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Humming Away


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This may be a bit beyond the 2-Channel forum postings; my system is more of a 4-Channel setup.  I cranked up my system tonight, as the wife was out.  I started with some LP's on my Merrill-Modified Thorens 160HD turntable into a McIntosh MC130 preamp.  Twin monoblocked McIntosh MC2125 powered Belles in the front, and McIntosh MC2200 powered Fortes in the rear.  Once I had the volume up to 50/100 on the preamp, there was a hum which became progressively louder as the volume increased, to the point it overpowered the sound of the music.  I normally listen at volume levels of 15-30/100 on the preamp, so I had not noticed this before.  The hum was not present when I listened to CD's through my McIntosh MCD 7007 CD player, regardless of the volume.  The turntable is grounded.  Everything is plugged into a MonsterPower HTPS 7000 Powersource.  I'm getting some serious feedback (not the good kind) from the turntable.  Any ideas of where I should look to resolve the issue?  I rarely, if ever push this system.  Still, I would like to keep the sound from the turntable as pristine as I can.  

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It's enough to make you a luddite!


Someone who is more into turntables than I am will probably help you.  When I used to have my Thorens turntable set up, there was hum at high volume levels.  From CD players, nothing (except music).. 


Does your tone arm have a grounding wire?  I think my SME did.


I'm not sure what you mean by feedback in this case, but does the "feedback" and hum happen when the tonearm is suspended over the LP, but not playing it? 

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OK, here is what MAY help, depending on a number of things, such as:  Is your turntable ISOLATED from effects of reverb?  If this is the cause, then you need to look at what the turntable is sitting on, AND you may need to pay attention to the turntable dust cover, because dust covers are notorious for throwing reverb back to the stylus.  ME? I have found that the HEAVIER and MORE STABLE the platform the turntable sits on, the less chance of reverb affecting it from the FLOOR (ESPECIALLY if the floor is NOT a concrete slab!).  As for turntable dust cover issues, the dust cover can ACTUALLY reduce the effects of reverb UP TO A POINT, beyond which it will magnify the problem, acting as a DRONE speaker cone and throwing that reverb to the stylus.  How far from a reflective wall is the turntable (with its dust cover); you can put a curtain between the wall and it, and that will act to reduce reverb effects, but PRIMARILY only the reverb coming at it from directly BEHIND it (you have to think out of the box for reverb coming back from opposite walls or corners).  Reverb effects a stylus as the decibels in the room increase, so the louder you play the music, the worse the possibility of reverb effects on the stylus.  The lighter the stylus tracking pressure is, the more open to reverb effects the stylus becomes.  BLUF:  insulate the turntable from possibilities of reverberation affecting it; increased weight AT the stylus tracking point reduces the effects of reverb; Mass of what the turntable sits upon reduces the reverb coming from the floor, because that mass stabilizes the floor itself (especially for suspended floors!).  A suspended turntable is a wonderful thing, and eliminates a huge amount of reverb effects possibilities, due to severely reduced reverb transmitted through mass to the turntable body, and to the stylus.   Take some 17-ply Baltic Birch, put a piano hinge at its rear mounted to the wall (be sure to GREASE the hinge thoroughly so that it can't RATTLE any), then hang from the two chains from the ceiling which will each go through a large hole at the front corners of the wooden panel; then take some short lengths of all-thread or brass welding rod and slide one through the link of the chain which is directly underneath the hole at each corner to hold the panel up at its front.  take a torpedo level and play around with it until everything is LEVEL (BE SURE YOU ARE USING YOUR TURNTABLE OR SOMETHING IDENTICAL TO ITS WEIGHT TO SIT ON THE PANEL WHEN MAKING THE ADJUSTMENTS!)  Once everything is level...tighten everything down, then insulate the wall behind the turntable, and see the HUGE difference this kind of turntable platform makes!  It really works!  Just be sure that nobody bumps into it when the turntable is playing.  I used to have this kind of suspended set up with tiers of panels, the top tier had a TEAC A2340R reel machine, the next panel down had the turntable (Technics SL-1300), the next panel down had an H/K 900+ quad receiver, the lowest panel had a Technics RS-676-AUS cassette deck.  And with all of that mass being suspended the stability was AWESOME!  feedback on the turntable...NILL!  Just ask Jim Hunter, he saw it and heard it...and he was walking around and every step he took the floor of that old farmhouse just south of Emmett, AR would shake, but the equipment was NOT affected by that, or much of anything else!


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