mechanical resonance in MMs

Most 78’s weren’t even cut at precise speeds.

Robert Johnson’s records were cut about 20% too fast as an example.

Most of the gear they cut those albums on was pretty suspect, unless you are talking the top quality plants pressing classical etc.

For me that isn’t what I’m into- I like the Americana, folk and blues stuff which requires an adjustable idler and really good sense of pitch if you want perfectionism.

An SP-10 or whatever is not your friend in these circumstances.

I doubt the loading is relevant given all of the other compounded issues.

Also depends on what kind of cart you use. Denon makes a very nice 78 cart and stylus... I think it’s moving coil technology?

Nonetheless I still enjoy listening to 78’s. Some times you just have to relax and let yourself enjoy the scuzz as part of the experience.

Check out Robert Crumbs 78 mono rig. That’s about out where 78’s are going to max out at for playback quality.

Pre-Riaa LPs I think will load just the same, as it’s the same pick-up yes? Again, so much variance in the curves not worth getting too whacky about unless you’re at the library of Congress. They probably don’t get nearly as bent out of shape as us, come to think of it.

Personally, I only have the patience for so much esoteric, finicky technology. I’ll keep the 78’s and RIAA vinyl and everything else gets sourced digitally or disregarded for sanity’s sake.
 
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Space, I have an old Lenco L75 built into a solid birch CLD plinth, I will be using this and my grace cart for 78s, There are .7 conical, 1.0 conical, .3x.7 elliptical .2x.7 elliptical, HE, Shibata, and SAS stylus out there that can work for the grace f8 with a bit of rake adjustment. Also 2.5 78 styluses, both conical and elliptical, should be enough for most records. Not sure though about the high compliance of the grace cart and how much extra vtf I can apply. :-\


Bill, thanks! When I do get this all working I will let you know here how it sounds.
 
Hi spaceistheplace,
I'm collecting 78 RPM records as my wife loves them. I have to rebuild another record player that does 78 RPM records. I'm using those old "record carver" type changers with a built in amplifier and speaker. All self contained.

-Chris



The Lenco, as another has mentioned, is the obvious choice for max versatility.

You can do a plinth with two arms/ carts... One for dollar bin albums and so on.

I have used the TD-126 II for years as well which I think is your daily player?

My guess is that if you pursue this route you will never look back.
 

anatech

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2004-06-06 8:31 pm
Georgetown, On
Hi spaceistheplace,
Yes, I use both a TD-126 MKII and also a TD-125 MKII. Both of which were recently rebuilt by an excellent Linn technician. Unfortunately he is no longer with us. Somewhere around here I have a TD-126 MKIII. I'll have the same service done to that one.

If you have a Linn technician near you, see if you can get the tech to install the Linn springs and dampers. They fit the Thorens tables, but not exactly like the original Thorens springs and dampers. He made a very positive difference to my tables and the work is well worth getting done. He tamed the bouncy suspension issues. During the service, the tech discovered that the Thorens tables were very good, and so is the factory arm. :)

I think that I'll use a dedicated turntable for 78's, or simply another head shell that I can swap and rebalance easily. I don't think I want two arms on a single table.

One thing that I should mention is how much I love using these tables. I'm currently looking for a modern mat as good as the old Platter Matters. They also make a huge difference in noise and dynamics. I guess I should have mentioned that I have a Platter Matter on each table.

-Chris
 

gpapag

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2002-11-17 6:42 pm
Athens-Greece

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anatech

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2004-06-06 8:31 pm
Georgetown, On
Hi David,
Thanks! The Platter Matter used to be tacky and stick to the record as well. Now that they are old, they aren't tacky anymore.

Does that Oracle mat have a part number or any other identifier? I need to replace the non-sticky Platter Matters. They are still very dead and tend to damp vibration in their current state, so they are a lot better than the stock mat, or any of the felt or cork mats.

-Chris
 

billshurv

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2014-03-01 11:53 pm
Initial results from measurements done by @dagfinn with analysis @Hans Polak both of whom I have to thank for ploughing on where I had stalled. Quite a lot to catch up on so going to spread the initial findings across a number of posts as time allows. Spoiler alert: so far no evidence of a mechanical resonance found. Test method and sources will also follow when I find my round tuit.

First up is the denon DL-109 a marvellous oddity from the golden era of wierd cartridges together with the equivalent model Hans produced. As you can see the electrical model predicts that the 'normal load' of 47K||150pF should be rolled off under 1dB by 20kHz.
 

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billshurv

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2014-03-01 11:53 pm
On to the testing. Now we have managed to get hold of A CH Precision pink noise test record, don't ask me how as I don't know! This is a very accurate pink noise cut so should give us a basis to see what the real FR is without worrying about test record artifacts. First image shows the full 1KHz up sweep and you can see that, up to 9kHz we have a straight line (note not a flat line as it's pink noise), above there some deviations. Second image shows that deviation zoomed in. The lower line is the expected for pink noise and the upper is the actual response.

One more thing is needed to test the model, which is an accurate measurement of total capacitance in the input resistance of the phono stage. That was done and 192pF||48k5 measured. This was plugged into the simulator with the equivalent model of the generator and the 3rd plot generated. This is within 1dB of the measurement, which for vinyl is pretty good going. tweaking the loading a little bit could flatten that out nicely. But does appear that there is no need and no evidence of mechanical resonances being bought into play to flatten out the response. Next up something people may have actually heard of...

BTW would like to hear from people who disagree with these measurements as always good to defend results.
 

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al2002

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2003-12-15 6:41 am
USA
Billshurv, intersting work here. Would appreciate clarification on the modulation of the test disc. Is is horizontal, vertical or 45/45 stereo? Also what is the groove velocity, 5 cm/s peak?

Do you have access to stereo test disc, e.g. CBS, with slow sine sweeps? Vinyl compliance - stylus effective tip mass mechanical resonances clearly show up in the crosstalk.
 
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billshurv

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2014-03-01 11:53 pm
Let me check and get back to you on the details of the sweep.

So far we have avoided 'std' test records as enough questions have been raised to suggest that they might not all be as accurate as thought. I have a side project to try and work out if cal files for popular test disks could be made to give a more level playing field.

I should note that I don't believe in vinyl compliance being a thing and do find the cantilever transmission line model to be more credible, even though I can't yet prove it. The stylus is rattling around in the grove being barely stable most of the time for sure and certain frequencies will cause more problems. You can see these playing a silent groove but these don't directly contribute to the frequency response.