JVC QL-7 Turntable; unstable speed

MonoMania said:
I'm no expert with test records, but... If the record is even slightly warped or off-centre that would introduce more w&f than the turntable, wouldn't it?
Click to expand...
JP said:
Record two, second turning the record 180 on the platter. Be sure to get the start of the track so there's an audible index. With that I can do two polar plots and see what eccentrices follow the record and which the platter.
Click to expand...

@JP you answered my question before I asked it! Thanks!

I'll have the recordings ready within a couple hours here.
 
MonoMania said:
Do I want to abrade the inside of the spindle hole with Scotch Brite, or the bottom of it?

I'll record any/all test tones I have access to and see what I can figure out.

I'm no expert with test records, but... If the record is even slightly warped or off-centre that would introduce more w&f than the turntable, wouldn't it?
Click to expand...

I don't know how that table seats the platter, most use a tapered seat on the shaft so the inside of the spindle hole is what you'd need to clean. You can look on the spindle to see if it has any corrosion or grime on it and do the same. Just don't use anything more aggressive than scotch Brite.
 
Just to make sure I do this right... For recording test tones, it shouldn't matter if the cartridge is set up properly, should it? For the cartridge that came with the turntable (Shure 97) alignment and VTA are way off - and I haven't bothered to set up my own preferred carts in a headshell for it yet.

Also, should I record in stereo, or is mono more practical?

I've dug out my few test records, at least one of which has a sequence of test tones.
Just need to reassemble the turntable and do the recordings, will upload clips ASAP.
 
It matters. A great deal of flutter in a test tone is arm/cart behavior. If the cart isn't set up right it'll be worse. Also want a healthy cart.
 
JP said:
It matters. A great deal of flutter in a test tone is arm/cart behavior. If the cart isn't set up right it'll be worse. Also want a healthy cart.
Click to expand...

It'll be a few hours before I post clips then :)

I have the VTA set right for my ancient Pickering 380 which requires additional weight added to the counterbalance of the tonearm... Will that be okay?
Alternatively I can set up and align the more conventional Audio Technica AT-130E...
Or set up the Shure M97 it came with, which I'm not overly familiar with...
 
Thanks for clarifying. I'll go with the Shure if the tip checks out under the microscope, otherwise I'll use the AT-130E. Both are much closer in vintage to the turntable than the Pickering from 1960.

Although in the long run, the PIckering is the main cart I plan to use with this tt. The arm seems to be able to handle it, with additional counterweight added.
 
First recording: https://www.filehosting.org/file/details/759673/testsignalsA.wav
Second recording: https://www.filehosting.org/file/details/759674/testsignalsB.wav

Between recordings I flipped the disc 180* on the the turntable

This file hosting site requires that you enter your email in order to download...
If you guys know of a better / more convenient place to upload just let me know.

I used the Shure M97, brush up, tracking at 1.25g.
From the 'tape out' of my GE 7700 tube amp, into an Akai audio interface.
Recorded in MONO (seemed to make sense) in Audacity.

For reference, the manual claims w&f spec of < 0.025% (WRMS) and "speed variation" of "within 0.002%"
 
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For future reference, a free Dropbox account will let you create share links that non-members can access.
 
Ah, okay. Was wondering what the best way to post audio here was.

Every site I tried had some kind of limitation... MP3 only... Email required... Files deleted after 7 days... etc. I'll use DropBox in the future.
 
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I took the 5kHz sample and slowed it to 3kHz so it'd look more like what we'd expect from a W&F polar plot. It's a bit all over the place. A looks fair, but B has a wide rotation to rotation variation. Almost like the spindle to hole relationship changed. Was this at 33?

Plots deleted - were done wrong.
 
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Well, at least that confirms that the problems are real, and that the strobe itself isn't the problem. Looks like error is around 0.5% (as much as 9-15hz), much higher than spec.

Thanks for checking W&F for me @JP , every bit of information helps towards solving the mystery.

The disc itself is somewhat suspect, but can't be too far off...
This is the one I used:
https://www.discogs.com/No-Artist-Audio-System-Test-Record/release/5790402

My other test discs have many warble tones, but no steady test signals.

Back to the drawing board... I suspect something is off in the 'balance adjustment' circuit...

Yet I also suspect that the bigger problem is mechanical rather than electrical...
 
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Don't know. A looks normal, and the worst of what's there could just be the record or the arm and cart. I can't explain B.
 
How literally should I take JVC's published w&f specs?
0.5% seems very far from 0.025%

Those graphs you just linked me to seem to show a maximum of ~5hz deviation vs ~15hz for the ones you did from my audio clips...
 
A way to figure out how much the test record I used is a factor might be for me to re-record the same tracks with different turntables... Not sure how much trouble it is for you to run the analysis though.
 
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