Ground loops and hum
Printed From: Graham Slee Hifi System Components
Category: DIY AUDIO
Forum Name: DIY Audio questions and answers
Forum Description: www.diy-audio-kits.com ... superb audio kits for experienced constructors
URL: https://www.hifisystemcomponents.com/forum/forum_posts.asp?TID=483
Printed Date: 27 Mar 2026 at 2:12am
Software Version: Web Wiz Forums 12.01 - http://www.webwizforums.com
Topic: Ground loops and hum
Posted By: knob2001
Subject: Ground loops and hum
Date Posted: 07 May 2009 at 2:22am
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Hi... I just finnished my novo kit, and besides some problem cutting the pot (solved right now), everything went as the manual says... but i have a big problem with a ground loop, but only with low impedance headphones. I have at home some AKG141 Studio and a K240DF both rated at 600ohm, and the Novo works like a charm with them (a little exhausted becouse those high ohms, but perfect for my ears). The problem appears with the other low impedance headphones: I have a k181DJ rated at 42Ohms and a ATH-W1000 rated about 40ohm if i don't remember wrong. With those low impedance heads, the hum is complety insane, on both channels. If i touch the Jack connector with my hands, breaking the ground loop, the hum tends to dissapear, although some hum is still audible. I have checked twice the components, and everything seems to be ok, (both two ground wirings from the enclosure to the RCA's and the POT too) Do you have any idea of what is happening here? Tomorrow i will add the capacitors you say at the manual (10pf, 50v or more) to see if something changes. Btw, i'm using and IPOD (batteries) and a good minijack-rca cable. I tested it with two CD players (RCA-RCA) with the same behavior at low impedances. Thank you. Knob2001. |
Replies:
Posted By: Graham Slee
Date Posted: 07 May 2009 at 1:45pm
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Hi, I had exactly the same problem with a phono preamp I built yesterday. It turned out to be the case ground continuity. Stick your multimeter (set on Ohms) between a phono socket outer contact (circuit ground) and a front panel screw (case ground). It should be less than 1 Ohm (my phono preamp showed 25 Ohms and buzzed). If not check that the serated washer is "breaking" through the anodise to make contact between circuit ground and case (that was the fault on my phono preamp). Also, check the instructions on "distressing" the panel screw countersinks - this is to ensure the screws make contact with metal instead of the slightly insulating anodising. And please keep us all informed here. ------------- That none should be able to park up and enjoy the view without a smartphone and the knowledge in how to use apps |
Posted By: knob2001
Date Posted: 07 May 2009 at 8:33pm
Hi! That was exactly my problem  For a reason i can't explain, the washer i used was a normal one, not the serated one you told me about and the anodise was repelling the ground connection. It's funny how the smallest thing can ruin everything, isn't? Anyway, the hum has dissapear, and it sounds the way is supposed to sound. No matter the impedance of the heads. I have learned a very usefull tip for the future, so thank you twice. Regards knob2001 |
Posted By: mrarroyo
Date Posted: 07 May 2009 at 10:55pm
Good to see all ended up well. Still hoping to buil my Novo, but I can't pull away from the Solo SRG w/ the PSU1.  ------------- Miguel |