Cambridge Audio Duo Phono Stage Review (Updated)

[SimpleTheater]

Time for a lesson (and I'm not giving one, I'm asking for one). @amirm wrote "Moving coil input naturally has lower SINAD due to much higher gain"

I know SINAD isn't the end all be all, but many consider MC's as better than MM's. Does this issue of much higher gain essentially eliminate any advantages MC's have over MM's?

 

[TheBatsEar]

I just realized for the first time that the phono preamp is another fundamental limitation on the SQ of vinyl. So, even everything else in your chain is perfectly transparent (the disc, the cartridge, etc.) the best SINAD you’re ever going to get with MC is ~-63 dB. That’s even worse than most speakers above ~300 hz. Am I missing something? What do measurements of vinyl test recordings deliver in best-case systems?

I hope you never learn about background room noise.
You might look for a new hobby if you live in a city.

 

[CT Man]

Thank you. Exactly the device I need! Guys, how would you make this wireless to connect it with the preamp that can't sit next to it? Any wireless repeater you'd recommend that will not impact sound quality too much?

I have my tuner and turntable in a room separate from my newer, main system. My main system has a WiiM Pro for streaming Roon, Qobuz, TIDAL, etc. My turntable and tuner are connected to a vintage Adcom GFP-555 preamp with the tape monitor output going to an Amazon Link preamp that used to be in my main system. The WiiM and the Amazon Link can be set up as an Echo group. So it goes turntable/tuner cabled to Adcom preamp cabled to Amazon Link wireless to WiiM Pro connected by optical to my main integrated amp. Even with the turntable source going through an ADC to DAC process the sound is very good to my ears when playing well-recorded LPs in good condition. I play vinyl and CDs mostly for older jazz reissues that aren't available through streaming services. In some case I prefer the mastering on those reissues to digital streams.

I also have a vintage Adcom GCD-700 5 CD changer cabled to the Amazon Link's coax in. That's a pure digital path from the CD changer to Amazon Link to WiiM Pro to my main integrated amp. I can't hear the difference between that and direct 16/44.1 streaming.

Might be pricier than you want to do from scratch, but worked well for me since I had already retired my Amazon Link preamp.

 

[BadAudioAdvice]

@amirm If you still have the unit on-hand, would you be able to review the headphone amplifier that is built-in?

 

[MediumRare]

I hope you never learn about background room noise.
You might look for a new hobby if you live in a city.
View attachment 301194

Actually, I’ve measured mine. It’s about 20 dB. I play music more than 60 dB louder. So, what’s your point?

 

[amirm]

@amirm If you still have the unit on-hand, would you be able to review the headphone amplifier that is built-in?

That was in the original review. From what I recall it was pretty mediocre.

 

[mppix]

There was a substantial change in methodology. For the first few reviews, I was keeping the output level constant and changing the input level of the preamp to get that level. This causes input levels of MM to be 11 millivolts in the case of this phono stage (from what I recall). This led to complaints that this was too high a level for MM cartridge. So I changed things around where now the input level is fixed (5 mv for MM and 0.5 for MC), and output is variable. The former method gave an advantage to Duo in that it allowed it to have twice as high an output, resulting in better SINAD.

The new method is not without its faults. We are now mostly measuring noise in the dashboard. And gain of the phono stage can bias the results. But it is what we have. The committee decision won.

Do all measurements in the SINDAD chart follow the new testing procedure?
I'm mostly interested in the Parks Audio Puffin.

 

[Endibol]

This is an updated review of the Cambridge Audio Duo phono preamplifier. It is on kind loan from a member and costs US $349.
View attachment 301088
The Duo has a solid build and is attractive to boot for its price. Back panel shows independent sets of inputs for moving magnet and coil cartridges:

View attachment 301089

I like the inclusion of balance control and built-in power supply.

The original version was tested very early on when I had gotten into phono stage testing. My protocols have evolved since then making it hard to compare those measurements to current phono stage reviews.

Cambridge Audio Duo Measurements
It was challenging to reduce ground loops in both channels. After some messing around, I got close to optimal on both channels:
View attachment 301090
This lands the Duo essentially at the top of the class:

View attachment 301091

We still have that odd spikes around 19 kHz. Moving coil input naturally has lower SINAD due to much higher gain:
View attachment 301093

Distortion is vanishingly low when measured without noise:
View attachment 301094

RIAA equalization is essentially perfect in both modes:
View attachment 301095

Headroom could be a bit better:
View attachment 301096

Fortunately the same performance remains up to 10 kHz:
View attachment 301097

Conclusions
While the cost has gone up $50, the Duo is still reasonably priced for a solid package both physically and electronically. The only miss is with respect to overload due to output maxing out at 10.5 volts. Otherwise we have excellent frequency response and state of the art in distortion in a phono stage.

