Three speed automatic turntable replacement

No, that was not your point. You stated something that was absolutely incorrect. No one has ever cut a phonograph record that was predistorted to compensate for tracking error.

Linear tracking is theoretically correct. Whether a particular arm implements it in a way that's simple and reliable, and doesn't introduce its own problems, is another matter.

Tracking distortion was not one of them.

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This discussion has morphed into something very interesting, however and regardless of what anyone may think of the validity, or even the sanity for that matter of my original post, the stuff of which has somehow disappeared from this thread, it doesn't solve my problem as to where I might find a replacement for an old mechanical three speed automatic turntable with a simple high output ceramic cartridge. Lenny

and regardless of what anyone may think of the validity, or even the sanity for that matter of my original post, the stuff of which has somehow disappeared from this thread, it doesn't solve my problem as to where I might find a replacement for an old mechanical three speed automatic turntable with a simple high output ceramic cartridge.

I said nothing about this, because it seems unlikely you can find a /direct/ replacement. These changers usually sit in product-specific cutout.

You might try looking for an early KLH with the Garrard changer you could mount different pickups in. (I might have one I could sell you cheap.) The problem is... How are you going to mount the unit?

You can buy cheap phono preamps. If you can find an easy way to power one, you could substitute a 'table with a magnetic pickup.

Generally to mount it you hopefully have a standalone case. You cut the ori= ginal cutout out usually with a jigsaw or something, even a sawsall, being = careful of course. Then you take the top of the case and make it fit in tha= t spot. I used to only remove the material that needed to be removed which = was determined by laying the new piece over the old and marking it.

I forsee trouble making a ceramic cartridge fit in an arm designed for magn= etic. It might almost be better to just find a standalone preamp. That adds= a little bit of cost but will save alot of time and trouble.=20

What it does also boil down to is whether the customre is willing to pay en= ough to make any money off this. Fixing the original starts looking attract= ive when all of what the changeover entails is considered.=20

Plus we are talking about a turntable that works IIRC, just not automatical= ly. Automatic turntables that take magnetic cartridges are available but le= ss common than full manual ones. Audiophiles usually shunned "record change= rs", only accepting "auto return" for obvious reasons.=20

Thrift stores? Flea markets? I've seen a lot of them collecting dust. How about the radio & phono newsgroup? news:rec.antiques.radio+phono

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Those are some good ideas guys. I wouldn't even bother with this but he's an old guy, (even older than me) and seems very attached to his "record player", so I thought I'd try to help him out. I never thought it would be so difficult to find one of these things new. I guess I should have. The problem is I've been doing this for so long I've lost track of how many years ago it was that I could just walk into my jobber's store and pick up one for 12.00 or so. I typically never had the luxury of having a proper mounting board though. I would have to "cut and paste" to make the replacement changer fit but it always worked out. Funny thing is I just realized that I actually have an old changer with a ceramic cartridge in a plastic cabinet. My wife used this cheapie in her Pre School until she recently retired and it went up into the closet with some of my other relics I've no doubt also lost track of. I'll have to get it out and check it over. I would not play my records on it and so we'll never use it again. I have two Thorens machines and a Benjamin Miracord all with magnetic cartridges. Lenny

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Only one link gives any support to amplitude response. Nor do i trust that one.

If you check the physics it is force responding, which is neither amplitude nor velocity responding.

?-)

Mr Barrett, I urge you to do your own research on this, rather than assuming you know what you're talking about. You don't.

A ceramic pickup is, indeed, an amplitude-responding device. This is fact. I gave multiple references but you don't believe them. I can only refer you to the work of Pierre Curie. (You know him. He was Monsieur Madame Curie.)

Hot-lookin' guy. (No wonder Marie was attracted to him.) Certainly better-looking than Walter Pidgeon.

The displacement of a piezo device is proportional to the force applied. (Ever hear of Hook's Law?) Ergo...

I'll sum it up this way... An LP is cut with constant-amplitude response. * If you play a test record with a ceramic pickup, you will get flat response.

Case closed. I don't have time to discuss this further. Take Pope's advice to heart: "A little learning is a dangerous thing."

• Between the turnover and rolloff frequencies. Between them, LPs are constant-velocity.

That should have been...

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I will do some if i remember.

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Well we agree on that.

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I do believe you have that backwards. It is amplitude only between 1000 Hz and 2122 Hz (barely over an octave), and velocity otherwise. It has = to do with bandpass changes before the cutter head gets into the act. And yes, the cutter head is an amplitude device (much like a speaker), the signal that feeds it results in a mostly velocity groove. Try looking at it with a microscope.

?-)

response.

Got it backwards. I corrected this error in a following post several days ago.

response. *

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Get out your microscope and look at the grooves and compare to the playback waveforms. Complex waveforms are ok but something like a square wave groove would be best.

?-)

Do you know of a disk that has a square wave cut on it?

I have a lot of test disks, but I don't remember one. I'll have to look.

Think about what the stylus would have to do. That's why you won't find a test disk with a square-wave groove on it.

Isaac

I assume you mean the cutting stylus. It is possible to send a signal to a cutting head that would, in principle, produce a square wave on the blank. For example, you could cut a 200Hz square wave with 36dB of pre-emphasis at

What the groove would look like is another matter. Obviously, the cutter head cannot move instantaneously, and there would probably be ringing from system resonances. Still, I expect that the groove modulation would be readily identifiable as a square wave, and not some other waveform.

No; I mean the playback stylus. In the groove, the rising and falling edges of the waveform would be perfectly perpendicular to the motion of the disk, and so there would be no possible way for the stylus to follow it. And if they were not perpendicular, then it wouldn't be a square wave.

That still would not be truly a "square" wave, because the rise and fall times would not be infinitely fast. You could do it by stopping the rotation of the disk while the rising and falling edges were being cut, for example, but no matter; the groove still could not be tracked by a mechanical stylus.

Isaac

I don't know what the logical fallacy is involved here (other than intellectual petulance), but it's impossible to have zero rise time on any square wave. There is no infinite bandwidth in either the electrical or mechanical realms.

You're saying that because we cannot generate perfect ("infinite-bandwidth") square waves that there is no such thing as a square wave. I suggest you look at the output of a square-wave generator on a 'scope, and tell us whether a reasonable person would consider the waveform "square".

In practical terms, if the highest harmonic in a square wave is significantly higher than the bandwidth of the DUT, then the DUT should behave as if a "real" square wave were being applied.

That's a very good working approximation.

And, again, in practical terms, once you make the "angle" in the (near) square wave you have cut/pressed sharp enough, a mechanical stylus just won't track it. The angle of the groove's motion side-to-side, the V-shape of the groove, and the shape of the stylus (typically an elliptical cone) will be such that most of the mechanical force generated by the pressure of the stylus on the groove will be upwards rather than sideways. The stylus tip will accelerate upwards more rapidly than it will accelerate sideways, and it'll pop out of the groove entirely.

The Sheffield Direct to Disc pressing of the 1812 Overture was notorious for this... the "fire the cannon" passage would pop almost any cartridge out of the groove. It wasn't quite at the point where it was literally impossible to track... but it was a *really* severe test of a cartridge's ability to follow a groove.

I think you're thinking of the Telarc disk. (I don't remember a Sheffield "1812".) I don't know what the waveform "looked like", but I doubt it approximated a square wave.

I do remember it knocking the pickup out of the groove. Not only did you need a good-tracking pickup, but the arm-mass / stylus-compliance resonant had to be very low -- so low that it would not normally be considered a reasonable resonant point.