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Old 28th June 2012, 12:40 PM   #1
jpetek is offline jpetek  Germany
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Default Design for a special MC Prepre needed

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
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Old 28th June 2012, 02:23 PM   #2
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Salas pre-pre
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File Type: jpg Salas Simplisitic pre-pre Low MC 20dBs.jpg (253.1 KB, 269 views)
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Old 28th June 2012, 04:46 PM   #3
kevinkr is offline kevinkr  United States
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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..
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Old 28th June 2012, 04:55 PM   #4
jpetek is offline jpetek  Germany
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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.
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Old 28th June 2012, 05:12 PM   #5
kevinkr is offline kevinkr  United States
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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.
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