AT-VM95ML SRA and Compliance Qs

[Wray & Ting]

I recently bought an AT-VM95ML mainly to improve my inner groove distortion that I found present on brand new records with my previous elliptical (Clearaudio Concept MM v1). I aligned it in Lofgren A, and it has done that job very well, so overall I'm happy. Now that I have my setup in a better place, I'm trying to dial in a few outstanding details. It sounds like the cartridge might not be giving me all it can.

First of all, I've taken some macro shots of the stylus resting on a CD, and my measurements suggest the needle shank is making about a ~97 degree angle with the disc (using a 3mm cork mat, stock Rega headshell). To try getting the SRA closer to the "ideal" 92 degrees, I've added a couple records to the mat. Trigonometry tells me that the ~4 mm I've added at the platter has only made a 1 degree difference in SRA, but it's a bit closer.

I've done a few needle drops with and without the extra height and the difference is subtle, but maybe the high end is a touch clearer with the extra height. I don't like running with the stacked LPs, so if I make that change in angle permanent I'd probably lower the tonearm by 4 mm by replacing the spacer with a shorter one. With the extra LPs on the platter the tonearm is about level, for whatever that's worth. So, how should I go about getting closer to the ideal angle? Is there anything I can do with the headshell to change the angle? Is the stylus tip angle offset relative to the shank? Does the cantilever flex a bit more once broken in?

My second question is the compliance and calculating resonance frequency. The listed effective mass for my tonearm with the stock headshell is 16 g and the cart weighs 6.1 g plus screws (let's call it 7) so total effective mass is 23 g. The compliance values given for the cart are 10 cu (dynamic @ 100 Hz) and 20 cu (static). I used 15 cu as a compromise so:

f = 1000 / ( 2 * Pi * sqrt( 23 * 15 ) ) = 8.57 Hz

This puts me just inside the target range of 8-12 Hz. Is 15 cu a reasonable estimate for the compliance of this cartridge? Is there a preferred choice when estimating dynamic compliance @ 10 Hz between static/2 or 1.5x to 2x dynamic @ 100 Hz? If it's more like 20 cu that puts me below 7.5 Hz and I'd have to get lighter if I wanted to improve it. Shimming the cartridge for SRA is definitely something I don't want to do given my already 'heavy' setup.

 

[patient_ot]

Western compliance of that cart is between 12-14 CU - that's per measurements, not multipliers which DO NOT work. If you have a medium mass tonearm you will get a good resonance number. Forget the calculators and multipliers - they don't work in this situation where you have Japanese compliance specs.

Now, re: SRA get an acyrlic VTA block and set the VTA to 23 degrees with an average record in your collection, then call it a day. Don't worry about SRA and VTA after that because as soon as you put a thicker or thinner record on the platter or one that is not 100% flat your microscope SRA setting goes out the window.

RE: shims, you can use lightweight shims if necessary made out of delrin.

What turntable are you using this cart on? The Rega listed in your sig or something else?

 

[Wray & Ting]

Western compliance of that cart is between 12-14 CU

Thanks for those compliance numbers. A value of 13 gives me f = 9.2 Hz

I'm not too worried about the difference in SRA between a thick and thin record as it would be less than 0.5 degrees. I'm still 4 degrees off of 92 in my measurements even with the stacked LPs on my platter. My measurements (not with an acrylic block) give a VTA of about 22 degrees, so only 1 degree off of AT spec.

Yeah, this is the Planar 3 I'm dealing with.

 

[patient_ot]

Thanks for those compliance numbers. A value of 13 gives me f = 9.2 Hz

I'm not too worried about the difference in SRA between a thick and thin record as it would be less than 0.5 degrees. I'm still 4 degrees off of 92 in my measurements even with the stacked LPs on my platter. My measurements (not with an acrylic block) give a VTA of about 22 degrees, so only 1 degree off of AT spec.

Yeah, this is the Planar 3 I'm dealing with.

What arm is on the Rega? The Rega arm or the old style Japanese arm? In any case it is doubtful you will have a problem with too low of a resonance number.

Do you have spacers underneath the Rega arm? How thick is your mat?

 

[Wray & Ting]

It's the R200 arm made by Acos. Between the arm and plinth is a ~12 mm bushing which I could replace with a thinner one to reduce the arm's height. The cork mat I'm currently using is 3 mm but the extra LPs add about 4 mm.

 

[knotscott]

... How thick is your mat?

That was my question too....increasing the mat thickness is about $15, 15 second fix.

 

[Wray & Ting]

Just to be clear, 7 mm (3 mm mat + 2 LPs) gives me just enough spindle to still spin a record on top, and my SRA is still 4 degrees off from "ideal". I'd like to at least hear if 92 degrees sounds better, but the 1" thick mat option isn't on the table, no pun intended. patient_ot suggested I set the VTA and forget the SRA, which would leave me more or less where I am right now. I guess I was hoping someone had an unorthodox idea I could try to achieve a 92 degree SRA, such as shimming the cartridge to achieve a tilt, but that would also throw off VTA. Do other users of the VM95ML and VM95SH achieve both SRA of 92 degrees and VTA of 23 degrees, or close? It doesn't seem possible with my cartridge, so did I just happen to get a sample that's a little out of spec?

 

[patient_ot]

Just to be clear, 7 mm (3 mm mat + 2 LPs) gives me just enough spindle to still spin a record on top, and my SRA is still 4 degrees off from "ideal". I'd like to at least hear if 92 degrees sounds better, but the 1" thick mat option isn't on the table, no pun intended. patient_ot suggested I set the VTA and forget the SRA, which would leave me more or less where I am right now. I guess I was hoping someone had an unorthodox idea I could try to achieve a 92 degree SRA, such as shimming the cartridge to achieve a tilt, but that would also throw off VTA. Do other users of the VM95ML and VM95SH achieve both SRA of 92 degrees and VTA of 23 degrees, or close? It doesn't seem possible with my cartridge, so did I just happen to get a sample that's a little out of spec?

There is a company that sells delrin shims - you can shim the cart at the headshell, which is what I used to do before I moved to a different table with adjustable arm height. You can also swap the mat for a thicker one. I probably wouldn't use a mat thicker than 6mm. If the headshell is one of those thin stamped aluminum headshells, try something else made of thicker metal. That will also give the cart some additional height/pseudo shim.

Get one of those acyrlic VTA blocks ($10-15 usually) if you can and make your adjustments that way. Forget the microscope.

If you are off by a couple degrees it won't matter. If things are way, way off then you may have a problem.

Mind posting some pictures before we go any more into the weeds here? I'd like to see how the arm is, not just the cantilever and stylus.

 

[Wray & Ting]

If the headshell is one of those thin stamped aluminum headshells, try something else made of thicker metal

It is that type of thin headshell, but the thicker ones also seem to come with in around 9 g, and I'm already down near the heavy end for resonance frequency.

Mind posting some pictures

Here ya go, taken minutes ago while playing the A side of Led Zeppelin:



These were all taken with the mat + 2LP stack. Without the extra LPs, the tonearm has a very slight downward angle.

 

[patient_ot]

It is that type of thin headshell, but the thicker ones also seem to come with in around 9 g, and I'm already down near the heavy end for resonance frequency.

2-4g of extra weight at the headshell end won't put the compliance match in jeopardy. When I used the 95ML on my JVC, with the delrin shim from the auction site and and LPG Zupreme 10g headshell I got a 9hz resonance per measurements, not calculators.

The 95ML can handle an arm up to 25g effective mass if necessary.

Your problem is you don't have VTA adjustability and the thin cheap headshell is not helping matters either.