so it gets pushed into clipping with 20 millivolt input level. Note that I had to lower the input level for MC to get the full graph (was too lazy to document it in the graph). Bottom line, you have to use a lot more gain with MC input and that translates into nearly 20 dB higher noise level.
We get the same view if we measure THD+N versus level:
You have to push the Duo to more than 6 volts output to generate any distortion. Since most power amplifiers need less 2 volts (or even 1 volt), you can compute your headroom using this figure.
Switching to headphone amplifier, the outcome is disappointing. Here it is with 300 Ohm load:
Even when you force the unit with far higher levels than any cartridge provides, you only get 10 milliwatts of power. My standard is 100 milliwatts here. With typical cartridges, you are likely to get single digit output power in milliwatts. Better have a sensitive headphone to get much value here.
Kind of odd is how quickly the graph flattens. Seems to be high level of noise there to dominate that way.
The situation is not much better with 33 ohm load:
You will be lucky to get 10 milliwatt output with any real cartridge.
There is good news however in the form of low output impedance:
Conclusions
The Cambridge Audio Duo phono preamp comes in an attractive package despite its budget price and branded label. Its amplifier is essentially distortion-free and performance is mainly limited by power supply hum/mains leakage using MM input. MC incurs a penalty of 20 dB so you may hear some hiss there that would not with MM.
Sadly the headphone stage is a throw-away design. You can use it in a bind but don't be surprised if it has too little power/too high of a noise floor.
The Duo seems to be competently designed and attractively priced so I am happy to put it on my recommended list.
------------
As always, questions, comments, recommendations, etc. are welcome.
Have craving for some good Dim Sum. Nearest place is 35 miles away so I need gas money for that. Please consider donating money using:
Patreon: https://www.patreon.com/audiosciencereview), or
upgrading your membership here though Paypal (https://audiosciencereview.com/foru...eview-and-measurements.2164/page-3#post-59054).
Last edited:
