| Minion |
Hi, I have built a PSU useing LM7XXX Pos and neg regulators but they don"t seem to be working......
I am useing the 15v regulators and I am useing a 18v 0v 18v Torroid and the PSU is supposed to Provide 15v regulated for Preamps and Unregulated 25v for the Power amp stage.....
When I measure the Voltages I get -10v on the Neg regulator and 0 v on the Positive regulator but the unregulated power is Fine at 25v......
Here is a Pic of the Schematic and my PCB layout......
The only change from the Schematic is that I am useing 10,000uF caps as the filter caps as opposed to 1000uF used in the schematic.......
Can someone please point out were my Problem is???
Thanx a Lot..... |
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| Christer |
| Check again that you didn't rotate the regulators 180 degrees. |
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| Minion |
That was the First thing I checked, and the regs are in correctly
Wait!!!! I think I have got it,....OK....I think I have found the Problem , I think I might have the Pos and neg regulators switched......
I"ll check later to make sure.....Thanx |
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| p27182 |
the 7900 series has pin1 as the ground...
i think...
-p |
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| p27182 |
nevermind. im an idiot and didnt look at your schematic carefully enough.
my bust.
-p |
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| Christer |
I also thought he had got the pins wrong at first, but it turned out the pins are numbered in the order 1,3,2, not 1,2,3 for some obscure reason.
Edit: Or maybe not so obscure. It is probably so they can have the same pin number for the same function for all package types, but is confusing. |
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| Minion |
Thanx Guys....I figured it out....It was that I accidentaly put the Pos reg on the Neg rail and the Neg reg on the Pos rail....
After changeing the regs the Amp is working correctly, it still has a Pretty Bad Hum problem even though I star grounded everything to the same Chassis ground point.....
It was a simple 18w Guitar amp useing a couple BC550/560 and an OPA627 and a couple Tip41/42 Transistors for the Power amp stage and an all J-fet preamp stage.......
Cheers |
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| Nordic |
minion , the fixed voltage regs tend to be more noisy than a properly used variable one.... you may want to increase the caps on output side to about 100uf... not more, as you will start the reg. ringing...
Just after the bridge, I would (if I desgned it) probably have used 2 sets of filtercaps (and probably only 2200uf each) seperated by a 1 or 2 Watt 10R resistor... |
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| Minion |
Hi, I actually Have some 100uF caps on the Preamp and Power amp PCB"s close to the Opamp pins and close to the Output transistors......
I was going to use the LM317/337 regs but It turned out that i ran out of the Positive 317 regulators so I use the 7XXX regs as that was all I had on hand.....
Cheers |
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