Funk Vector pulleys, motor, Achromat comparison

[tim_bissell]

I'm going to use this topic to post Audacity waveform screenshots of the the same track (first 14 or so seconds of Money by Pink Floyd) as recorded on my PTs.

This is to avoid the continuing hijack of Simon's thread, and to make it more easily locatable!

This was prompted by my comparison recordings for my :

• Original PT1 (Escap motor, Maplin Linear regulated 1.2A 9V PSU)
• PT mini-anniversary (Escap motor mounted on mini-anni sub chassis, mini-anni suspension and plinth and PSU)
• PT1 with Funk Firm Vector upgrade (Funk K-drive motor, vector drive, vector sub chassis, mini-anni suspension and plinth)

The common features were:

• Funk FXRII tonearm with AT33PTG m/c cartridge
• Audiolab 8000PPA phono stage
• Edirol FA66 firewire ADC into an iMac with Audacity 1.3.12 software
• Soundstyle support with glass shelves, Sorbothane Foculpod feet supporting a second, Ply base under turntable.

I noticed large differences in the looks of the waveforms when viewed in Audacity; the PT Vector looking much cleaner than the two Escap/PT1 extracts.

I will try and isolate what makes the difference by removing the achromat from the Vector, and trying to run the vector drive with my shortest PT belt, bypassing the pulleys of the Vector drive, so the drive is as on the PT mini-anni.

I'll publish the original three waveforms for the right-hand channel in the next post.

[tim_bissell]

OK this is the comparison of the first 14 seconds, right channel only

[tim_bissell]

And this is the PT Vector, first one with achromat and vector drive. Second without achromat (and VTA adjusted). Third is with my smallest PT belt, and no vector pulleys in play. Unfortunately the latter does not work, as it was playing noticeably fast; but this short comparison is interesting anyway (not much change).
My feeling is that the main reason for the clean waveform is the Vector motor and K-Drive, with the

[Alex M]

It looks as if the Vector is suppressing a mode at around 10 Hz. My feeling is that this is a mechanical, rather than electrical, resonance, perhaps an oscillation of the suspension and belt system.

My prediction is that the K-drive is not the main contribution to the cleaner signal...

Alex

[tim_bissell]

I'm sure it is mechanical, but the motor and controller is the only thing putting energy into the systems! The PT1 and MA waveforms look very similar, and have the same motor and speed controller; but the mechanics are different the MA has the motor mounted on the (carbon/balsa) sub chassis, a bit like the Vector, and the PT1 has it hung off the suspension T-bar, not connected to the sub chassis.

Glad to get some debate going!

-- Tim

[Alex M]

I'm sure it is mechanical, but the motor and controller is the only thing putting energy into the systems! The PT1 and MA waveforms look very similar, and have the same motor and speed controller; but the mechanics are different the MA has the motor mounted on the (carbon/balsa) sub chassis, a bit like the Vector, and the PT1 has it hung off the suspension T-bar, not connected to the sub chassis.

Glad to get some debate going!

-- Tim

I agree - these are fascinating measurements!

Alex

[SimonLogan]

Good stuff Tim! Are you able to try a test tone and run an FFT? (or use the platterspeed app if you have the special test record). That would tell you how well the drive system is able to maintain constant RPM under steady state conditions.
One other thing that would be possible on a motor like the escap is to plot the tacho pulse frequency vs time. This would tell you how well the drive system is able to maintain constant RPM while playing real music. This was apparently the reason why PT moved to an ac motor.

Simon

[tim_bissell]

Good point; I've got one on my HFN test disk - I'll try that. I can send you the file on which to run an FFT; not sure how myself... House is cold at the moment; heating pump is not working, so things might take some time to warm up 8-(

-- Tim

[SimonLogan]

... House is cold at the moment; heating pump is not working, so things might take some time to warm up 8-(
-- Tim

Not fun. We had our electricity off for about 4 days over Christmas one year and the house got unbelieveably cold.

Good luck!
Simon

[SimonLogan]

Hi Everyone,

Sorry for the delay - been busy.
Tim sent me some recordings of the 3k test tone taken with the following configurations
1) PT Vector + FXR
2) PT MA + FXR
3) PT Anniversary + Helius Orion
I believe all three used an AT32EII cartridge.
I ran some FFTs are saw some interesting differences.

First the vector


Then the mini-anni


Then the Anniversary


Some observations
1. Not all playing at exactly the same speed:

Code: Select all

PTA  2910Hz 3% slow
PTMA 2940Hz 2% slow
PTV  2950Hz 1.6% slow

2. We can see a lot of spikes to the right of the graphs. These are clearly harmonics of the test tone, probably coming from arm or cartridge resonances. The vector seems to damp these a lot better than the other two. Given that the mini-anni used the same arm, I'm guessing that the Funk Firm subchassis is performing better than the mini-anni in this respect.

Code: Select all

Harmonic  PTA      PTMA     PTV
--------------------------------
  2nd     -32dB    -33dB    -51dB
  3rd     -45dB    -50dB    -59dB
  4th     -58dB    -63dB    -72dB
  5th     -66dB    -74dB    -70dB
  6th     -69dB    -77dB    -81dB
  7th     -78dB    -78dB    -79dB

3. I saw marked differences in the low frequency output (suggestive of bearing noise or speed instability). I ran some more FFTs on the 4-100Hz range with 1Hz resolution (the best my analyser will do).

First the vector


Then the mini-anni


Then the Anniversary


The anniversary has very high output in the region up to 10Hz, which was also clearly visible in the time domain. I'm not surprised you said it sounded wobbly. There is also a large (+13dB) 50Hz peak in the Anni graph, suggesting the power supply isn't working so well.

[natty_dredd]

Interesting stuff Simon!

To jump to conclusions, I wonder if the bass region indicates that the idea that the fancy Swiss, Escap motor being better is slightly false because the use of the servo means too slow a servo loop for the speed control.

That's not to say the Escap isn't a better motor than the Premotec they use now, but the implementation isn't as good.

My very late Anni doesn't have a servo and uses the Premotec, so I wonder if it makes much difference.

Or it could just be woble in the suspension depending how it's set up?

When my earlier Anni was exhibiting a wobble, I found that one rubber motor mounting had come unstuck and so the motor plate could lift up on one side. Since I've been mucking about with decks and now have another and both currently in bits, I can't remember if that solved it or not!

[tim_bissell]

Hmm, I'll pop the platter and top-plate off and take a look at the motor mount. I've no idea what could be wrong with the PSU (not too much as it still sounds fine to me with music) but perhaps some new electrolytic capacitors and and bit of TLC from a hardware engineer would help - anyone know of one in the Huntingdon/Cambridge area?

-- Tim

[natty_dredd]

On later ones, the motor mounting plate is bolted on to the rubber bushes whereas the others the metal bit of the bush is only glued into the whole in the mdf motor mount. The one with the most stress from the belt pulling (furthest from the bearing) was the one that had come unstuck.

As I say, I can't remember if that fixed it.

I also took a guess that it could be the smoothing cap not doing its job through age so changed that too. Not many other electrolytics I don't think as they're either the round flat, lentil like ones or orange tantulams types (kind of fudging my way through the terminology there).

[Alex M]

As I have already said, these measurements are very revealing and altogether fascinating. Arthur does seem to have got his sums right with the Vector and K-Drive!

Alex