Fabio Ba283 driver board problem

I have built one of those fabio driver boards ,every thing is ok but it sounds very hissey ,what would cause this effect , is it the transformer ,caps or my smoothing stage i dont know myself.I have  changed the cap on the psu but that makes no difference.

Also i can hear a silt hum from the out as well is this too much volage or current ?

needs some help on this



regards

skal1

OK it has been just under a year since i built this board and i still can not  lower the hissey noise from this pre .

I started testing it but i can not find a problem the noise level is to high for me to use it  is 42 db i have changed 2n3055 a couple of times and the bc184s,

can some with a bit more knowledge on this card  help with this.

thanks in advance

skal1

What does fabio say about it ?

I've tried to reach him thru email recently but no response ?

i think the 184's were supposed to be tested [ most digital multi meters will do it ]
for an hfe of 600 or better
have you isolated it to the driver board ? with nothing  [ or a simple load ]
connected it still makes that much noise ?

okgb  with no input tx the noise is the same with plutec filter sec  the noise is the same , out tx carnhill gaped vtb 9049 could it be the 2n3055 they are not motos

skal11

okgb said:

i think the 184's were supposed to be tested [ most digital multi meters will do it ]
for an hfe of 600 or better

Click to expand...

+1

JLM specifically mentions this on their BA283 page:
http://www.jlmaudio.com/neve_ba283.htm


I just went through 20 BC184s and found about 8 that measured 620+ hFE.
Most were in the 550–580 range.

No, I don't think it's your 184s...  You clearly have a major problem.  Like a wrong value, or a bad connection, or a reversed transistor put in backwards.  Or wiring problem.  Go over everything again.  Rebuild it (in your mind and eye) part by part.  Compare it with a known working card.  There is nothing wrong with Fabio's cards. It's something wrong with the build.

Ditto Tommypiper on this.  Your 184's are fine. 

My guess is it's the grounding.  Make sure there is only ONE connection between the audio ground and chassis/earth ground, preferably near the AC connector.  More than one connection between these two grounds and you'll have noise pretty much exactly like what you describe. 

Also, make sure the audio transformer cores are grounded to the chassis.

And your power should be +24vdc.  Each 283 draws about 100mA of current, so double that per channel so you have some current in hand for power-up, and you should be just fine.

JC

I don't know about the fabio boards,
I had loads of problems with mine (self-etched) and then I etched a version I found somewhere on the forum that was more of a straight xerox clone of the ba283 and it was puuurrrrrfect.  The fabio board makes a connection to ground through the 2n3055(iirc), i.e. it depends on good contact from both screws that hold the heatsink and the housing of the 2n3055 to the board and this was not working ideally on my boards.  the real neve boards have a connection to the heatsink/2n3055 but it's only to ground the amp, not to make the whole circuit properly grounded. 
take an alligator clip to ground and play with this a little, maybe you just need washers with teeth to make the connection work properly or you need to solder a little jumper in between the offending grounds
Good luck
Kelly

Sleeper said:

I don't know about the fabio boards,
I had loads of problems with mine (self-etched) and then I etched a version I found somewhere on the forum that was more of a straight xerox clone of the ba283 and it was puuurrrrrfect. 
Good luck
Kelly

Click to expand...

Hey kelly have you a copy of that board to hand might .

skal1

yeah right in your case , i agree with rascal
trace parts against the schematic for values
it almost sounds like a gain staging issue
,maybe as suggested through a wrong value
while checking the parts double check the traces
at the same time you know
at point A , parts x,z, y  connect ,point b t , s connect

i find the 1% resisters agianst blue , hard to read but
start from the start and work your wau through

@okgb did this last night everthing as it should be , i even went as far as to remove the coupling caps and it still excebits the same noise
{hiss}  i think i will sell the iron


skal1

;D found the prob looks like the 220pf had dry joint  ;D

skal1 lets hope it is the same on the other channel

Good to hear!   

FWIW those Fabio boards are perfect.  I used two of them in the outputs of my original 1084's.  The BA283 in one of them went south, and I never did find the problem, so I sold that board 'as is' (yes, I told the buyer it was jacked, and he was cool searching the problem for himself).  I populated one of Fabio's BA283's to replace it, and then did another exactly the same way for the other 1084, so they'd be a 'matched pair' so to speak. 

I kept the good original 283 as a spare.

So if someone's having a problem with one of those the problem is in the build, not the pcb.

JC

yes i agree, what did your noise level measure ? mine is about 50 db is this ok


skal1

hey guys
came across this thread while searching for a pultec neve gainstage board...
where do you order fabios driver board??
cheers