Yes indeed. Been reading up and he is the man for sure !
NAD 5120
- Thread starter Jlee964
- Start date
I'm glad you have no hum. It was never very loud, but they improved the ground coupling between the main bearing and the sub chassis and the arm pillar and the star earth point with minor changes. If yours has three small screws underneath for suspension leveling, its the final and ultimate version.
Yes setting up all the parameters is quite complex. I couldnt find a weight for the cartridge provided nor the compliance online , except amazon who quote 0.04kg (40g) which is I suspect the weight of the cartridge in its packaging. 5g seems about right, I weighed a Shure M75 and it was 6.
I reckon your parameters look right based on my interpretation of the Cartridge Tuning Guide, possibly the the oil damped needle at 3 ?
5g - 1.85 = 3.15 cross referenced with the curve of Q=10 ?
https://drive.google.com/file/d/1C9ZI0t9OlI1I81jz55NCMVPdICko3PR-/view?usp=sharing
Yes you are right... It was originally on 2 when I got it and adjusted to 3. So the needle is deep into the oil fluid.I'm glad you have no hum. It was never very loud, but they improved the ground coupling between the main bearing and the sub chassis and the arm pillar and the star earth point with minor changes. If yours has three small screws underneath for suspension leveling, its the final and ultimate version.
Yes setting up all the parameters is quite complex. I couldnt find a weight for the cartridge provided nor the compliance online , except amazon who quote 0.04kg (40g) which is I suspect the weight of the cartridge in its packaging. 5g seems about right, I weighed a Shure M75 and it was 6.
I reckon your parameters look right based on my interpretation of the Cartridge Tuning Guide, possibly the the oil damped needle at 3 ?
5g - 1.85 = 3.15 cross referenced with the curve of Q=10 ?
https://drive.google.com/file/d/1C9ZI0t9OlI1I81jz55NCMVPdICko3PR-/view?usp=sharing
Also couldn't find the parameters for the cartidge to use reference the second graph. Anyway sounds good.
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Wow, also very clever. Wonder if it works well ?
Jives11,
Haven't used the turntable for a while but it now has a hum. Have checked the wire to the phono stage and it is suitable grounded.
It has a backgroud hum now and wasn't there before. How do I get rid of that hum or what do I check and how ?
Thanks for the words of wisdom
Well hum can be caused by 3 or 4 different things and they are not necessarily mutually exclusive, so you can get a choir of hum. You mention its background, so I assume you can hear music on both channels, and perhaps the hum is only noticeable during quieter passages or when you are close to the speakers or using headphones. I ask because if the arm wiring was broken , often you get VERY loud hum and no signal through one speaker.
I assume nothing has been done to the deck i.e alterations too ? There is not much you can do but installing RCA sockets is one thing and not dressing the wiring properly can cause problems.
I think the first step is to rule out the motor as a cause, so if you turn off the deck at the wall, even unplug it, but on the amp/receiver behave as if you are playing a record i.e select phono, turn the volume up, is there hum present ?
with the motor off we are ruling out mechanical hum and EMF from the motor being picked up by the cartridge. Some cartridges such as Grado have a tendency to be susceptible to motor magnetic fields. Most of these decks in the UK seem to have had an ortofon OM series cartridge and these appear quite hum resistant.
Next, dressing the leads coming out of the deck so they are clear of any mains cables is also a good idea. The standard cables are just about OK, and I speak as a total cable sceptic. I'd keep them away from any other power wires or transformers
If you turn the deck on, does the hum increase as the arm arcs across a record i.e the cartridge gets closer to the motor ? That would suggest the cartridge is susceptible to the motor EMF ?
The hum grounding issues I alluded to are the poor electrical contact between the major metal parts in the deck (NOTE: I don't mean the the motor). If you have a multimeter , set it to continuity or the 100 range on resistance and test from various points on the deck (the tip of the platter spindle, the side screw head on the arm pillar) all the way to the tip of the ground wire. You want there to be a circuit and the resistance to be as low as possible, this will reduce hum from the arm wiring from the tone arm socket to where the thin tonearm wires meet the main black interconnect wires.
I can't recall if you have a flat or round arm model and what colour the front light is. The later RED LED models show some effort to improve electrical continuity for example metallic thrust pads in the bases of arm and main bearing wells. Also a green wire from the base of the arm pillar to the star ground point, check to see its not broken.
With the flat arm they added metal cueing handle which fastens using the same bolts that hold the cartridge. I'd suggest removing it as its not really needed if you are careful and I think it actually shorts the two signal grounds as the only insulation at that point is the Green NAD paint. The dot pattern on the arm suggests to me it was designed not to have the side lift. If you need one make one from plastic is my advice
Plenty to think about. I think some residual background hum is inevitable with these decks, its a question of getting it as low as possible
Jives11,
Nothing done to the deck, hum is low constant background hum, music from both channels is fine.
