Vintage HiFi Audio Forum
Audio Discussion => DIY => Topic started by: OldiesButGoodies on April 06, 2013, 11:15:32 PM
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Still searching for a lower noise floor for the Sunfire True Subwoofer, I am testing what claims to be the top dog of all ground loop isolators - a Jensen Iso-Max filter.
For $105 these folks will send you a top caliber filter designed for sub freq ranges. I tested it by maxing out the sub output out of the Parasound 2100 and maxing the volume and x-over potentiometers in the Sunfire sub. Using brand new double shielded sub interconnects. I tried several configurations, including w and without the filter, feeding the L or R input on the Sunfire and feeding them both together using a Y adapter. Then I switched the electricity source between phases and fed from the Monster station and not. I measured the results using a db meter. They are shown below:
(http://i1122.photobucket.com/albums/l538/namikis/IMG_0904_zpsb078446b.jpg)
Bottom line - the filter helps but is not perfect. The Monster power stations lower the noise floor by about 2 dbs vs straight feed - good enough. The Iso-Max reduced it by an additional 10dbs on average - decent enough but still makes you wonder if $10/db is worth it. Here are some pics of the device:
(http://i1122.photobucket.com/albums/l538/namikis/IMG_0888_zps0217072a.jpg)
(http://i1122.photobucket.com/albums/l538/namikis/IMG_0890_zpsf25478b7.jpg)
(http://i1122.photobucket.com/albums/l538/namikis/IMG_0892_zps27687430.jpg)
(http://i1122.photobucket.com/albums/l538/namikis/IMG_0896_zpsee7f68db.jpg)
Will I keep it or return it? Not sure. Will test it some more for a couple of days and decide.
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Have you peeked at the innards?
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Hey Al - in trying to reply to your post, I deleted it. My bad.
Your suggestion was that I take a look at the innards of the Iso Max. Will do that soon. Here's a picture of teh cheapie I was using before:
(http://i1122.photobucket.com/albums/l538/namikis/IMG_0886_zps864e2f79.jpg)
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In my opinion, $100 for a 10db improvement in S/N ratio is a bargain. However, I think all these little "black boxes" are doing is sticking a notch filter at 60 hz and maybe 120 hz as well. To truly isolate the ground hum requires something be done at the 120 volt end of things. Or.....
Is there any cable TV wiring anywhere in the system (as in coax running to a cable box, plugged into a pre/pro)?. If so, try disconnecting the coax to see if the hum goes away. If it does, isolating the hum at that point might help.
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Ok... how much does it help eliminate the hum from the sub? Is it worth the $ for the difference? Are there other alternatives ? ???
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King:
I was hesitant at first, but then I used the digital sound meter to test out the actual effect. It indicates a 10db improvement. So it is probably worth it in that context.
MacGeek pints out the need for further investigation on the 120V side of things. So I may explore using an isolation transformer of some sort or improving the quality of the ground by hammering a new one into - well - the ground. If the 120V side of the problem were fixed, the 10dbs of the Iso Max (and the undesired extra filtering in the signal path) would be irrelevant.
But one thing left out is the incredible sensitivity to ground noise my particular Sunfire sub has. If I add up all the money and time I have invested in quieting down that sub I could probably buy a pair of Fathom F113s. On the other hand, it gives me an excuse to drop by the shop. My wife, who has little knowledge or interest in audio, has gotten to asking me if the sub is humming again whenever I tell her I need to go to the shop (I say "yes - I need Anders to take a look at it", though I am often going for some other reason, usually a free beer with Tom in exchange for a gallon of diesel >:D). So the investigation continues. One test I will try is swapping in the Emp Teks to see if they are as finicky.
OBG
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Thanks Pepe! I have a slight hum also and suspect the Sunfire sub as well. I have a lot of wiring crossing each other behind my stereo cabinet and also TV and cable box. Do you think the isolator in your other thread would be worth buying?
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if you remove the coax from the cable box and the hum disappears, the TII isolator is your next best friend, IMO.
adios
OBG
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TX! I'll try it.
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Well - I removed the Sunfire altogether from the mix and the hum is not popping up with the Emp Teks. So I may be at the limit with this little Sunfire sub. It may be parted out in Ebay for recycling. >:(
I tried close to everything, need to put my soldiers to work on something else.
OBG
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And this is what the insides of the Iso Max filter look like:
(http://i1122.photobucket.com/albums/l538/namikis/IMG_0943_zpsbb9a646c.jpg)
(http://i1122.photobucket.com/albums/l538/namikis/IMG_0944_zpse5a03007.jpg)
(http://i1122.photobucket.com/albums/l538/namikis/IMG_0945_zps0df985ce.jpg)
(http://i1122.photobucket.com/albums/l538/namikis/IMG_0942_zps16f4e235.jpg)
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Before entirely giving up on the sub, if the sub has a three wire plug, I suggest trying a three to two prong adapter. Make sure the little green tab is bent out of the way so it does not come into contact with anything.