Thanks Demian, for the very useful input. Your deeper experience is appreciated. I too measured and listened to the STAX FM cartridge. I was non-plussed, but it was interesting. I didn't know that you worked on it, back then. I know that Jack Bybee has had similar experiences to you with many of these designs and he is back to an MC phono cartridge.
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Sound-Smith aduiphoolish bable ignores basic linear systems theory
they blow their credibility for any serious engineer with the claim:
"The Strain Gauge cartridge is a displacement device, producing an output that is dependent and directly proportional to the amount of displacement of the stylus, NOT the velocity, like magnetic cartridges. It therefore inherently plays the RIAA encoded groove correctly. If one inspects the RIAA EQ, one will discover that there are discrepancies that occur where a displacement type cartridge deviates from a perfectly flat playback of the recorded RIAA grooce, and therefore will not produce a perfectly flat response.
Attempts made in the distant past to absolutely correct Strain Gauge cartridges for any amplitude anomaly have required equalization circuits, which not only add circuitry, but also introduce phase or time shifts. It is the Soundsmith’s belief that human hearing is much more forgiving of amplitude errors than time errors, so we have made minimal efforts to correct for any amplitude deviation from absolute flatness.
" Strain Gauge details
if they do get a good built-in "compensation" for for the 1st order slope between velocity and displacement then they still have the 500/2122 Hz shelf to EQ - not doing so results in More "phase or time shifts" since the EQ preemphasis and correction is "minimum phase" - certainly for mid band audio frequencies - any amplitude error is exactly related to a phase error by Bode's Integral of Phase
they blow their credibility for any serious engineer with the claim:
"The Strain Gauge cartridge is a displacement device, producing an output that is dependent and directly proportional to the amount of displacement of the stylus, NOT the velocity, like magnetic cartridges. It therefore inherently plays the RIAA encoded groove correctly. If one inspects the RIAA EQ, one will discover that there are discrepancies that occur where a displacement type cartridge deviates from a perfectly flat playback of the recorded RIAA grooce, and therefore will not produce a perfectly flat response.
Attempts made in the distant past to absolutely correct Strain Gauge cartridges for any amplitude anomaly have required equalization circuits, which not only add circuitry, but also introduce phase or time shifts. It is the Soundsmith’s belief that human hearing is much more forgiving of amplitude errors than time errors, so we have made minimal efforts to correct for any amplitude deviation from absolute flatness.
" Strain Gauge details
if they do get a good built-in "compensation" for for the 1st order slope between velocity and displacement then they still have the 500/2122 Hz shelf to EQ - not doing so results in More "phase or time shifts" since the EQ preemphasis and correction is "minimum phase" - certainly for mid band audio frequencies - any amplitude error is exactly related to a phase error by Bode's Integral of Phase
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Demien, we fortunately have MUCH better elastomers available these days. Likewise PLLs, so that the S/N issue with FM could be overcome with some pretty straightforward engineering. Modern piezopolymers give yet another option not available to earlier designers. And of course, as Scott points out, there's some pretty advanced MEMS technologies available.
I'm fairly well equipped on the elastomer formulation and fabrication end of things if any of you pros wants to play with some of these more creative approaches.
I'm fairly well equipped on the elastomer formulation and fabrication end of things if any of you pros wants to play with some of these more creative approaches.
I've seen this before, yes they gloss over the fact that displacement to velocity is a single derivative. I'm still interested in the actual location of the sensors. Assuming people are familiar with the relationship between stress and strain, a strain guage is not a position sensor but the elements need to be mounted where "bending' (more like stretching) actually occurs due to applied stress. A strain guage is usually made so that when mounted securely to a mechanical element the strain changes the length of the element, and its resistance. They are "snaked" back and forth along one axis to maximize the effect.
Worst analog playback system ever.
