Techtalk

yes on both channels, exact the same

in the motherforum someone changed the rectifiers , and then his hum disapeares

...change the retrifiers still hum

all looks good at the photo.
when you disconnect the heaters from one side, is there still hum on the other side ?

waldorfcave hat geschrieben:gain ratio have to be tuned like volker said (i use sowters) i do it later....

one problem is, that my unit hums a bit. more then it is ok for me

how much is "a bit" ? (LA2As are not famous for low noise)
is the hum constant or gain depended ?

hum is to loud, not normal

hum is constant not gain depended.

rewire my ac heaters and check in one minute

Did you mount the 7805 isolated from heatsink and caseground? Doppelkühlung You may have a ground loop. Is hum frequency pre (mains side) or post rectifier (double mains frequency)?

-Harpo

Lars,
did you use shielded wires for pots, output tranny and XLR? The HT wiring is a real pita.
Never mind, Volker
regards
Bernd

7805 is isolated, i checked without heatsink...

shielded wire for pots and xlr, output tranny has no shielded wire...

i disconnected the ac heaters from other side and nothing happens
rewireing of the ac heater not helped

for info: hum is there also when nothing is connected to input

later i will measure the hum

here u can see and listen to my hum

direct patch the output of one side in my motu hd192 converter

http://www.waldorfcave.com/humla2a.wav

just a guess, did you connect the output tranny to ground? (black wire) XLR outs to ground as well? hmm, strange?

at first I thought the soundfile is empty - never try to hear this on the Computer

but in Pro Tools I can hear it. compared to mine: yes, there must be something wrong

mhm - have to think about it ...
may be do the Gain pot change first.

Bernd, the black wires from the 8940 are grounded on the PCB.

The HT wiring is a real pita.

it is just the 3rd layer of the PCB

thx...

but can i also use a 25k log pot? where should iconnect the 75kr resistor?

25K log is even better. the 75K resistor goes between pin3 of the pot and pin3 of the molex connector. (the circuit stil sees a 100K pot, but you can only move it from 0R to 25K). less gain, but even with this "mod" I never went behind the middle of it.

cool volker, i order such pots.

tomorrow i will measure some voltages, maybe there is afault

whats about with this "grid stopper" thing?

i read a lot in prodpro forum. should i try it?

http://www.prodigy-pro.com/forum/viewtopic.php?p=258781