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I don't need a schem because the amp is working, but I would like to know if the little pot in the power amp board is indeed a crossover adjust pot.
Thanks,
JC
Thanks,
JC
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VR1, wired to R13 and Q4? Only pot I see there. it is the bias adjust. Is that what you mean?Education is what you're left with after you have forgotten what you have learned. -
Hi Enzo. If there is just one pot it must be the one I see. Indeed it goes to a TO-220 style cased component. Does the schem have any annotation about it's adjustment?Originally posted by Enzo View PostComment
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Adjust it the same as any othe solid state power amp. Back it off for least current flow, then run a strong sine wave through it and scope the output. Expand vertical so as to watch just the crossover notch, we don't care what is on the peaks offscreen. Advance the control until the notch JUST disappears. Go no further. In fact I would bring it back a hair. No one will hear a tiny smidge of crossover distortion anyway.
Another simple method that doesn't require a scope or a signal works pretty much just as well. Consider how it works. The crossover notch disappears right when both polarity circuits are just on the verge of conduction. If both sides are a bit shy, then the waveform has to rise or fall a little before they turn on, that makes the notch. If both sides are past the point, then both sides are conducting and current flows from one rail to the other. This makes the amp run hot, but it also starts to increase the draw from the mains. After all we are not just running vurrent between suplies. Too much of that and fuses blow.
SO plug the amp into an outlet with a current meter, or insert your ammeter in series with the amp in the mains. Start with the control at minimum draw, shouldn't be a lot. Monitor the mains current. Advance the control. The current won't move until you hit the spot where noth sides are on. Then the current will start to rise fairly rapidly with advancing control setting. It is easy to spot - you cross a threshold and up it moves. When you hit that point, stop, it is adjusted. As before, I'd back it off a hair to allow for drift. Do this with the amp warmed up.
It is quicker to do than to explain. Watch the mains draw, turn up the control and stop when the current starts to rise. Back off a tiny bit.Education is what you're left with after you have forgotten what you have learned.Comment
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I din't realize about the current draw monitoring method, from now on I will use it along with the signal/scope one. Thanks for your clear procedure explanations.
Is the weather getting any better overthere? I saw in the news you were having some nasty floods..Comment
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Floods, schmuds, our CABLE was out for three days!!!!!
We had a small tornado here in town, not at all far from my shop - like two blocks away. Lots of down trees, missing siding and shingles, and the main power plant by the river had several ov those cooling towers blown over.
http://www.lansingstatejournal.com/a...6090806&Ref=PH
Rivers are rising, and there are a lot of floods, and flash floods. SOme rivers won't crest for a couple days.Education is what you're left with after you have forgotten what you have learned.Comment
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What a mess. Poor trees.. I'm glad you "missed" it.Comment
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