Headphone Amp
August 15, 2007
Gur. The headphone amp whice I’ve been working on… isn’t. The damned things just blows fuses. It was working fine one morning, that evening there was crackling fading in/out in the left channel, and the following day it just blew fuses. I didn’t change anything between the days.
It’s not the tubes, as I’ve tried another pair for them.
<sigh>
is it grounding out on the chassis perhaps?
It happens when out of the chassis, and there’s no direct short to ground. When I meter Vcc and Vdd I see 33.8Ω, which just about matches the two tube heaters (~12Ω each) plus the resistor sitting betweent he heaters (~10Ω). So, that’s right.
I’m suspecting there’s something up with one of the transistors or FETs, but I don’t know how to check those without pulling them. Hell, I can’t even isolate individual channels because of how the board is laid out.
any caps in line that could be flakey?
(pardon my stabs at the simple stuff… I like replacing the cheapest parts first. my own brand of Occam’s razor. ;) )
I don’t think so, because I don’t see any dead shorts, although it’s possible. However, isolating the caps in a purely analog audio amplifier will require loads of desoldering. Check out the schematic.
And thanks for the suggestions, I’d just be a bit more apt to build a new one than rip out and replace all the caps, one at a time. :\
my, but that is a lot of caps.
go for the obvious. any of them can type? if so, any less than perfectly flat tight X tops? sometimes the meter can distract… go for the old mark I eyeball. I’ve repaired a few motherboards that way.
They are all spot-on, no bulges, no leaks, and no funky smells. :( They are all larger ones (See this photo) and kinda pricy (audio grade) and I wouldn’t have spares before next week. :( Check out my next post, though… It’ll be there soon.