Pro-Ject RPM5 Improved rumble noise floor

[chalmh]

Recently I became an owner of an RPM5 turntable.



Since my whole setup is very low noise and transparent (used for LP ripping to digital format), I noticed a low level of rumble noise that comes from the AC motor.
I captured its spectrum on my computerized system and analyzed it. The rumble noise comes from a fundamental 50Hz and harmonics. when the arm is in lift position that noise is not heard or can be captured.
I captured it while the motor was operating and the belt was removed. I placed the arm on a record as the platter is not turning and the motor is still operating.
The root cause of that rumble noise is the O-Ring which floats the AC motor from the plinth. some of the motor vibrations are leaking through the O-ring rubber and slightly vibrates the 4 screws which are supporting it.
Just for reference of the setup: I use an AT440Mla cartridge, a self designed and built very low noise Phono stage ("Le Bonbonniere"), Samson 260 PA and Tannoy Reveal 6 shelf monitors.

The rumble noise varies in magnitude related to the arm position on the record. The outer tracks are more noisy while the inner track is less noisy. this confirms a mechanical problem which might be inherent of all RPM5s (I cannot prove it since i don't have another RPM5 to compare). The mechanical condition of the turntable is excellent and all parts are absolutely not faulty including the smooth turning of the motor.



As the bottom cover of the motor housing has a hole, I placed my pinkie and supported the motor by lifting it up slightly. What I discovered was amazingly improving the attenuation of the rumble noise. i was able to attenuate the main 50Hz rumble by -14dB as well as most of the harmonic frequencies. You may review and compare the spectrum graphs. The top graph is the genuine rumble noise and the lower graph is the improved spectrum.



The attenuation of the rumble noise improves the sound of the RPM5 by getting a more "vivid" and accurate bass frequencies and allows you to listen to a higher audio volumes.

These days I'm in a process of designing an upgrade kit for the RPM5 model in order to float the motor in a better way. I hope that this can place the RPM5 in a higher league of turntables.

I would like to understand from other RPM5 users if they would upgrade their turntable using the kit. However I don't know yet what will be the cost of that kit but I may assume it will not be too expensive compared to the quality and value improvement of the turntable.

[Rap]

You forgot the possibility to vote : "Why would I ever want a RPM5 ? "

[chalmh]

Rap,

The option

[chalmh]

3 days ago I was able to modify the motor suspension at it's final version. The rumble was attenuated almost competely (it cannot be noticed anyway and it can be detected only with the spectrum analyzer since the magnitude is very low.

I separated the spectrum region into 2 graphs. the first is showing the lower frequency region up to 35Hz and the 2nd graph deals with the frequency band 30Hz-200Hz.

In the first graph you can see the tonearm resosnace frequency while in the second graph you can see the 50Hz motor rumble including its harmonics after my improved motor suspension. be aware that the motor ruble was higher by 15dB prior the improvement and could be noticed in precise low noise systems.

I hope that Pro Ject will adopt my solution for their turntable families which are using that same 20 pole synchro motor.

[flavio81]

Sorry man but that rumble curve (the 1st one) is completely unacceptable for anything that pretends to be an audiophile turntable.
There is a HORRIBLE 100Hz component at -60dB there!!

I mean, you are very clever for having found a solution, but the stock performance is awful. Awful.

http://www.avland.co.uk/pro-ject/rpm5/rpm5.htm

-70dB weighted "signal-to-noise" (actually Rumble.)

Even the cheapest Technics direct drive, those who can be bought for pennies, have better rumble performance. Better flutter too.

That's why i always say: Stick to the reputed brands: Sony, Technics, Pioneer, Thorens, Garrard...

[chalmh]

Dear flavio81,

I think you are mistaken.
Do you understand what means a weighted "signal-to-noise ratio"?
Do you know what was my phono stage amplification at this spectrum?
do you know that this was measured on a playing record in between the 2 first tracks gap?
Do you understand the graphs are just relatively expessing the curve?

I bet you all those brands can be tested under the same DOE and you'll be surprised.

[flavio81]

[chalmh]

Dear flavio81,

Firstly, I'm not angry about you at all.
My self designed and build phono stage "Le Bonnbiniere" is a variable gain very low noise phono stage that varies gain from MM to MC position by using a potentiometer. The gain in that particular test was higher than required for a MM cartridge which I used. This was done to amplify the noise floor to get a good precision of the gap sound in between the tracks.
So what you see as -60dB is not the real value.
Hence that the overall signal to noise ratio at the proper gain is lower by about 10dB.
Actually when you listen to a record only the vinyl surface noise signature can be observed while before my improved motor suspension, it was able to hear the 50Hz and 100Hz rumble (very low, but it could be noticed).
I'm not angry with the manufacturer either, but they can improve easily their turntables like I did.

