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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
sidssp
1,077 posts
 
What you are experiencing is indeed feedback into your cart. It is very common
in LP playback. There are many ways to solve this. The key is to place the TT far
enough from the standing wave or at a base null. Since you didn't post a picture
of your setup, it is difficult to imagine where the problem might have been. I am
going to list a few things for you to try out.

If your TT is inside a cabinet, take it out. Cabinet will increase resonance.

If your TT is placed at a corner of your room, move it out of the corner. Standing
wave is stronger at the corner.

If your TT is placed very low close to the floor, move it to a higher place.

If your TT is placed in between two speakers, move it in and out a foot or two to
see if the situation improves.

With bass heavy music playing, walk around the room and listen at the hight
where your TT can be placed and listen for bass null. If you find one, that will be
the place to move your TT to.
jjrenman
279 posts
 
I agree with all of the above excellent recommendations. However I had a similar situation develop and found that I had to to decouple my TT from its shelf as well as the tube phono stage from its shelf before I could eliminate the feedback altogether.
tanathen78
25 posts
 
Check the ground between your tt and preamp. The signal seems to be from the platter from what you are saying. If you want to test it to confirm take a piece of wire connect it to the same preamp ground and touch your platter while the cartridge is lowered but not while its spinning. If that takes care of it, call vpi and see what they suggest for the best grounding solution. If that's not the issue, make sure your cartridge is hooked up correctly, I know that seems silly but I've made that mistake before when swapping out a cart. Hope you get it worked out.

Regards,
Bill
buconero117
2,311 posts
 
Acoustic energy is one possible reason, assuming the condition only exists when music is actually being played. Find a way to acoustically shield the equipment as a test.
sounds_real_audio
1,012 posts
 
When you say you turned up the gain to 75% just what do you mean. Is that 25% below the point where your amplifiers would clip, or just 75% of where the dial would turn?
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