Quad 303 issue "HELP"

[Gravenstede]

hey-hey

iv bought a quad 303 a little while ago [serial 1568 ] so this is a real old one but sadly the right hand channel has always been really quite 😕

iv changed the audio board capacitors with elna ones and i upgraded the power supply with the main kit from NET AUDIO, it didnt blow up 😀 however the right channel is still really quite, it almost does nothing.

right and left audio boards both have 33v supplys and iv set the bias on both 😕

could it be the power transistors at fault? if so is this a chance to upgrade further?

im 19 and have a limmited knowledge on electronic stuff so please dont blow my mind with anything to complex lol

 

[Thomo]

Hi, nice work so far.

I would definitely change those trim-pots to something better. The values may drift with temperature after all these years.

I'm fairly new to all this too, but I recently sold my upgraded 303. I would compare the voltages on the bad board to the good board and that may help you trace the fault.

Upgrading the transistors did improve the sound for me.

Regards, Lee.

 

[Gravenstede]

cheers man, iv kinda been comparing the two boards but it hasnt really helped much in finding a fault

as for those trim pots jesus your so right, mine are totaly crap almost constant change iv had, il change them next,

thanks dude

 

[Thomo]

I had a similar problem with my old 303. The bias will drift if the value of those pots changes with the temp.

Multiturn pots are the best, but enclosed type will be ok. I bought mine from Maplins.

Lee.