A Test of my Turntable that I don't Understand

welcomdmat

welcomdmat

Super Member
I wish I could have created a better title to this question. Please know it is only because I don't understand.

I have adjustable gain on my amplifier. I usually set it so that my volume is loud at 10ish. That puts my amp gain at 8-8.5. I have set it so that loud is 11, and that puts me at 8 to a little under.

My amplifier goes from 7 to 5 -- as does my preamp volume

I was doing a test on my turntable and whether I would benefit from more shock absorbing feet. I set my amp around 10. I set my volume to 8. I put my needle down on a record that was not moving. I turned my volume to 9. I turned my volume to 10.

At this point, I sat down to write the person I was corresponding with.

Suddenly, the sound started to get louder. Then it started to get exponentially louder. I ended up diving across the room to turn the volume down -- and it was not that loud to begin with.


What does this mean? Does this mean that I have a huge amount of feedback even at low volume levels? What is my best course of action to solve this?

I have my speakers on stands. They are not particularly aimed at the table that holds my turntable/ preamp/ amp. I am on a concrete slab. Foot falls and drops have never caused a skip.

I had a moment of concern that the whole bit was go before I reached it. The exponential increase of volume from a system where the record was not spinning really caught me off guard.
 
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The fact that nothing dynamic was happening probably lead to a situation where feedback could dominate the system. Has anything like this ever happened while actually playing a record?

Feedback happens when whatever frequency is feeding back excites a resonance (in this case, in your cartridge/stylus most likely). It's possible that playback, with it's infinite variability doesn't allow for this to happen but with the needle just sitting on the record there was nothing to stop the system from simply exciting at whatever frequency caused the issue.
 
Somewhat comically, I have had a spinal injury that gets tweaked every now and again. It is from a skateboarding accident when I was 13. It is out of whack right now.

The volume when up so quickly that I moved to turn it down with speed and force -- and then vomited in my bathroom sink from the radical increase in pain.

Not a great story, but it does give an idea of my concern and the speed of volume increase.
 
I get it with both cartridges. It seems to be more tied to my amplifier than my preamp (gain as opposed to volume).

I have used a Shure M97xE on a Technics headshell and an Audio Technics VM540ML on an AT-HS10 headshell. The preamp is a McIntosh C712 and the amp is a McIntosh MC2100.

If I have the needle on the record, I cannot turn the gain on the MC2100 up past about 11 without the speakers giving a feedback that increases in volume very rapidly.
 
I can take the volume to the top and the gain to the top -- but not if the needle is in contact with a record.
 
welcomdmat said:
I can take the volume to the top and the gain to the top -- but not if the needle is in contact with a record.
Click to expand...
I can offer a theory... When your stylus is up in mid air, it's not picking up enough vibes (resonances) from the environment and there's basically, nothing substantial for the amp to amplify. When you drop the stylus on the record, it picks up all the resonances from the environment via the feet, the deck, the spindle and now you got signal in your pre-amp. Since you cranked up the gain almost to max, your pre-amp is now overloading the phono input of your amp (exceeds the maximum input sensitivity), and the result is an ever cascading feedback loop. The same thing would happen if you actually play music, but the amplification would just be too much for your speakers and ears.
 
tnsilver said:
I can offer a theory... When your stylus is up in mid air, it's not picking up enough vibes (resonances) from the environment and there's basically, nothing substantial for the amp to amplify. When you drop the stylus on the record, it picks up all the resonances from the environment via the feet, the deck, the spindle and now you got signal in your pre-amp. Since you cranked up the gain almost to max, your pre-amp is now overloading the phono input of your amp (exceeds the maximum input sensitivity), and the result is an ever cascading feedback loop. The same thing would happen if you actually play music, but the amplification would just be too much for your speakers and ears.
Click to expand...

Would that mean my turntable handles resonance at all reasonable volumes, or does it show that my environment necessitates increased care with regard to turntable isolation?

I think I understand what you are saying. I am not sure what my best course of action is (if any is called for)
 
This is relevant mainly to the turntable itself and the amount of gain level, not the cartridge or the amplification. A really good isolated turntable should do better at resonance and feedback management. Remember that analogue record playback is a process of sensing vibrations from the record surface, physics.
 
Your turntable handles resonances at all volumes in the same way - it's just that suddenly you had become aware.
It does show that resonances exist in your environment and it almost always does. You can always go nuts about it and
add granite slates, vibrapod feet, sorbothan isolation and be OCD about it, but it was never intended to be used in the
way you described. As long as you keep your gain level within the amp's input sensitivity range, and the amp's volume
reasonable for the room you're at and for the distance the speakers are from the stylus, you should be OK.
Is this a Technics turntable? Oh boy... these things are designed to handle a lot but there's a limit to what any turntable
isolation can take.
 
It is a Technics turntable. Perhaps that is a sign that I am asking more than is reasonable from a cost/ benefit point of view.

The whole thing is because I was looking at different feet. My turntable seemed to pass the test that the dealer asked me to perform. I then when all Mythbusters on it, and I got an outcome that I didn't expect.

Would sorbothan feet remove this feedback loop amplification? I am not clear if they would have an impact.
 
Depends on whether the loop is thru the base and shelf, or thru the air to the record. If number one, isolation feet may or may not help. If two, a record clamp may or may not help.
 
welcomdmat said:
Would sorbothan feet remove this feedback loop amplification?
Click to expand...

If you have a feedback loop it's too late. You may want to mitigate what's causing it.
  • Sorbothan feet can help isolate your turntable from the environment. It actually absorbs some of the vibrations and transforms them from mechanical energy to molecular level heat, so there's less of it to travel to the stylus.
  • Mass helps combat resonances for the same reason. The more of it, the better.
  • Wall mounting helps when you want to isolate your turntable from bouncy floorboards that create resonances when you walk on the floor.
  • Spikes might help decouple resonances from your turntable.
  • A combination of granite slates (mass) sandwich separated by Sorbothan all on top of spikes might help too
  • An industrial rubber band trampoline would likely do the trick as it did for DJ's in the big apple clubs in the 80's...

All of these methods will help you combat environmental resonances.
None of these would help you stop a feedback loop.
Best use the appropriate gain/volume for the environment.
 
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Post a photo of how the speakers and turntable are set up. Could help us see a problem with the room.
 
Just don't put the stylus down on your record without the record turning. Then you shouldn't get the acoustic feedback loop. Why did you do this test? Is there a problem when you are actually using your turntable to play records?
 
Was your dust cover up or down? Some turntables perform better with the cover on and others with it off.
 
This does demonstrate an isolation problem with your turntable setup. Many systems would do this if the loudness was sufficient, but good setups shouldn't.
 
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