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Re: Phono capacitance measurement

Thanks John

I am using a Shure V15III with a recommended capacitance loading of 400-500pF (A lot higher than the 250pF of the V15V or the M97)

My readings indicate that the interconnects are around 100pF.
If the phono pre is 50 PF then the total is only 150pF; only about 1/3 of Shure's recommended 450pF.

Capacitance is really easy to change on my Audio Design Model 1. It has external 47pF capacitors mounted beside the RCAs. The wires on the capacitors just push into a pair of small sockets. On the face of it, I should look for some 350 pF capacitors and try those but I am not sure if there is additional capacitance inside the preamp. I doubt that I can find a circuit diagram as this is an old preamp that is not that common.

If I use my Sugden A28B, I have the circuit diagram but my reading of circuits may not be up to the task of determining what capacitance the source sees. The signal comes in through a BiFilar choke (whatever that is) and the line then splits with a resistor to ground (marked .2m7) and another (marked 20R) which goes to a common point from which a 150pF capacitance goes to ground and a 1uf capacitor (different capacitor symbol) goes on to the rest of the circuit.

I would appreciate any further thoughts.

Thanks

David Warden



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