Moving coil cartridges have improved a great deal over the last ten years so that they are now much better than anyone here wants to admit. I don't see any advantages to using a different technology. The strain gauge cartridges I've heard don't perform nearly as well as the best of the MC cartridges, like the Airtight Supreme or the Haniwa.
John
I have not seen the current examples. The ones I was familiar with were all made by Panasonic. Panasonic must have miscalculated badly because the same original batch from the dawn of CD4 was around for 10 years or more.
They had two "paddles" one for each channel fixed at one end parallel to the stylus. A rubber "t yoke" couped the free end to the stylus. More like a crystal/ piezo cartridge than anything else. A current source of about 1 mA (I think) was enough to make it all work. The currents needed to be reversed for each channel to keep them in phase.
John Iverson tried to convince me that it worked on some other principle but he had to come clean when I confronted him with my measurements. There was some discussion of individual eq adjustments but no evidence of them in the hardware. The cast box for the electronics was impressive.
They had two "paddles" one for each channel fixed at one end parallel to the stylus. A rubber "t yoke" couped the free end to the stylus. More like a crystal/ piezo cartridge than anything else. A current source of about 1 mA (I think) was enough to make it all work. The currents needed to be reversed for each channel to keep them in phase.
John Iverson tried to convince me that it worked on some other principle but he had to come clean when I confronted him with my measurements. There was some discussion of individual eq adjustments but no evidence of them in the hardware. The cast box for the electronics was impressive.
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The Stax was an interesting problem. The cartridge had a static capacitance of about 2 pF. The modulaton was a lot less. They used 100 Mhz and it barely worked. I was pursuing 1-3 GHz and got access to a team that was pretty skilled in the technology. We could not run it up the cables so we had to put the electronics in the housing. Either you use FM and modulate the frequency or you make a bridge that sense the change in capacitance. For either to work you need a good stable low noise oscillator. I was targeting at least a 90 dB SNR or it was not worth the effort.
Sennheisers RF mics do very well, but the C is more than 10X higher. The Q of the resonant circuit was as important as the oscillator. The Brownian noise might preclude 90dB @ 2pF
Another idea, a fiber optic probe to send the image back of the cantilever position.
I whould like to talk about the stylus. Lyra uses an Ogura professional quality diamond that is polished several times and has a profile that does not dig too deep into the groove to avoid pickup of dust. The profile is optimised to sound "quiet". Different profiles produce diffent kinds of noise when the stone hits the plastic. I use Lyras since 1991 and never had a worn stylus so reliable they are. Most of the time the suspension gives up before the stylus is worn to any dangerous degree. I listen aproximately 2 hours a day and ship my carts back to readjustment each 3 to 5 years. I have my Titan now for over 5 years and shipped it back ones so if i had to pay the full amount of ca.5000,- $, one hour of music whould cost me 1 $ if i use the cart for 6.85 years. Well, thats a lot but more affordable then to drive to town and attend a life event. I do that too from time to time but rarely sound is as enjoyable as in my home. Life sound is much too often very loud and distorted. Classical, Folk and acoustic Jazz being an exception of cause especially when played in a good sounding room. That experience is still hard to copy with High End Audio but i think we can make progress still. My system sounds much better now then it did 2 years ago since i changes to high sensitivity dipole speakers.
There's an interesting way around that. Involves a second beam in quadrature, not unlike the old slotted-wheel mice. You can get resolution down to 1/4 lambda. Nice thing about fringe methods is that you can go almost straight to digital, overcoming a lot of noise limitations inherent in magnetic and resistive sensing methods.
I mean getting "lost" as in moving the mouse over a piece of surface that does not do the right thing, or pick the mouse up and put it down. Say your detector goes from 0 to 1mv for the first 0 to 2pi of fringe, now it goes back to 0 and you have to remember how many mV you have already gone. So far I have not seen a robust way of doing this, theoreticaly you can just say "keep track" good luck.
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The minute you go digital, it ain't analogue anymore, the analogue 'magic' is gone.
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