Possible grounding issues?

mosshorn · 7417

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Offline mosshorn

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on: January 13, 2012, 09:31:48 AM
First of all, let me thank this forum for how much help it's been. You guys really know your stuff :)


Anywho, to the problem. I've had this occuring hum since I initially built my Crack. I thought it was the tubes, but remove the RCA plugs, no hum. Several things has been possible culprits, and I've taken them out:

New tubes
switching DAC to different circuit
different DAC
different RCA cables

Well, I go outside to resolder the RCA's solder pot (in other news, I hate soldering soldering pots!). It seems successful. I go inside, plug everything back in, turn it on and wait.

I plug in my headphones, and the nasty "this is probably not good" cracking goes on. I promptly turn it off and unplug my headphones. Could this be due to that RCA jack REALLY not being well grounded? What else could that hum come from?

Thanks,
Brian


Offline Jim R.

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Reply #1 on: January 13, 2012, 10:20:34 AM
Did you use the insulating washers for the RCAs?  The RCAs should not be grounded to the chassis plate.  Also, did you paint or powdercoat the plate, and if so, did you make sure to scrape all paint off at the main grounding  point (near the power inlet, and at the tube sockets?

Assume all your voltage and resistance measurements are ok.

-- Jim

Jim Rebman -- recovering audiophile

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All ICs homemade (speaker and power next)

Offline mosshorn

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Reply #2 on: January 13, 2012, 10:59:25 AM
The plate on the transformer? or the main plate?


Offline Grainger49

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Reply #3 on: January 13, 2012, 11:47:14 AM
He's talking about the top plate, the white washers around the input RCA jacks and your top plate finish.


Offline Doc B.

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Reply #4 on: January 13, 2012, 11:59:09 AM
Clarification time-

Only happened with cables plugged in - is that the hum or the crackle? Or both?

If the crackle only happens with the cables plugged in it could very likely be a broken cable. That break could be causing the hum too. If it is caused by the RCA jack itself the jack probably needs to be replaced.

Dan "Doc B." Schmalle
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Bottlehead Corp.

Offline mosshorn

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Reply #5 on: January 13, 2012, 12:28:02 PM
The hum was the original sound, that happened only when the RCA plugs were connected. Tried 3 different pairs of cable (including the monoprice pair that I just got in the mail) to no avail. The crackling happened when I tried to fix the black RCA jack by resoldering the wire into the pot.


From there I resoldered the ground buss and wire B8U (which apparently I didn't solder  before), and now I'm getting crazy readings from not having a ground. So it goes, time to retest joints lol


Offline mosshorn

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Reply #6 on: January 13, 2012, 02:16:21 PM
Alright, update. It powers on now, and everything seemed ok, my voltage checks were okay, but the TRS check came out odd at first (peaked at 10v or so on the ring, then nothing really, nothing much on the tip).


I plugged in my headphones, and it still made the crackle noise. Also, I've been using my 6080 tube that came with my Crack to test (keeping my 6AS7's to the side), and it got hot, fast. It also started smelling like burning (not the typical hot smell at all), so I promptly turned it off.


Any ideas? I'm lost at this point, and kind of worried to plug in one of my 6AS7's to test and see if it was just that tube :/

EDIT: Just put in my RCA 6AS7 tube, and the crackle/fuzz noise is still there. Since my voltages check out, I'm guessing it might be the RCA jack that I messed up. Any way to confirm this?

Even more EDIT: I'm noticing I have more hum than I did before, and even remotely moving the pot causes for some nasty, nasty popping. Hope this helps.
« Last Edit: January 13, 2012, 05:22:15 PM by mosshorn »


Offline mosshorn

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Reply #7 on: January 14, 2012, 06:44:04 PM
Bump if anyone knows. I'm going to mess around with it more tomorrow afternoon.


Offline howardnair

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Reply #8 on: January 15, 2012, 05:40:04 AM
moss-first -ck what you have done  with the directions-take your time doing this-second ck your soldering-when you say you resoldered the rca wire into the pot-i take it you mean resoldered the input wire from the rca at the voume pot-you may have dropped solder into the pot or over heated the pot-if you have large blobs of solder -get a solder sucker and suck them clean then resolder-at your rca's make sure you did not melt the inner insulation or blob solder from the inner part[positive] of the rca to the outer part[ ground ]


Offline mosshorn

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Reply #9 on: January 15, 2012, 04:50:59 PM
Thanks for the help Howard, you named off what I was thinking of doing as my short list. I suppose I had a short around my RCA jacks, but I resoldered quite a bit of stuff tonight.


Everything works! But I still have the hum. Oh well, I'll try resoldering some of the driver tube section tomorrow.


By the way, I found I enjoy the sound of my stock Electro-Harmonix ECC82 more than my old Telefunken 12AU7, with a significantly greater soundstage. Who woulda knew? :S

Thanks for everyone for all the help!


Offline InfernoSTi

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Reply #10 on: January 16, 2012, 09:08:49 AM
This is a long shot, but if your rectifier circuit is bad, it may. be passing AC which will sound like what you are describing. Might start there next....

John

John Kessel
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Paramount 300B w/MQ All Nickel Iron,  Mundorf S/G 5.5 uF,  and  Vcap Teflon .1 uF
Auralic Taurus Preamp/Auralic Vega DAC/Auralic Aries Streamer
and lots of room treatments!

Offline Laudanum

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Reply #11 on: January 16, 2012, 10:19:33 AM
Does the hum increase when you turn up the "volume" or is it the same regardless of where the volume is set?

Desmond G.

Offline mosshorn

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Reply #12 on: January 16, 2012, 11:50:56 AM
It slightly goes up when turned up, but oddest thing, I'm noticing it makes weird cutting out noises when I wiggle the pot itself via the volume knob. Connection issue?


Offline Grainger49

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Reply #13 on: January 16, 2012, 12:25:52 PM
I bookmarked this site when another Bottlehead posted it.  It could be some help:

http://www.geofex.com/Article_Folders/potsecrets/potscret.htm


Offline 2wo

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Reply #14 on: January 16, 2012, 12:28:17 PM
Sounds like it. You could try connecting a jumper from the wire from the center of the RCA jack to ground, better yet the end of it that connects to the pot. Do both chanels and see if the hum stops...John

John S.

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