C4 preamplifier dc fluctuation
- Thread starter Hifibythekg
- Start date
Hifibythekg
Super Member
Yes.
Strangely, just spraying one side settles down the behaviour of both channels. Haven’t tried spraying the transistor on the other side.
Strangely, just spraying one side settles down the behaviour of both channels. Haven’t tried spraying the transistor on the other side.
Hifibythekg
Super Member
Scrub my previous post.
DMM was on higher DC setting and wasn't displaying the range.
The problem is still the same, testing again
DMM was on higher DC setting and wasn't displaying the range.
The problem is still the same, testing again
Hifibythekg
Super Member
DC settled upon +/- 200mV ...ish. Thanks again for help on that guys.
But now....
HUM !
Symptoms:
Present with Tone Bypass activated but it’s much less so, about a third.
Tone controls set to ‘defeat’ has same hum level as Tone Bypass.
Go either side of zero on the bass or treble and the hum is immediately louder.
Loudest at +5 bass and +5 treble.
On Input selector:
Loudest hum is
Phono MC
then Phono MM 1 and 2.
Tuner and Aux are identical and about half the hum level of Phono 1 and 2.
Where is this ‘ground hum’ most likely to be originating?
All switches have been serviced, including the wafers.
Reflowed solder and checked over the main boards.
Attached TT’s and unattached and touched the ground plug and RCA sockets but this makes not the slightest difference in hum tone.
Obviously I’ve missed something... but where best to look now?
But now....
HUM !
Symptoms:
Present with Tone Bypass activated but it’s much less so, about a third.
Tone controls set to ‘defeat’ has same hum level as Tone Bypass.
Go either side of zero on the bass or treble and the hum is immediately louder.
Loudest at +5 bass and +5 treble.
On Input selector:
Loudest hum is
Phono MC
then Phono MM 1 and 2.
Tuner and Aux are identical and about half the hum level of Phono 1 and 2.
Where is this ‘ground hum’ most likely to be originating?
All switches have been serviced, including the wafers.
Reflowed solder and checked over the main boards.
Attached TT’s and unattached and touched the ground plug and RCA sockets but this makes not the slightest difference in hum tone.
Obviously I’ve missed something... but where best to look now?