MM vs MI vs MC

[dlaloum]

Anyone have a Shure M97Xe with any of the Jico SAS they could plot?

A couple of comments...

The cartridge used - the Shure MT105p, is the p-mount version of the M97xE - same inductance and impedance - the needles are interchangeable - and for an experimental rig, the p-mount was VERY convenient.... (hence my use of the p-mount and p-mount versions of various cartridges)

The needle used was a Jico M97xE-SAS purchased circa 8 to 10 years ago, with a Boron cantilever

Above 1kHz the smooth lines show the electrical modeling of what is expected (ie: the impact of the electrical circuit)

Below 1khz I was trying to work out what and how to model that light bass boost - which I never did work out! - so Ignore that!

All the wiggly lines are the actual measurements at various R loadings (10k, 21k, 43k, 60k), and each chart is at a different C loading

Other comments:

The original Shure styli have a subsantial damping effect - the Jico equivalents have a very minor damping effect (still an effect, but not much!)

The Shure hinge had some sort of grease on it which gave it the desired damping - the Jico doesn't

If experimenting with a SAS stylus in the "world of Shure" - there are many closely related bodies, that the stylus can be moved to - their inductance can vary from around 420mH to up around 700mH (from memory) - so messing with cartridge inductance is another possible parameter.

The V15's use a slightly narrower Shank - so the styli are not interchangeable.... the V15's also have laminated core poles, so as to reduce eddy current effects - the M series and their variants don't (have the laminated core). - The V15V also has substantially lower inductance - circa 350mH (from memory). I don't have the maths with which to model eddy currents - the solid core bodies like this one should have an eddy current effect baked in, which is minimsed in laminated core models such as the V15's.

If you compare the electrical model to the measured response, you can see how the 60pf measurements quite dramatically expose the cantilever resonances of the SAS... with the lower resonace being around 12kHz, and the upper out at 27kHz or thereabouts.
I also have charts where I deducted the electrical from the measured.... which makes things even more obvious....

I have a feeling that the lower resonance is related to the SAS proprietary tension wire at the rear of the cantilever.... it varies a bit (I have several SAS styli) between 12kHz and 16kHz where the upper resonance tends to be the same.

My suspicion is that the upper resonance reflects the effective mass, and the lower one is related to the mounting system... they are excellent styli - but they are also a bit idiosyncratic.

 

[JP]

Why not just do the mangling at 96k?

 

[Digital1955]

I just wanted to consolidate the info as the script is getting used by more and more people. I think that future adopters may well be likely to only have access to 44.1 rate recording. (I know a few people with that ART USB Phono Plus, for example.) I'd personally like to have confidence in other's measurements or else it's all just well-intentioned noise.

I do understand wanting to standardize on a way of inverting the RIAA curve if a phono pre-amp that applied the curve was used, but remember that analog RIAA phono amps aren't perfect either, so....

What I actually did was use a signal generator and sweep my phono preamp directly. Then I built a EQ filter curve for audacity, with 34 points and b-spline interpolation.

 

[JP]

I just wanted to consolidate the info as the script is getting used by more and more people. I think that future adopters may well be likely to only have access to 44.1 rate recording. (I know a few people with that ART USB Phono Plus, for example.) I'd personally like to have confidence in other's measurements or else it's all just well-intentioned noise.

Confidence is really difficult.

 

[USER]

Lol. Oh I understand, especially with all the variables the medium brings. (How many of these measurements include cable capacitance? How dependable is this FR method anyways?) Regardless, knowing of a nice IRIAA filter that works at 44.1 (or knowing how off it is) and having it available to potential adopters isn't a bad thing. I just want the public to see through all the marketing and subjective review bullshit. Having some kind of modestly sized measurement catalog helps. As does knowing how much modern cartridges suck by comparison.

 

[Digital1955]

Confidence is really difficult.

We aren't splitting the atom here.

 

[JP]

We aren't splitting the atom here.

We're not?

On a regular basis I see measurements that appear to have compound errors of several dB, which is meaningful.

 

[dlaloum]

The problem is, there are variations of several db between different test records....
Then there are variations in some of the IRIAA curves... several more db

It is really difficult to get a truly trusted baseline!

 

[dlaloum]

With Pink noise tracks used for measurement - you can sometimes use 45rpm as a solution (or at least variable)...