[flavio81]

[Dave Cawley]

Send it back and get a refund!

Dave
_________________
/ Technics SL-1200MKII / Jelco SA-250ST arm / Shelter 501 II cartridge / Neglex arm interconnect / A.N.T. Kora 3T MC phono stage / Marantz SC-7S2 preamp / 2 x MA-9S2 Marantz power amps / Focal Electra 1037Be loudspeakers /

[abelb]

Hi chalmh,
I also experience an audible rumble from the motor of my 1-Xpression III turntable which is the model below the RPM 5, and which I suspect uses the same motor. Mine also has a hole in the plinth below the motor and making contact with the motor while it’s running reduces the rumble. I tried a few amateurish things not having all that much equipment on hand, such as attaching lead car balancing weights to the motor in the hope that the extra mass would push the vibration into a lower and less audible frequency, however, it didn’t work! I took the turntable back to the distributor seeking a motor replacement as I had no other Pro-Ject for reference and comparison, but they did not find an issue with the motor and just “adjusted” the suspension. This improved the situation slightly but not satisfactorily. If you’re coming up with a better solution which is reasonably priced then yes, I’m interested! For the time being though I have embarked on an ambitious project to restore an old turntable using a DC motor, although that’s not ready and I would love to keep the Pro-Ject if a reasonable upgrade became available.
Cheers,

[chalmh]

Dear abelb,

I'm in a kind of an almost "dead end" negotiation with Pro-Ject about my solution which is very simple and probably a low cost. Actually I have 2 kind of solutions. The low cost solution is solving the problem and no adjustment is required. The second solution is also reasonable in price but you can get a very precise low rumble noise adjustment. They are a bit "clumsy" with their approach. I think Pro Ject users should "push" them to be more proactive to accept the propsed improvement and cooperate with me. Their representative provided me an offer which was a bit confusing (to define it politely), like they would like to get my solution and I need also to pay for it. This places me in a position that I must hold my solution "close to my chest". Once I spread it I'll not gain from it nothing.
I'm also cosidering to apply a patent for that solution but I need to check its possibility to be registred world wide. This is a huge investment of money beside the research if such a patent was applied already in all countries. So the simplest would be that Pro-Ject would get my solution and drive in order to improve their products. It is strange that manufacturers are "ignoring" innovations and improvements.

So at the moment there is only a single RPM5 with the improved sound. there is a big difference in the low frequency sound like bass which is precise without a sustaining effect followed by a rumble.

I'll update you for the further negotiation and availablity of the "kit".

[Conrad Hoffman]

Convincing a company to change something or make an improvement is nearly impossible. They tend to suffer from "not invented here" syndrome, plus they look at the cost and ask a very simple question- "How many more widgets will we sell if we make this change, and does it increase our profits?" They usually find a way to say no.

Patents are both good and bad. Companies are loath to pay royalties on a patented idea unless it's something fundamentally game changing. Getting a patent almost insures the idea will languish in obscurity. Patents are more like poker chips that companies use as negotiating points when divisions are being bought and sold. The small/individual inventor-patent-profit idea has always been somewhat of a myth. Not that people have never made money from a patented idea, but the percentages are incredibly bad. Also, unless you've worked in the tt industry for a long time, your chances of coming up with something not covered in prior art are minimal. Not that you can't get a patent on it, but defending it will be difficult and probably beyond your means. Remember, a patent is just the right to defend. Worse, at least in this country, you're obligated to defend every potential infringement, or you lose the force of the patent.

So what to do? IMHO you should try to sell kits privately. Your market is tiny and it might be hard to make any money at it, but it's worth a try.

Only other comment is that IMO the word "rumble" is traditionally reserved more for bearing noises. If you've got coupled motor noise, call it that!

Best,
Conrad

[flavio81]

[chalmh]

Dear Conrad,

You are absolutely right about the patent application "combat". I'm aware of it from my past experience (I have already 2 registered patents in the USA). That's why I commented previously that I'm "considering" it. So in this case we have the same impressions.

I'll be waiting for Pro-Ject for some more time (not too much). In the meanwhile I'll get some other "raw materials" for my kit development which I'll chose for the final model upon the spectral test results. Once it will be completed and if Pro-Ject will not provide any positive feedback, I'll probably sell the kit privately upon request.

BTW, I'm listening to my improved RPM5 for several days since the improvement and it sound so good, especially in the bass region. I feel like I want to listen to it endlessly. It can be noticed at the points when bass is not recorded in a track, it is simply not there while with even a slight rumble you get the bass even it wasn't recorded.


Dear flavio81,

I like your definitions