Hi there everybody. I'm asking you to be patient with me cos I a total noob. I copied once a schematic and everything went ok, then I made a decision to assemble some circuits together to get the preamp I wanted.
I'm talking guitar here btw.
I use a bogner ecstasy signal preamp [here: http://www.mif.pg.gda.pl/homepages/tom/files/xtcod.gif ] and an AX-84 plate psu with some mods.
For the filaments I use a switching mode psu. I get 9v outta it and then pass it thru 3 x 7805's grounded with 2 diodes each. This gets me 6.29v on the filaments with load connected.
I use a 1000uF cap to ground before the 7805's and a 100uF cap for each 7805 output.
Now, problem is I get a really bad hum, a sort of hi-pitched whistle [I can record it if you want] and I know it comes from the filaments psu cos I put a switch on it and when I turned it off the hum disappeared very soon,,,
If I ground the 7805 casing [which I thought to be the same as the ground pin] to the negative of the first cap of the plate psu I still get 6.29v on the filaments and no hum at all but this is only with the guitar plugged in,,, as soon as I unplug the jack from the female on the amp it hums back again,,, if I just unplug the jack from the guitar, it doesn't hum,,,
I also tried a different psu for the filaments and it did just the same,,,
any suggestions on what to check? this amp sounds very good, just it has this prob it would be a shame and a personal failure if I had to give up,,,
I'm talking guitar here btw.
I use a bogner ecstasy signal preamp [here: http://www.mif.pg.gda.pl/homepages/tom/files/xtcod.gif ] and an AX-84 plate psu with some mods.
For the filaments I use a switching mode psu. I get 9v outta it and then pass it thru 3 x 7805's grounded with 2 diodes each. This gets me 6.29v on the filaments with load connected.
I use a 1000uF cap to ground before the 7805's and a 100uF cap for each 7805 output.
Now, problem is I get a really bad hum, a sort of hi-pitched whistle [I can record it if you want] and I know it comes from the filaments psu cos I put a switch on it and when I turned it off the hum disappeared very soon,,,
If I ground the 7805 casing [which I thought to be the same as the ground pin] to the negative of the first cap of the plate psu I still get 6.29v on the filaments and no hum at all but this is only with the guitar plugged in,,, as soon as I unplug the jack from the female on the amp it hums back again,,, if I just unplug the jack from the guitar, it doesn't hum,,,
I also tried a different psu for the filaments and it did just the same,,,
any suggestions on what to check? this amp sounds very good, just it has this prob it would be a shame and a personal failure if I had to give up,,,