Cartridge Loading for a phono pre amp

In illustration using a very low output cartridge vs a very high output cartridge connected to the Current Input vs Voltage Input on the P1 

 

My Sonic Lab Ultra Eminent BC: 0.6Ω output 0.29mV 

 

Voltage Input: At 0.29 mV, the Wizard determined the optimal gain level at +70 dB of gain. This setting has audible hiss coming from the speakers at 30% volume without any record playing. On careful listening, the gain level was sufficient. Optimal loading was determined to be 180Ω by the Wizard. 

 

Current Input: At 0.6 Ω, the Wizard determined the optimal gain level to be I/V + 20 dB, but based on listening test I preferred a much lower setting of I/V + 5 dB. 

 

According to Ohm's Law where I = V/R, Current = 0.29 / 0.6 = 483 Micro Amps, a very sufficient level of gain based on the low impedance of the cartridge. 

• Are you using ohms law with voltage to compute the output current?
• I thought that the motors were generally current generating devices?
• So is the impedance of the phono stage a DC reading?
• And does and external loading become more like a V=I*R(total)

My question is how significant that affect the cantilever to be stiffer and introducing possible tracking issues, OR its effect is negligible?

Your target for mechanical resonance is between 7-12Hz. The mechanical resonance is a product of the mass of the cartridge in the arm vs the compliance of the cantilever of the cartridge. Changing the load from 47K to 100 Ohms can easily get you outside of this target window- and that can cause tracking problems.

So, all those very well regarded designers are wrong?

IF they have ignored the significance of the inductance of the cartridge in parallel with the capacitance of the tonearm cable in their design

THEN yes, they blew it.

If you doubt this I recommend a simple test, which is to run a square wave through the cartridge itself and observe the results on an oscilloscope. If the square wave rings, then loading will affect it at audio frequencies. If you do this with any LOMC cartridge you'll see that the inductance of the cartridge is so low that a square wave at any audio frequency will look perfect on the oscilloscope. So its obvious then that the loading isn't affecting the tonality of the cartridge. Something else is.

So if the loading does not affect the cartridge at audio frequencies, why would it affect how the cartridge sounds- because in some preamps that is quite audible. The answer is simple- the preamp itself is reacting to the RFI generated by the cartridge (hence the emphasis on 'some'). I've explained this a good number of times, I've dropped links to Jim Hagerman's site http://hagtech.com/loading... If the preamp is designed with the RFI present at the input of the phono section, the loading resistor will make little difference- it won't tone down the high end nor will there be a need; it will sound fine with a 47K load.

How does one safely send a square wave through a cartridge? Just curious as I have no intention of trying it.

So I have a Cadenza Black mounted on a VPI printed tone arm, on a VPI Classic 3 table. My previous phono pre was a Zesto Andros 1.2. With that one, when I dialed the resistance much past 400Ohms the sound became somewhat shrill and screechy. If I recall at 1000 Ohms and above it was unlistenable to my ears. Down below 100O the soundstage collapsed 

My current phono pre is a PS Audio stellar with which I can easily flip between 100 and 47k Ohms using the remote. There appears to be no significant difference between the two settings - maybe a bit more extension at the extremes, but difficult to tell during my short listening session. That extension I hear is probably expectation bias. 

The obvious difference between the Zestos and PS Audio as loading changes is clear as a bell.

Your target for mechanical resonance is between 7-12Hz. The mechanical resonance is a product of the mass of the cartridge in the arm vs the compliance of the cantilever of the cartridge. Changing the load from 47K to 100 Ohms can easily get you outside of this target window- and that can cause tracking problems.

@atmasphere 

Thanks for your reply, really appreciate it!

Any one own a Hi-Fi News test record can easily determine how significant that loading resistance affect the cantilever to be stiffer and introducing possible tracking issues, just play with the loading resistance setting and run the cartridge/arm resonance test.

If you doubt this I recommend a simple test, which is to run a square wave through the cartridge itself and observe the results on an oscilloscope. If the square wave rings, then loading will affect it at audio frequencies. If you do this with any LOMC cartridge you'll see that the inductance of the cartridge is so low that a square wave at any audio frequency will look perfect on the oscilloscope. So its obvious then that the loading isn't affecting the tonality of the cartridge. Something else is.

I don't have any record with square wave test track on hand, can you recommend one?