Run the 33rpm record at 45 rpm... if the compensated Frequency Response is different - and variations have risen by the speed change factor - then the pink noise track is unreliable (and you can identify its flaws!).

Once you know those flaws, you can compensate for them in various ways... (eg: if the variation is at the high end, running at 45rpm may move it beyond 20kHz... - great as long as you don't need to measure up beyond 20khz)

The better option (IMO) is to measure that variation and adjust the measured values as a calibration...

Basically - calibrate your test records!

 

[levimax]

The problem is, there are variations of several db between different test records....
Then there are variations in some of the IRIAA curves... several more db

It is really difficult to get a truly trusted baseline!

Don't forget different phono pre-amps have different responses.

Since my measurements are taken directly from cart to ADC without RIAA I guess they are the best then ... but still variations in tone arms, tracking forces, loading, etc. makes a lot of potential variations. Having said all of that there is still some amazing consistencies such as consistent small FR variations of the STR 100 test record.

 

[Holmz]

Don't forget different phono pre-amps have different responses.
…

You mean, just the RIAA part, Right?

…
Since my measurements are taken directly from cart to ADC without RIAA I guess they are the best then ... but still variations in tone arms, tracking forces, loading, etc. makes a lot of potential variations. Having said all of that there is still some amazing consistencies such as consistent small FR variations of the STR 100 test record.

How does ^that^ work?

I thought that MC carts changed their responce and ability to track as the loading changed?

 

[EJ3]

It's like the hurricane tracking modeling: many variables and not always treated the same.

 

[dlaloum]

Don't forget different phono pre-amps have different responses.

Since my measurements are taken directly from cart to ADC without RIAA I guess they are the best then ... but still variations in tone arms, tracking forces, loading, etc. makes a lot of potential variations. Having said all of that there is still some amazing consistencies such as consistent small FR variations of the STR 100 test record.

Cart to ADC is great, but you need to make sure that you are well within the dynamic range of the ADC...

If the ADC is good enough I much prefer doing RIAA in the digital domain.... every db of Dynamic Range counts!

Best way to identify FR variations is to measure at 45rpm as well as 33rpm, and look for the variations that shift...

To do that you will need to adjust the RIAA to compensate for the speed variation though.... but - yes we can calibrate...

 

[levimax]

You mean, just the RIAA part, Right?

mostly RIAA bit any FR non linearity.

How does ^that^ work?

I built a SUT followed by a balanced transmitter (designed to create the same load as a phono pre-amp) then balanced cables to an ADC. For RIAA I use FIR filters but I can capture the signal directly with Audacity.

 

[Holmz]

Preamps are generally linear.
Carts less so.

 

[dlaloum]

Preamps are generally linear.
Carts less so.

Given the preamp is providing the loading for the cart.... and the loading can have a massive impact on linearity (for high inductance cartridges), the boundary between preamp and cart is a bit fuzzy.... (!!)

 

[Holmz]

Given the preamp is providing the loading for the cart.... and the loading can have a massive impact on linearity (for high inductance cartridges), the boundary between preamp and cart is a bit fuzzy.... (!!)

Please review post #959, as this was my question from the 957-960 range.

He said he is loading the cart without a preamp, and not using RIAA except after going through the ADC.

 

[dlaloum]

I tried doing that - use a MIC amplifier to boost the signal to ADC level - results were variable, perhaps could have been better with better Mic Pre's (or with a custom flat pre to boost the signal).

In the end I convinced the maker of the JLTI phono stages, to make a lightly customised version, with the RIAA circuit switchable - and no onboard loading - instead RIAA jacks so I could simply plug in my own loading plugs. (at the time he was still hand building them, since then he has moved to manufacturing, probably in china, and customisation is no longer available )

It has switchable gain for MM/MC - and I can then run it directly into an ADC ...

 

[mackat]

I just received my Focusrite Scarlett 2i2 and have been playing around with it. The following is a plot of the 150MLX, which seems to have a very sharp rise in the high end, more than I would expect at 190 pF from previous graphs I have seen. I measured my turntable capacitance at ~140 pF, and the designer of the phono stage I am using told me that it has 50 pF input capacitance. Does this look right to you? Compare with VM95ML plot below it. I am recording at 96 kHz and using the latest Nyquist plugin.

 

[JP]

How did you measure the C?