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 Post subject: Rumble filter ideas, anyone?
PostPosted: Nov Sun 11, 2018 8:05 am 
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I have a 1980 Akai direct drive turntable playing through a 90's-vintage Kenwood receiver and ported speakers. When playing records, rumble is intense...woofer cavitation is wild, so much so that it produces an echo effect, and I'm worried that they might self-destruct. The turntable is isolated from the speakers, so no feedback worries.

It would seem to me that rumble is the culprit, and if so, what is the most cost-effective option of dealing with it? Keep in mind that I don't have the ability to construct something, I need something that is plug/play. Some sort of filter that went between the turntable and receiver would be ideal. What would you recommend?

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 Post subject: Re: Rumble filter ideas, anyone?
PostPosted: Nov Sun 11, 2018 9:15 am 
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Location: Albuquerque, NM 87123
There is something wrong with the TT. No amount of filtering is going to help you.


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 Post subject: Re: Rumble filter ideas, anyone?
PostPosted: Nov Sun 11, 2018 6:10 pm 
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Wrong with the turntable? Like what?

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 Post subject: Re: Rumble filter ideas, anyone?
PostPosted: Nov Sun 11, 2018 7:00 pm 
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Like something that is effecting the rotational stability of the platter. Has it been serviced?


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 Post subject: Re: Rumble filter ideas, anyone?
PostPosted: Nov Sun 11, 2018 7:15 pm 
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Nope. I know how to service a record changer, but what needs to be done to a tt? Are there platter bearings like in a changer that need to be cleaned/greased?

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 Post subject: Re: Rumble filter ideas, anyone?
PostPosted: Nov Mon 12, 2018 12:11 am 
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What model do you have?


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 Post subject: Re: Rumble filter ideas, anyone?
PostPosted: Nov Mon 12, 2018 12:32 am 
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It's an Akai AP-Q50

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 Post subject: Re: Rumble filter ideas, anyone?
PostPosted: Nov Mon 12, 2018 12:36 am 
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I'll go out on a limb and assume you're not having speed control issues, since you don't mention noticeable W/F, meaning no defective electronics.

If you're lucky, a good cleaning and relube of the spindle shaft/bearing, if possible, will cure it.

Perhaps the worst case is debris from serious wear on the spindle shaft. I doubt you'll be able to find a new part, so you'd have to go looking for a donor unit.

There could be inadequate damping of the tonearm, if yours had it originally, which can result in resonance, throwing compliance out the window and can result in rumble.

There could be something amiss in the table suspension.

If you don't have the service manual, you can get it here: https://www.vinylengine.com/library/akai/ap-q50.shtml
And if you don't have an account at VE or don't want to register, it's here, too: https://www.manualslib.com/manual/10138 ... tml#manual

Perhaps best case is just a bad stylus. Even if the tip looks good under high magnification, the cantilever suspension could be shot, meaning poor compliance and tracking. Of course, a badly worn needle won't track properly and can also cause other symptoms.

A test LP with unmodulated and tracking bands can be very helpful in making sure sources of noise have been corrected after repairs, and in diagnosing stylus (and cart) issues.

I wouldn't bother with a rumble (hi-pass) filter. If your unit didn't have rumble and now it does, you've obviously got a new problem somewhere and that should be corrected, rather than attempts at external compensation.


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 Post subject: Re: Rumble filter ideas, anyone?
PostPosted: Nov Mon 12, 2018 12:45 am 
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It is also possible you have a cartridge/tonearm mismatch. If you are running a very high compliance cartridge in a medium to high mass arm, it can give those results.


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 Post subject: Re: Rumble filter ideas, anyone?
PostPosted: Nov Mon 12, 2018 2:36 am 
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Guys, thanks for the help, it's much appreciated.

I just recently bought this, and it's had problems with rumble since I got it. No speed issues, it's very stable. I replaced the AT cartridge it came with with a new Grado Prestige Black. I adjusted the tracking at 1.5 grams, which is what Grado recommends.

I will definitely remove the platter to see what kind of shape the bearing is in, and relube if possible.

