LM3875. Single chip amplifier. +/-38 volt rails, 1000 uF filters. I'm 99.9% sure I got everything right--nothing blew up, and my meter told me all was well.
Still, I hooked up a speaker and--+V rail appears at the output. Whoops.
Does this mean the chip is dead? Or do I just have something wired wrong? It's not a super big deal... it was an ugly hackjob anyway... but from what I'd read, the chips mostly didn't swing one way or the other when they died... This is my first attempt and I don't know if I should just move on or check my connections for a 43rd time...
Thanks all.
(PS - it actually made a pretty neat noise when I turned it on with a load connected... too bad it burned out the speaker in the process.
)
Still, I hooked up a speaker and--+V rail appears at the output. Whoops.
Does this mean the chip is dead? Or do I just have something wired wrong? It's not a super big deal... it was an ugly hackjob anyway... but from what I'd read, the chips mostly didn't swing one way or the other when they died... This is my first attempt and I don't know if I should just move on or check my connections for a 43rd time...
Thanks all.
(PS - it actually made a pretty neat noise when I turned it on with a load connected... too bad it burned out the speaker in the process.
)
Details, details...
It's the most sloppy, horrible implementation ever. I'm positive that I got the connections right--the problem was, I'm sure, my own laziness.
One question that I didn't ask, out of both laziness and embarassment, because at the time I bought my caps, I thought I'd be using a 35 volt rail... just how bad is it to run these things outside spec? They've gotta have some headroom, right? 38V isn't THAT much above the rating...
...
The caps are just fine. No signs of degradation. There isn't actually any sign of trouble anywhere, other than the whole project looks like $#!%. The only thing that's amiss is that, while I was testing, I did a boo-boo with a multimeter and momentarily shorted one of the transformer leads to ground... it sparked alot, gave my dad a heart attack, but didn't even throw the breaker.
I'm moving on to a better project now, with proper circuit boards and stuff... this time I AM going to trim off the unused leads on the chip and I AM going to get capacitors the right rating... and I'm going to ground everything properly and take my time.
Still, I can't help wondering... is my chip maybe still good? Is it worth the trouble of pulling it out of its current home or should I just toss the little POS PCB I used?
Thanks everyone...
It's the most sloppy, horrible implementation ever. I'm positive that I got the connections right--the problem was, I'm sure, my own laziness.
One question that I didn't ask, out of both laziness and embarassment, because at the time I bought my caps, I thought I'd be using a 35 volt rail... just how bad is it to run these things outside spec? They've gotta have some headroom, right? 38V isn't THAT much above the rating...
...
The caps are just fine. No signs of degradation. There isn't actually any sign of trouble anywhere, other than the whole project looks like $#!%. The only thing that's amiss is that, while I was testing, I did a boo-boo with a multimeter and momentarily shorted one of the transformer leads to ground... it sparked alot, gave my dad a heart attack, but didn't even throw the breaker.
I'm moving on to a better project now, with proper circuit boards and stuff... this time I AM going to trim off the unused leads on the chip and I AM going to get capacitors the right rating... and I'm going to ground everything properly and take my time.
Still, I can't help wondering... is my chip maybe still good? Is it worth the trouble of pulling it out of its current home or should I just toss the little POS PCB I used?
Thanks everyone...
When I first slapped my gainclone together, it just wouldn't pass audio. I had 2 or 3 mV DC offset at the output, but no audio. It just seemed really wierd. It could be because I just grabbed parts out of my spare parts bin, but gainclones are supposed to be pretty tolerant of different parts. It should have at least passed audio.
Nappy, if your chip is fried, I've got 2 more at the shop. Let me know if you need another one.
Cheers,
Zach
Nappy, if your chip is fried, I've got 2 more at the shop. Let me know if you need another one.
Cheers,
Zach
Right values?
Hi,
if you browse around this forum, you will find many Gainclone implementations using:
2x18V/160VA (and at least 1000uF/35V caps) on a 4 Ohms load
2x24V/160VA (and at least 1000uF/50V caps) on a 8 Ohms load
These values should be ok to prevent the current limiter of the 3875 from switching on and to have a reasonable dissipation of power (=less heat).
Ciao, Massimo
Hi,
if you browse around this forum, you will find many Gainclone implementations using:
2x18V/160VA (and at least 1000uF/35V caps) on a 4 Ohms load
2x24V/160VA (and at least 1000uF/50V caps) on a 8 Ohms load
These values should be ok to prevent the current limiter of the 3875 from switching on and to have a reasonable dissipation of power (=less heat).
Ciao, Massimo
UseKQB: I'd be very interested in seeing your work in person; I've been dying to get out and don't have a car. I agree--we should put our heads together.
I have 4 more chips and I plan on ordering some more from National--eventually I want to have a 6-channel amp to replace the one I blew up last month. (That was an RCA home-theatre amp that, after opening up its poor fried carcass, found out it was a hybrid--no wonder it sounded so bad--and the thermal grease hadn't even turned brown. Those pioneer chips apparently have a glass jaw...)
I bought one of those nifty copper-clad fiberglass PC boards from Radio Shack and I'm working today on the layout and traces and stuff. Please email me at dr.napalm@attbi.com and we can talk in more detail...
I have 4 more chips and I plan on ordering some more from National--eventually I want to have a 6-channel amp to replace the one I blew up last month. (That was an RCA home-theatre amp that, after opening up its poor fried carcass, found out it was a hybrid--no wonder it sounded so bad--and the thermal grease hadn't even turned brown. Those pioneer chips apparently have a glass jaw...)
I bought one of those nifty copper-clad fiberglass PC boards from Radio Shack and I'm working today on the layout and traces and stuff. Please email me at dr.napalm@attbi.com and we can talk in more detail...
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