Pro-Ject turntable motor hum? Isolation is the key, apparently. (pics included)

Mr. Lin

Lunatic Member
Well, a few nights ago, for the first time in nearly two years, I set up my Pro-Ject RM-5 to play some records. Long story short, I moved, the RM-5 got packed up, I bought a bunch of amazing CD players, and then when I was ready to listen to records again I only had the Thorens TD125 MKII on hand - not that that was a bad thing.

It's always been clear to me that the Pro-Ject is sonically superior to the Thorens, despite how great the latter sounds. But one thing the Thorens has had on the RM-5 is background silence. For the first few years I've had my RM-5 I struggled with noise issues: first hum, which was eventually cured with the right pair of purpose-made interconnects, and a new grounding approach, then surface noise (not the inevitable, usual kind), which was reduced when I realized I was turning the gain on my phono preamp too high, and finally, the infamous motor-induced hum audible in the background when records are played at 45rpm on some Pro-Ject turntables.

Truth be told, I'd gotten kind of depressed about the Pro-Ject while it was packed away, and decided maybe I should just forget about it until I have the money for a newer, better turntable. After all, background silence is more important to me now than ever, largely because of my recent experiences with good CD players. Then a recent thread popped up on AK about the new kit for Pro-Ject turntables that's supposed to fix any hum problems, just as I was preparing to finally pull the thing out and use it again. Not encouraging.

So here's what happened: First I placed it on the piece of furniture I'd previously put the Thorens on. Mind you, this is a new house, and I'm talking about different furniture. All listening is now through headphones (see signature for equipment list). I installed the Dynavector 10X5 cartridge, from which I'd removed the plastic body. Initial results were not good. There was lots of surface noise, and even a bit of hum audible at the 33rpm speed.

Then I realized I'd forgotten to level the turntable (whoops). That reduced surface noise considerably. And then, I got the idea to have my phono preamp (on a different piece of furniture) switch places with the RM-5.

This might be getting a little drab so I'll get to the point. With the turntable on this other piece of furniture - which is sturdier and better isolated - I immediately noticed a dramatic reduction in noise all around. This was promising, and rather exciting. Next I tried using one of my sets of Herbie's "Iso-cups" with his "db Neutralizer" material balls, on top of Herbie's Super Sonic Stabilizer discs (I have a bunch of that stuff lying around). Despite the silly names, these things work wonders with certain components, and this was about the best result I've gotten yet. Steve Herbelin doesn't just have balls, he's got balls that get results.

First of all, the background silence is now on par with the Thorens, and that's huge. Second, there's absolutely no hum audible when playing at 33rpm, unless I turn the volume knob all the way up, which is waaay higher than listening levels, and that hum is from my tube phono preamp. Third, I tried playing a 45rpm record with the volume cranked at the beginning of the lp (where you could normally hear the hum the instant the stylus touched the vinyl), and the hum is gone!

Obviously people have known about the importance of turntable isolation since before I was even born, and I knew about it before this experience too, of course. But at my previous residence, I had my RM-5 on a piece of furniture that, looking back, wasn't really appropriate for that application, and must have been significantly degrading the sound. This is an exciting development because the sonic strengths of the RM-5 (largely due to its carbon fiber tonearm I believe) are many, and now its biggest weakness - motor-induced noise - is basically eliminated. Right now, as I'm listening to Sun Ra's Supersonic Jazz, I can confidently say this is the best the RM-5 has ever sounded with the Dynavector 10X5 installed. It has the detail, the finesse and refinement, the imaging, dynamics, and timbrel accuracy, and, of course, the sought-after "black" background.

Below are some pictures of the turntable with the Herbie's Iso-cups underneath. The balls are interchangeable, but the "db Neutralizer" type is supposedly designed specifically for turntables, plus it's not slippery like the ones made of various gemstones and wood, so the turntable is not at risk of sliding off the footers.

