Ground Loop? Bad Wiring?

[Alonzo]

Got a little problem with my current setup I'd like opinions on and hopefully a direction to start of the fix.  My setup is a couple of sources to a modified Quickie out to either a DIY45 or EL84 or to a Crack.  The problem I have is either a ground loop or a bad modification I've made to the Quickie.  When the Crack is connected to the Quickie, there's hum when the 45 amp is played.  Disconnect the interconnects from the Quickie and the hums gone.  Also there's a spark when I touch a wire from the interconnects ground to the Quickie ground (I was probing around with the Quickie on and the Crack off).  So the Crack is the source of hum when connected, I'm looking to connect the case of my server, the Quickie ground, the Crack ground and the amps grounds to get rid of the hum.  Also, I'm going to rebuild the battery wiring and switch wiring on the Quickie to make sure it's isolated and I haven't mis-wired and connected the batteries thru the ground.  Can anyone think of any other ideas to check? Thanks!!!

 

[Grainger49]

Alonzo,

Let me get this right you have two sources feeding a Quickie feeding three amps in parallel, right?  You play one of the three amps (Crack being one) but leave all of them wired up at the same time. 

The first problem "When the Crack is connected to the Quickie, there's hum when the 45 amp is played.  Disconnect the interconnects from the Quickie and the hums gone." sounds like there is a Quickie/45 amp reaction.  Check the ground to the plug on both amps.  Also check the resistance from the RCA outer connector to the chassis ground.

This one "Also there's a spark when I touch a wire from the interconnects ground to the Quickie ground (I was probing around with the Quickie on and the Crack off)." I'm not sure about.  Which interconnect ground to the Quickie circuit common gives a spark?  The Quickie common should be connected to the Quickie input RCA outer connection.  The spark bothers me, low voltage doesn't jump far, so I am wondering if you have 55V AC here.

If you ground everything make it a star ground.  One run from each component to a central ground.  I once ran a series grounding wire through all my stereo (in the 70s) and the noise was awful.  I got all kinds of hiss coming out. 

 

[Alonzo]

Hi Grainger,
I wasn't too clear on the description, but you got it right,.  The quickie has 4 inputs and 2 switchable outputs.  When everything is connected (45/EL84 via a Y connector) and the source, quickie and 45 turned on, there's hum in the 45 amp (not affected by the hum pot). If I disconnect the interconnects to the Crack, the hum goes away.  I've got everything on the bench now, checking resistances.  I would think the switch for the outputs would isolate the Crack.

 

[Grainger49]

Alonzo,

If the input switch acts on both the hot and common you get isolation, if not you don't get isolation.  The same thing goes for the switched outputs.

 

[Alonzo]

Well, the Quickie checks out, input selector switch, on-off switch and output selector switch all measure out correct, the ground buss is OK, everything measures right.  Only thing wrong is this Quickies 1.5v batteries are wired backwards, I never corrected it on the original build.  Put it back in the rack and it's playing Jazz.  The Crack is next up for inspection.

 

[Paul Birkeland]

Hi Grainger,
I wasn't too clear on the description, but you got it right,.  The quickie has 4 inputs and 2 switchable outputs.  When everything is connected (45/EL84 via a Y connector) and the source, quickie and 45 turned on, there's hum in the 45 amp (not affected by the hum pot). If I disconnect the interconnects to the Crack, the hum goes away.  I've got everything on the bench now, checking resistances.  I would think the switch for the outputs would isolate the Crack.

Is everything plugged into the same outlet?  When you switch outputs, are you also switching the grounds?

 

[Alonzo]

Everything is plugged into a Monster Line Conditioner (HTS3500MKII) with the ground connection from it connected to the chassis of each component.  I'll try moving outlets after work today. 

No,when the outputs switch the ground doesn't, it's just a 2 position switch from the output of the 3S4's to a different set of caps and RCA's.

 

[Grainger49]

Alonzo,

Try measuring the ground lug of one of the outlets to the ground lug of the Monster power cord, unplugged of course.  It is possible that ground of some of the outlets is lifted leaving the interconnects to connect the grounds.

It is worth a try!

 

[Alonzo]

Well Grainger,
Nothing has worked.  I've measured, changed interconnects, re worked grounds, almost everything I could think of.  I give up (for the time being).  There may be a shutdown coming up so I'll have some time to build a simple switch box and use my sources volume control and order a Crack to make into a preamp.  The Quickie will go on the shelf until I have the patience to tackle it again.  Thanks for the suggestions.

 

[Alonzo]

Just noticed you changed avatar's.  Love me some Elvira!!!!!

 

[Paul Birkeland]

Also there's a spark when I touch a wire from the interconnects ground to the Quickie ground

Elaborate more on this.  What do the interconnects need to be plugged into or need to touch in order to do this?

You do have a grounding issue, a little more investigation should sort it out.

-PB

 

[Grainger49]

That has been bothering me since my first response.  I was suspecting an ungrounded device with some voltage on the chassis.

 

[4krow]

  G,

  I am behind you with the switching hots and grounds when selecting. Doesn't it seem that there are too many 'irons(grounds) in the fire' not to have some kind of trouble?

 

[jrebman]

I wonder if maybe one of the outlets somewhere in the chain is wired with hot and neautral recersed or maybe there is a neutral to ground connection somewhere in a piece of gear?

Just some things to check.

-- Jim

 

[cpaul]

I agree, 4krow, all those grounds connected via the "Y" splitter sounds like a recipe for hum.  But...are you saying, Alonzo, that you only get the hum with the 45 but not the Crack (while the 45 is plugged in and connected)?  Can you put some other amp in place of the Crack, plugged in and connected, and see if you also get a hum?  You've got a long, convoluted ground path for loops to form, so I'm guessing this will be hard to resolve.

 

[Alonzo]

Hi Everybody,
Thanks for all the suggestions.  Sorry I haven't responded to the posts, the "F##kUps" in D.C. put us on furlough, and there's a thousand things to do to get a project stopped so I've been a little busy.  I tried to recreate my spark condition, but after all the rebuilding and changing around I couldn't.  Here's where it's at, still have hum when all the items are connected, individual amp to speakers " no hum".  Here's a pic of the quickie, batteries in the back, RCA's out to 45 or el84 on one side, RCA's out to Crack on the other.  White wire running across plate goes to power block ground post, red wire to Crack ground.  I think there's a problem with my Quickie switch, looking for a replacement but I don't see how that would induce hum into the amps.

 

[corndog71]

Have you tried it without all of those extra ground wires?

 

[Grainger49]

Well, I see the problem with the system, it is upside down!

Sometimes lots of grounds create hum problems.  I would take all the ground wires off.  Remove the system interconnects and verify chassis and signal grounds are tied to the power cord ground.  Easy peasy just grab your meter and check that it is less than 1/2 ohm from the power cord ground to both the chassis and RCA plug shells.

Then plug in each component, turn it on and verify that from ground at the wall or the power conditioner to the chassis you have zero volts.  You want no floating voltage on the component chassis. 

Now get a cold beer.  Slowly plug in each component into the system and see when the hum comes back. 

Since the hum is in the 45 amp when the Crack is also attached, I assume a Y-Adapter of sorts, the interaction of the two might be the answer.  One or the other doesn't have as good a ground in the signal path as the other.  My ST-70 had a 10 Ohm resistor between the RCA jack ground and the common/ground.  It caused problems with the FP III.