My excellent recommendation rating for Cambridge Audio Duo remains.

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

Any donations are much appreciated using: https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/

@amirm: perhaps I am misunderstanding things.. the two dashboards for MM and MC both show approx. 500 mV rms input levels.
Shouldn’t this read 5 mV resp. 0.5 mV rms? Or do the dashboards show output levels?
Which numbers were used for the SINAD results?

 

[SuicideSquid]

I'd like to voice my appreciation for the double-labelling of all the inputs so they can be read upside down when you're leaning over your stereo trying to hook things up. This is a great idea and should be stolen by other manufacturers.

 

[amirm]

@amirm: perhaps I am misunderstanding things.. the two dashboards for MM and MC both show approx. 500 mV rms input levels.
Shouldn’t this read 5 mV resp. 0.5 mV rms? Or do the dashboards show output levels?
Which numbers were used for the SINAD results?

The numbers in dashboard show the output, not input. It just happens that the gain difference compensates for 5 mv vs 0.5 mv input.

 

[amirm]

The SINAD table reflects MM only.

 

[amirm]

Do all measurements in the SINDAD chart follow the new testing procedure?
I'm mostly interested in the Parks Audio Puffin.

Pretty sure they do.

 

[Endibol]

The numbers in dashboard show the output, not input. It just happens that the gain difference compensates for 5 mv vs 0.5 mv input.

Thanks for the clarification Amir!

 

[USER]

The one thing I noticed with the Solo is the frequency response measured by Amir seems to be a little wonky for whatever reason. Whether or not it can be perceived is another thing.

View attachment 301238

I think that because cartridges are generally within ±2dB in the most audible regions and there are infinite forum posts about how wildly different they all sound, this may make a meaningful enough difference. I recently saw a phono pre with a -1dB slope that clearly affected the measurements to the point that I would rather throw away the measurements than make them public. The more measurements I see the more important RIAA compliance becomes for me, matching what Amir emphasizes. So the Solo would be a very, very (very!) hard pass for me.

 

[wemist01]

I gather there is no way to adjust load for MC? If not, would some consider that feature disposable?

Also, I have to be pleased that my phono amp has adjustable gain because my Denon DL-103R clipped in two other phono amps when set on MC, so I had to run them on MM. Per Denon, "the DL-103R is a low output Moving Coil cartridge with an output voltage of 0.25mV with an output impedance of 14 ohms."

 

[USER]

I gather there is no way to adjust load for MC? If not, would some consider that feature disposable?

Also, I have to be pleased that my phono amp has adjustable gain because my Denon DL-103R clipped in two other phono amps when set on MC, so I had to run them on MM. Per Denon, "the DL-103R is a low output Moving Coil cartridge with an output voltage of 0.25mV with an output impedance of 14 ohms."

I think I've said this before but that's a great record you have as your avatar. Have you heard this, by another Sun Ra collaborator?

I remember grabbing both LPs when they were reissued around 20 years ago (wow) and I was working at a record store.

 

[SuicideSquid]

I think that because cartridges are generally within ±2dB in the most audible regions and there are infinite forum posts about how wildly different they all sound, this may make a meaningful enough difference. I recently saw a phono pre with a -1dB slope that clearly affected the measurements to the point that I would rather throw away the measurements than make them public. The more measurements I see the more important RIAA compliance becomes for me, matching what Amir emphasizes. So the Solo would be a very, very (very!) hard pass for me.

View attachment 301246View attachment 301248
View attachment 301249

Two things I think might affect this comparison: First, the total average variation of those cartridges is about 4dB (+2dB above, and -2dB below), with the Grado having an 8dB variation, vs. only 1dB (+/-0.5dB) for the phono preamp. In most instances it's fairly easy to hear a 4dB difference and you'd have to have serious hearing impairment not to hear 8dB, but it's fairly difficult to hear a 1dB difference.

Also, psychoacoustics, lack of blind testing, and all that. Are the people claiming these cartridges sound night-and-day different testing them in a controlled environment?

