With great respect for my learned cyber-friends and fellow Nutmeggers Doug and Michael (Swampwalker), whose formidable expertises lie in things other than EE stuff, I would point out that the 9.5 volt maximum output spec on the Phono Box is being misconstrued.
The Phono Box provides specified gains of 40 db for MM (moving magnet) cartridges and 60 db for LOMC (low output moving coil) cartridges. I assume the OP would be using a MM cartridge. 40 db corresponds to a voltage gain of 100x. Under standard test conditions MM's are usually specified as providing outputs in the area of 3 to 5 millivolts (mv) or so. Therefore under those conditions the Phono Box will provide an output of 300 to 500 mv or so. During extremely high volume dynamic peaks on some recordings, that output level will be exceeded by a factor of several times, I believe, meaning perhaps something like 2 or 3 volts or so. The 9.5 volt figure is simply the maximum output voltage the Phono Box is capable of without clipping or severe distortion, but under any reasonable circumstances it will never receive an input voltage that causes it to approach that figure.
As Michael mentioned earlier, the specifications for the Audioengine A2 speakers do not indicate input sensitivity. However, it can be calculated from various numbers in the specifications and in
John Atkinson's measurements (26.8 db gain at 1 kHz, 6 ohm average load impedance seen at the output of the speaker's amplifier, 15W specified RMS amplifier power capability) that an input of roughly 433 mv will drive the speaker's amplifier to full power at 1 kHz, with the volume control at max.
JA notes that in part of the deep bass region the amplifier provides an equalization boost of up to 9 db. 9 db is a voltage gain of about 2.8x. So the speaker's amplifier will be driven to full power by an input of roughly around 433/2.8 = 155 mv at those frequencies (where recordings often contain particularly high energy levels), with the volume control at max.
Those numbers all add up to an expectation that pairing the Phono Box and the A2 speakers will result in a reasonable match in terms of gain, sensitivity, and the parts of the range of the volume control that are likely to be used. There will of course be a bit of a downside in terms of convenience, in that the volume control is located on the rear of one of the speakers.
Another factor that should be considered is impedance compatibility. An output impedance spec is not provided for the Phono Box, but the 21 to 24K input impedance JA measured for the speaker's amplifier makes it unlikely that impedance compatibility will be an issue.
The bottom line, IMO, is what ZD and Yogiboy said, and what Doug eloquently said in his last paragraph.
Best regards,
-- Al
