Very low frequency hum when playing records at high volume

birkbott

AK Subscriber
Subscriber
I noticed today that if I crank up the volume during playback on my TT I get a very low frequency hum through the speakers, almost inaudible but I can see the woofer moving like crazy. It only happens while the needle is touching the record.

Is it some kind of feedback? Or some other kind of motor hum? There is a slight hum in the system already, I believe from the ground, but this is different as it is only while playing and only at higher volumes (80-90db) If I turn the volume down it goes away. Most noticeable during the gaps in songs or quiet sections.

I do have it pretty close to my left speaker which is why I'm thinking feedback but curious to hear any other opinions.
 
That is feedback. Speakers are too close to the TT, and/or the TT is not isolated well enough. You have to realize that a phono stage (internal or external) is a very high gain stage, as compared to a "normal" line-level input--even with a MM/MI cart, you are taking a 3-6mV signal and bringing it up to a 1.75-2.25V line level signal w/RIAA equalization--MC carts require even far more gain due to lower output voltages.
 
That is feedback. Speakers are too close to the TT, and/or the TT is not isolated well enough. You have to realize that a phono stage (internal or external) is a very high gain stage, as compared to a "normal" line-level input--even with a MM/MI cart, you are taking a 3-6mV signal and bringing it up to a 1.75-2.25V line level signal w/RIAA equalization--MC carts require even far more gain due to lower output voltages.

I tried moving the speaker away a few feet and it was still an issue, but they are bookshelf speakers that live on the same surface as the TT. I have isolation platforms (DIY, particle board with rubber feet) under both speakers and the TT which I was hoping would isolate it enough but apparently not.

I also have a sub that lives in the same furniture unit so that could be feeding back as well I suppose.

Is the feedback usually because of contact/isolation or would it come through the air as well? Is it just generally difficult to play vinyl at high volumes because of this?
 
Is the feedback usually because of contact/isolation or would it come through the air as well?

Both actually--more so from the contact--I'd get that sub onto the floor and off the rack for sure, but as you hit higher SPL, just proximity and air resonance can be a factor, as well.
 
I can see the woofer moving like crazy. It only happens while the needle is touching the record.
That is the classic tell tale sign of sub-sonic frequencies. It seems like you got a spaghetti ball entanglement of various origin interferences like a grounding issue mixed up with feedback, but woofers moving like crazy with no audible output is definitely sub-sonics. The first and major cause for sub-sonic frequencies is a tonearm/cart mismatch and resonance frequencies. Yes, it's the twilight zone of turntable physics but that's the likely cause.
 
That is the classic tell tale sign of sub-sonic frequencies. It seems like you got a spaghetti ball entanglement of various origin interferences like a grounding issue mixed up with feedback, but woofers moving like crazy with no audible output is definitely sub-sonics. The first and major cause for sub-sonic frequencies is a tonearm/cart mismatch and resonance frequencies. Yes, it's the twilight zone of turntable physics but that's the likely cause.

So you think my cart is not a good match for my TT? That's unfortunate. How would I know which one to replace it with? Or is it trial and error?
 
It's actually a function of the tonearm's effective mass and the cart's mass + compliance figures. Tell us what you got running then we could point you in the right direction - if still necessary.

EDIT: Oh... I see it in your tag line. So which is it, the Technics + Shure?
 
It's actually a function of the tonearm's effective mass and the cart's mass + compliance figures. Tell us what you got running then we could point you in the right direction - if still necessary.

EDIT: Oh... I see it in your tag line. So which is it, the Technics + Shure?

Yep that's the current setup. It came with an AT cartridge but I swapped it out.
 
That is feedback. Speakers are too close to the TT, and/or the TT is not isolated well enough. You have to realize that a phono stage (internal or external) is a very high gain stage, as compared to a "normal" line-level input--even with a MM/MI cart, you are taking a 3-6mV signal and bringing it up to a 1.75-2.25V line level signal w/RIAA equalization--MC carts require even far more gain due to lower output voltages.
Yes.
 
The static compliance of the M97xE is 25cu and weighs 6.6 grams. Shure, amazingly, frees themselves from the curtsy of measuring dynamic compliance for their carts. Can you believe that??? It's the dynamic compliance that we need, not the static compliance... Dang! There's a loose way to extract the dynamic compliance from the static compliance figure, but it's highly inaccurate. You just multiply by a constant that's anything from 1.5 to 2.0, so let's just assume the dynamic compliance of the M97xE is more than 30cu, which is bordering the rather high range, and makes the M97xE rather 'springy' if you will. I guess the Technics universal tonearm has about the standard 12.5 - 14 grams of effective mass. Either way, 12.5 grams or 14 grams, it's a mismatch. The Shure is just too springy!

