Hey all,
I'm working on a Phase Linear 4000 preamp for a friend of mine. It needed a recap and several cold solder joints repaired. I've completed that, and it's working great except for a few quirks. As I don't have another one here to compare to, I'm trying to determine if these are normal, or if further investigation is required...
#1 (This existed before I started the recap etc) - It seems like the first 1/4 turn or so of the volume pot is a dead zone. I don't get any change in volume until it's at 1/4 turn, then it seems normal.
I took the volume pot out, and checked both gangs on the ohm meter, it's reading 4 ohms on one end and 86k on the other - seems OK. I don't see any dead spots in the pot itself when I check with a simpson meter and slowly turn it. The resistance goes up smoothly as you turn it. Is this normal? I did find a post here mentioning they used a linear instead of a log pot, I guess that could explain it? He also noticed that when it's all the way off, some volume still bleeds through, but the Phase Linear fast field service manual says this is totally normal.
#2 I thought many of the RCA inputs were bad, but it seems to me like they are extremely picky about the type of cable used. Almost none of the RCA cables I have make this happy except for the ones that are built into my Audio Technica AT-LP120 and an old RCA to 3.5mm adapter I had. It seems like other designs don't go in far enough to disengage the shorting switch inside the jack. I notice a more positive 'click' feel when I use the RCA cables it likes. Do I just need to tell him that's normal and he will need to experiment with RCA's until he finds some that this thing likes?
#3 If you switch off the pre, but leave your power amp on, it takes several seconds for the sound (and front panel power LED) to shut off. Clearly caused by energy stored in the capacitors, but I'm surprised they didn't design the circuit to avoid this?
Any feedback appreciated. Thanks!
I'm working on a Phase Linear 4000 preamp for a friend of mine. It needed a recap and several cold solder joints repaired. I've completed that, and it's working great except for a few quirks. As I don't have another one here to compare to, I'm trying to determine if these are normal, or if further investigation is required...
#1 (This existed before I started the recap etc) - It seems like the first 1/4 turn or so of the volume pot is a dead zone. I don't get any change in volume until it's at 1/4 turn, then it seems normal.
I took the volume pot out, and checked both gangs on the ohm meter, it's reading 4 ohms on one end and 86k on the other - seems OK. I don't see any dead spots in the pot itself when I check with a simpson meter and slowly turn it. The resistance goes up smoothly as you turn it. Is this normal? I did find a post here mentioning they used a linear instead of a log pot, I guess that could explain it? He also noticed that when it's all the way off, some volume still bleeds through, but the Phase Linear fast field service manual says this is totally normal.
#2 I thought many of the RCA inputs were bad, but it seems to me like they are extremely picky about the type of cable used. Almost none of the RCA cables I have make this happy except for the ones that are built into my Audio Technica AT-LP120 and an old RCA to 3.5mm adapter I had. It seems like other designs don't go in far enough to disengage the shorting switch inside the jack. I notice a more positive 'click' feel when I use the RCA cables it likes. Do I just need to tell him that's normal and he will need to experiment with RCA's until he finds some that this thing likes?
#3 If you switch off the pre, but leave your power amp on, it takes several seconds for the sound (and front panel power LED) to shut off. Clearly caused by energy stored in the capacitors, but I'm surprised they didn't design the circuit to avoid this?
Any feedback appreciated. Thanks!
