pinkmouse said:
Does that mean when the last track of a CD is finished I should turn the GC off in case there is no input signal that it may get into oscillation? Wow I need to remember not fall to sleep when listen to my GC then it may start up a house fire after the last track, this reminds me of the mission impossible TV series...not good
Regards,
Chris
No, this is not the case 
You just need to have your interconnects attached, so the amp sees some impedance at the input, that's all.
It's only when you leave it with no inputs connected, it may start oscilating and getting warm. You might try to disconnect the cables and see what happens, usually some noise appears at the speakers.
As a side note, I had my output cables shorted at least for an hour one day. The amp got pretty warm, but nothing happned.
You just need to have your interconnects attached, so the amp sees some impedance at the input, that's all.
It's only when you leave it with no inputs connected, it may start oscilating and getting warm. You might try to disconnect the cables and see what happens, usually some noise appears at the speakers.
As a side note, I had my output cables shorted at least for an hour one day. The amp got pretty warm, but nothing happned.
I'm kind of having a similar problem, so in the interest of not starting another thread, I thought I'd post it here.
After listening to my IGC for a while, I have the tendency to fall asleep and leave it on. There's never a problem when there's a signal, but after I've been asleep for a couple of hours, a sort of low frequency oscillating humming can be heard from the speakers. Its not very loud, but its not soft either and it sounds like this:
...wubwubwubwubwubwubwubwubwubwubwubwub....
The input cables are plugged in and I haven't changed anything else. Also, its worth noting that it does not happen right away-- it usually takes about two hours or so before the noise begins and once I turn it off and back on it goes away.
Any ideas on this one? Is it oscillation? Drives Mrs. Annan crazy. Crazier, anyway.
Kofi
After listening to my IGC for a while, I have the tendency to fall asleep and leave it on. There's never a problem when there's a signal, but after I've been asleep for a couple of hours, a sort of low frequency oscillating humming can be heard from the speakers. Its not very loud, but its not soft either and it sounds like this:
...wubwubwubwubwubwubwubwubwubwubwubwub....
The input cables are plugged in and I haven't changed anything else. Also, its worth noting that it does not happen right away-- it usually takes about two hours or so before the noise begins and once I turn it off and back on it goes away.
Any ideas on this one? Is it oscillation? Drives Mrs. Annan crazy. Crazier, anyway.
Kofi
Are the heatsinks warm? Could be noise coming from your transformer which can expand slightly as it gets warm. If your transformer is bolted to the amp chassis, try putting a layer of rubber, or bits of rubber, between it and the case and tighten it reasonably firmly (but don't over tighten). I use three little rubber feet meant for speaker isolation, or chunks of an ordinary eraser would work.
If that doesn't work, try an alarm clock.
If that doesn't work, try an alarm clock.
Ropie-- good to hear from you and thanks for all the great advice in the past!
Well, the amp chassis is made of wood (a breadbox, actually) and its insulated with rubber on the top and bottom. Also, the noise stops when I switch it off and then back on almost immeidately, so I'm not sure that the trafo is what's causing it, but what the hell do I know.
I'll dry to duplicate the wubwubwubwubwubwubwubwubwub this weekend and see if I can poke around and find the problem.
Thanks for the advice!
Kofi
Well, the amp chassis is made of wood (a breadbox, actually) and its insulated with rubber on the top and bottom. Also, the noise stops when I switch it off and then back on almost immeidately, so I'm not sure that the trafo is what's causing it, but what the hell do I know.
I'll dry to duplicate the wubwubwubwubwubwubwubwubwub this weekend and see if I can poke around and find the problem.
Thanks for the advice!
Kofi
Hi Kofi,
Well, you are probably right in that case, though physically isolating the trafo in an 'integrated' amp is usually a good idea anyway, especially if it's a toroid type.
The best way to solve small problems with hi-fi is to try the 'process of elimination' method. In your situation this may take several days as the problem doesn't arise for a couple of hours. First of all, if you can, try changing sources to see if the problem goes away (then you will know it's the source). Next try changing speakers if you have a spare pair, though IMO it's unlikely to be the speakers that are causing this problem but it might be worth a go anyway. If the problem persists then move on to the amp and try adding that zobel.
Well, you are probably right in that case, though physically isolating the trafo in an 'integrated' amp is usually a good idea anyway, especially if it's a toroid type.
