Hello.
I have been working on a nice KA-7002 that had a slight preamp power hum. I recapped the tone board and replaced the c458 transistors with KSC1815s. All was well, until I got super OCD and decided that the phono stage had too much background hiss when volume was turned up.
I set my sights on the protection board (based on some other AK threads) and discovered that one of the c458 transistors on this board (Q2) had its emitter lead was not soldered to the board - I took care of this problem and upon testing, the unit was producing very little sound. A little more sleuthing and I discovered that D2 was faulty. All good after replacing with a modern zener diode.
That is, until focused on the low level board. I swapped Q2 on this board with a KSC1845 (ran out of 1415s) thinking I would compare the two sides to see if the new transistor helped with background hiss. What I heard when testing was the phono signal completely out of phase/vocals almost non-existent etc. I immediate put the original back in and it still sounds out of phase. Aux input sounds great...
I have triple checked that I installed the transistor just as it was previously (I took pictures)
I have also noticed that the Null Balance button has no effect when playing phono signal, and there appears to be some power issue when switching the selector pot which now produces a loud pop."
Any guidance would be most appreciated.
I have been working on a nice KA-7002 that had a slight preamp power hum. I recapped the tone board and replaced the c458 transistors with KSC1815s. All was well, until I got super OCD and decided that the phono stage had too much background hiss when volume was turned up.
I set my sights on the protection board (based on some other AK threads) and discovered that one of the c458 transistors on this board (Q2) had its emitter lead was not soldered to the board - I took care of this problem and upon testing, the unit was producing very little sound. A little more sleuthing and I discovered that D2 was faulty. All good after replacing with a modern zener diode.
That is, until focused on the low level board. I swapped Q2 on this board with a KSC1845 (ran out of 1415s) thinking I would compare the two sides to see if the new transistor helped with background hiss. What I heard when testing was the phono signal completely out of phase/vocals almost non-existent etc. I immediate put the original back in and it still sounds out of phase. Aux input sounds great...
I have triple checked that I installed the transistor just as it was previously (I took pictures)
I have also noticed that the Null Balance button has no effect when playing phono signal, and there appears to be some power issue when switching the selector pot which now produces a loud pop."
Any guidance would be most appreciated.
