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ELAC Miracord 50H thumpa-thumpa sound... other causes than idler???

S

ssmolkin

New Member
I recently had the good fortune to acquire a 50H that appears to be remarkably good condition. However, when I play, I get a thumpa - thumpa sound from the turntable, continuously repeating with no silence in between. Playing at different speeds (other than 33 RPM) causes the same problem.

I'm brand new to working on turntables and understand that the most likely cause is a flat spot(s) on the idler pulley. But, before I spent around $40 to have the idler re-rubbered, I'm wondering if there is any other likely cause I should check that would cause this continuous thumpa-thumpa when playing?

Or... is there a good way to confirm that it IS the idler pulley? Visually I don't see any evidence of flat spots (although perhaps these are unseen to the naked eye?).

Thanks in advance for any suggestions. Right now, this noise is too loud to enjoy the turntable.

Cheers.
 
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Measure the inside of the platter and the idler wheel diameter to figure out the ratio so you can calculate the RPM of the idler wheel. Now time the "thump, thump, thump" for 30 seconds. Is that number equal to half the RPM of the idler wheel? If so, it's the idler wheel.

BillWojo
 
ssmolkin said:
I recently had the good fortune to acquire a 50H that appears to be remarkably good condition. However, when I play, I get a thumpa - thumpa sound from the turntable, continuously repeating with no silence in between. Playing at different speeds (other than 33 RPM) causes the same problem.

I'm brand new to working on turntables and understand that the most likely cause is a flat spot(s) on the idler pulley. But, before I spent around $40 to have the idler re-rubbered, I'm wondering if there is any other likely cause I should check that would cause this continuous thumpa-thumpa when playing?

Or... is there a good way to confirm that it IS the idler pulley? Visually I don't see any evidence of flat spots (although perhaps these are unseen to the naked eye?).

Thanks in advance for any suggestions. Right now, this noise is too loud to enjoy the turntable.

Cheers.
Click to expand...

408A Rubber Renue by MG Chemicals

https://www.mgchemicals.com/products/electronic-cleaning-products/specialized-cleaners/rubber-renue/

it’s some rather toxic stuff, but it’s amazing when used properly.

8AF53F36-52BB-4C66-B141-CA41BC86458F.jpeg


It expands the rubber for a proper cleaning.


use a Q-Tip and scrub the idler wheel until you don’t get any dirt off it. Will take a good 30-40 Q-Tips and some scrubbing but you will be left with soft new grippy clean rubber. I use it on my tape decks on pinch rollers and idler wheels that I’m not able to find replacements for. The stuff is pretty amazing but again super toxic. Where gloves and a mask.

$13-15 on Amazon or eBay

good luck with it!
 
I did once have a problem with a Garrard that turned out to be a strand from a brush stuck in the bearing. Every time one of the bearing balls rolled over it, it would make the platter vibrate and caused a funny noise. That happened about once per revolution.

Multiple times per revolution sounds more like idler problems.

Sometimes you can chuck the idlers in a hand drill and use sandpaper or an emory board to re-true the tire. Usually I've found its more a case of a hard spot than a flat spot. You can usually feel it if you hit it with something abrasive while it spins. The rubber renew may also get it done, I've never personally tried it.
 
I've sanded the idler by hand with an emery file, on a Dual 1218 and a Garrard SL72B. Got rid of it totally with the Dual (great w and f spec!) but still working on it with the Garrard. Between 3 and 4 thump thumps per second, as far as I can tell.
 
BillWojo said:
Measure the inside of the platter and the idler wheel diameter to figure out the ratio so you can calculate the RPM of the idler wheel. Now time the "thump, thump, thump" for 30 seconds. Is that number equal to half the RPM of the idler wheel? If so, it's the idler wheel.

BillWojo
Click to expand...
Bill, your suggestion is much appreciated. I did the test, and the thumps per 30 seconds are a close match to the idler RPMs in 30 seconds (see attached screen capture). So, it looks like fixing the idler dead spot will solve the problem. If you have any thoughts on where to purchase a replacement idler, or have the old one fixed, kindly let me know. Thanks very much.
 

Attachments

  • 50H idler test.jpg
    50H idler test.jpg
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Before you go for the idler wheel take the platter off and have a good look at the black cycle trip linkage that is triggered by the eccentric bump on the platter gear. I have run across a few 10H and 50H tables that had a rhythmic “thump-thump-thump” noise and found it to be caused by dried out lube preventing the linkage from resetting to its proper starting point after cycling. When it gets really bad the machine will get stuck in an eternal change cycle where the arm will lift, move over, sit down, lift, move over, set down over and over again until you yank the plug. Of course if you do that and leave it then you will put a flat spot in the idler wheel because it will still be engaged against the drive pulley, so you’ll have two problems ;)
Also if the idler has a flat spot you’ll be able to see it and hear it if you engage the idler into the motor pulley by hand with the platter removed, it will be quite obvious once you do.
 
Look up Terrys Rubber Rollers. He just rebuilt one for my Russco for 35 bucks.
I see MRL_Audio beat me to it.

BillWojo
 
audiojones said:
Before you go for the idler wheel take the platter off and have a good look at the black cycle trip linkage that is triggered by the eccentric bump on the platter gear. I have run across a few 10H and 50H tables that had a rhythmic “thump-thump-thump” noise and found it to be caused by dried out lube preventing the linkage from resetting to its proper starting point after cycling. When it gets really bad the machine will get stuck in an eternal change cycle where the arm will lift, move over, sit down, lift, move over, set down over and over again until you yank the plug. Of course if you do that and leave it then you will put a flat spot in the idler wheel because it will still be engaged against the drive pulley, so you’ll have two problems ;)
Also if the idler has a flat spot you’ll be able to see it and hear it if you engage the idler into the motor pulley by hand with the platter removed, it will be quite obvious once you do.
Click to expand...
AudioJones, thanks very much for this tip. Actually, I acquired two 50Hs at an estate sale and the second one (which I just briefly tested) appears to have exactly the problem you describe. So, even if it is not the thumping problem on the first 50H, it's definitely a problem needing attention on the second 50H.
 
Seems like little to lose by sanding the idler. You might feel something when sanding too.

I'm guessing there is no way to see the idler in action, but can you hold it against the spindle with your finger with the platter off?
 
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