Under the Iso-cup you can see the gray SS Stabilizer disc. Info on those is available on the Herbie's Audio Lab site, but it's basically meant to add "virtual mass" to the tops of components, the same effect as when you just rest your hand on the chassis of something. But I've started using them as bases for footers, and Steve Herbelin confirmed that that is another thing they're meant to be used as.

Under that, the rather unsightly pieces of folded paper. Why? Well, I used college-ruled for a linear frequency response... Seriously, although it looks sloppy, sliding these under certain bases, one piece at a time (like the famous playing cards trick) allowed me to level the turntable as accurately as possible (with the leveling tool I have, that is), thereby bypassing the built-in cone feet of the RM-5:

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And of course there's room left for the indispensable Speed Box to be tucked neatly under the plinth:

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In what other ways have I approached the battle against vibrations? I'm about to start another thread - don't worry, it will be more succinct - about the last cherry on top of everything here, ZYX Silent Metals.


...
 
Update:

Although the steps described above went a long way in reducing motor-induced hum, if I turned up the volume really loud during silent parts of an lp, I could still hear some of the hum. I could have left well enough alone here, since, even with headphones, it was barely audible. But I wasn't satisfied, so I tried this:

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What you're looking at is the motor of the RM-5, which is suspended by rubber bands. That, specifically, is the root of the problem; the motor hums (you can really feel it if you put your finger on the motor and turn it on), the vibrations are transmitted to the rubber bands, and the rubber bands are touching the plinth, so the vibrations apparently go all the way to the tonearm and finally to the cartridge.

In the picture above, you can see how I tried using little squares of Herbie's "db Neutralizer" (same thing the balls in the original post are made of) to decouple the rubber bands from the plinth. I then stacked two of these little squares under each "wing" of the motor mount, where the mounting screws originally went to prevent damage during shipment.

This made the problem worse. Apparently it raised the resonant frequency, so the motor hum was not only louder, but higher in pitch and therefore even more noticeable than ever! :sigh: I first removed the four pieces of db Neutralizer that were under the wings of the motor mounts, and left the other pieces under the rubber bands. This returned things to normal, but a little quieter than when I'd started, so it wasn't a complete waste of time.

Frustrated and annoyed, I decided to see if one of the extra tube-damper-style Herbie's rings I had on hand could be fit onto the RM-5 9c tonearm. For some reason I thought I'd already tried this in the past and it didn't fit, but I was apparently wrong about that:

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I adjusted the VTF (since the damper made it higher, obviously, with more weight), and gave the same lp I'd been using another try (Peter Gabriel 3 "Melt"). Wow, did that make a big difference!

I encourage anyone with one of the Pro-Ject tables that has these problems to consider trying out a Herbie's damper, or one of the other methods of tonearm damping that can be found on the internet. I guess I thought since the 9c tonearm is made of carbon fiber, it was the last thing I needed to address. But that last frontier, so to speak, just before spurious vibrations work their way to the stylus, is one that's easy to modify in such a way.

I've since added a smaller Herbie's damper to the back section of the tonearm assembly where the counter-weight is attached - it's much thinner than the actual tonearm. Haven't taken a picture of that yet.

I'm surprised that the simplest, easiest thing to do, was the most effective. Looks a little funny, but that's ok with me.
 
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And just one other thing I'd like to add about all this. Until a few days ago, I'd been using my Wright Sound Company 200C tube phono preamp. As much as I like that preamp, crystal clear resolution and an extremely low noise floor are not its fortes. It has other strengths.

For the past few days I've been using my Sutherland Ph3D phono preamp instead. This has a lot to do with why I've been so motivated to address the hum problems with this turntable. With the Ph3D, everything is laid bare, good and bad. This level of transparency and information retrieval (or more accurately, preservation) are some of the reasons I absolutely love this preamp. It's due in part to the fact that the Ph3D is battery powered, and also because it's a quality, well-executed, solid state design.

