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Turntable Question

So I have Technics SL-1300 that I picked up recently. Got it set up with my Denon AVR-1602 receiver and a Rolls pre-amp. Sounds pretty darn good. Only problem is for some odd reason it seems to be picking up some local radio station and reproducing it at a very low amplitude whenever the receiver is set to Phono (well in this case there is no build-in preamp, and therefore no specific Phono setting -- but in essence whenever the receiver is set to the turntabnle input) even if no record is spinning. Is my needle picking up radio frequencies? How do I remedy this? Thanks!

Uptown1
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RF interference

That is always an interesting and frustrating problem. It can have a lot of causes. You can receive RF from the air or from the power line. You can shield the components so that you don't get it from the air and you can filter/absord it from the power supply.
Grounding or lack thereof is usually the fix, but it can be tricky locating the trouble spot. You may simply have a bad cable. First check the ground from the turntable to the phonostage. If it is intact, then try replacing the interconnect cables from the phonostage to the receiver (not with anything expensive, just different). If that does not solve the problem, try running the turntable ground to the receiver rather than the phonostage. If that doesn't work try running the turntable ground to the phonostage plus another ground wire to the receiver.
I guess that you are getting the idea that there is a lot of trials here to find the source. Once you find it, you are shunting it to ground by using better shielded/grounded cables. You might also try moving the phonostage to another location or using another power cord to it. Even using another outlet or line filter to plug it into. Eventually, you will find and rid yourself of the noise. The worst case is going to be a broken lead from the turntable which will be more difficult as it will require a repair. Maybe as simple as replacing the RCA ends, but a repair nonetheless. Good luck!
-Bill

Uptown1
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grounding

You can ground your phonostage to your receivers chassis by loosening one of the receivers cover screws on the back of it and attaching a wire there. You should find one that is screwed into bare metal rather than a painted one if possible, if not it should work anyway if the screw is not painted as the actual threads should be bare. You could also scrape the paint from the area just around the screw head to get a better ground point.
Have an electician take a look at your AC outlet there. A lot of old houses have three conductor wiring, but only two prong outlets. The ground wire may either be unused or attached to the outlet box. That is only if the wiring has been replaced which is possible if you have circuit breakers instead of fuses at your main panel now. If you are wired for it, it is really easy to install a proper three prong (grounded) outlet and that should not cost so much. You should also know that your power strip will offer absolutely no protection to your gear unless it is plugged into a grounded outlet. It will simply allow more stuff to be plugged in.
-Bill

Uptown1
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Re: grounding

Turntables and phonostage designs started before there were MP3 players, CD players, or even computers so they are not designed to be shielded completely from such. Those more recent products emit a ton of electrical garbage both into the air and back into the AC power chain and so have to be designed to meet FCC standards for emmisions of EMI/RFI as well as suceptibility to the same. Otherwise they would not work in any proximity to each other.
Phonostages have very high levels of gain as opposed to line level stages. For example a typical line level stage that you would plug a CD player into for instance would have a gain factor of perhaps 4 or 5 times. By contrast, a phonostage will have gain factors of 100's or even 1000's of times to achieve the same output level.
What this means is that it will amplify any signal that finds its way into that input by that amount and so any noise that gets into the phono section will be amplified along with the signal and that is one of the reasons that it is difficult and sometime expensive to achieve really good SNR figures for analog equipment.
You can check for the effectiveness of a particular ground path by simply touching with your finger (a length of wire with bare ends would offer a lower resistance) the tonearm and phonostage, the phonostage RCA connections and or chassis and amplifier chassis at the same time. This will simulate a ground connection and the noise should either increase or decrease as you hunt for the best place to shunt it. Once you find the most quiet location, then you install the actual ground wire between those points. If it is in the AC signal itself, it is going to be more difficult, but still doable and sometimes they act in tandem, feeding on each other, so by using the ground wire or swapping out interconnects for another type, you may actually be able to fix that without addressing the AC.
I am not suggesting that you neglect the AC ground though as that is important to protect the equipment, your health, and your home.
-Bill

Jim Tavegia
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Re: Turntable Question

Ferrite cores are available from Radio Shack for about $5 each and may help on your gear ac cables as well as the interconnects. This is a cheap trial as it is the same basic principle as the "lumps" on high end ac cables. If your receiver has a tuner that is basically on all the time it may be an internal issue. The Rolls phono pre may also be the issue.

Jim Tavegia
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Re: Turntable Question

You are definately becoming a member of the Michael Fremer Fan Club. When you have the resolving power of Mr. Fremer's system I have no doubt that the "cogging" phonomenon is an audible commodity. My system...probably not.

I eagerly await a review of the new Thorens 350. I hope MF gets first crack at it.

Still the best I have heard in my own home is the Thorens 850 with only a RB 250 arm. For the money... that heavy platter and belt drive was a winning combo for me. I would love to hear one with a RB 700 or better arm on it through a Manley Steel Head or the Boulder. That would be some serious Hi-Fidelity! Not the Continuum, but still pretty sweet I would think. VPI owners know how good a massive platter sounds, or doesn't sound, in actuality.

Jim Tavegia
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Re: Turntable Question

Ya, I'm nuts!!!!

commsysman
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Re: Turntable Question

In general, the comments on grounding are certainly relevant, but I have found that getting rid of the problem you speak of requires a direct fix if grounding is not found to be the solution.
Installing a capacitor of approximately .002 microfarads will usually do the trick. I would first try installing one across each of the output jacks just inside the turntable
base. This will shunt the RF energy to ground but have no effect on the sound.
If that does not do the job, you may have to install one internally on each channel of your phono preamp stage. This is a job for a knowledgable technician.

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