Tuesday, September 6, 2011

Oatley/Mongrel Dog Audio - JFET phono preamp

I originally housed this preamp in a timber enclosure but 50Hz hum invaded the signal. This enclosure is a lot more flimsy than I might normally use but, when connected to mains earth, did provide good shielding. See the earlier entry for more information about the cct.

I did ensure that I used isolating gold plated RCAs. The signal/power earth and the mains earth are separate. Usually I don't do this. With the gain of the front stage around 100 X good shielding and earthing is necessary. The sound from this AU$30 kit is quite astounding when you consider the common parts used. The PS having a capacitor multiplier does a very good job of DC filtering .

The bass is deep and very extended. It is also well articulated and not one noted or boomy. Mids are rich and detailed with treble well extended and well defined. But what really shines through with this "build-in-an-afternoon" kit is the sound stage. Both the active stages of this preamp have local negative feed back. This is achieved by neither of the JFETs having a bypassed source resistor. I have found on my single stage valve preamp this does appear to produce a very deep and highly detailed sound stage.

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