Additionally, the Ph3D allows for impedance setting adjustments. The Dynavector 10X5 I'm currently using prefers to be at 10kohms, not 47kohms, despite the fact that it's a HOMC cartridge that can be used at full throttle. With the 10kohm setting, the sound from the 10X5 fills out, bass becomes more powerful, and some of the treble glare and brightness disappear.

So things are sounding pretty fantastic right now!
 
It sounds like you're saying the vibrations in the suspension ring are being transferred by direct contact to the plinth. If that's the case, how about slipping a faucet washer onto each of the four screws, below the suspension ring?
 
It sounds like you're saying the vibrations in the suspension ring are being transferred by direct contact to the plinth. If that's the case, how about slipping a faucet washer onto each of the four screws, below the suspension ring?

That might help, but the problem with the rubber bands, it seems, is that they're literally touching the plinth, they're not just in contact with the plinth at the points where the screws are. See how I have those white squares right under the rubbers bands in the picture? Normally, the rubber bands rest up against the plinth at those points.

The other problem, which I haven't addressed, is that the motor is not level, as it's pulled just a little bit toward the sub-platter by the belt. I've seen a number of ways people have fixed this on the internet. I'm thinking perhaps blu tac would work well there; I could put the blu tac underneath the one side of the motor, and shape it such that the motor is held in place by the blu tac, and the motor is level at all times.

But like I said above, once the tonearm dampers went on there, the noise was barely noticeable through headphones, and is only heard when the volume is turned up really loud - louder than I listen the vast majority of the time.
 
That might help, but the problem with the rubber bands, it seems, is that they're literally touching the plinth, they're not just in contact with the plinth at the points where the screws are. See how I have those white squares right under the rubbers bands in the picture? Normally, the rubber bands rest up against the plinth at those points.

The other problem, which I haven't addressed, is that the motor is not level, as it's pulled just a little bit toward the sub-platter by the belt. I've seen a number of ways people have fixed this on the internet. I'm thinking perhaps blu tac would work well there; I could put the blu tac underneath the one side of the motor, and shape it such that the motor is held in place by the blu tac, and the motor is level at all times.

But like I said above, once the tonearm dampers went on there, the noise was barely noticeable through headphones, and is only heard when the volume is turned up really loud - louder than I listen the vast majority of the time.

My thought was aimed at exactly that. The washers wouldn't be to isolate the ring at the screw. They would be to elevate the ring by the height of the faucet washers. I'm thinking of a washer maybe 2mm thick, at least.
 
Elevating the suspension band is a tweak others have found success with. It's also a component of the semi-official fix by Henley in UK. Some have used grommets. I followed a tweak Moon Unit posted - unscrewing the 4 suspension screws slightly to raise them and putting small pieces of rubber band under the suspension band to raise the band on the subplatter side (leveling it in the process).

It's not perfect but it helped a lot.

Very interesting about the tonearm damper. Although on my Xpression I'd need a heavier counterweight. And I'd wonder about the implications of increasing mass like that.

What does the damper weigh?
 
My thought was aimed at exactly that. The washers wouldn't be to isolate the ring at the screw. They would be to elevate the ring by the height of the faucet washers. I'm thinking of a washer maybe 2mm thick, at least.

Ok I see what you're saying. I have been considering trying something like that.

Very interesting about the tonearm damper. Although on my Xpression I'd need a heavier counterweight. And I'd wonder about the implications of increasing mass like that.

What does the damper weigh?

I'm not concerned about adding weight to it because of the particular cartridges I'm going to use. The naked tonearm is about 9g effective mass, I believe, which is a little light for MC cartridges. I can't tell you how much the damper weighs because it overloaded my stylus force gauge, but that only goes up to 3.5g I think. The damper is very light, you wouldn't need a different counter-weight unless you're using a very heavy cartridge and/or headshell weights. The damper is made of Teflon and the little rings are silicone.

Also, you can use one of the smaller dampers right behind to the counter-weight to balance things out a little (I'll try to put a picture of this up soon).

