[wdahm519]

Hey guys,
 
I finished my EHHA Rev A build about a week or so ago.  I noticed that there was a very subtle ground loop noise in the background.  When I removed the alternate wiring it got worse (louder) so I put the alternate wiring back in, and I also made sure that the star ground was tied to earth ground.  However, there is still that tiny ground loop sound hanging around in the background (its really very faint) and I can't trace its source.
 
Any ideas?
 
By the way, everything else works fine, everything else measures extremely well, etc.  There is a transformer hum from the Avel Lindberg toroidal 9-0-V transformer.  This transformer is located in a separate case underneath the amp portion.  Could be part of it?
 
EDIT:  I'm also using an AMB e27 board that the Alps RK27 pot is mounted on.  Maybe there is noise here?  I remember one case of someone having a grounding issue with the board.  I have each channel ground going to the respective ground on the e27, and same for the output (ground of each channel's output goes to the channel ground on the amp board where its labelled IN).

 

[cfcubed]

Though I don't have suggestions to offer yet, I can commiserate.  I've built a lot of amps successfully & have exactly the same problem you have for my EHHA.   Know its "my problem" somewhere likely in ground wiring but its been no fun chasing down, in fact I abandoned my nearly complete EHHA build because of it (very low hum).
 
The boards worked fine & sounded great on the bench but after careful planning & case-up have a very low-level hum.  It's a 2-case build w/the transformers, DC conversion & regulation in a separate plastic case far away from the amp.  Again know its a fault in my wiring/case-up and was just getting around to re-approaching the build to fix it.  Been "getting by" very well w/a 2-channel Beta22 in the meantime.
When/if I solve the problem I'll post what I think it was (in the unlikely case that the the problem is the same as yours
Best of luck!

 

[wdahm519]

I would venture a guess that our problems are the same.  Your set up is so very very close to mine.  
 
I found I can actually use the EHHA with the HE-500's very well because the sensitivity is so low the HE-500 that I don't hear the sound at all, not even in the least.  Its only apparently in the audible noise floor on the DT-1350's which are sensitive (Tesla technology). 
 
It still bugs me though, knowing that its there hiding below my hearing range.  
 
I still have my Bijou to get me by when I'm not feeling the EHHA so I'm a happy camper too.  
 
 
I will also let you know if I magically come across the solution.

 

[jdkJake]

Have either of you installed a ground loop breaker between star ground and chassis ground?

First though, I would lift star ground from chassis ground and then measure for resistance between signal ground and chassis ground. Be sure the two are fully isolated before you tie them together (either with or without a ground loop breaker). That will make ultimate isolation of the issue far easier.

wdahm519, I would move the transformers out from under the amp chassis and see if that helps as well. A torrid will radiate upwards on it's axis greater than radially outward.

EDIT: try this first and then we can move on to the pot.

 

[cfcubed]

No to the GLB for me, I've only used/needed them in one-box builds (where A/C/earth/mains ground + transformer is in same metal case as amp).
This 2-box EHHA build has the amp box's ground = signal ground = center/ground of bi-polar supply = EHHA PCB grounds (IIRC).  Earth ground does not get to the amp box.
But I'll certainly be considering your suggestions when I dive back into this problem... Thanks!
 

 

[jdkJake]

Are your RCA jacks isolated from the chassis or are they connected?

 

[BK_856er]

GLB worked fabulously for my single-box build.  In fact, jdkJake suggested it and walked me through it (thanks again, man!).
 
My EHHA revA is stoopid quiet with the GLB with all my headphones.
 
Could the tubes also contribute some hum??
 
BK
 
 

 

[wdahm519]

 
Quote:

Have either of you installed a ground loop breaker between star ground and chassis ground?
First though, I would lift star ground from chassis ground and then measure for resistance between signal ground and chassis ground. Be sure the two are fully isolated before you tie them together (either with or without a ground loop breaker). That will make ultimate isolation of the issue far easier.
wdahm519, I would move the transformers out from under the amp chassis and see if that helps as well. A torrid will radiate upwards on it's axis greater than radially outward.
EDIT: try this first and then we can move on to the pot.

 
I do not have a GLB.  
 
I moved the transformer's box next to the amp box, I will let you know if it solves any issues but I've done this before in the lab where I was testing and I don't think it helped much -- but we will see in this more quiet environment.  
 
For this build, earth ground is connected to the chassis of the transformer box.  I also ran a wire from the earth ground connection at the power inlet through the umbilical cord (where power passes through) and connected star ground to true earth ground.  
 
Quote:

Are your RCA jacks isolated from the chassis or are they connected?

 
RCA jacks are not isolated from the chassis, they are connected to the chassis.
 
Quote:

GLB worked fabulously for my single-box build.  In fact, jdkJake suggested it and walked me through it (thanks again, man!).
 
My EHHA revA is stoopid quiet with the GLB with all my headphones.
 
Could the tubes also contribute some hum??
 
BK
 
 

 
Hum won't be coming from these tubes.  I'm using NOS Telefunken's that are really, really great.  The noise is definitely something else.  
 
