WTF is going on? ground/hum/noise/beer?

jerdude · 20th February 2006, 08:52 PM

ok, first off.... i am an idiot.

second... this was not happening till friday night. i thought it was a weird fluke thing and it would go away.

before...

plug anything into ltd-1 (line, mic, guitar), patch ltd-1 into la3a, sounds f***in' great!

friday night

plug anything into ltd-1 (line, mic, guitar), patch ltd-1 into la3a, sounds f***in' great!

patch ltd-1 into 33609 for some variety, sounds f***in' great!

patch ltd-1 back into la3a for more sounds f***in' great and f***in' sounds like poo. awful ground loop noise hum thing happening suddenly out of the blue for no reason except to F with my brain. NOW i am guessing on the description of the sound in order to try and describe it to you... i do not "technically" know that it is a ground loop. i was able to eq out the fundamentals of the hum/noise. it had three noticeable pitches... 200, 336 and 468hz. and then a nasty buzz mostly around 7k but some extending higher. Nasty huh?

in my effort to find the problem i discovered some interesting things that may tell some of you what the hum/problem is... it does not tell me what the problem is... as i have said already... i am an idiot!

here are my observations from trying to elminate this awful noise.

the noise is only present when i patch a mic pre into the la3a. when either is taken out of the path everything is fine.... mic pre into 33609 fine, 33609 into la3a fine, mic pre by itself fine, la3a by itself fine... mic pre into la3a = hum noise thing.

i jiggled the power cord of the la3a while the hum/noise was happening and the noise became intermitent as the power cord was moved around... if i held the power cord in a certain place the num/noise was almost completley gone.

then i started jiggling and turning the patch cord plugged into the la3a from the mic pre. the noise became intermitent again and at one point was completely gone... but if i moved the patch cord or moved it out and in, the noise would come back.

then i did something interesting. i pulled the IN patch cord out slightly (about 1/4 inch). and i pulled the opposite end cord (on the opposite side of the patch bay, the connection going to the input of la3a) out slightly too (1/4 in again). BINGO... hum/noise completely gone.

Is this a 1 or 2 pin hot thing?... (check first line of post

)

I assume i am somehow phase cancelling the hum/noise by pulling the cords out 1/4 inch. But i don't understand why this only happens with a mic pre (ltd-1, calrec, joe meek cheapoQ something, etc) and the la3a and no other combination.

would someone be kind enough to give me... "electrical engineering 101 for musicians who play with compressors and eq's because they goo there trousers when it all comes together and sounds pretty ok".

WTF?

your reigning gearslut idiot!

guitarbill · 17th February 2008, 12:54 AM

Have you got flying in and out leads or are you racked and patch bayed? It sounds like you may have some intermittant cables or some problem with the LA-3 wiring or internal circuitry. You said you isolated the LA-3 and it was ok. I would try that again with a known good input source and known good monitoring setup. If this is a vintage unit has it ever had its electrolytic caps replaced both in the power supply and signal chain? The frequencies you described sound more like digital noise or machine noise whine rather than ac hum. Faulty caps could be the prob. even if it's intermittant. Your cables should also be tested. Bt the way if your racked the rack itself may be causing intermittant ground loops between your units that are in that rack.

gb

Kiwiburger · 17th February 2008, 01:45 AM

Pulling a 1/4" plug out 1/4" is not "slightly". You are practically removing it, breaking the switch and the connection and therefore the buzz goes away.

Caps don't usually fail that bad overnight. You say all your preamps are doing it - it's got to be either ground noise or EMI that the preamps are picking up.

Get good cables, tested and cleaned. At least make sure it's not just one dodgy cable you use each time.

If it's ground noise, it might go away at times during the day/night. Electrical equipment in your house, or your neigbours house, or something down the block could be causing this.

Have you got a UPS? If you can run your audio gear off batteries, completely disconnected from the mains, you can see if it's anything to do with mains or ground noise. That's a good start.