 

[USER]

Also, psychoacoustics, lack of blind testing, and all that. Are the people claiming these cartridges sound night-and-day different testing them in a controlled environment?

Oh, I was trying to be generous and a little funny. I find most vinyl forums to be hubs of misinformation and usually roll my eyes when I read such anecdotes. Old ears and stubbornness is a bad combo! Most people don't know how to set-up their turntables so it's as uncontrolled an environment as can be. Nonetheless I believe that it is generally accepted that we can distinguish a 0.5 dB difference--not that we can necessarily make a value judgement on it (correct me if I am wrong, anyone)--so a spec of plus minus 0.65 dB I think should disqualify a phono preamp. But more generally, at least for my measurement purposes, if it can show up cleanly in the results, I don't want it! As far as that grado goes, I chose it because I think its an example of a mediocre cartridge, mostly for that 2dB dip at 5kHz. That 8dB swing above 12kHz I think would not be too audible to me because its mostly past my limits and there is seldom much useable info on records there anyways. That's why I tried to stress the most audible frequencies.

Anyways hopefully in the not too distant future we will have high quality AB comparisons of cartridges (including some EQed similarly!) on the library thread for the public to consider and learn from.

Edit: as far as the phono preamp with -1dB slope goes, I do think it can make a big difference depending on the cartridge. And I'm not saying people could not like it. We are trying to see what kinds of cartridge tunings have been well received in the past and it seems that we can distinguish this one in particular.

Here is an example of a distinct, highly popular, and well made cartridge. (It is similar to the Nagaoka MP-500 from what I have seen).
It only slopes down -2dB at 10kHz. Exaggerating the slope I think would alter its sound by a bit.

 

[andrewskaterrr]

So I posted this on the Solo review last night.

I guess I'm a little stuck on what to do. I dot follow Phono stages so I’m not familiar with what’s “normal” results, so I'm trying my best to compare. I put a "?" where I guess or don't know. I bolded the downsides. I underlined the best.

Cambridge Audio Duo $350: Large, SINAD 84dB, FR +0.2dB, HPF ~6dB/octave @30hz, Balance knob, Head Room 76mv (?dB Gain).
Cambridge Audio Solo $230: Medium, SINAD 86dB, FR +/-0.65dB, HPF ~12dB/octave @25hz, Balance knob, Head Room 95mv? (?dB Gain) ($170 used).
Schiit Mani 2 $150: Small, SINAD 81dB, FR +/-0.18dB, HPF ~3dB/octave @250hz, No Balance knob, Head Room 63mv (44dB Gain).

Setup:
Technics SL-1200 MK5
AT VM540ML (4.0mV at 1 kHz, 5 cm/sec)
DIY ~40ft Canare L-3CFB + Rean RCAs
JBL SDP-55 Pre/Pro
I run the official +4dB Harman Curve from JBL, and have 4x PB-1000 Pro subs, 2 of which are on either side of the Turn Table shelf. While I don't think I hear any rumble with my current MP-4 which does not have a HPF, I still would like a HPF to make sure. My in room response reaches @13hz @-6dB but is on a fast slope down after that.
The Solo may be the one to get because it has the best High Pass Filter and SINAD, but it also has the worst Frequency Response. The Schiit Mani 2 seems to be an all around ok choice with switch options, but slow HPF. In reality though, that slow HPF barely impacts the 20-250hz, but I still wish it cut off below 20hz faster. It looks like it's only -6dB @10hz, which isn't much cutoff. It will only require me to move my TT over maybe an inch for more breathing room which is another positive. I'd like a Balance knob, but I'm not sure if I'll ever need it? I level my TT so I don't have needle drift, but I'm not sure if some records may need it? I don’t even listen to vinyl that often, it’s just for fun. So the thought of spending $350 (more than my Cartridge) on a Preamp hurts a little, but I can afford it. What do you guys think?

 

[torgeirs]

Time for a lesson (and I'm not giving one, I'm asking for one). @amirm wrote "Moving coil input naturally has lower SINAD due to much higher gain"

I know SINAD isn't the end all be all, but many consider MC's as better than MM's. Does this issue of much higher gain essentially eliminate any advantages MC's have over MM's?

Sinad measurement of a phono stage must always include the output impedance of the cartridge.
We are way down at the fundamental noise source , the thermal noise. So a mc phono amp need a pickup to lower the hf noise. 10 ohm with mc pickup vs 200 ohms without