Direct drive vs belt vs rim vs idler arm

Henry, If you tell me how to do it, since the photos are on my desktop, not on the internet, I will post a photo of my "new" 1959 Alfa Romeo Giulietta Spider Veloce.

As you may know, I have owned (in the past) just about every model of 356, up to a Carrera GT Speedster, and finally a 550RS Spyder. But I have been bereft of old cars for more than 10 years, until now.

Lespier,

Your results for the tt101 are interesting but more telling (as you have multiple arms) would be to place the smaller feickert test disc on top of a (heavily modulated?) 12" lp and play the lp with one arm and the test disc with another. This will give us a picture of what's going on in real time under dynamic conditions.

That's exactly what I have done on my latest Posting which shows 4 photos for each turntable.
The last two photos of each....show the effect of another arm dropped midway onto 'heavily modulated' disc whilst the test tone is being played by another arm
Please read the descriptions beneath each photo?

Agree with Tony......very impressive results from your turntable. Congratulations.
Can you describe the motor and modifications you have made?

I am beginning to suspect the accuracy of the Feickert Platter Speed App and/or Adjust 7" Test Record?
As I mentioned previously......every time one does a test on the same turntable with the same arm and cartridge....slightly different results appear in the Data.
Additionally....as Tony has pointed out.....turning the disc 1/4 turn at a time will give differing results due to record eccentricity.
But the real problem as I see it....is that one can achieve far better results from a 10 sec-20 sec Test than with a 4 minute or 6 minute test?
Hmmm.......

All measurement equipment has an accuracy and a repeatability factor. As engineers we have to measure our measurement equipment and it can get frustrating and confusing at times. Like the old saying: "A man with two watches is never sure what time it is." I still think the weak link is the test record. Eccentricity tolerances of the center hole is the first and foremost issue; but another problem is flatness. Any variation in the surface of the record is going to cause a speed change at the stylus- ie. the linear speed of the stylus in the groove. I see the same things. The longer I play the test tone the higher the values. The better that I center the record on the platter, the lower the values that I see. Overall, I have results that vary from 0.01% up to 0.04% with my turntable. I have my own 25 year old test record. Maybe the 7" disc is better with respect to flatness as compared to my test record. It would be nice to find a 180g test record.
As for the iPhone app, it occurred to me that I have a test CD with a 1kHz test tone. So I just did a test with the CD. The app reports a mean frequency of 1000.7Hz. The line is dead flat. The deviation is 0%. Short or long test had the same results; but here is an interesting observation. First, I held the iPhone in my hand and the result was 0%; but the raw result showed waviness in the line. Very small peaks and valleys. So I placed a small table in front of my speaker, placed the iPhone on that table and reran the test. This time the line was dead flat, but still had a small wiggle right at the beginning where I had to hit the start button on the screen. So as I suspected before and just saw, holding the iPhone in your hand while recording will cause additional variation. I suspected that before and always rested my iPhone on a table for the tt tests. This just proved my suspicions.

Also, it looks like to me that the app is reporting peak values, it is not averaging. I noticed that while looking at the handheld CD test results vs. resting the phone on a table. So like I was saying, one blip on the test record, like a high spot and the resulting values will increase.