[Sathimas]

Took a bit longer than I thought ...
 
With the inputs grounded directly on the boards there's no hum on the right
and more hum on the left than with the pot connected.
 
I'll try separate input ground wiring now.
 
 
Btw: With my 250Ohm T90 the amp is dead quiet

 

[Sathimas]

Next results:
 
I wired input ground from the jack to the pot separately for each channel.
Ground pins on the pot are not connected to each other.
 
Result is the same as with inputs grounded directly at the board:
 
Worse than having everything hooked up like before....

 

[jdkJake]

Took a bit longer than I thought ...

With the inputs grounded directly on the boards there's no hum on the right
and more hum on the left than with the pot connected.

I'll try separate input ground wiring now.


Btw: With my 250Ohm T90 the amp is dead quiet

Okay. At least you are down to one board. Since the right one is fine, it is just a matter of tracking down the difference between the two.

I would verify your ground connections on the screw headers are making contact properly (no cold soldier joints, etc...). Using a multimeter, can you verify the star ground connection on the input header is making contact with the ground plane? You can measure between that point and any other ground point. Or, you can use O3 on the output header as long as it is not wired up (disconnect temporarily).

You may also want to swap the left and right channels and see if the problem follows the board. That would help rule out chassis wiring and isolate the problem to the amp board itself.

BTW, What are you using for output resistors? (R22/R23) Did you build the MOSFET or BJT?

 

[fishski13]

good points. i would take out fhe boards, swap them, and double check all wiring. if the noise follows the board, then it's the PCB - maybe even a cold solder joint on one of the Phoenix connectors that broke loose with the force of tightening the wire in with a screwdriver. also, pay attention to Phoenix header/slots that have more than one wire. i prefer to only use one terminal wire per slot. if you need to connect two wires, just solder the 2nd wire just up stream and use some heatshrink if necessary.

 

[Sathimas]

Well, I'll try - but maybe I cant swap the boards because of the tube-socket wiring...

 

[Sathimas]

I built the mosfet version from the kit of glass jar audio.
 
Do you want to know the values of the resistors?
Can't find the glassjaraudio bom at the moment and
the multimeter is dead because of an empty battery.
(Gonna get a new one tomorrow)

 

[jdkJake]

I built the mosfet version from the kit of glass jar audio.

Do you want to know the values of the resistors?

Yes.

BTW, did you ever swap the tubes between the two channels to see if the problem is with one of the tubes?

 

[stixx]

I seem to remember that Sathimas did swap the tubes as one of his first attempts to track down the cause of the hum...

 

[Sathimas]

Swapping the tubes brings no change, hum stays left.
 
 
What confuses me most is that each channel alone, with the other
one being not connected, is quiet. Only having them both running
brings up the hum.
 
Here's the resistor-values: 2.2 Ohm
 

 I would verify your ground connections on the screw headers are making contact properly (no cold soldier joints, etc...)

 
Did that already to be sure - got 0 ohms from all ground connectors to star ground.

 

[Sathimas]

Some more experimenting:
 
Swapped the boards, both wired that way:
(The configuration in which channel alone is quiet)
 
Output ground - output jack
 
amp_ps ground - ground on amp board
 
heater_ps ground - star ground
 
SG on amp board - star ground
 
 
GLB between SG and mains ground on the AC-inlet
 
 

The hum is still on the left side after swapping the channels.
So the "left" board is not the problem.

Well, this conlusion seems wrong or at least not complete...
 
 
Having everything wired like the "alternate wiring scheme",
now the right channel exhibits the hum. (The board that was left before...)
 
This is really crazy.
 
 
[Edit Nr.2]
 
Having all wired after the normal wiring scheme the hum stays right.

 

[Sathimas]

Took out the probably faulty channel once again and carefully reflowed all solder joints.
 
Back in the case, wired after the alternate wiring scheme  I now have the same
subtle hum on both channels - wooohoooo!
 
 
With my ATH W1000, it is barely noticable without music playing.
With the Beyer DT1350 it's the same - barely there, but still there...
 
 
I'll try out some other wiring options now - having some new hope now...
 
 
[Edit]
 
Transplanted everything back (re-swapping channels), tidied up the wiring
and there was no bad surprise after switching on the amp

 

[stixx]

Hang on in Sathimas, you are almost there...!
 
Your head must be buzzing from all that rewiring, checking and test-listening 

.

 

[Sathimas]

My head is indeed buzzing :-D
 
 
For the moment I'll settle with what I have accomplished 'til now.
 
 
I really gotta concentrate to hear the hum on the left.
On my right ear I can't hear it anyway since I got a 40dB hearing loss
up to 1Khz - maybe the only benefit of that screw*** acute hearing loss...
 
 
Now I'll wait until I get the AMB e12 and see what happens after
adding that to the circuit.
 
 
Next step is cutting a piece of acryl glass that will hold the pot.
 
 
Thankfully, a friend of mine has already done some tests on that:
 
http://eigenbaukombinat.de/bastlerglas-frasen-versuch-nr-3-4-und-5/

 

[FOXY]

Anyone using ehha with HD800?

 

[Mullet]

  Anyone using ehha with HD800?

 
I've been curious about this as well. Don't have them, but I could see getting them in the future.
 
Anyone know if Jeff Rossel at Glass Jar Audio is away on vacation or still selling kits? I've emailed twice and haven't gotten a response. Maybe, I'm just being a little impatient.