Using the OM40 as an example, I measure the cantilever to be 0.54mm diameter, 0.1mm wall thickness aluminium, 5.0mm long. Using transmission line equations, I calculate the 1st available resonant mode to be at 25.5kHz.
In the past, I measured the actual resonant f to be c 27kHz IIRC. I think the difference is within the tolerance of how accurately I can measure the cantilever.
Using classic bending equations with the cantilever as a spring (L^3/3EI etc), would yield an effective mass spec of between 0.32mg and 0.37mg, which seems plausible.
Neither of these models requires any vinyl compression or compliance, I should add. Though I point out that the classic cantilever bending spring-mass model requires the stylus end to move freely, which isn't actually an available mode IMO, whereas the TL model doesn't.
Trust this illustrates how the industry might work backwards from mechanical resonant f to obtain spec effective tip mass, perhaps, but also that this probably doesn't describe anything meaningful in terms of what stylus inertia really is. Also that the TL model can yield realistic results for the top resonance which only involves the cantilever vibrating.
LD
Characteristic impedance changes along the line, so it's one way of providing a low mechanical impedance for the stylus (good for trackability) whilst matching it to the relatively high impedance generator. In real terms, the stylus end is flexible, which IMO is good for hf trackability at a penalty.
Cantilevers are relatively short TLs, so only at hf or for high jolt is there any meaningful difference between TL and a lumped model. For much normal programme material, the lumped model where the cantilever moves as a rigid body applies. IMO.
LD
Is this a modern version of the QR2010 test disc?
Ortofon Stereo Test Record - ( Test LP ) - 180g LP - SCOTT NANGLE AUDIO
Thanks, good to see. That should be fine to address issues at hand here.
No 3150Hz tone, no silent band, no pink or white noise, no sweep below 800Hz..... etc etc, so seems very targeted.
LD
Great! Transmission line model can account for classic model
That's close enough, I think. Plus the transmission line model delivers the next resonant mode at about 2.5 times the first, as in post #60. Also good!
So the way forward is:
Yep, I wouldn't have thought the stylus/vinyl interface would come into play until much higher frequencies were applied. Anyone know different?
Well, all the cantilever model asks is zero bending moment and zero shear force at the stylus end, an assumption I'm happy to embrace given the MUCH greater magnitude of both moment and shear at the "fixed" end of the cantilever.
The alternative is to load the stylus with a model of the stylus/vinyl interface. I'd hesitate before taking that step as it's not far from there to a full finite element model, and it's not a complication that seems warranted.
PS: I gather that there is a school of thought that it's the stylus/vinyl interface that produces the resonances of the cantilever assembly. Anyone have the literature on that?
That's close enough, I think. Plus the transmission line model delivers the next resonant mode at about 2.5 times the first, as in post #60. Also good!
So the way forward is:
- explicitly translate the mechanical cantilever into the transmission line analog (anyone have an analog?);
- and/or measure the first (and even second) resonant mode of a cartridge and "tweak" the transmission line until the model "delivers".
Yep, I wouldn't have thought the stylus/vinyl interface would come into play until much higher frequencies were applied. Anyone know different?
Well, all the cantilever model asks is zero bending moment and zero shear force at the stylus end, an assumption I'm happy to embrace given the MUCH greater magnitude of both moment and shear at the "fixed" end of the cantilever.
The alternative is to load the stylus with a model of the stylus/vinyl interface. I'd hesitate before taking that step as it's not far from there to a full finite element model, and it's not a complication that seems warranted.
PS: I gather that there is a school of thought that it's the stylus/vinyl interface that produces the resonances of the cantilever assembly. Anyone have the literature on that?
I think 'possibly'. I looked at this before and the biggest issue is calibration. So for example the CBR test record has been used by many people and scott has a copy so there is an ability to calibrate. I suspect I'll end up buying a copy and sending it to one or more people to compare with the other references.
Main reason for my paranoia on this is that a log of people use the pink noise track on the hifinews test disk but there is evidence its not actually very pink!
Now it should be generated digitally, past technique was an R/C ladder approximation filtering white noise.
Yes, that's about right - see also the Happ/Shibata plots in post #63. You were right first time, Bondini.
Actually, bending moment is OK at the stylus end. Cantilever, and the stylus, is free to pivot about its contact with the vinyl, but otherwise the stylus is not free to move because it is retained in contact with groove walls via VTF. This, in combination with conditions at the cartridge suspension end, determines what vibration modes are available to the cantilever. Both the TL model and classic bending models converge on similar answers, of course.
Just about all conventional literature assumes that the spring comes from vinyl compliance, rather than cantilever flex. Decades of stuff by very credible authors assume it, and take it as read, but I doubt it is either true or possible. Rather, I prefer that the spring physically lies in the cantilever. Heresy, I know, and a minority of one against a body of conventional wisdom, but I'm pretty convinced conventional wisdom is wrong on this one...........!
It matters, IMO, because it affects what one needs to look for of merit in a cart/cantilever to manage/avoid audioband mechanical resonance, as well as stylus profile selection and all manner of corollaries.........
LD
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If someone can measure the behavior of Decca cartridges with the totally different cantilever construction from all the other cartridges, the origin of the resonance may be traced more realistically.
George
Attachments
Still not happy with the results, I decided to trying to get better noise figures, more flexibilty in gain setting and much better CMMR figures.
So below is the final circuit diagram that I designed with LTSpice.
- S/N ref 5mV@1Khz is now 78.8 dBA, an improvement of a full 10dB over the original SE circuit diagram in posting #204.
- The 318u and 3180u correction network is now made passive, making it possible to change overal gain just with R2.
In the original design, gain setting resistor was part of the correction network making gain changes very complicated.
- Overload margin is more than 30dB over the whole audio range
- CMRR is now ca. 60dB when using 0.01% resistors and when including U3. With the SE version there is no CMRR at all.
- FR is within 0.1dB up to 400Khz.
Hans
So below is the final circuit diagram that I designed with LTSpice.
- S/N ref 5mV@1Khz is now 78.8 dBA, an improvement of a full 10dB over the original SE circuit diagram in posting #204.
- The 318u and 3180u correction network is now made passive, making it possible to change overal gain just with R2.
In the original design, gain setting resistor was part of the correction network making gain changes very complicated.
- Overload margin is more than 30dB over the whole audio range
- CMRR is now ca. 60dB when using 0.01% resistors and when including U3. With the SE version there is no CMRR at all.
- FR is within 0.1dB up to 400Khz.
Hans
Hans you must be telepathic. I was just mulling some questions to you on this and here it appears. I'll ask the unanswered ones.
1. Have you an idea of how low you can go with this generator impedance wise? Whilst the noise is too high out the box for a 0.25mV MC the 2.5mV of the Benz ebony H I will be getting should work, but no specs for the coil other than R.
2. Have you given any consideration to an MC version of this
3. For feeding miniDSP balanced input with the 318u and 3180u correction removed I need around 38dB gain. I was considering just dropping the second stage. Any thoughs?
I do need to build this one. If anyone is considering laying it out I'm game for a few board. If you wait for me to do a layout you'll be waiting about 2 years!
1. Have you an idea of how low you can go with this generator impedance wise? Whilst the noise is too high out the box for a 0.25mV MC the 2.5mV of the Benz ebony H I will be getting should work, but no specs for the coil other than R.
2. Have you given any consideration to an MC version of this
3. For feeding miniDSP balanced input with the 318u and 3180u correction removed I need around 38dB gain. I was considering just dropping the second stage. Any thoughs?
I do need to build this one. If anyone is considering laying it out I'm game for a few board. If you wait for me to do a layout you'll be waiting about 2 years!
With this Aurak design the trick is to add a resistor in line with the cart, to get a -3dB point at ca 150 Hz.
The first stage then starts increasing its gain at 150 Hz an stops at 75 usec, the third Riaa time constant. The combo of cart and first stage now having their -3dB at 2Khz. From thereon the other two time constants have to be applied and that's it.
But now for an MC Cart the world looks completely different, because its coils has a very low inductance not causing any roll off in the audio range.
So when using a miniDSP you could use the virtual input of an amp with a flat FR and do all the time constants within your DSP.
The AD797 is a very good Amp for this purpose, but there any more options depending on your wishes.
I have no experience with virtual input MC amps, but I do not see an advantage over a conventional voltage amp. None of the commercial top performers IMO has a virtual input, but it is certainly worth trying, especially when having a design that can be switched between current and voltage amplification.
Hans
The DL-102 produces 3mV at 5cm/sec @1Khz and has 240 Ohm DC resistance so it looks more like an MM to me.
Your Benz is definitely an MC.
Amplify the signal a factor 100 and you are able to do the rest of the processing with your miniDSP.
Hans
It's great to see the concept sketches of Aurak being developed well: that is always my intention with such stuff. Yes, it has good potential to level the field, IMO. Let's hope it sticks to the web for longer than last time 
The upside is for MM only, Bill. Try it with your S-120 for an iconoclastic experience on a shoestring......or with an OM40 for something sublime.
LD
The upside is for MM only, Bill. Try it with your S-120 for an iconoclastic experience on a shoestring......or with an OM40 for something sublime.
LD
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Even though the design has evolved a bit past the schematic I posted at post 202, I meant to give credit to my friend Vladislav (username "Poty" at audiocircle) for drawing up the schematic and doing much analysis. All I really did was forward him LD's Aurak 3.0 schematic and asked him how he thought a balanced iteration would perform. I posted the schematic with Poty's blessing and I want to thank Hans for all the work he's put in subsequently and of course LD for sharing it in the first place.
Well I now have another S-120 stylus this time with the cart attached
. I think I need to stop buying cartridges for a bit. We still haven't found any mechanical resonances that need filtering, but I think we are going good work here