I'm trying to repair a Sony F 630 ESD, from which the volume pot has broken off.
I know of ALPS pots that have a 4th lug, unfortunately I can't fit those between the PCB and the faceplate. I went for a normal 100k pot instead, not feeding anything back to the loudness circuit. Which results in a strange feedback and hum.
How do I overcome this? I'm confused on how the circuit works (see attachment). I'm guessing I can hardwire the source direct switch to a "always on" but I still want to keep the EQ
I know of ALPS pots that have a 4th lug, unfortunately I can't fit those between the PCB and the faceplate. I went for a normal 100k pot instead, not feeding anything back to the loudness circuit. Which results in a strange feedback and hum.
How do I overcome this? I'm confused on how the circuit works (see attachment). I'm guessing I can hardwire the source direct switch to a "always on" but I still want to keep the EQ
Attachments
From what I understand from this schematic is that there is no loudness control there but rather volume level related tone control. I.e. the effect of tone control is reduced from the center tap "upwards". You can wire it to function as classical tone control (without volume related impact) while keeping the source direct on/off switch functionality.
Measure the resistance from this 4th tap to the input and ground legs of the original pot (eg 50k-50k or 25k-75k).
Make a parallel equal divider network with the same sum resistance of 100k.
Inject the output of this divider upon the wiper of the volume pot (you might use an extra cap of 1µ0).
It's a bit quick & dirty, but see if that suffices.
Make a parallel equal divider network with the same sum resistance of 100k.
Inject the output of this divider upon the wiper of the volume pot (you might use an extra cap of 1µ0).
It's a bit quick & dirty, but see if that suffices.
That did it, thanks!
In a wild search on ebay I also found some 2x100k pots with a 4th tap at 50k, I'm gonna test those as well.
Great!
100k is almost 120k, expect the original 4th lug at approx 1/3 from ground - it's for loudness.
These 100k's will perform better.
100k is almost 120k, expect the original 4th lug at approx 1/3 from ground - it's for loudness.
These 100k's will perform better.