Wrestling with rumble (Empire 208)

[beatcomber]

I had a 208 that the only thing I did was replace the tonearm with a Jelco 750D and used heavy automotive panel damping on the plinth and had no rumble at all. You metioned using Mortite, is that a heavy material or just a plastic clay? If it is I would try the pre-adhesive rubber panel material.

Mortite is a brand of rope caulk, a fairly heavy-duty insulating clay. The auto panel damping might be a better solution, I don't know. No rumble, huh?

Edit.. Have you cleaned and lubed the motor?

Yes. The motor is as quiet as a mouse when decoupled from the top plate.

[cafe latte]

So if I understand correctly if the belt is off and the motor is switched on and the stylus is on the runout groove you get rumble? If so this could also be interference from the motor. The Commonwealths had an add on that was retro fitted motor shield to stop hum with some carts I just mounted my arm differently and rotated my whole TT. Another idea I have done before is get a very large thick O ring and put it round the motor it should help damp vibrations.
If your Motor bearing have been getting such light oil they may run quiter with a heavier oil too. Also does your motor shaft (at the bottom ) have height adjustement? If so adjusting this may help reduce vibration. How free does the motor spin with fingers only?
Also try a dab of moly grease too at the bottom of the TT spindle as well as the compressor oil.
Regards
CL

[AR_Legend]

I doubt that the rumble is due to any sort of motor generated electromagnetic field interacting with the cartridge. Empire mounted the motor as far away from the cartridge as possible. But I suppose anything is possible.

I firmly believe that the real fix is to use a plinth that is heavier and more mechanically solid than the original hollowed out casting. As mentioned in an earlier post this is what Atma-Sphere discovered as well and offer the Atma-208 with a solid aluminum plinth.

This is what I’m in the process of doing right now but by using a local machine shop to cut the plinth. It’s much cheaper than what is currently available off the shelf and much more fun as well.

[Doug G.]

What was the original rumble spec. of the 208, though? I mean, if Empire was able to attain a low rumble figure with the plinth as is, it means there is something else as a cause which may be able to be mitigated with a band aid fix but it would be better to really fix it.

Doug

[beatcomber]

Thanks guys! I may have made some progress but I want to evaluate it further before commenting.

[AR_Legend]

What was the original rumble spec. of the 208, though? I mean, if Empire was able to attain a low rumble figure with the plinth as is, it means there is something else as a cause which may be able to be mitigated with a band aid fix but it would be better to really fix it.

Doug

In my opinion the attraction of the Empire 208 is the quality of the bearing, platter (although it rings) and especially the motor. The plinth leaves much to be desired.

I’m sure Empire needed to design to a price point that would insure high sales numbers along with a decent profit and still exude a look of quality. The plinth is one logical place to do that.

The plinth is less than a quarter of an inch thick over most of its surface and for some reason there’s a large pie shaped cutout under where the platter sits. I think it’s a relatively flimsy foundation on which to build a turntable.

Damping the original plinth with various compounds will only go so far in reducing rumble and resonances, in my opinion. Rumble is particularly difficult to deal with because its energy is located at the lower end of the frequency range.

In my opinion the only real fix is to jettison the original plinth in favor of a much more solid alternative. That’s what I’m doing.

[beatcomber]

I think I've managed to get the rumble down to an acceptable level.

I removed the platter and again cleaned out bearing well. I was surprised that there was still some dirt on the Q-Tips, since I had cleaned it out not that long before and thought I had done a thorough job. Instead of the sewing machine oil I used before, I oiled the spindle with a few drops of the 5-20 Mobil 1 that Marc Morin had sent me for use with my AR-XA.

I also decided to dampen the platter, which is prone to ringing and is probably contributing to the motor noise reaching the cartridge. I packed the concentric opening in the bottom of the platter with some Mortite, since I had about a 1/2 box on hand. I was concerned about the platter possibly being thrown off-balance, but there is no evidence of there being any problem. The dampened platter has made a HUGE improvement in timing, dynamics and, especially, bass response, which is now very powerful and full.

I am now getting virtually zero rumble! At normal listening volume I pretty much need to put my ear right up to the subwoofer's port to hear any rumble; it's inaudible from the usual listening position.