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limono 11th January 2013 03:50 PM

Cartridge Step -up conundrum
I definitely smoke too much lately and have a senior moment , need some clarification . I have grado 1.5mV MM cart with measured 8 Ohm internal dcr.
The output is too low for my current MM stage .
So I'm taking 1:2 step up small signal input transformer with 50 Ohm /1250 Ohm 15dB spec counting that I'll have healthy output of more or less 3mV and around 12k loading on Grado cart ,when connected to 47k input of phono stage. Right ? wrong -I don't get that healthy 3mV output even if I load primary nor secondary winding down. Yes it is little louder but not nearly like 3-4mV MM cart sounds on that phono . Where is the catch?

kevinkr 11th January 2013 04:33 PM

The internal dcr is not a reflection of the source impedance of a typical MM cartridge, the cartridge will deliver progressively less output into a lower impedance load. I am not sure what sort of effect loading this cartridge into 50 ohms will have on mechanical as well as electrical resonances, and therefore cartridge frequency response. The cartridge source impedance is likely much higher than this so you are effectively heavily attenuating its output by loading it into 50 ohms and then the 15dB of gain is insufficient to make up the losses.

limono 11th January 2013 06:42 PM

Well , it's not a "typical MM" cart . I think what I have is low version of Grado Sonata which is 0.5mV and they list DCR at 2 Ohm . I measured again and with interconnect and resistor in series I got around 4 Ohms from all the shebang , counting for oxidated input socket and cart tags I am certainly sure it's a 0.5 mV since it's playing on similar to MC level trough 1:20 step up.(Hashimoto borrowed from a friend). Interestingly I hated Grado sonata reference 5mv but this one is REALLY nice on mass loaded Rega arm , I'm surprised actually . I was mislead by specs sheet attached to this (used ) cartridge.
No wonder signal level was low. Kevin , Thanks! I'm going to write you a PM

SY 11th January 2013 06:54 PM

No catch- I use a 1:2.5 stepup for another oddball MM (Technics EPC100C Mk4), but load the secondary with a 300k resistor and a Zobel. Works like a charm.

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