The best way to solve small problems with hi-fi is to try the 'process of elimination' method. In your situation this may take several days as the problem doesn't arise for a couple of hours. First of all, if you can, try changing sources to see if the problem goes away (then you will know it's the source). Next try changing speakers if you have a spare pair, though IMO it's unlikely to be the speakers that are causing this problem but it might be worth a go anyway. If the problem persists then move on to the amp and try adding that zobel.
Do you have a DC-path for both inputs of the LM3875? You must have resistive path from the input to either ground or the output of the IC (feedback).Dennis Hui said:
DC current must be able to flow to or from the inputs, otherwise the IC gets hot and nothing works.
The input transistors in trhe IC must get their base currents in order to work.
You know, I thought that too, but it confounds me that it only happens after a couple of hours of no signal. Could it have something to do with the overheating shut-down capabilities of the chip?
Another possibility is that the amplifier has spent too long without a signal and it simply can't resist the urge do get down: wubwubwubwubwubwubwubwubwubwubwub....
Hail Yeah.
Too expensive, unless you know of a "Crazy Phil's Ocscilloscope-o-mania!" near me. He's got prices on oscilloscopes so low, he'd HAVE to be crazy! Any "Jorge's Discount Sine and Consine Extravaganza!" would also do nicely but alas, only in Greenland.
I suppose it could also be the preamp-- I have a Bugle phono preamplifier from Hagerman Technologies that I really like. I'll try taking that out of the mix and see what happens.
Will do.
Will also do. Hey-- can I add the Zobel across the speaker binding posts grounding to the negative post? Its a resistor and cap in series NOT parallel, right?
Kofi
>> can I add the Zobel across the speaker binding posts grounding to the negative post? Its a resistor and cap in series NOT parallel, right?
Can I refer you to the definitive Gainclone Glossary?
http://ampchipdiy.com/phpBB2/viewtopic.php?t=224
Can I refer you to the definitive Gainclone Glossary?
http://ampchipdiy.com/phpBB2/viewtopic.php?t=224
Wow! That's really fantastic, but I wish you could make it more Dr. Seuss-like. Since I noticed that there's no "Q" entry, allow me to elaborate using this character for example:
Q is for Questions
Which Kofi asks much
All asenine, obvious
Numbskulled and such
Irksome conundrums
To try Ropie's patience
This guy's the head of
the United Nations?
Something like that. Or, the way you have it is fine too.
Thanks!
Kofi
Q is for Questions
Which Kofi asks much
All asenine, obvious
Numbskulled and such
Irksome conundrums
To try Ropie's patience
This guy's the head of
the United Nations?
Something like that. Or, the way you have it is fine too.
Thanks!
Kofi
If you still haven't found the source of your problem, let me make one suggestion since I just solved the same problem myself last night with a 4780.
Make ABSOLUTELY sure that your grounds are seperated until they return to the star ground.
I had my circuit working such that it was overheating like mad with no input (and oscillating). I then added some more caps and resistors for filtering, which made it safe to plug speakers into (but it sounded crappy). After that, it would play for about 40 seconds and then go into a warble/crackling noise which I attributed to oscillation.
Finally, I just said "to heck with it" with keeping things compact (where I had every ground hooked into a rail that was hooked into a ground star) and made sure to just hook up all the ground symbols in the schematic using seperate wires all to the same point (length doesn't matter). Once I hooked up the ground star properly, it ran perfectly and I had it playing this morning for over an hour at loud volume with no issues whatsoever.
Hope this helps,
Chris
Make ABSOLUTELY sure that your grounds are seperated until they return to the star ground.
I had my circuit working such that it was overheating like mad with no input (and oscillating). I then added some more caps and resistors for filtering, which made it safe to plug speakers into (but it sounded crappy). After that, it would play for about 40 seconds and then go into a warble/crackling noise which I attributed to oscillation.
Finally, I just said "to heck with it" with keeping things compact (where I had every ground hooked into a rail that was hooked into a ground star) and made sure to just hook up all the ground symbols in the schematic using seperate wires all to the same point (length doesn't matter). Once I hooked up the ground star properly, it ran perfectly and I had it playing this morning for over an hour at loud volume with no issues whatsoever.
Hope this helps,
Chris
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