There is one thing about the tonearm I should point out. On Akai models, the counter-balance weights on the back of the tonearm were known to sag after awhile, and mine is as well--would this cause a problem? It's not sagging horribly, but it's definitely noticeable

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 Post subject: Re: Rumble filter ideas, anyone?
PostPosted: Nov Mon 12, 2018 5:12 pm 
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One comment out of the era, specifically aimed at wow meters.

"Wonderful, but now you are measuring how accurate the hole placement was done
when the disk was pressed."

also

90's-vintage Kenwood receiver and ported speakers.

Try blocking the port with a dense pillow and see if the forward and back
cone excursions are reduced.



Attachment:
j aes disk recording John Eargle RCA records NY  NY 1969.jpg
j aes disk recording John Eargle RCA records NY NY 1969.jpg [ 101.42 KiB | Viewed 1748 times ]

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Last edited by radiotechnician on Nov Mon 12, 2018 5:20 pm, edited 1 time in total.

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 Post subject: Re: Rumble filter ideas, anyone?
PostPosted: Nov Mon 12, 2018 5:18 pm 
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tubes4life wrote:
Guys, thanks for the help, it's much appreciated.

I just recently bought this, and it's had problems with rumble since I got it. No speed issues, it's very stable. I replaced the AT cartridge it came with with a new Grado Prestige Black. I adjusted the tracking at 1.5 grams, which is what Grado recommends.

I will definitely remove the platter to see what kind of shape the bearing is in, and relube if possible.

There is one thing about the tonearm I should point out. On Akai models, the counter-balance weights on the back of the tonearm were known to sag after awhile, and mine is as well--would this cause a problem? It's not sagging horribly, but it's definitely noticeable


That may be your problem. Watch the tonearm and the stylus cantilever. Do you see any kind of low frequency motion of the headshell over warps? It should follow the warp without any kind of wayward movement. Grado cartridges were known for going into a kind of low frequency oscillation when used with an improperly matched tonearm. This is where I would start.

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 Post subject: Re: Rumble filter ideas, anyone?
PostPosted: Nov Mon 12, 2018 5:58 pm 
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radiotechnician wrote:
One comment out of the era, specifically aimed at wow meters.

"Wonderful, but now you are measuring how accurate the hole placement was done
when the disk was pressed."

Lesson learned. This is compensated for with test records such as the Denon XG-7004, which has a blank, concentric groove that helps the user eliminate eccentricity. The record's hole is slightly larger diameter than the standard spindle, allowing for this adjustment. With care, the tonearm can be made dead still during tests, giving a much more accurate W&F reading. That's my experience with the XG-7004's, but as always YMMV...

But yeah, that does only apply to the test record itself. Even though the measurement can be reliably compared to published specs for the TT, obviously the whole point of such a test record, "normal" records with inaccurate pressings can still give mild wow effects on a perfectly fine table. Of course, they aren't the same as speed variations and they won't be noticeable unless extreme — but I never underestimate the capability of golden ears to hear whatever they want to hear. :mrgreen:


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 Post subject: Re: Rumble filter ideas, anyone?
PostPosted: Nov Mon 12, 2018 6:47 pm 
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These are some great tips, much appreciated. Unfortunately, it's looking like I probably won't be able to delve into it further until my 4 days off for Thanksgiving--I'm working 6 days a week, always tired.

I don't see any wayward movement of the tonearm/cantilever on the warped records.

I could try plugging the speaker ports, but I would imagine that would have a negative impact on the sound quality.

I see/hear no evidence of wow/flutter. This does have a built-in strobe with quartz lock speed control, and the strobe stays rock-steady when in quartz lock mode.

But I did notice something this morning when I was looking at it. The rubber feet seem to be "bottomed out", as in the weight of the unit over the years collapsed the feet. If I press down on the plinth, shouldn't there be a little springiness to it? If so, it doesn't have any

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 Post subject: Re: Rumble filter ideas, anyone?
PostPosted: Nov Tue 13, 2018 2:09 pm 
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Location: Houston, TX
In the service manual, it appears to have cup style feet. Unfortunately, the manual doesn't seem to show these in the exploded view.
But from your "collapsed" description, I'll assume they are rubber cups (i.e., rubber all the way up to the base plate), with maybe felt rings on the very bottom, which is common.

If they don't have springs atop them, then of course the only damping will be from the rubber itself, so if that's hardened (or compacted as in your description) they should be replaced or a substitute rigged.

