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Review and Measurements of Cambridge Audio Duo Phono Preamp

Laserjock

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If one needs only MM and no headphone output, does the Solo do what the Duo does as far as measurements?
 

Ecaroh

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If one needs only MM and no headphone output, does the Solo do what the Duo does as far as measurements?

I doubt that anyone here has measured the Solo. But you might want to check the owner's manual (one manual for the two products). Oddly enough, the Solo and Duo differ in the spec for RIAA Curve accuracy. +/-0.65 dB for the Solo, +/-0.3 dB for the Duo. The subsonic filters also differ. You can download the manual, e.g. here --
https://www.audioadvisor.com/prodinfo.asp?number=CASOLO
 

Laserjock

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I doubt that anyone here has measured the Solo. But you might want to check the owner's manual (one manual for the two products). Oddly enough, the Solo and Duo differ in the spec for RIAA Curve accuracy. +/-0.65 dB for the Solo, +/-0.3 dB for the Duo. The subsonic filters also differ. You can download the manual, e.g. here --
https://www.audioadvisor.com/prodinfo.asp?number=CASOLO

Thanks!
 

SPOautos

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Please excuse my ignorance but I'm fairly new to phono equipment and all the testing and I'm trying to understand all this better.....

Wouldnt it be better if the Duo had settings for input impedance? Do they basically just use a generic factor that should work for every cartridge? If so does that mean you will see different volume levels with differed cartridges (that have different output voltages). For instance if my cartridge output is 3mv and another is 5mv wouldnt the 3mv have a lot less volume?

And if so, would distortion go up and down with this? Where having adjustments kind of levels everything out to keep everything in a sweet spot of low distortion? I read somewhere that different cartridges need to see certain amounts of impedance load to perform their best and operate at their spec distortion levels.

If that's true then wouldnt the input impedence adjustments be very important?
 

sergeauckland

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Please excuse my ignorance but I'm fairly new to phono equipment and all the testing and I'm trying to understand all this better.....

Wouldnt it be better if the Duo had settings for input impedance? Do they basically just use a generic factor that should work for every cartridge? If so does that mean you will see different volume levels with differed cartridges (that have different output voltages). For instance if my cartridge output is 3mv and another is 5mv wouldnt the 3mv have a lot less volume?

And if so, would distortion go up and down with this? Where having adjustments kind of levels everything out to keep everything in a sweet spot of low distortion? I read somewhere that different cartridges need to see certain amounts of impedance load to perform their best and operate at their spec distortion levels.

If that's true then wouldnt the input impedence adjustments be very important?
Input impedance is pretty much standardised at 47k for MM cartridges. What isn't standardised is input capacitance, as that depends very much on the cartridge, and the capacitance of the arm cables and arm-phono stage interconnect cables. Capacitance makes a considerable difference to a cartridge's frequency response, so should be switchable, or have loading plugs. However, unless one tunes by ear and chooses what sounds 'best', one needs an accurate frequency response test record and a means of measuring level accurately, i.e. an audio millivoltmeter.

Some MM cartridges may benefit from a different load to 47k, combined with capacitance, and that's even more complicated, so very much a labour of love to get it right. Obsessives might prefer a phono stage with external loading plugs rather than switchable loading so any combination of R&C can be tried.

Fortunately low output MC cartridges are much less sensitive to loading, to the point where it hardly matters. As long as the load is 10x the cartridge's own resistance, it makes hardly any difference. If a LOMC cartridge has, say, a 20 ohm resistance, then as long as it gets more than a 200 ohm load, its frequency response will be what it is, regardless. High Output MCs are slightly more sensitive, but nowhere near the levels that MM cartridges are, and as with MMs, most HOMC are designed for a standard 47k loading. In the case of HOMCs, capacitance matters much less, so is seldom catered for as phono stages that offer switchable capacitance offer something between 100pF and a few hundred pF, which will have little effect on a HOMC and no effect on a LOMC.

S.
 

SPOautos

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Input impedance is pretty much standardised at 47k for MM cartridges. What isn't standardised is input capacitance, as that depends very much on the cartridge, and the capacitance of the arm cables and arm-phono stage interconnect cables. Capacitance makes a considerable difference to a cartridge's frequency response, so should be switchable, or have loading plugs. However, unless one tunes by ear and chooses what sounds 'best', one needs an accurate frequency response test record and a means of measuring level accurately, i.e. an audio millivoltmeter.

