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Phasemation Cartridge Compliance or Alignment Issue?

I think I may be having a compliance mismatch issue with the tonearm on my MoFi Ultradeck and my new Phasemation PP-300. I'm fairly new to selecting matching components in analog systems - the Ultrdeck had the mastertracker MM cartridge preinstalled. I had that cart for several years and noticed some degradation to the sound and looked to upgrade my setup with something new.

I've come across two records where I'm getting some distortion across the first song on a side. My speaker's woofers also pulse like they are trying to play a really low note. The record plays fine closer to the center. 

Tracking down the mass of the MoFi tonearm was actually a challenge. From various threads that I've read online, the effective mass of the arm is different than what MoFi states in their specifications. Based on this thread, my assumption is that the effective mass of the arm is 25.14 grams.

https://forum.audiogon.com/discussions/cartridge-reccomendations-for-the-mofi-ultradeck

I was searching for a low compliance MC cartridge to match with this tonearm and came across the Phasemation PP-300 as an option. This cartridge has an effective mass of 11.1g and a compliance of 8.0x(e-6)cm/dynamic@100hz. Using an online calculator, i thought I wad made a good selection, however based on some research, I've since learned that you need to convert this figure to compliance at 10hz for proper evaluation and system matching (1.7x multiplier). Recalculating with the new figure yields a resonance of 7.0hz. Have I made a mistake going with this cartridge? Many of the records that I've played have no issues whatsoever. One of the poor performing records is a live recording and the other is an album with low frequency electronic synth sounds.

I set up the cartridge with a Dr. Feickert protractor. Looking closely at the cartridge, it appears that the headshell and cantilever are very slightly askew from each other. I aligned the cartridge to the headshell. Is it possible that a slight misalignment would make the low system resonance more problematic? I don't notice any skew to the image and both channels seem balanced to my ears but of course that is challenging to determine.

Is there anything that can be done to raise the resonance of the system to a more optimal value?

Any help or insight would be appreciated!

ajnackman
yogiboy's avatar
yogiboy
5,865 posts
 

The last thing that you want to do is damage the woofers. I have done that with a cartridge arm mismatch. You might want to try a rumble filter. 

https://www.kabusa.com/frameset.htm?/rf1.htm

ajnackman OP
68 posts
 

Some photos of the cartridge - it looks like the cantilever isn't mounted plumb to the head shell. If this is the case, it makes it very hard to align with my protractor. Is it possible that a misalignment could compound the resonance issue I may be having?

https://imgpile.com/p/hvQlA5Z

ajnackman OP
68 posts
 

Troubleshooting this a bit more. I realigned the cartridge and the same behavior is occurring with the woofers. My last thing that I could try was to swap my phono preamp out. I mentioned before that I purchased a Sutherland Mini Loco Mkii at the same time I purchased the phasemation cartridge. This is a current driven phono preamplifier which should pair well with the low impedance output from the phasemation cartridge. My old phono pre is a parasound JC3 jr. This preamp can drive the cart with a little more oomph from my integrated amp.

After making the swap, I would say that the woofer pumping is decreased by about a third of the previous excursion. Again, this behavior lasts for the first 1-2 songs per side. I’m sure the voltage vs current driven typology of the preamps is at play here. If the cartridge and tonearm match is borderline based on what I’m now seeing. The higher system gain mini loco mkii could be exacerbating the problem. I should probably look into the subsonic filter yogiboy recommended. I’m curious now to try another voltage driven phono pre to see if there is any difference related to that. I had been looking at the Pass Labs XP17. Any thoughts on what I might experience changing out the phono pre beyond what I’ve already tried? I like the sound of the phasemation a lot and would prefer not to abandon it if possible since it was such a large investment. I haven’t experienced any tracking issues.

bill_k
935 posts
 

Record warps typically present as a resonance in the 4 to 6Hz range and are most prevalent in the outer grooves. So as a rule you'd like to keep your arm/cartridge system resonance higher than that frequency range but below the audible bass range and 7Hz is too close. Since you're only experiencing the problem in the outer grooves it seems likely that even slight warps could be exciting your resonant frequency which results in woofer pumping. Sorry but it seems like the cartridge is a mismatch with your arm.

jasonbourne71's avatar
jasonbourne71
1,404 posts
 

Get the Kabusa filter. No need to have the cartridge play down in the subsonic region.

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