But I have to say again that at this point the noise has been so dramatically reduced it's a non-issue now. If I were to try one of my lower-output MC cartridges, however, it might be a different story.
 
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One last vent on Pro-Ject

I most certainly hope that you all are successful in eliminating the Pro-Ject turntable hum issues.

I just need to vent one last time about these tables though.

My experience with the Xpression III really soured me on Pro-ject. How they sold thousands of turntables ranging in price from $400 to $1,300 a pop with a major design flaw and then making the buyers of tables have to tweak them themselves just to make the table sound right.
This is especially annoying in that the design flaw is in the motor suspension isolation….. After all, isn’t this the basic premise of a belt drive anyway?
 
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I most certainly hope that you all are successful in eliminated the Pro-Ject turntable hum issues.

I just need to vent one last time about these tables though.

My experience with the Xpression III really soured me on Pro-ject. How they sold thousands of turntables ranging in price from $400 to $1,300 a pop with a major design flaw and then making the buyers of tables have to tweak them themselves just to make the table sound right.
This is especially annoying in that the design flaw is in the motor suspension isolation….. After all, isn’t this the basic premise of a belt drive anyway?

The motor suspension was not executed in an ideal way, that's true. However, I have to point out that I used my RM-5 for years and wasn't at all bothered by the noise. Recently - since I have better phono preamps and I'm listening through headphones - the noise became somewhat audible. I honestly don't think most people would even have noticed it once the RM-5 was on a proper piece of furniture (before any of the other stuff in this thread), and therefore it really is not absolutely necessary to do any of this, provided you have an adequate spot to put the turntable - and that's really true for all turntables anyway.

So the turntable already sounded "right." I've seen a similar comments on AK about Pro-Ject turntables regarding this topic, specifically that there are tweaks to make them sound "normal." The RM-5 has always sounded normal.

How has Pro-Ject been so successful? It's because many of their models can sound downright phenomenal with the right cartridge and other associated playback equipment. All the effort I've put into addressing the vibration issue here - beyond proper isolation on a piece of furniture - is perfectionist stuff. If you have a Pro-Ject turntable and the hum is very noticeable or seriously detracts from the sound, you need to find something else to put it on, that's the biggest point people should take away from this thread.

I just wanted to put that out there because I vehemently disagree that Pro-Ject turntables are seriously flawed or don't sound "normal." If either of those things were the case I would have ditched it long ago.
 
If gvalent was never able to solve the issue I can understand the frustration. My Debut III actually doesn't have this problem, so I can only speculate as to possible solutions. My own theory is that the motor needs more torque so it doesn't vibrate under the strain of turning the pulley. But since it does vibrate, the next best thing is to isolate that vibration effectively. Then again, maybe it is just poorly made and would vibrate regardless.
 
Have to agree with gvalent. Sold my Pro-ject because I couldn't cope with the hum.

It really is not satisfactory that a manufacturer can continue to sell a flawed design on the market, then turn around some years later, admit there is a fault and then charge for the fix.

They may be musical decks, but I wouldn't buy another.
 
The motor suspension was not executed in an ideal way, that's true. However, I have to point out that I used my RM-5 for years and wasn't at all bothered by the noise.

How has Pro-Ject been so successful? It's because many of their models can sound downright phenomenal with the right cartridge and other associated playback equipment.

I agree. I also think that the reason this problem doesn't always show up is simply that the rubber suspension band doesn't always touch the plinth, and if it doesn't, all is cool. I suspect that it doesn't when new, but then sags after a time as the rubber stretches.

A problem design-wise is that a thinner band will transmit less noise, but will sag more easily. Beef it up and it won't sag, but now you have much less isolation. It's a trade-off.

On the last Pro-Ject player that came through my shop-- a Debut-- I added some small rubber grommets to each of the four support screws and then refastened the rubber support band through the grommets. I also added some washers to the screws (under the grommets) nearest the platter to raise the motor slightly higher on that side. This counteracted the pull of the platter belt and kept the motor level.

