Matching output impedance of preamp with 306 input

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06-Nov-2018 10:35 AM

casa nienti

casa nienti

Posts: 1

I've read that the input sensitivity of the Quad 306 is low. A preamp/DAC I'm considering says that "analog RCA and Tube pre-out outputs impedance: 600 ohms." How do I determine if this will be compatible with a stock Quad 306, and if it is not, can the modification correct the input sensitivity for this preamp?
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26-Nov-2018 12:42 PM

Fabian

Fabian

Posts: 60

No, the input sensitivity of the 306 is not low at all. It is rather (too) high (for some modern sources). An input voltage as low as 0.375 V will lead to the maximum power output of 50 W into 8 ohms load (20 V output voltage).

Don't worry about impedances. The 306 has an input impedance of 20 kohms. The source impedance should be a lot lower than that. 600 ohms is absolutely perfect, even a bit lower than e.g. Quad's own 34.

You might have to worry about the output level of the DAC/peramp at full volume. Many modern sources have output levels up to 2 V or even more. This would limit you to a very small useable range of the volume control. Depending on the type of volume control this could result in bad channel balance, inconvenient volume steps, reduced resolution, bad sound ...

This is no show-stopper for the 306, though. Take a look at the current Dada revision manual. The input sensitivity can easily be reduced to 0.775 V or 1.0 V by replacing just one resister per channel.

Even lower sensitivity values could be achieved with higher resistor values, but personally I think you shouldn't go lower than 1.0 V.

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