However, the hum noticeably increases if I touch the middle spindle and a a little bit more if touch the cartidge
Tonearm seems seated properly.
thanks. I think you will never gets these decks perfectly quiet as the signal wires from the cartridge to where they join screened interconnects, are not really screened at all, in contrast to a typical tonearm with a metal tube. But it's possible to get them quiet enough when listening from > 1M . Sorry to ask, but is it possible this amount of hum was always present but you have just noticed it ? It's impossible to unhear something, I know from similar experiences. I don't know if you have another cartridge to try just in case, the ortofon OM series were popular in these decks. I know Grado cartridges have a reputation for humming due to the absence of a metal screen in the cartridge body.
Do you have a simple multimeter with a resistance scale ? if not I'd urge anyone to get one, there are simple ones on ebay for < £10 and they are massively useful both with diagnosing audio problems and around the house.Most of the time I use the continuity/resistance reading to establish how good the circuit is between two points.
In this case I'd test from the tip of the spindle to the end of the ground wire, and from the metal arm pillar (the side grub screws are a good point) to both the tip of the ground wire and back to the spindle. There should be a circuit (continuity mode will buzz) and the resistance should be as low as possible. On more conventional decks with impeccable star earthing arrangements, its < 10Ohms. Here it may be more.
If the arm pillar to ground is open circuit (infinite resistance) I'd suspect that a wire has broken free which links the arm pillar to the ground point. Alternatively you can see if this is so but it means removing the arm and the top of the plinth
Check that the copper foil washer is on the spindle (upper side) and this contacts the bare metal part of the metal sub platter
the remaining things which help are quite invasive. Both the arm horizontal bearing and platter bearing are the same fitting, a black inverted-mushroom shaped bushing with brass sleeve. Its hard to tell from looking but the bearing sleeve is open at the bottom, so originally the thin platter bearing made point contact with the metal sub-chassis ! Having dismantled a number, some have a plastic disc in the bottom which acts as a thrust pad. These are about the size of this letter "o". I'd guess these might have been used to address some rumble ? Not sure, but they unfortunately insulate the spindle from the ground route. Even later metal "o"s were used and these complete that circuit, and I have seen examples of no o, plastic o and metal o. metal o was used last I think, and again improves the ground continuity from spindle to sub-chassis to star earth point to ground wire. I've tried to locate former Livotel employees to get their input, but no luck and sadly Jiri janda died back in the 90's.
Jives11, I switched out the cartidge to a Rega bias from the K9 and that has sorted it. It appears the wires to the cartidge were not as tightly attached to the cartidge as they should be - pulled off cartidge super easy. I recrimped them a bit tighter to fit the Rega and all
Is well. I think if I put the K9 back on, it would be fine too. Bit alas, already changed cartidge, aligned and balanced to correct tracking weight so will leave it on. Thanks for the useful advice again !. A real oracle of info on these quirky turntables. Still enjoying it as my second deck
It is the red led version so presumably this is the later version as you mentioned ?
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I want to say couple things about Tesla - NAD 5120 80's model. Even an interesting model from mechanical point of view, and declared as 70 dB S/N, it has some electrical designing issues that induces hum, are obvious, but that can be fixed. The main problem is that 230 V circuits are around two edges of the device, and to be sure that is no way the hum is missed, the neon bulb is just couple cm next of the cartridge. What kind of accoupling is mostly, inductive or capacitive? It is easy to find. If you have the signal cable of NAD 5120 connected to the preamp and the audio system on at a bit higher level, if also are able to deal with electric circuits with no accidents, just connect a single pine of the power plug of the NAD 5150 to the hot power hole of your wall socket and you will get a "nice" hum. That means that by parasite capacity between power circuits of the device and audio circuits, including the cartridge, the S/N is affected since the design. The effect is variable and depends also of the quality of the cartridge. Anyway if the capacity is only 1 pf, at the value of 230V effective and 50 Hz 0f power supply, if taking in account only DC resistance of cartridge of around 400 ohm, still induce at list 0.02 mV. If the output of cartridge is 4 mV/1000 Hz, compare to 0.02 mV only 46 dB of S/N remains. If take in account that at 50 Hz (3180ms) RIAA EQ means + 17 dB, only 29 dB remain of S/N. Ok when evaluating S/N is also about the distribution in frequency, etc. but the real result is a bit wrong to the ear. Is something possible to reduce the hum? Yes, the AC should remain just where it is needed, close to the motor. If a diode bridge on the alternative pines is serial connected to the motor, next to motor and if you short + - pines of the bridge you will make the motor run. From + - of the bridge you can go by screened cable to the start switch that can be serial with a proper connected 10 mA LED diode. This way the whole AC circuit for starting motor became a DC one. A condenser similar to the one on the start switch should be also connected parallel with alternative pines of the bridge to reduce the on/off click sound. The one from the switch can be removed an installed in parallel with + - of the bridge. The power supply cable can be replaced by 3X0.75 screened cable. The screen of power cable is only connected to the ground at the socket. The third wire of the cable is connected also to the ground and also to the screen of the cable going to the on/off switch. The case of motor is also connected to the ground. NO CONNECTION between power ground and signal ground going to preamp.