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Rega Planar 3 measurements

davidsrsb

davidsrsb

pfm Member
I have been experimenting with my RP3 (240V motor) to measure speed, wow and flutter.
I have two test records, the HFS75 with a 3000 Hz tone and the Epsilon Ultimate with a 3150 Hz tone.
By recording the tone using Audacity, a bit of cleanup and then processing in a PLL circuit in LTSpice simulation., I can see what is going on.

The HFS75 speed is almost spot on at 2999 Hz, the Epsilon is 3200 Hz, about 1.5% fast.
Probably the truth is somewhere between, most beltdrives run a little fast.
Both tones show about +/- 10 Hz FM at 0.55 Hz, which is eccentricity at 33 rpm
What is odd is that both tests show this FM also AM modulated at about 20 second period. I wonder if this is my mains as I cannot think of any mechanical resonance this slow.
 
If you’re saying the speed variation occurs once per rotation of the platter, then re-lubricating the bearing might fix that. Possibly also the belt may have an effect too.
 
I don't think the bearing is involved.
The only slow process I can think of is how many rotations it takes for the belt to creep around to the same relation with the platter.
 
davidsrsb said:
I don't think the bearing is involved.
The only slow process I can think of is how many rotations it takes for the belt to creep around to the same relation with the platter.
Click to expand...
Given that belt length and platter pulley diameter are analogue measurements, that may well be a large value.

Trivia - some hand drills have mutually prime drive/driven gears, so that all the teeth combinations are gone through. This makes gear wear perfectly uniform!
 
It could be there's been some update in the newer Audacity versions which is causing problems - I'll investigate

Edit: Yes it's not doing anything under 3.4.2 no debug info either :-(

Strangely my W&F calibrator (generator) plugin still works though.
 
Open "wow_flutter_visualiser.ny" and change ";type analyze" to ";type Analyze", it now needs to be capital 'A'!

Input file must be 3kHz, mono, 44.1kHz sampling rate.
 
Are you sure the record is not eccentrically pressed? I’ve seen a surprising number of test records that are! Just a mm or so will show up on a measurement even if you can’t personally hear it.
 
I would expect eccentricity to be consistent through the track.
I can also detect slight play in the acrylic platter to the pulley spindle. The main bearing itself has no play
 
If capital 'A' doesn't work try changing type string to "effect" the visualiser will now show up in the 'Effect' menu.

I'm seeing lots of weird plugin behaviour with this latest Audacity version :( Previously this just worked fine across all platforms.
 
The "A" worked and I end up with graphs as similar to your better examples, but with the weird AM modulation of the 0.5% max plot. This happens with both test records. I didn't have to modify the plugin for what is actually 3200 Hz
 
Can you post the result here? As regards frequency presumably the tone on your record is 3.15kHz and turntable is running slightly fast.
 
This is the 3 KHz HFS75 plot
RP3HFS75_3k.PNG
 
That is really weird! Can you FLAC your 3kHz file and share it somewhere?

Do you have access to a direct drive TT you could do a comparison with using same source disc?
 
I get similar waveforms from two different test records, so I doubt that it is the source.
I have treated the belt with French chalk, so I will redo the test soon. The belt is the most likely culprit for a rotation related modulation.
If you PM me your email, I can send a FLAC version.
 
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