Have a look at this chart which is generated for a 12.5g eff. mass tonearm. You take the Shure's compliance of 30cu and look at the Y axis of the graph, then cross it with 6.6g + 0.5g = ~7g (cart mass + fastening screws) on the X axis and you get 7Hz, that is bellow the golden range of 8 - 12 Hz. It gets worst in this chart, if you punch in 14g of effective mass for the Technics tonearm, with RF at 6Hz for the same figures. That's very low! I'm afraid the Shure M97xE isn't the best match for your tonearm and explains much of the sub-sonics.

I was actually very liberal in transforming the Shure's static compliance to dynamic compliance. I suppose it's actually higher than 30cu which makes it a worst case for you.

In my online queries for this post I've come across recommendations for the Shure M97xE and this turntable combination. Some of those originate from some turntable dedicated forums with reputable web sites. Needless to say I don't understand what's the basis for those recommendations since it's an obvious mismatch.
 
The static compliance of the M97xE is 25cu and weighs 6.6 grams. Shure, amazingly, frees themselves from the curtsy of measuring dynamic compliance for their carts. Can you believe that??? It's the dynamic compliance that we need, not the static compliance... Dang! There's a loose way to extract the dynamic compliance from the static compliance figure, but it's highly inaccurate. You just multiply by a constant that's anything from 1.5 to 2.0, so let's just assume the dynamic compliance of the M97xE is more than 30cu, which is bordering the rather high range, and makes the M97xE rather 'springy' if you will. I guess the Technics universal tonearm has about the standard 12.5 - 14 grams of effective mass. Either way, 12.5 grams or 14 grams, it's a mismatch. The Shure is just too springy!

Have a look at this chart which is generated for a 12.5g eff. mass tonearm. You take the Shure's compliance of 30cu and look at the Y axis of the graph, then cross it with 6.6g + 0.5g = ~7g (cart mass + fastening screws) on the X axis and you get 7Hz, that is bellow the golden range of 8 - 12 Hz. It gets worst in this chart, if you punch in 14g of effective mass for the Technics tonearm, with RF at 6Hz for the same figures. That's very low! I'm afraid the Shure M97xE isn't the best match for your tonearm and explains much of the sub-sonics.

I was actually very liberal in transforming the Shure's static compliance to dynamic compliance. I suppose it's actually higher than 30cu which makes it a worst case for you.

In my online queries for this post I've come across recommendations for the Shure M97xE and this turntable combination. Some of those originate from some turntable dedicated forums with reputable web sites. Needless to say I don't understand what's the basis for those recommendations since it's an obvious mismatch.

I'll try switching back to the stock cart, it was a AT-71E Cardridge with ATN-71EB Stylus and see if that solves the problem.

Given your knowledge what do you think would be a good cartridge to look at if I want to upgrade?
 
I don't believe so, I was trying to look up subsonic filters but people seem to dislike the way they affect the overall sound.

Generally, they are low enough that it can help with the woofers pumping, but still below the range of normal frequency response. On the Yamaha preamp I have handy to look at it's 15Hz.
 
I have used these products in the past to "tame" TT rumble or feedback--no affiliation.

http://www.hlabs.com/products/crossovers/index_files/Page384.htm

The website sucks, but the product you can use, is the PFMOD HP-SUB. It has an adjustable high pass output that can be set at 20, 25, 30 or 35 Hz with a 12 dB/octave slope. I inserted it in a tape monitor loop (not directly between the TT and preamp) and it provided great protection from unwanted extremely low frequencies destroying/overextending woofers, and sapping the amp of power from amplifying low frequencies that cannot be reproduced by the drivers, or even heard, for that matter. IIRC, I used the 25 or 30 Hz setting. I can look, they are in a drawer here somewhere.
 
they are bookshelf speakers that live on the same surface as the TT.

I also have a sub that lives in the same furniture unit

While the Shure may be a mismatch Im thinking the TT placement is the real culprit. Try taking the speakers temporarily off the shelf the TT is on and see if it goes away. Bob
 
...I was trying to look up subsonic filters but people seem to dislike the way they affect the overall sound...

The good infrasonic filters that are sensibly designed, with a corner frequency and slope that doesn't affect vinyl playback, are completely transparent to listeners.

Some are too steep and too high, others are too low and not steep enough.

It can be a crap shoot with a low/subsonic/infrasonic filter switch on your amp or preamp. I have some that are essentially useless and others that are absolutely perfect for the job.

Attached are few of old saved plots for your amusement:

Sansui AU-505 filters (low filter- purple)

AU505.jpg

Yamaha CA-810 (low filter L/R Green/Yellow)

CA810.jpg

Marantz 1152DC (low filter white- combined with high filter too)

marantz 1152dc filters.jpg
 
WOW, just WOW--that Sansui just murders anything beyond vocals, while the other two seem to do what they're supposed to.
Yes, that looks just wrong - it takes off a huge amount in the audio band and yet is only taking off 8dB at 10Hz. Subsonic filters need a much steeper slope and they need to come in at a much lower frequency. The others look much better.
 
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