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Ground noise	emreyazgin	So much gear, so little time!	4	19th June 2006 01:04 AM
Hum Noise	anne_paranoid	So much gear, so little time!	3	20th April 2006 03:10 PM
Help with Hum, Buzz, RF noise, etc!!!	tubeman	So much gear, so little time!	13	11th February 2006 06:05 AM
Ground hum (?) when splitting instrument signal	bnath	So much gear, so little time!	3	7th December 2004 10:38 PM
Missing post on hum and noise	Jay Kahrs	So much gear, so little time!	5	28th October 2002 06:17 AM

20th February 2006, 08:52 PM	#1
jerdude Gear maniac Join Date: Apr 2004 Location: L.A. Lower Arnold Posts: 277	WTF is going on? ground/hum/noise/beer? ok, first off.... i am an idiot. second... this was not happening till friday night. i thought it was a weird fluke thing and it would go away. before... plug anything into ltd-1 (line, mic, guitar), patch ltd-1 into la3a, sounds f*in' great! friday night plug anything into ltd-1 (line, mic, guitar), patch ltd-1 into la3a, sounds fin' great! patch ltd-1 into 33609 for some variety, sounds fin' great! patch ltd-1 back into la3a for more sounds fin' great and f**in' sounds like poo. awful ground loop noise hum thing happening suddenly out of the blue for no reason except to F with my brain. NOW i am guessing on the description of the sound in order to try and describe it to you... i do not "technically" know that it is a ground loop. i was able to eq out the fundamentals of the hum/noise. it had three noticeable pitches... 200, 336 and 468hz. and then a nasty buzz mostly around 7k but some extending higher. Nasty huh? in my effort to find the problem i discovered some interesting things that may tell some of you what the hum/problem is... it does not tell me what the problem is... as i have said already... i am an idiot! here are my observations from trying to elminate this awful noise. the noise is only present when i patch a mic pre into the la3a. when either is taken out of the path everything is fine.... mic pre into 33609 fine, 33609 into la3a fine, mic pre by itself fine, la3a by itself fine... mic pre into la3a = hum noise thing. i jiggled the power cord of the la3a while the hum/noise was happening and the noise became intermitent as the power cord was moved around... if i held the power cord in a certain place the num/noise was almost completley gone. then i started jiggling and turning the patch cord plugged into the la3a from the mic pre. the noise became intermitent again and at one point was completely gone... but if i moved the patch cord or moved it out and in, the noise would come back. then i did something interesting. i pulled the IN patch cord out slightly (about 1/4 inch). and i pulled the opposite end cord (on the opposite side of the patch bay, the connection going to the input of la3a) out slightly too (1/4 in again). BINGO... hum/noise completely gone. Is this a 1 or 2 pin hot thing?... (check first line of post ) I assume i am somehow phase cancelling the hum/noise by pulling the cords out 1/4 inch. But i don't understand why this only happens with a mic pre (ltd-1, calrec, joe meek cheapoQ something, etc) and the la3a and no other combination. would someone be kind enough to give me... "electrical engineering 101 for musicians who play with compressors and eq's because they goo there trousers when it all comes together and sounds pretty ok". WTF? your reigning gearslut idiot!

17th February 2008, 12:54 AM	#2
guitarbill Gear Head Join Date: Jul 2006 Location: South Central Alaska Posts: 67	Have you got flying in and out leads or are you racked and patch bayed? It sounds like you may have some intermittant cables or some problem with the LA-3 wiring or internal circuitry. You said you isolated the LA-3 and it was ok. I would try that again with a known good input source and known good monitoring setup. If this is a vintage unit has it ever had its electrolytic caps replaced both in the power supply and signal chain? The frequencies you described sound more like digital noise or machine noise whine rather than ac hum. Faulty caps could be the prob. even if it's intermittant. Your cables should also be tested. Bt the way if your racked the rack itself may be causing intermittant ground loops between your units that are in that rack. gb __________________ "Eat the fresh sockeye with wild blueberries" Copper River Red

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search
Display Modes	Rate This Thread
Linear Mode Switch to Hybrid Mode Switch to Threaded Mode	Rate This Thread:

17th February 2008, 01:45 AM	#3
Kiwiburger Lives for gear Join Date: Feb 2006 Posts: 3,675	Pulling a 1/4" plug out 1/4" is not "slightly". You are practically removing it, breaking the switch and the connection and therefore the buzz goes away. Caps don't usually fail that bad overnight. You say all your preamps are doing it - it's got to be either ground noise or EMI that the preamps are picking up. Get good cables, tested and cleaned. At least make sure it's not just one dodgy cable you use each time. If it's ground noise, it might go away at times during the day/night. Electrical equipment in your house, or your neigbours house, or something down the block could be causing this. Have you got a UPS? If you can run your audio gear off batteries, completely disconnected from the mains, you can see if it's anything to do with mains or ground noise. That's a good start.