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Harmonic Feedback Through Turntable!

racfan9

racfan9

Super Member
I've been working on an old Silvertone console for a friend. The original record player with ceramic stylii was junk so I decided to put a mid-80's Sony in place of the original. I had to use a phono preamp since it was a magnetic cartridge, anyway it sounds great until I get to 1/2 volume then I start to get a low hum and vibration which seems to run up the tonearm. Anybody out there have any suggestions or fixes for this issue. I did cut a piece of 1/4 inch foam and set the turntable on it hoping to isolate the table from the cabinet but that didn't help.

Thanks,
racfan9
 
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Yes, the quick and easy way to minimize feedback like this in the same cabinet is to swap the polarity of both speaker channels. The theory is that if you have a positive acoustic feedback loop now, reversing the polarity of one end of the loop will help reduce feedback.

It may not completely correct it but should help. Next thing to do is to isolate the turntable at all possible spots. Also, lower the gain on the phono preamp will help take things down a notch.

Cheers,

David
 
Hi
Yes. Probably is running up the tonearm as you think. Try moving the table out of the console using longer cables and see if it helps. Then you will know if the path of the sound is coming through the suspension or being absorbed by the tonearm and resonating. The console may have a peak that matches something in the turntable. The new cart could be feeding the console more of some frequencies than the old one. You can either try to identify that peak in the sound spectrum and reduce it or try to damp the chassis of the turntable or the tonearm depending ou which one resonates. Search on resonance, turntable, feedback and the like. There are a lot of ways to handle it.
 
If you find this unfixable, you have company. I tried to put a Dual 1009 in an early-60's Magnavox "Stereorama" console, and got insuperable feedback regardless of polarity. I had to back out the change and go back to the old changer and cartridge. (That was the beginning of the end for the Mag, as I was becoming aware of how it was beating up my records.)

Dave
 
Isolation is going to be your best bet. The originals had somewhat marginal bass response and spring suspension to deal with this stuff. Bump the bass control down some if you can, and maybe see about putting springs under the new turntable to help isolate it.
 
I've got a 1976 Magnavox SS Console that I swapped out the original W750 changer for a more modern TT.

Same as you, I had to install a phono-pre etc...

First TT I tried in there I could NOT seem to overcome "feedback," this was a 90's Crap-tastic Sony table. Isolation (I tried springs, rubber/gel mats etc.) helped but some frequencies would just start to reverb through no matter what.

Finally got sick of it and tried another TT (kept the same phono-pre, wiring, grounding etc.). Second TT was an 80's (also crap-tatstic) Fisher Studio Standard Linear Tracker (MT-728). No isolation needed and have never had a feedback issue again.
As well, the console itself has never sounded as good (IMO it sounds very good considering what it is)

My theory is that the reverb was traveling up the tone arm, and the Linear Tracking arm is "more isolated" than a standard arm... again just a "theory."

In summation: My suggestion, if all else fails...try a linear tracker.


Good luck!
I think console modification is great fun!

Ben
 
polypetalous said:
I've got a 1976 Magnavox SS Console that I swapped out the original W750 changer for a more modern TT.

Same as you, I had to install a phono-pre etc...

First TT I tried in there I could NOT seem to overcome "feedback," this was a 90's Crap-tastic Sony table. Isolation (I tried springs, rubber/gel mats etc.) helped but some frequencies would just start to reverb through no matter what.

Finally got sick of it and tried another TT (kept the same phono-pre, wiring, grounding etc.). Second TT was an 80's (also crap-tatstic) Fisher Studio Standard Linear Tracker (MT-728). No isolation needed and have never had a feedback issue again.
As well, the console itself has never sounded as good (IMO it sounds very good considering what it is)

My theory is that the reverb was traveling up the tone arm, and the Linear Tracking arm is "more isolated" than a standard arm... again just a "theory."

In summation: My suggestion, if all else fails...try a linear tracker.


Good luck!
I think console modification is great fun!

Ben
Click to expand...

Bet it's the length of arm (i.e. short!).
 
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