Some MM cartridges may benefit from a different load to 47k, combined with capacitance, and that's even more complicated, so very much a labour of love to get it right. Obsessives might prefer a phono stage with external loading plugs rather than switchable loading so any combination of R&C can be tried.

Fortunately low output MC cartridges are much less sensitive to loading, to the point where it hardly matters. As long as the load is 10x the cartridge's own resistance, it makes hardly any difference. If a LOMC cartridge has, say, a 20 ohm resistance, then as long as it gets more than a 200 ohm load, its frequency response will be what it is, regardless. High Output MCs are slightly more sensitive, but nowhere near the levels that MM cartridges are, and as with MMs, most HOMC are designed for a standard 47k loading. In the case of HOMCs, capacitance matters much less, so is seldom catered for as phono stages that offer switchable capacitance offer something between 100pF and a few hundred pF, which will have little effect on a HOMC and no effect on a LOMC.

S.


I just didnt want to get a Duo or Solo then a year later want a cartridge that isnt 47k....but your saying 47k is nearly a standard so it shouldnt be a issue.
 

sergeauckland

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I just didnt want to get a Duo or Solo then a year later want a cartridge that isnt 47k....but your saying 47k is nearly a standard so it shouldnt be a issue.
That's right. Every MM cartridge I know of is designed for a load of 47K.

S.
 

SPOautos

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That's right. Every MM cartridge I know of is designed for a load of 47K.

S.

Thank you for all the info! I appreciate it

Up to now I just plugged a turn table into a receiver and didnt give much thought to it. Now going with seperates and a seperate phono pre and all that, I have to actually understand some of this lol.
 

rwortman

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Fortunately low output MC cartridges are much less sensitive to loading, to the point where it hardly matters. As long as the load is 10x the cartridge's own resistance, it makes hardly any difference. If a LOMC cartridge has, say, a 20 ohm resistance, then as long as it gets more than a 200 ohm load, its frequency response will be what it is, regardless. High Output MCs are slightly more sensitive, but nowhere near the levels that MM cartridges are, and as with MMs, most HOMC are designed for a standard 47k loading. In the case of HOMCs, capacitance matters much less, so is seldom catered for as phono stages that offer switchable capacitance offer something between 100pF and a few hundred pF, which will have little effect on a HOMC and no effect on a LOMC.

S.

And yet there have been millions of words written in the audio press about how particular LOMC cartridges are to loading. Hmm.
 

rwortman

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Thank you for all the info! I appreciate it

Up to now I just plugged a turn table into a receiver and didnt give much thought to it. Now going with seperates and a seperate phono pre and all that, I have to actually understand some of this lol.

You can still buy a receiver with a decent phono stage. As is true for most of high end audio, the difficulty of amplifying the signal from a phono cartridge is over blown. The hardest part is noise. Essentially correct RIAA EQ and much lower distortion than a cartridge produces are easy. If you have a nice quiet phono stage in your receiver or outboard, just use it. It can be a little noisy as the record is very noisy. If the phono stage is 10 or 12 db quieter than the surface noise of the LP it will be fine. Anyone extolling the virtues of 7 figure phono stages should be asked how much weed they are smoking and what kind.
 

ribosradagast

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I picked this up on the recommendation of the forum. Mine has a high-pitched whine when it's turned off, surprisingly - it goes away when it's powered on. I don't know if I've ever had a piece of electronics act like this.

Anybody know what would cause this? I asked Cambridge customer support and they have no idea.

I can measure it tonight if anyone's interested in what specific frequency it is.
 

detlev24

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In case somebody else wants to know: I recently asked the Cambridge Audio support for the Duo's RCA output impedance, as I would like to connect it to an 'RME Adi-2 Pro' [the series has an - unbalanced - input impedance of 9,000 Ω].

I was told that, unfortunately, the output of the 'Duo' is around 20,000 Ω. This seems a bit high to me but they verified the information; I was hoping for something below 900 Ω...

With its 20,000 Ω output impedance, connected to an 'RME Adi-2 Pro', the signal loss would be 10.16 dB and this is a lot to recover. Any idea for a (simple) workaround? :)
 

SIY

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In case somebody else wants to know: I recently asked the Cambridge Audio support for the Duo's RCA output impedance, as I would like to connect it to an 'RME Adi-2 Pro' [the series has an - unbalanced - input impedance of 9,000 Ω].

