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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
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.
sounds_real_audio
1,019 posts
 
I suspect your amplifier may be clipping which is why I asked. This will make things go haywire.
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
stringreen's avatar
stringreen
6,501 posts
 
Bifwynne....your light Ikea table may be perfect for a Linn, however, as I said before...you have to have a solid support for your VPI. If you have a light budget, even get pavers, cinderblocks, etc. to support your VPI. Those isolation pads are not the audiophile answer. As I said before...a SOLID path to the center of the earth is what you are looking for.
jjrenman
279 posts
 
Glad the "pads" are helping out the situation. They are decoupling the TT from the resonances of the shelf that it is sitting on. Something I suggested you look into in an earlier post.

It is the opposite approach of Stringreen which seeks to couple the shelf and table to "the center of the earth" which is highly effective but can be costly or impossible to do in some situations.

If you can't switch to a much more solid base you can experiment a bit by adding some other dissimilar materials with the "pads" to possibly gain even better isolation from the shelf. You can try layering say a maple block on top of pads than another set of pads then the TT. Some TT makers build their plinths in a similar manner.
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