My subwoofer hates my turntable

very nice. did you have a similar problem before using this system?

 

The older I get the less I know for sure but I have plugged a few guitars into amps in my time and I wouldn't say it sounds anything like that. Thank you for your suggestions, I will take your suggestions and make another run at it.

 

It may be possible that it's a ground loop between sub and tt:
try to invert the power socket of rel or try a link from tt ground and
rel ground

 

Just a guess but maybe it's some low frequency rumble from the turntable motor or some kind of arm cartridge oscillation resulting from a compliance/mass combination that's being excited by vinyl resonances or even just the motor, especially if the level of the subwoofer pumping isn't changing with the volume level of the signal and it's pumping even at low volumes with the table and sub in different rooms.

One thing to try, to see if it's motor vibration coming up through the plinth to the arm, is to take the belt off the subplatter (I assume this is a belt drive table yes?), put the arm down on an unmoving record on the platter, then switch the motor on. Obviously with the belt off it won't spin the platter, but if motor vibration is making it's way through the plinth to the arm as the source of the woofer oscillation, you'll know. If not, you'll have eliminated that as a probable cause (of course motor vibration is coupled to the platter via the belt and sub platter so motor vibration could still be a factor. There was much talk some years ago about motor vibration issues with the Project Debut and I know at some point they started using sorbothane to reduce motor vibrations making it to the plinth.

 

I went back and reread the first post. I read it wrong the first time. I thought the OP meant when he separated the turntable from the room, it solved the problem. It's the opposite. The problem remained. My error. Unless the whole house is being excited by the subwoofer, and I have seen that happen (do you get rattles elsewhere in the house?), it's unlikely that your problem is normal acoustic feedback.

Dennis, this sounds good to me and I like chervokas' test.

One more question, Dennis: do you see your subwoofer driver flopping around? It really shouldn't move that much, and any movement should be directly tied to the music. If you are seeing large excursions of the driver even at low volume levels, often independent of the music, it's a telltale sign of a mechanical problem elsewhere.

 

Thanks! I took the belt off, turned on the motor, dropped the needle, turned up the volume to the sub and the rumble was there just as if the record was playing. but wait, there's more... I then turned off the motor, keeping the needle on the record and the rumble was still there without the motor running.

 

Like a crazy hooker strung out on meth

 

At least we have determined it is a subsonic problem. Now the question is from where. Your experimenting with the turntable is very insightful but at this moment not enlightening to me. I'm leaving now for the Y to do my workout. Maybe going mindless on the treadmill will help.

 

OK, so not motor rumble, and not related to anything having to do with the arm moving in the groove. That's some crazy stuff. Does it go away when you lift the arm off the table?

 

Wait a minute. You're using a Musicial Fidelity phono preamp, correct? You're not plugging that into the phono input on the AVR988, are you? I see the AVR988 has a MM phono preamp built in. In that case you would be double pre-amping the turntable. If you use an external preamp like the Mobile Fidelity, you have to plug that into an AUX, tape, CD, minidisc (I see your amp has one) input. You should NOT be plugging that Musical Fidelity external preamp into the phono preamp of the receiver!

 

with the arm up it, only makes a faint rumble when I turn the volume on the sub to the max. with the arm down, it only takes about three percent of the volume to begin to rumble.

 

nope, I'm going into to the "CD" input. I'm not doubling up on the phono stage.

 

Why don't you remove your preamp and use the MM input on the Denon to determine if the fault lies in the Musicial Fidelity and not the turntable? I'm beginning to suspect the MF preamp.

 

So there's some woofer pumping even with the tonearm off the record? And the receiver has a phono stage built in? Have you tried that phono stage, and if so, do you get the pumping with that?

 

I was using the built in phono stage for some time and one of the reasons I bought the Music Fidelity was in hopes of solving this problem. It was exactly the same.

 

What a nightmare. I don't know what PIEP meant, but maybe look into it:

'It may be possible that it's a ground loop between sub and tt:
try to invert the power socket of rel or try a link from tt ground and
rel ground'

 

I had a rumble, but it was woofer pumping. It was all what I had my gear resting on. I have none of that stuff happening now after setting up the massive Mapleshade Sampson.

 

I don't quite understand the advice. How to invert a power socket or a link from the ground. The REL and the B&K power amp are plugged directly into the same outlet. on another wall and a different outlet, I have a Monster power strip that all the other components are plugged into. I'm 99% sure it is all on the same circuit.

 

What he wants you to do is use a cheater plug on the REL sub. Assuming it is a three prong AC plug, that will turn it into a two prong one and you can then flip the AC plug 180 degrees (you might have to file or cut down one of the spades on the cheater plug to do the flip), which will lift the ground. chadbang suspects a ground loop between the sub and the turntable. Lifting the ground will eliminate that ground loop.

His thinking is solid. I have often heard subs cause 60 Hz ground loops in stereos and this is the standard solution.

I still think the issue is mechanical, not electrical, especially since you have determined that cueing up the tonearm will mostly get rid of the rumble, but at this point we are all grasping for straws. This is a really strange problem. The question is where is the feedback starting? Normally, bass on the album is being put out by the sub, which shakes your cabinet/turntable, which shakes the stylus, causing more bass, which is then put out by the sub, and so on and so on. But in your case, the feedback occurs simply because the needle is cued down on the record and no music is playing. What is the initial source of the feedback?

I'm totally vamping here (I had no inspiration on the treadmill - sorry) but why don't you try unplugging the turntable from the wall and see if the rumble still occurs when you cue the tonearm down. Also, is the meth whore woofer movement rhythmic in any way? An amplifier when it goes bad often becomes an oscillator. I'm trying to absolutely eliminate the turntable or the Denon from being the cause of the problem.

 

Are you grounding your turntable to the external phono preamp or to the receiver? Some phone preamps don't have a grounding lug so you usually have to loosen a screw on the case (making sure to clear off any paint) to attach a ground. If your Denon doesn't have a ground wire, it's getting ground from the outer conductor of one of your RCA phone cables and that can be problematic. You may still have to connect the phone preamp to your receiver (using the screw on the case trick) to get rid of the ground loop. You can also pull the ground off of the cable using a ground loop isolating transformer. I have an antique cable I bought years ago at Radio Shack for just such debugging.

Also, make sure that you shut off the internal preamp on that Denon TT. It's a switch under the mat.

 

I wonder if it could be a bad cart? Is it possible a cart could be pumping out this. A short? Maybe pull off the cart leads and see what happens?

 

The setting adjustments in the Denon are not the most user friendly but there does seem to be many adjustments that can be made. I did get in there and the crossover frequency was set at 80hz by default and I changed from LFE to LFE+main. No progress. I am only using one input on the REL, the high level. I've tried using the others (one at a time as well) with no difference.

The fact that every other source works perfectly makes me think that the denon needs to do something different to the signal from the TT. BUT...the phonostage should be accomplishing that making that signal similar to other sources. I was thinking that it might be incompatible with the REL but if you're running analog to it without problems that might not be the case.

 

I did just switch from the Ortofon red to the blue and they have the impact.

 

Thanks but only the receiver is a Denon, the TT is a Pro-ject. It doesn't have the internal preamp. The RCA connecting the TT to the phonostage has ground wire on both ends.

 

If swapping the entire cart (not just the stylus on the Ortofon) doesn't help, what about changing the interconnects? Is the tonearm hardwired? Can you swap the phono out interconnects with others?