I was told that, unfortunately, the output of the 'Duo' is around 20,000 Ω. This seems a bit high to me but they verified the information; I was hoping for something below 900 Ω...

With its 20,000 Ω output impedance, connected to an 'RME Adi-2 Pro', the signal loss would be 10.16 dB and this is a lot to recover. Any idea for a (simple) workaround? :)

I'd start by verifying that number, not via their help desk, but experimentally. It seems highly unlikely. The help desk person is probably confused between source impedance and suggested load impedance.

Do you have a voltmeter? If so, you can check this easily. Attach a 20k resistor in series with the output, then inject a 1V signal between the "free" end of the resistor and the unit's ground. If the measured voltage across the resistor is 0.5V or so, then they're right and what you have is a badly bungled design. Replace it, it's useless. If the voltage is still close to 1V, then you learned never to trust help desks. I'll bet on the latter. :D
 

AnalogSteph

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<1 kOhm does in fact seem way more likely.

I noticed this one hadn't received any answer yet:
I picked this up on the recommendation of the forum. Mine has a high-pitched whine when it's turned off, surprisingly - it goes away when it's powered on. I don't know if I've ever had a piece of electronics act like this.

Anybody know what would cause this? I asked Cambridge customer support and they have no idea.
Probably coil whine from the integrated switching power supply. I've had several (older) PC monitors do this, it seems to be getting rather worse with age (secondary-side capacitor ESR?).

You'd think that the power supply in a unit like this would be low enough in power for coil whine not to be a major issue. If this is not typical, I would suspect that a coil may have a loose winding (people have tried to quieten them down with some success), or a secondary-side electrolytic cap being bad.

Looks like Cambridge Audio's tech support may be outsourced just like their designs.
 

ribosradagast

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<1 kOhm does in fact seem way more likely.

I noticed this one hadn't received any answer yet:

Probably coil whine from the integrated switching power supply. I've had several (older) PC monitors do this, it seems to be getting rather worse with age (secondary-side capacitor ESR?).

You'd think that the power supply in a unit like this would be low enough in power for coil whine not to be a major issue. If this is not typical, I would suspect that a coil may have a loose winding (people have tried to quieten them down with some success), or a secondary-side electrolytic cap being bad.

Looks like Cambridge Audio's tech support may be outsourced just like their designs.
Thanks for the reply back. I sent it back to Cambridge with a note asking the tech to let me know what they found, but no word back yet...
 

Bushmeister

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Sorry, I think I have missed a trick here. But the headphone amp is critiqued for poor noise and output with a 100 millivolt Input :

"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."

But surely the headphone amp will be receiving the signal from the phono stage, rather than direct from the cartridge. So the input will be much higher than that from a cartridge?
Otherwise it won't have gone through the RIAA correction etc.
Does this mean the headphone amp is more viable?
Thinking about a purchase and trying to avoid getting a separate headphone amp too!
Thanks for the help.
 

Bushmeister

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Sorry - think I have just answered my own question here - I thought the test was done with a separate line in phono input - but I see it doesn't have one!
So I presume it was done through the MM/MC inputs - therefore the above points about low output and gain are entirely true - will need some seriously sensitive headphones! Dang.
 

sergeauckland

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In case somebody else wants to know: I recently asked the Cambridge Audio support for the Duo's RCA output impedance, as I would like to connect it to an 'RME Adi-2 Pro' [the series has an - unbalanced - input impedance of 9,000 Ω].

I was told that, unfortunately, the output of the 'Duo' is around 20,000 Ω. This seems a bit high to me but they verified the information; I was hoping for something below 900 Ω...

With its 20,000 Ω output impedance, connected to an 'RME Adi-2 Pro', the signal loss would be 10.16 dB and this is a lot to recover. Any idea for a (simple) workaround? :)
I think they got it wrong, even if they did 'verify' it. Unless they're taking the output from a pentode's anode, NO SS output will have such an output impedance unless really perverse.

It's like so many power amps quote an output impedance of 4-8 ohms, when they mean the load impedance.

S.
 

Urushi

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Would this be a good match for a Marantz TT15 turntable? Not sure how important or how much I should spend. I know for digital (at least with my setup) the DAC makes the least difference.
 
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