Preamp 47K load. Cartridge needs 330 ohm

The loading is not the main issue.  The PV7 has a phono input designed for MM cartridges.  It is expecting an input voltage of 2.5mV to 5mV.  Your MC cartridge only has an output of 0.35mV.  You need a phono Step Up Transformer (SUT) that provides the required increase in amplification voltage and will also address the loading issue by its presence.  You will need to do some research but a 1:10 (20db) step up would also give you a loading of 470ohms if my memory is correct.  That would be adequate to get started.  Another option is an active phono head amp  that does not have the RIAA curve in its amplification because going into the PV7 MM phono input the signal will pass through the RIAA equalization within the Conrad Johnson (don't want to do that twice). Last option is a total external phono preamp capable of handling the MC amplification and loading that would plug into an auxiliary input on the PV7.

A 1:10 SUT is perfect for your needs. And no cartridge has an absolute requirement for a single particular load resistance. A 1:10 SUT will result in a 470 ohm load and that is just fine for your cartridge. See above for other viable solutions.

your cartridge is 0.35 signal strength; it's coil impedance is 2.5 ohms

the answer:

Exactly as said above: Step Up Transformer with a (+/-) 1:10, ratio (which is it's xFactor),

Like lewm said: result of 1:10 x factor will change your cartridges 2.5 coil impedance to 470 which will be 'shown' to your PV7 MM Phono input'.

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the math:

your .35 cartridge strength will be  Stepped Up (multiplied .35 x 10 and be increased to 3.5V, a perfect strength for your PV7 MM Phono Input.

Impedance load is a 'guideline', kind of a minimum that the cartridge wants to be 'shown to PV7'.

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Choosing a SUT, the indicators on the front often do NOT tell you the xFactor, you need to find out/ask which SUT has a transformer inside which can do a (+/-) 1:10 xFactor. 

i.e. my SUT, Fidelity Research FRT-4 (I had to find the specs) has optional indications on the face, the face option of 100 ohm results in an xFactor of 10.55. which results in 423 ohms 'shown' to your PV7 for your cartridge.

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I put copies of the research I did about SUTs as one of my Virtual Systems.

Click on my name, choose 'details', it will take you to a page with a list of Virtual Systems, one is named 'SUT info'. One column shows the xFactors.

Small print of scanned pages: temporarily change your monitor' ZOOM from 100% to 150%s. Put back to where it was, i.e. 100%. 

An xFactor of 12 would be good.

.35 signal x 12 = 4.2 mv, a very good signal strength for MM Phono Inputs.

xFactor 12 results in an impedance of 326 'shown to your PV7, very close to recommended 330 ohms

Where is the OP going to find a SUT with a 1:12 step up ratio? If such a one exists off the shelf, it might be unique. Whereas there’s a plethora of choices among 1:10 SUTs.

Nad used to make inexpensive electronic pre-phono box that boosts necessary gain pretty much for any cartridge.   Classe Audio NIL is probably higher priced pre-preamp.

Where is the OP going to find a SUT with a 1:12 step up ratio?

If you like Jensen the JT-347-AXT  transformer is 1:12.

lewm

I just wanted OP (or others following this) to know, 1:10 is not absolute, as a matter of fact anything up to 1:12 will be good, 1:12 might be best.

I agree 1:12 is limited; and 1:10 is more common, however, IF the OP searches, asks for help, and gets answers like above, he can end up with 1:12 or very close (my FRT-4 has 1: 10.55, who would look for that?

imhififan

Good find, seems like a very versatile unit. Independent Control of Gain and Impedance it ideal for current and future cartridges.

Allasso was on my chart, but I’ve never seen one, and never know if what I find is old or current.

I don’t see PASS for an MM, but it only has ONE input, so who needs PASS?

PASS would let you change to an MM cartridge or headshell with alternate MM pre-mounted/aligned and leave the cables Tonearm to SUT and SUT to MM Phono EQ (external or internal)  in place, that’s a big advantage IMO.

samssa

another good find!

I just wouldn’t perpetuate the myth that the OP needs precisely a 330 ohm load for his cartridge. If he goes away believing that then he won’t have learned anything.The Cello Miyabe is an MC cartridge with an internal resistance of 2.5 or 3 ohms, based on two different sources. (To the OP) Generally you want the input impedance of the phono stage to be about 10X the internal R of the cartridge. Therefore technically you could load your cartridge with any impedance greater than 30 ohms, on up to even 47K ohms. You could even go below 30 ohms load, but then you begin to sacrifice cartridge output. Many say they hear differences in tonal balance exquisitely related to input impedance with LOMC cartridges, but actual measurements usually don’t support this belief.

Thank you all for input.  Conrad-Johnson phono is 40 dB.  I have checked other preamps for moving coil, they would suggest 60 dB is a good target amplification.  So I need 20 to 24 dB.  The Chorale is rated at .35 MV.  I have feedback that suggests it is lower than that, maybe .25 or .15 mV.  Agree, don't need 330 ohm exactly.  Need to have a step up and be 100 ohm to 500 ohm.  My other pre-amp the Nagra PL-P is 58.7 dB gain and 330 ohm.  I feel that is a lowish and want a bit more output.

So what should I get.  I owned two Ortofon's in the past.  One called MCA-76.  The cleanest would be a transformer like Lundahl or Jensen.  Solder it inside the preamp and no need for interconnects.  I would like to stay under $ 1,000.  Happy with used step-up.