As a test, you might try putting rubber under them and see what effect it has on rumble. You can cut rubber squares out of just about anything you like, but several layers may be necessary — bike inner tube, shelf liner, grip pads, silicone kitchen products, whatever, as long as the rubber has sufficient damping/pliability.

If the feet turn out to be the problem, there are many aftermarket feet options out there, or you can just trim your jerry-rigged test pads so they won't show (if aesthetics matters).

What do you have your TT sitting on, and is that on carpet or hard floor?


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 Post subject: Re: Rumble filter ideas, anyone?
PostPosted: Nov Tue 13, 2018 4:57 pm 
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1. Make sure the feet are working correctly.
2. Make sure your plinth is resting on something solid.
3. Make sure there's nothing on/under the floor causing vibration.
4. Remove the dust cover.
5. If your amp has a subsonic filter, use it. In a perfect world, you wouldn't need it, but....
6. Make sure your cartridge is set up correctly.

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 Post subject: Re: Rumble filter ideas, anyone?
PostPosted: Nov Tue 13, 2018 6:36 pm 
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Location: Northeast Florida
Thanks, guys.

I don't have anything to substitute the rubber feet for, but I can certainly buy new ones. The rubber isn't hardened, just collapsed. I have to press down hard on the plinth to get any movement at all.

The tt is sitting on a shelf (on a metal shelving unit), which in turn is sitting on a wood floor (no carpet). The nearest speaker is only 12" away, but it's on a different shelving unit. I feel no vibration at all on the shelf where the tt sits, even on bass notes (they're just small bookshelf speakers). But I suppose I could try relocating the speakers to see if it makes a difference.

No rumble filter, unfortunately

EDIT; how accurate are the old mechanical Garrard stylus pressure gauges? That's what I used to set tracking force

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 Post subject: Re: Rumble filter ideas, anyone?
PostPosted: Nov Wed 14, 2018 2:43 am 
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tubes4life wrote:
I feel no vibration at all on the shelf where the tt sits.

You may not feel it, but your stylus/cart might. :)
The first thing to do is to ensure isolation from all potential sources of vibration. More details keep coming about your situation. It seems now that you may have more than one cause of the rumble. They add up.

Quote:
how accurate are the old mechanical Garrard stylus pressure gauges?

No idea, but the 5g digital one I ordered direct from China for a little over $7 is dead accurate and repeatable.
https://www.ebay.com/itm/Professional-D ... :rk:5:pf:0

NB: I got mine from a different seller that has no listing for it now, so YMMV with buying experience.

It's the exact same gauge that can be seen for sale in the USA for upwards of $50 or more by sellers intent on ripping people off (no, those inflated prices don't include overnight delivery :lol: ).

I tested its sensitivity at spots over its range and it does register in .01g increments. It holds calibration over time, also (remove batteries, put 'em back in months later, boom, same exact results as before). It's spot on 5g with the included cal weight, and the nickel and penny tests are accurate every time. I've had this one for almost 2 years and it still works as well as the day it arrived — but I don't use it every day, so take that reliability evaluation for what it's worth.

If you need .001g resolution or need to go above 5g, you might consider one of these:
https://www.ebay.com/itm/Digital-0-001g ... Swvr1bokid


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 Post subject: Re: Rumble filter ideas, anyone?
PostPosted: Nov Wed 14, 2018 5:40 am 
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A lot of direct drive phono motors will have a small metal ball at the bottom that the spindle sits on. If something was amiss there (worn ball, dirty ball ETC...) that could cause the rumble.


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 Post subject: Re: Rumble filter ideas, anyone?
PostPosted: Nov Wed 14, 2018 2:19 pm 
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tubes4life wrote:
The nearest speaker is only 12" away, but it's on a different shelving unit. I feel no vibration at all on the shelf where the tt sits, even on bass notes (they're just small bookshelf speakers). But I suppose I could try relocating the speakers to see if it makes a difference.
As a long-time broadcast engineer dealing with solving turntable audio problems over the years, I think the cause may be direct acoustical feedback from the speaker to the platter or tone arm. Relocating the speaker further away may be the only solution. In my experience, having a speaker located only 12" from a turntable is asking for trouble.

Dave


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