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EHHA Rev A - Interest Thread - Page 108

post #1606 of 1733

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 :-(

post #1607 of 1733

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....

post #1608 of 1733
Quote:
Originally Posted by Sathimas View Post

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?
post #1609 of 1733
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.
post #1610 of 1733

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

post #1611 of 1733

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)

post #1612 of 1733
Quote:
Originally Posted by Sathimas View Post

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?
post #1613 of 1733

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

post #1614 of 1733

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

 

Quote:
 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.


Edited by Sathimas - 1/12/14 at 4:02am
post #1615 of 1733

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.


Edited by Sathimas - 1/12/14 at 6:13am
post #1616 of 1733

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 ;-)


Edited by Sathimas - 1/12/14 at 9:31am
post #1617 of 1733

Hang on in Sathimas, you are almost there...!

 

Your head must be buzzing from all that rewiring, checking and test-listening  ;).

post #1618 of 1733

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 f****** 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/

post #1619 of 1733

Anyone using ehha with HD800?


Edited by FOXY - 1/19/14 at 4:57am
post #1620 of 1733
Quote:
Originally Posted by FOXY View Post
 

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.

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