Oldsansui441
Super Member
Hi, l have just been working on a Akai AA-6000 from around 1971. It had a low level hum in the left channel with volume between 1/4 and 3/4. I narrowed the noise down to the pre amp/tone section as l desoldered the inputs at the LH main amp board and all was quiet with headphones.
The unit was full of 2SC458's (14 on pre amp and 1 each on main amps) so l replaced all of these and recapped the pre amp also. Hum was still present in left channel.
After hours chasing this hum, checking/adding earths etc l finally found that it was the power switch interfering with the adjacent tone control board. The LH lower portion of the tone board closest to the power switch is for the left channel. I made up a little shield board out of a new piece of circuit board and soldered/glued it in place (a little rudimentary l know but does the job). I first just used the large piece in photo to separate the power switch and board, this eliminated most but not all hum. Then l added the little piece behind the power switch and now hum is 100% gone.
Anyway just thought l would post this hoping it may prevent someone spending hours like l did. I am also wondering if in fact this amplifier may have always had this concern, hard to believe though. I saw an old for sale ad for one that also had this exact concern (volume dependent hum in left channel).
BTW this is a nice sounding amp.
The unit was full of 2SC458's (14 on pre amp and 1 each on main amps) so l replaced all of these and recapped the pre amp also. Hum was still present in left channel.
After hours chasing this hum, checking/adding earths etc l finally found that it was the power switch interfering with the adjacent tone control board. The LH lower portion of the tone board closest to the power switch is for the left channel. I made up a little shield board out of a new piece of circuit board and soldered/glued it in place (a little rudimentary l know but does the job). I first just used the large piece in photo to separate the power switch and board, this eliminated most but not all hum. Then l added the little piece behind the power switch and now hum is 100% gone.
Anyway just thought l would post this hoping it may prevent someone spending hours like l did. I am also wondering if in fact this amplifier may have always had this concern, hard to believe though. I saw an old for sale ad for one that also had this exact concern (volume dependent hum in left channel).
BTW this is a nice sounding amp.
Attachments
Last edited:
