sirion
New Head-Fier
- Joined
- May 22, 2002
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I just finished soldering a pocket cmoy (Using an OPA2132, and guided by Tangent's tutorial on Chu Moy's design) to drive some Senn HD600s coming in a week or so.
In testing it (using alligator clips and a mini-to-mini cable, before I start adding minijacks, switches, pot, etc) I've noticed that it's producing hiss on my Koss earbuds, and on some crappy sharp stock earbuds. My source for these tests is a Sharp MD 877.
The hiss is a somewhat quiet and even white noise, coming out of both channels equally. It's at the same level no matter how I set the volume on the Minidisc player (and I don't have a pot installed on the amp yet, so I'm not sure how that will affect it), and continues going if I pause the player. If I disconnect the cable from my MD player or shut it off, the hiss goes away.
I've tested the cable, and it's definitely not that. The MD player produces no audible noise without an amp.
As for the amp...
The voltages on the + and - side, with respect to ground, are 4.13 and -4.10, respectively. All resistors are matched, and at their default values. R5 is installed on both channels at 47 ohms. The amp pumps up the volume enough to make those sharp earbuds audible across the room(albeit distorted, and I probably broke the earbuds
Right now there's no crossfeed, so it's just the simple circuit. Will this just go away with the higher impedence Sennheisers? Ideally, I'd like this amp to work with whatever I stick into it...
Stuff I've tried:
I've bridged R5 with a lead to see whether removing it would make the hiss louder or anything, and I couldnt hear any difference at all (which seems kinda weird, as forum posts seem to point out that R5 will clean up most of anything, though it won't eliminate the source of the problem)
I've put the amp in aluminum foil, and didn't hear any changes in the hissing.
I left it connected for a few hours today, and when I came back, the battery was dead (Well, at the very least, the battery's voltage is at 7.5V and drops down to 2.5 within seconds of putting it in the amp. I assume that means it's dead). That seemed kind of weird, in that it's a brand new battery...aren't these amps supposed to last longer, particularly when there's no music playing?
Anyway, I'm running out of ideas!
In testing it (using alligator clips and a mini-to-mini cable, before I start adding minijacks, switches, pot, etc) I've noticed that it's producing hiss on my Koss earbuds, and on some crappy sharp stock earbuds. My source for these tests is a Sharp MD 877.
The hiss is a somewhat quiet and even white noise, coming out of both channels equally. It's at the same level no matter how I set the volume on the Minidisc player (and I don't have a pot installed on the amp yet, so I'm not sure how that will affect it), and continues going if I pause the player. If I disconnect the cable from my MD player or shut it off, the hiss goes away.
I've tested the cable, and it's definitely not that. The MD player produces no audible noise without an amp.
As for the amp...
The voltages on the + and - side, with respect to ground, are 4.13 and -4.10, respectively. All resistors are matched, and at their default values. R5 is installed on both channels at 47 ohms. The amp pumps up the volume enough to make those sharp earbuds audible across the room(albeit distorted, and I probably broke the earbuds
Right now there's no crossfeed, so it's just the simple circuit. Will this just go away with the higher impedence Sennheisers? Ideally, I'd like this amp to work with whatever I stick into it...
Stuff I've tried:
I've bridged R5 with a lead to see whether removing it would make the hiss louder or anything, and I couldnt hear any difference at all (which seems kinda weird, as forum posts seem to point out that R5 will clean up most of anything, though it won't eliminate the source of the problem)
I've put the amp in aluminum foil, and didn't hear any changes in the hissing.
I left it connected for a few hours today, and when I came back, the battery was dead (Well, at the very least, the battery's voltage is at 7.5V and drops down to 2.5 within seconds of putting it in the amp. I assume that means it's dead). That seemed kind of weird, in that it's a brand new battery...aren't these amps supposed to last longer, particularly when there's no music playing?
Anyway, I'm running out of ideas!
