Design for a special MC Prepre needed

[jpetek]

Hi,

I need for my Cartridge (a VDH Colibri Platin 500 Ohm internal!, 0,4 mV) an PrePre.

Datas:

47 k input
20 db Gain
47 k output

Any Ideas?

best

Josef

[merlin el mago]

Salas pre-pre

[kevinkr]

Sure that internal cartridge resistance isn't 5 - 50 ohms? 500 ohms seems very high for any LOMC, and would be quite noisy.. My SPU is 6 ohms and my DL-103D 33 ohms as an example.

Might want to check out the Partridge 977 SUT still cheaply available on eBay - this should be a good match to your cartridge assuming 50 ohms internal impedance. Gain would be 6X or about 15.6dB..

[jpetek]

No the Internal resistance is 500 Ohm. I spoke with Vandenhul himselve.

This is excatly the problem with this Cartridge. A Transformer will not work. The most of the PrePre will not work too because they are optimized for low resistance.

[kevinkr]

Now I understand the issue..

I would modify the Salas for 47K input impedance.

Change R2 to 47K, the cartridge source resistance will swamp it from a noise perspective and since it is a fet input there is no significant input current to be concerned about.