Cardboard backed PVC sheet blanks

[Angus McCarthy]

Hi all!

In preparation for last Saturday's exhibition at the Bloomsburg Children's Museum's Maker Faire, I decided to delve beyond the confines of plastic plates and Lexan. I had read In other posts here about making DIY picture discs and embossing onto plastic sheeting, so I have investigated a similar configuration. I am happy to report that my results, while not hi-fi perhaps, were more than acceptable for my purposes in concocting a quick and relatively inexpensive recordable blank.

I have currently landed on a combination of 8.5x11 10mil PVC presentation covers (Houyee brand), printed card stock, and 30mil chipboard backing - all spray glued together. This gets me an appx. 8-inch diameter disc, with a little more than 3 minutes of playback time before the auto stop on my test rig Crosley kicks in. Much like the venerable cardboard Wilcox-Gay discs, they are lightweight, and a little flexible. The PVC is hard enough that I found I could drop the full weight of the head onto the surface when embossing and still get a relatively clear recording with a reasonable level of surface noise, unlike with the 7mil sheets I began with. The thicker sheet has yielded more reliable results in playback, although I may yet be able to achieve deeper grooves by adding more weight to the recording head. As usual, a good polish with spray Turtle Wax lubricates the surface to reduce noise when embossing.

The signal chain for the following audio samples was as follows (with the exception of the demonstration disc): Live mics of various makes and models in-room, fed into a 4 channel Pentron MM-4A preamp/mixer, sent through an MXR compression pedal (for head safety and to reduce the risk of over-cutting), output to the HI-Z mic input of the Presto K-8 onboard amp. Recording head is an early Presto horseshoe, with a rather short DIY embossing stylus ground down from a gramophone needle. No inverse RIAA curve was utilized, however high-frequencies were boosted on the amp to compensate for the lack of curve. Samples were captured raw, directly from the GE VRII lateral mono playback head on a Technics SL-1200 TT, again with no RIAA curve applied.

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BCMMMF2022 CTR Demo Disc.mp3

Demonstration disc that I played for visitors while prepping the mics and polishing the fresh disc.
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BCMMMF2022 Cub Scouts.mp3

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BCMMMF2022 TW.mp3

Recorded with a c1930 double button carbon mic, easily overdriven.
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BCMMMF2022 Simple Song.mp3

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BCMMMF2022 Baby Babbling.mp3

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BCMMMF2022 Sitar Guitar.mp3

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BCMMMF2022 Music Of Erich Zann.mp3

The last recording of the day, after the crowd had left. Obviously much less background noise.
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Pictures of the process in making the blank discs:

20220419_143233.jpg

20220419_151116.jpg

20220421_205944.jpg

20220331_121256.jpg

[markrob]

Hi Angus,

I would have liked to made a trip up to Bloomsburg to check this out (I'm a little over 2 hours away here in Philly), but I was busy on that date. Nice work and great info! I have to give this a try. Have you tried PET sheets? I see they are available from Amazon in up 12 mil thickness ? Maybe they are too soft.

https://www.amazon.com/Binditek-Binding-Presentation-Polythylene-Terephthalate/dp/B08XYNZ2P5?th=1

I'm wondering if the sheets could be embossed against a metal or other hard plate surface prior to binding to the backing to allow for heavier head weight and/or better control of the forces?

Mark

[Angus McCarthy]

Hi Mark!

Aw, that's a shame, but it is a busy time of year after all, especially after the last 24 months! I've got a friend based in Philly, and there's a good chance I'll be bringing my rig into town to cut some sides with him in the future - maybe then?

I took some screenshots of a portion of the Demo Disc, just to show the difference applying a basic RIAA curve makes. The high end static comes down significantly, but there is definitely a rumble present below 100hz (even considering this is with a pure lateral pickup) probably from the old original rubber tire and motor bushings still present on the K8. It sounds much better, somewhat like a well-played LP. My cutting head only has a nominal range up to 8K, so I'm willing to bet a higher-range head could get good HF to print without much trouble.

Without RIAA:

Sample No RIAA.png

Sample Zoom No RIAA.png

With RIAA:

Sample With RIAA.png

Sample Zoom With RIAA.png

Leadout without/with RIAA:

Lead Out No RIAA.png

Lead Out With RIAA.png

[grooveguy]

Hi, Angus! Thanks for sharing this experience, and even more-so thanks for doing this public demo. Chances are you may well have inspired future Trolls! I can't find mention of what speed you were embossing at; the one video on your Facebook page looks like 33-1/3. If so, that's really quite acceptable results: good SNR and crisp top-end.

[Angus McCarthy]

Ah, yes! I was recording at 33 1/3 during all the above examples. Thank you for pointing out my (now painfully obvious) omission.

Also, I realized that some, though not all, of the low-frequency rumble included a 60hz hum from the GE VRII pickup. At home, it is not bad, though evidently there was much more RF intruding at the museum location.

[grooveguy]

Not sure about you, Angus, but I've tried all manner of modern, 'high-end' expensive cartridges for playback of 78s. I keep reverting to my VR-II. It's nowhere near as compliant, but it sure tracks better and, to me, sounds better than today's cartridges, both for shellac pressings and (for sure!) wide-groove lacquers. Also, your results with the Presto K8 makes me kick myself for not spiriting-away the one my high school had in "obsolete inventory." They'd never have missed it. Same with a Universal portable lathe and a Presto 8DG in college, too!

[Angus McCarthy]

Same here for the venerable VR-II. It's the not so secret weapon when it comes to playing back pure lateral cuts of any kind, and you can still get them for a reasonable price compared to modern carts made specifically for that purpose.

I've been bashing my face against my K8 for years now, and I'm thrilled to be getting these kind of reliable results with this new blank configuration. Plastic Solo plates be damned - the last five batches I bought ALL had the same molding flaw in them, across different color batches! Same combination of bubble and trail of little pock marks. The QC is evidently not what it used to be wherever they get made.

[tragwag]

great work, and those blanks look awesome! I'm sure people were thrilled. Live gigs are always so fun to get face time with folks who've never even imagined records could be cut in front of their eyes.