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Low frequency rumble

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AdamG View Drop Down
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    Posted: 18 Mar 2012 at 7:44pm
Hello from a new member

I've just replaced a my pre & power amp with a new integrated and GSP Communicator phono stage and am getting woofer pumping that hadn't occurred previously.

The driver movement is cyclic, greater on the outside tracks where cantilever travel is greater compared to inside tracks, and relative to volume (obvious even just above low volume but increases with volume). It doesn't seem to be causing any obvious erroneous though.

I understand this to be low frequency rumble. Nothings changed with the TT which is Technics 1200 with ATM 440MLA.

Am I right in attributing the rumble to the change in phono stage or could there be another cause.

Thanks Adam
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tg [RIP] View Drop Down
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Post Options Post Options   Thanks (1) Thanks(1)   Quote tg [RIP] Quote  Post ReplyReply Direct Link To This Post Posted: 18 Mar 2012 at 8:25pm

Hello Adam and welcome to this forum,

The rumble is either in the turntable (unlikely with an SL1200 unless badly worn) or more likely either on the record or due to warps in the record.

The "woofer pumping" you observe is due to an attempt to accurately replay subsonic frequencies which are faithfully reproduced by the phono stage.

You do not say what your previous preamp/phono stage was, many older integrated amplifiers had phono stages either incapable of reproducing those frequencies or had a built-in "rumble filter", better models would often allow this to be switched in or out.

You are probably correct in attributing the visibility of the rumble to the change in phono stage, but it is not the source of the issue, which, as noted above, lies elsewhere.  I would expect that any other wideband phono stage not having an inbuilt "rumble filter" would exhibit the same behaviour.  I have recollection of discussion amongst people building their own phono stages about fitting such filters in their creations.

Unless you generally listen at very high sound levels or are seriously concerned for the life of the drivers - ie. the excursion seems excessive), I would suggest that the issue can be safely ignored.

If you are sufficiently concerned that you wish to eliminate it, then an aftermarket "rumble filter" such as that from Kabusa is worth consideration.

Graham may have other suggestions.

FWIW my drivers are very sensitive and I too observe this phenomenon, but I have never had any concern for the life of the drivers as a result of it.



Edited by tg - 18 Mar 2012 at 9:08pm
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AdamG View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote AdamG Quote  Post ReplyReply Direct Link To This Post Posted: 18 Mar 2012 at 9:12pm
Thanks for your reply tg - great explanation

My previous preamp was a NAD 1155 and the TT is in very good condition.

A majority of my listening is at relatively low levels.

I am somewhat concerned about the affect the extra work the woofers are doing is going to have on speakers.

When is this too much is a difficult question I guess but from what I've seen its definitely off putting towards turning it up occasionally.

Would any of the Harrison FMOD filters be an alternative to the KAB unit?

Adam
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Fatmangolf Quote  Post ReplyReply Direct Link To This Post Posted: 18 Mar 2012 at 9:30pm
Welcome Adam. It will be the records, I have seen the same subsonics on specific records on both my turntables. Unless the speakers are hitting maximum excursion or your amp is distorting, this phenomenon is disconcerting rather than destructive. It looks worse than it is because ported/reflex cabinets do not load the drivers at these subsonic frequencies, so the motion is greater.
 
Jon
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Open mind and ears whilst owning GSP Genera, Accession M, Accession MC, Elevator EXP, Solo ULDE, Proprius amps, Cusat50 cables, Lautus digital cable, Spatia cables and links, and a Majestic DAC.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote AdamG Quote  Post ReplyReply Direct Link To This Post Posted: 18 Mar 2012 at 9:36pm
Thanks Fatman that is reassuring

I haven't done a lot of listening with the GSP phono yet so will monitor.


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tg [RIP] View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote tg [RIP] Quote  Post ReplyReply Direct Link To This Post Posted: 18 Mar 2012 at 9:57pm

Adam,

the Harrison filters to which you refer are unknown to me and I would have to look them up.

As it happens I was looking for the reference on DIY kits that I recalled and came across this http://sound.westhost.com/project99.htm referenced from an article at http://www.mds975.co.uk/Content/vinyl05.html .

Looked up the Harrison filters, looks like a possibility - I note they only cut 12dB/octave - could be worth reading on the Elliot project for some more information even if that is not an option for you - his filter is much steeper @ 36dB/octave, checked the KAB unit and it is 18dB/octave but incorporates some other tech wizardry as well.

Seems Brian @ decibel has the Harrison Subsonic 30Hz high pass for $55 - could be a cheap experiment - if you note a drop in SQ resulting maybe go for the dearer unit or DIY.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote AdamG Quote  Post ReplyReply Direct Link To This Post Posted: 19 Mar 2012 at 4:27am
I think I already know the answer to this (i.e. No) but do other GSP unit perform differently in terms of managing rumble. For e.g. would the Gram Amp II SE deal with rumble differently to the Communicator.
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