Two things to be careful of: Don't raise the motor so high it hits the platter, and be careful when reinstalling the support band to not overstretch it-- the grommets add some extra distance that it now has to fit over.

I did have to replace the screws with some slightly longer ones to allow for the washers and the grommet, but the support band was lifted completely off the plinth by this arrangement, and it was a cheap, easy fix to say the least.
 
Wow. I shelved my Debut because of the hum. Found the source to be the motor/suspension. I also tried many of the things talked about here with little to no success. I ended up picking up a Technics SL1200Mk2 to solve the noise issues. I figured models higher up the Project chain had a better suspension/ isolation for the motor. Color me shocked.
 
I agree. I also think that the reason this problem doesn't always show up is simply that the rubber suspension band doesn't always touch the plinth, and if it doesn't, all is cool. I suspect that it doesn't when new, but then sags after a time as the rubber stretches.

A problem design-wise is that a thinner band will transmit less noise, but will sag more easily. Beef it up and it won't sag, but now you have much less isolation. It's a trade-off.

On the last Pro-Ject player that came through my shop-- a Debut-- I added some small rubber grommets to each of the four support screws and then refastened the rubber support band through the grommets. I also added some washers to the screws (under the grommets) nearest the platter to raise the motor slightly higher on that side. This counteracted the pull of the platter belt and kept the motor level.

Two things to be careful of: Don't raise the motor so high it hits the platter, and be careful when reinstalling the support band to not overstretch it-- the grommets add some extra distance that it now has to fit over.

I did have to replace the screws with some slightly longer ones to allow for the washers and the grommet, but the support band was lifted completely off the plinth by this arrangement, and it was a cheap, easy fix to say the least.

Thanks for sharing that, it's helpful. This is probably a long-shot, but do you happen to know what type (as in #) screw one needs for the motor mounts? I ask of course because I'm probably going to eventually try longer screws just for the heck of it, with an approach similar to what you described above, and what Bob mentioned.

Your theory about the rubber bands stretching and sagging over time is very interesting, that's something I hadn't even considered.

I figured models higher up the Project chain had a better suspension/ isolation for the motor. Color me shocked.

Well they must if none of these things solved the noise issue with your Debut III.
 
Two dots of sticky tack under the bands closest to the spindle straightened the motor on mine and fixed the hum I did have.
 
Two dots of sticky tack under the bands closest to the spindle straightened the motor on mine and fixed the hum I did have.

See, it can be simple as that, one needn't necessarily go to the lengths I've described in this thread. I'm really in a bit of an experimental phase with the RM-5, and I have a lot of things on hand that allow many possible approaches to the problem.
 
Well they must if none of these things solved the noise issue with your Debut III.

Looking at the photo you posted, the motor suspension isn't any different. Mine has been shelved for a while. Maybe I'll pull it out and give it another go. If for no other reason than to get a few pictures.
 
Here's what I know:

1. I had no hum till I installed the Speed Box II
2. The Speed Box requires one to use the larger pulley
3. This tightens the belt and cants the motor towards the spindle because of the cheezy rubber band suspension
4. Either the rubber bands are now buzzing on the plinth or the belt is causing a vibration because it's not running straight.
5. Either way something to raise the front bands (sticky tack in my case) should fix the issue.
 
One more thing. I live in an older house and all my gear WAS plugged into a single 15A circuit. I upgraded the fuse box to a 200A breaker box years ago and ran some dedicated lines to my shop and HT room BUT not my 2 channel rig. I always had some hum from my tube phono-pre that was very tube dependent. Some tubes had no hum, unfortunately all the good ones did.
I figured a 15A for my TV, QSC amp, AVR, all the rest of my gear, and 1/3 the house was a little much on this daisy chained circuit. So I had a electrician friend come by this weekend and we ran two dedicated 20A circuits for the 2 ch system. Long story short my phono-pre is now on a different circuit from my amp and ALL hum is gone now. Before everything was run through Furman and Isobar stuff FWIW, so that didn't help with the hum.
 
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