Bouncing tonearm when touching chassis

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75Turntable
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Bouncing tonearm when touching chassis

Post by 75Turntable » 17 Dec 2017 17:17

The tonearm on a CEC BD1000 bounces like crazy when playing a record a one touches the sub-chassis. Even a light touch causes the needle to skip over. I do not think there are much option there, because it has only a anti skate weight that rubs against the tonearm and cannot be adjusted as far as I know.
The original CEC headshell that came with the BD1000 turntable is used along with a Tenorel cart and needle.
This one;
Type moving magnet
Output Voltage 5.5 mV
Frequency Response 15Hz - 45kHz
Tracking Force 1 - 3g
Mass 7g
Channel Separation 25dB
Channel Balance 1.2dB
Load Impedance 47k ohms
Output Impedance 520 ohms
Dynamic Compliance 25 x 10-6cm/Dyne


Any thoughts or tips on this would be greatly appreciated!

thanks,
Dan

75Turntable
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Re: Bouncing tonearm when touching chassis

Post by 75Turntable » 17 Dec 2017 17:19

Some info of the CEC BD1000.
There seems to be an error here in the info btw, 7,0 kg should be 7,5 kg
as stats the manual.

Power supply: 220V 50Hz

Drive System: belt

Motor: AC synchronous

Speeds: 33.33 and 45rpm

Platter: 30cm 1.1Kg aluminium

Wow and flutter: 0.12%

Rumble: -62dB

Tonearm effective length: 215mm

Overhang: 15mm

Phono cartridge: MC 11

Tracking force: 2.0g

Frequency response: 20Hz to 20kHz

Replacement stylus: MC 11 S

Dimensions: 435 x 348 x 165mm

Weight: 7.0kg

Japi Roelofs
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Re: Bouncing tonearm when touching chassis

Post by Japi Roelofs » 17 Dec 2017 18:21

These turntables have a sprung subchassis. The springs cause the bounce, this is why there were pieces of foam rubber stuffed inside them. Over the years the foam perishes. You can stuff new foam inside the springs, this will dampen them and it should reduce the bounce considerably.

tlscapital
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Re: Bouncing tonearm when touching chassis

Post by tlscapital » 17 Dec 2017 19:39

I don't know these turntables but if I understand correctly your "bouncing tonearm" issue, when one touches the plinth, that you called the sub-chassis in your post, it makes the springs of the platter sub-chassis bounce and the tonearm on the spinning record bounces back. Is that right ?

If so, this is because the static force of the turntable needs more weight. A good tweak is to redo the bottom plate and uses something heavy in or on it. This will greatly improve it's bounce when touched.

If you were describing another sub-chassis issue when touched, I'm at a lost since how can one touch it while a record is spinning on the turntable at the same time ?

Or did you mean when one touches the top plate covering the chassis (as named in your title post) inducing the suspended sub-chassis springs to make the platter to wobble making the tonearm to bounce ?

That should indeed be the sign of the springs being too loose I believe. So dampening them some could participate but readjusting them could Help a lot also. Then once again with more static force, the turntable should be less subject to any external disturbances and such little accidents.

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Re: Bouncing tonearm when touching chassis

Post by 75Turntable » 17 Dec 2017 20:04

The foam in the springs were taken care of. So that should be an issue anymore I suppose, except if it had a sturdier type of foam which was somewhat hard to determine as it indeed crumbled to dust.

@tlscapital
What I meant was that even the slightest touch on the sub chassis, not the plinth, makes the tone arm skip like crazy. And I mean the slightest. I am aware of not tapping or something like that during play but even if one were to slide off a piece of dust of the sub chassis it bounces up and down, way more than other similar turntables that has the same construction principles. For example the Pioneer PL12D, (which I believe to be a CEC product as well) has less problems with that.

I discovered it also having a dampening problem. The tonearm cues way too fast up and down. Were can you apply the dampening fluid?

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Re: Bouncing tonearm when touching chassis

Post by musicmn » 17 Dec 2017 20:32

Hi, I have had this same issue with a number of turntables with the spring suspensions. And putting stiffer foam in the springs does Help a lot. I have tried various types of foam and have found that the type used for plastic flower arangments works well. It's not super stiff and the give it does have is just enough to soften the springs. On some turntables I have installed the shipping screws and just gave them a couple of turns to stiffen up the springs and remove some of that bounce. The damping fluid goes on the cue rod it self. And I believe 300,000 wt silicone damping fluid should work well with that tonearm. Some of these cue rods have a thread on them along with a nut and a spring that can be adjusted to speed up or slow down the drop rate of the tonearm. You might just need to adjust the nut if it's available on that cue rod. I hope this helps.