 
If someone would be so kind to let me know how to properly install a GLB (I've never done it before), I think that would be the best option for me.
 
 
EDIT:  Is this the general idea?
 
"The ground-connection of the mains-socket is directly connected to the case of the preamp. It is connected to the ground-plane of the audio-circuit via a 4.7 ohm resistor in parallel with a 100 nF capacitor. This resistor prevents 50/60 Hz currents from flowing freely along the ground connections between the various audio components in a system, and thus eliminates the 50/60 Hz hum."
 
Also, I think I need to float my input and output grounds.

 

[BK_856er]

Probably lots of ways to skin the GLB cat.  For mine I used some extra parts I had on hand for my beta-22 build.  AMB has some details at the beta-22 wiring section of his site.
 
Here's a pic of what I did.  Soldered the cap and resistor together and reinforced it with thick shrinkwrap.  You can see the connection to the chassis under the Bulgin stainless steel power switch in the upper right of the pic.  The terminal strip is my star ground.
 
Don't want to imply it's a cure-all or will work in your situation, but it did wonders for me.  Easily constructed and easily removed if you don't want to keep it.
 
BK
 

 

 

[cfcubed]

Quote:

Are your RCA jacks isolated from the chassis or are they connected?

Not for my amp case - they are connected...  The ground handling is not proper/correct in my amp case in general & certainly not star-grounding.
I'll be re-working that sometime this week, perhaps that'll fix it.   Thanks.

 

[wdahm519]

So I think my basic plan of attack is to:
 

• Lift the input and output ground from the chassis
• Lift star ground from the chassis
• Put input + output + star ground together again but disconnected from chassis ground/earth ground
• Put a resistor/capacitor combination (GLB) between my floating star ground and chassis/earth ground

 
I can either try this tonight or on Monday night.  Anyone have ideas for the size of resistor/capacitor I should use?  I might use the values I quoted above from a different website.  If you have a better idea though, I'd love to hear it.
 
Also, is my implementation correct?

 

[BK_856er]

Quoting AMBs instructions for the beta-22:
 
[size=x-small]"For option 3 above, the ground loop breaker is a 10Ω 5W resistor in parallel with a 0.1µF capacitor rated at least 250VAC. For safety this capacitor should be rated for class X or Y (good for across-the-line use) with flame retardant casing. The ground loop breaker should be connected between the signal ground and the chassis (which is in turn connected to AC earth ground via the IEC power entry receptacle). Mount the resistor and capacitor in a secure manner so that it will not come loose and come into contact with other circuitry. A good way to do this is to use a terminal strip."[/size]
 
[size=x-small]BK[/size]
 

 

[jdkJake]

While we are quoting AMB, I think you should take a quick read of the "wiring and ground" section of the b22 pages (http://www.amb.org/audio/beta22/).

wdahm519, the option #2 wiring schema is what you should probably shoot for prior to moving forward with a GLB. Cfcubed should shoot for option #1, although, based upon the responses above, he has a pretty good handle on the situation and what needs to be fixed to resolve the hum.

 

[wdahm519]

So I had a chance to try this today.  I'm writing as I test it, so we'll see how it ends up.
 
Here's what I did:

1. Lift all grounds off of the chassis except for input ground
2. Lift earth ground from the amp chassis -- earth ground is still on the transformer case chassis, AND is still running through my umbilical into a pin on my 10 pin umbilical connector
3. Build a GLB with a 10ohm 10W resistor and a 0.1uF 250V film capacitor wired in parallel
4. I tied all the grounds from the board together + ground from the output and attached this to one end of the GLB
5. I tied the other end of the GLB to the pin that is connected to earth ground and chassis ground on the transformer chassis

 
Did it work?
 
 I have to really strain myself to hear for a buzz, but I don't think I can hear it anymore.  I'm fairly certain its gone.  With stock apple earbuds, being pressed painfully into my ears with my fingers, I can hear a very faint buzz.  I think I'm going to call it good enough because if I can't hear it under normal conditions, its not there.
 
There is still a hiss though that is audible with 80ohm 109dB sensitivity Beyer DT1350's, and stock Apple earbuds.  This might just be form the high IEM-like sensitivity of the headphones though.    What do you think? 
 
I just wanted to say thanks guys, the amp is much much quieter now than it was already.  I'm not too concerned about the hiss with high sensitivity headphones because that's how many amps are but if its not supposed to be there, let me know!
 
I'm really only using the amp with HE-500's and it sounds great with them.
 
 
EDIT:  To add, I went with Option 2 but I didn't see the post until I did it. 

 

[jdkJake]

Interesting results. While I am not sure you actually need the GLB any more (leave the grounds tied together but leave them floating from the transformer case earth ground), I hesitate to suggest taking it out if the amp is performing to your liking.

As for the hiss, what are you using for a source? I only get a low-level hiss when I use something like an iPod line-out as a source. I do not get a low-level hiss from my gamma2 or NAD Universal as a source. This is true for the 1350's (which I have) as well as 32ohm Grados. I have not tried earbuds or my X5 IEM's, so, I cannot comment on that combo.

How loud is the hiss? Always there or only when no other input is present?