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Pro-ject RM RPM 5 5.1 6 6.1etc. Owners Fixed

I own a Pro-ject RM6 SB turntable and love the turntable. However, it has always had a low end rumble once the needle hits the record. I tried ignoring it attributing the issue to record surface noise or one of the other compromises of living with vinyl. I recently discovered that this is a common problem with many Pro-ject models. At the urging of my not-so-local dealer I replaced the OEM footers with a set of threaded Edensound brass footers which yielded a dramatic improvement in everything except the rumble (I consider THREADED brass footers a mandatory investment). I then placed a cork mat between the subplatter and platter and silicone between the cartridge and headshell, minimal improvement if any on those two. The low end rumble continued and it really wasn’t that noticeable or intrusive once the music started, or so I thought.
I started my internet search and found a bunch of postings about the rumble problem inherent with certain Pro-ject TTs. There’s even a youtube video on the problem. I then came across a site from an RPM5 owner who claimed to have resolved the rumble problem found in Pro-ject turntables. He shows the before and after effects graphically on a spectrum analyzer identifying the low-end rumble with peaks at 50 and 100hz before and after his method of fixing it. Go here if you want to read more.

http://www.theapplechap.com/TheAppleChap/Blog/Entries/2011/5/24_Enhancing_the_sound_from_Pro-ject_turntables_by_removing_rumble.html

He provides a beautiful narrative on the fix and his science seems solid, but obtaining the parts needed seems a little complicated and he is waiting for Pro-ject to come up with a retrofit solution. Anyway, I discovered the repair can be done easily, for cheap, and now. Using his method, kind of, the fix is to install four rubber grommets (I’m not saying or recommending that you should do this, I just want to share my story). Based on the AppleChap’s approach, I went to Grainger.com and ordered a package of 1/8” ID 3/16”OD rubber grommets part number 3MRT4. They don’t sell them individually so I had to purchase a packet of 100 for an astounding $4.20 plus shipping.
The grommets arrived 3 days later. I then removed the platter, located the 4 screws that hold the rubber suspension (rubber band) in place. I removed one screw, inserted the grommet around the washer surrounding the screw and re-screwed it in place. It might be a little tricky at first as the suspension is tightly fit. I did this three more times, and four minutes later I was done. An important note the rubber band fits between the lips of each grommet, not above or below, unlike the pictures shown in AppleChap’s method. This isolates and decouples the rubber band from the screw and plinth. Also, I had to make sure that the screws were placed back correctly because any shift in the motor’s original position may cause the edges of the motor to touch the rubber grommet. If that would have happened I could have shaved the side of the lip of each grommet that faces the motor.
I returned the platter to its home and played a record. The second the needle hit the record, there was no rumble. It had disappeared, like magic. The grommets not only eliminated the rumble, but it cleaned up the soundstage and things that were previously masked were revealed. An amazing transformation! AppleChap also recommends changing the belt to a round instead of flat belt; less surface area to transfer resonance. I ordered a belt but it had not arrived yet.
cinellipro
cinellipro OP
26 posts
 
I've seen the charts and listened to the before and after on my turntable and it is evident that the changes are profound and necessary to transform the turntable.

I believe that every Pro-ject table with the the O-ring suspension suffers from the low-level rumble problem, not just a few. It may not be detectable in all systems as they may not produce soundwaves as low as 50hz., and it may be too sublte for others (or those unaware) to even notice, but unless these turntables are made by hand then every one should have the same anamoly.
Regarding the placement of the suspension o-ring directly attached to each screw, it seems that the vibration would channel into the plinth through the screw. Wouldn't a rubber grommet with LIPS decouple the suspension from the screw and plinth? Wait I'm not an engineer so I'm guessing.
Show me the charts!
carlman
21 posts
 
Thank you! Thank you! I will do the grommets and belt upgrade to my RM6... can't wait.

The suspension design is inherently flawed. All they've done is shift the vibration directly to the platter... instead of moving the vibration into the plinth. Bad design. My workaround was to screw down the motor with the shipping transport screws... which really helped reduce the rumble... but added some other slight resonances.. but not bad compared to Pro-ject's intended design. What were they thinking? "Let's float a buzzing motor and connect it to the platter!" That maximizes the buzzing to the needle. Maybe next year they will put the motor into the tonearm... haha.. I'm a little irritated that such a nice table has such a bad design for vibration control... from a leader in the industry. And the solution isn't expensive... so why aren't they at least offering an upgrade kit? Just weird.

Regardless, thanks for the fix idea. :) :)
sbrownnw
692 posts
 
My Pro-ject Xpression III started with the rumble (or recently got worse). Cinellipro and I have talked before and he has been very helpful with info, time and more! :) Hopefully this solves my problem. Otherwise, my table is still under warranty. And a "to the top" action for this thread for anyone else that is experiencing this problem with the Pro-ject turntable.
sbrownnw
692 posts
 
The 4 additional rubber grommets problem did not fix my problem of excessive woofer movement at volumes at close to double normal listening levels (party mode I guess you can call it). I am lucky I am not getting this at normal or just above normal levels and I will have to keep an eye on the volume level. Hopefully it does not get worse.

Here is a link to a thread on what some people might think is going on:

resonant frequency
cinellipro OP
26 posts
 
Discovered one more effective resonance reducing method for the RM or RPM 6 series turntable. As you know the plinth transmits vibration to the tonearm from the motor. The tonearm assembly is connected to a recessed section of the the plinth with only three screws. You can remove the screws and install a square piece of rubber that fits into the recessed area, or use the grommets to isolate the tonearm plinth. The rubber square I used was 2 1/2 x 2 1/2 by 1/8 thick. Be careful holding the tonearm at the removal of the last screw as the cartridge will be exposed.
You will need to adjust the VTF and the tonearm lift the same height as the thickness of the rubber square. Easy to do with two smaller allen wrenches. Installing the rubber square was less than 10 minutes and getting the VTF and tonearm hold adjusted was another 10 minutes. In my system, it continued to significantly improve all the elements of the soundstage already mentioned.
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