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Re: Bouncing tonearm when touching chassis

Post by tlscapital » 17 Dec 2017 21:15

Your turntable should look like this;
Capture d’écran 2017-12-17 à 20.51.46.jpg
(150.79 KiB) Downloaded 352 times
The wood is the plinth.
The silky finish black painted alloy plate glued on the chassis is the top plate.
The sub-chassis is underneath the platter and so with the platter on invisible and untouchable.

Is that right ? I couldn't find much info on this turntable. So unless the silky finish black paint is applied directly on the chassis, this turntable would have no top plate then. Feel free to correct me or tell me better. I learn to be proven wrong without too much effort when acknowledge. Cheers !

75Turntable
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Re: Bouncing tonearm when touching chassis

Post by 75Turntable » 17 Dec 2017 21:18

Hi! It does have an adjustable rod and I already tried adjusting but it only makes it more fast rather than slow :?
I will have to order some fluid I guess. The problem is that I will just have to find out where to put it, I will try first what you said and see what happens

I am not quite sure I understand which foam you refer to

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Re: Bouncing tonearm when touching chassis

Post by musicmn » 17 Dec 2017 23:38

Hi 75turntable, the silicone damping fluid goes on the cue rod it self. If this turntable is like a Pl 12/12d,ect, to remove the cue rod you first remove the cue elevator by loosing the grub screw that holds it onto the cue rod. The grub screw could either be a slotted type screw or a hex head screw. Once the elevator is removed, then from the inside of the turntable you will need to remove the cue mechanism. Or you might just be able move it out of the way if CEC used a cable and wire to make the cue rod go up and down. Then it's just a matter of pulling the cue rod out of it's housing. Now be careful if the cue rod does not want to come out look closely at the rod where the grub screw hits on it. Sometimes the grub screw can leave a burr on the rod and if you try to force the rod out of the housing with this burr on it that will damage the inside of the housing. If you see any sign of a burr on the cue rod use a small file to remove it and then pull the cue rod out of the housing. Some cue rods have small grooves in them that's where you apply a small amount of the silicone damping fluid. If you find that your turntables cue rod has no grooves then place a small amount of the silicone damping fluid on the middle of the rod and insert it back into the housing. Push the rod up and down and rotate it to spread it evenly on the rod and in the housing. Assemble the cue control, then flip the turntable over and install the cue elevator. Install the head shell with the cartridge, then balance the arm and set the tracking force for your cart. Then give the cue mechanism a try. If you like the way it drops leave it be, if it's to fast you will need to add more damping fluid. If it's to slow then clean off the damping fluid from the rod and apply just a little less fluid to the rod and assemble every thing and try it again. You can even try adjusting the nut on the cue rod and see if this changes the tonearm drop rate before you tear everything apart again. It's a trial and error kind of service.

The foam I'm referring to is used to make silk flower arrangements and the like. This foam is not to hard or brittle so it can be shaped. And it has enough give to let the springs do there job. Another good foam is the type that is used in packaging of electronics this foam is similar to packing peanuts. Again it can be shaped to fit inside the springs and it also has some give for the springs. Sorry for the long post but I hope something here helps.

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Re: Bouncing tonearm when touching chassis

Post by nat » 18 Dec 2017 00:31

Have you balanced the arm, set the tracking force scale slip ring to 0, and then turned the counterweight until the scale now reads 2.5 grams or so? You might simply be tracking at too low a tracking force, either because the arm wasn't balanced and the scale zeroed properly, or because you have the common impression that lighter force is gentler on records - it's not. The needle needs to stay in firm contact with the groove so that it doesn't start crashing around from side to side. In your case, feedback, not just mistracking is happening, so it's a worst case scenario.
Vinyl is pretty resilient, and apparently the pressure and frictional heat as the stylus passes over it liquifies it momentarily, and it essentially bounces back as it cools. But being smashed with an errant stylus is going to gouge and dent the groove, and it can't bounce back from such damage. So, outside of laboratory conditions, it's safer to use a tracking force in the upper half of the manufacturer's recommended range.
Obviously different cartridges and different stylus shapes require different tracking forces to be at their best, so my recommendation is not to just jack up the tracking force to 11 (which is one more than 10), but to start with something nearer the top than the bottom of the recommended range. Then you can fiddle around and see what you can get away with.
Obviously all the recommendations about getting the suspension tuned up are good, but I think your problem may be simpler than that. If, after checking the tracking force, you still have problems, check to make sure that the top plate lock down screws have been loosened - if the top plate is screwed down to the base, you have no suspension.

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Re: Bouncing tonearm when touching chassis

Post by smee4 » 18 Dec 2017 02:05

I would lock the sprung table down using the travel screws, then provide suitable vibration damping under the wooden plinth.

75Turntable
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Re: Bouncing tonearm when touching chassis

Post by 75Turntable » 20 Jan 2018 20:08

I would lock the sprung table down using the travel screws, then provide suitable vibration damping under the wooden plinth.
That's exactly what I did, and it works. Maybe, not the solution you want but anything else fails.
Thanks

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