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Please Help Ambient Bass Resonance

I have a problem I just noticed last night. I believe it's mechanical. Perhaps the vinyl folks can explain what I am hearing and suggest a solution.

First my equipment: Lyra Delos Cartridge; VPI Classic TT; ARC PH-8 Phono Pre; ARC Ref 5 SE linestage; and ARC CD-8 CDP.

The Delos output is .6mV. The PH-8 fixed gain is 58db and its S/N spec is 75db. The Classic is grounded to the PH-8. I also use a Delrin clamp and periheral ring.

Because the Delos output is about as low as ARC recommends for the PH-8, I have to turn the Ref 5's gain up to about 70-75%. Normally, noise and hiss is acceptable.

Last night I was playing a record and I turned the gain up to 75+% and I heard a low freq bass ringing that started to feedback on itself and got louder as I left the gain up. It would stop when I turned the gain down to 65 or 70%.

I believe its mechanical because I did some experimenting with the rest of my gear. Step 1: I clicked the Ref 5 to the CDP and turned the gain up to over 95%. Dead silence. Step 2: I turned off the TT and put the stylus on the record. I heard the bass ringing. Step 3: I disconnected the lemco connector from the junction box -- that is I disconnected the cartridge from the PH-8. Turned the gain up. Dead silience. Step 4: I reconnected the cartridge and kept it suspended off the record, motor on or off, turned up the gain. Silence.

I believe that what's happenening is that the record is acting as a low freq. sound collector and the vibrations are being picked up by the cartridge and fed back on itself. Hard to be sure about the Hz level but it may be in the 60 Hz neighborhood. I surmise this because I get the feedback with or without my sub, which cuts off at 50 Hz and the him seems to come out of the bass woofers.

As I said, the problem becomes apparent when I turn the gain up past 75 or 80% with the TT on or off, when the stylus is on the record.

Any explanations and suggestions? Did I find Fishing's missing bass? Check his OP. LOL ;>')

Seriously ... what is going on?

P.S. Just tried something else. I checked the hum situation without the peripheral ring. Still have bass ringing feedback, but I had to turn the gain up even higher for it to kick in. Again, it only happens when the stylus is on the record -- regardless if the motor is on or off.

Thanks guys
bifwynne

Showing 7 responses by bifwynne

bifwynne OP
2,206 posts
 
Thanks for all of the suggestions. I think the idea that had the most chance of working was moving the TT further away from the speakers. It didn't really make a difference.

The best thing I've done so far is to use an extra rubber washer with the Delrin clamp. For those who own a VPI table, you'll know that the table comes with a single rubber washer which is put on first, then the record, then the clamp. I had an extra washer, so I put the extra washer on top of the record, directly underneath the clamp. That seemed to raise the feedback threshold well beyond the level I would ever listen to the music.

Btw, I've used MM carties before, Can't say I recall having the problem. Also, I used to use the Soundsmith Zephyr, a MI cartridge, and the Dynavector, a MC cartridge. Again, I don't recall experiencing the problem.

Just a thought -- I have a 3 gram headshell weight. I wonder if using it to increase the effective mass of the arm would make a difference??

Just thinking out loud here -- where the heck is the Delos picking up the ambient sound? Yes, there are motors throught the house and laundry room, but could that be the source? Or is it possible there is electrical inductance between the tone arm cables and maybe a power line that in some back is feeding a 60 Hz current back into the moving coil parts of the cartridge, thereby causing vibration to feedback through the system as Al described?? Al what do you think??

Thanks again.
bifwynne OP
2,206 posts
 
Thanks Al, I tried the grounding idea already. No change.

Not a lot of options about moving gear around. My wife finished the basement, carpet furniture, etc and there's simply not much I can do. So far, the double rubber washer trick seems to help a bit. At least the feedback oscillation doesn't kick in unless I turn the linestage gain up to ridiculous levels, which I never would use. There's no discernable feedback at "normal" listening levels.

Curiously, the peripheral ring seems aggravate the problem.

The delos is a nice sounding cartridge. As long as the problem doesn't get worse, I can live with it.

Thanks for the help.
bifwynne OP
2,206 posts
 
Al, quick follow up Q. Do you think using the 3 gram headshell weight would change the resonant frequency, perhaps ameliorating the problem?

Regards,

Bruce
bifwynne OP
2,206 posts
 
String..., I think you're onto something. I just tried something that is a temporary patch that seems to have nearly eliminated the bass feedback.

I have furniture pads that are used to stick onto the bottom of heavy furniture to prevent scratching hardwood floors. I doubled up on the pads and rested the mini-feet on a small part of the top pad. It seems to have nearly eliminated the problem.

You are right about the table too. It's an IKEA kitchen table. Not very sturdy or heavy. I could feel the sound vibrations on the table top, which I bet traveled right through the TT mini feet to the rest of the chasis.

Right now, I may have cobbled together an ineligant temporary solution, but I need a permanent fix. What about using a heavy piece of concrete slab that sits on styrofoam? Just sketching. Any other ideas? Isn't there something called sound bricks??

Thanks.
bifwynne OP
2,206 posts
 
Sound-Real-Audio, thanks for the thought, but I don't think my phono pre, linestage or amp clipped. If I didn't mute the phono stage, who knows what would have happened. But I muted the phono pre as soon as the oscillation became louder.

I think String... is on to something, especially in light of my meatball fix. I've got to do a much better job of isolating that turntable from the IKEA kitchen table. The IKEA table is like an antenna that is transmitting vibrations into the TT via the mini feet.

Thanks again,

Bruce
bifwynne OP
2,206 posts
 
There's another similar thread running. I read comments about using a sheet of balsa wood and using a maple block. I bet I'd have a nice TT surface by sandwiching balsa, then maple, then balsa again. I'll ask here -- where can one purchase a maple block and how thick should it be?
bifwynne OP
2,206 posts
 
Thanks Al -- perfect!
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