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Old 1st July 2011, 07:52 AM   #1
JAY X is offline JAY X  Spain
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Unhappy fear to power it up!!!

Hi friends,

Lately, i don't know why, maybe because of the time invested in the project, and because 3 psu kits didn't work, i have a fear to power up the circuits i build, even if they are very simple as summing amps (NE5532 dual opamp), balanced outputs, etc....

I always check and re-check all grounds, solderings, before powering up, but then...i just let it be...

What could go wrong?, what is the worst thing that can happen...
I know in electronics there is no place to mistakes, the circuit is perfect or it won't work.

Now i built a new psu with a DANTIMAX supply kit, (+/- 18v) it seems to go very well. But this is it: i have fear to "fry" the circuits...

Any help will be much appreciated,
Thank you very much

JAY X
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Old 1st July 2011, 08:36 AM   #2
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Hi Jay, I think the most important thing is to work out what when wrong with the previous projects. As long as you do that you learn not to make that mistake again

Probably the scariest thing I've had go wrong was that I soldered a 2200uF cap in backwards that was across the +15v supply rail. It made a very loud bang! I learnt from that not to solder things when I was tired and always double check the orientation of electrolytic capacitors

I know this doesn't really help get over the fear of starting up, but perhaps the fear is more one of failing than that it might fry. The only failure is if you don't give it a go. If you make a mistake, learn from it and start again!

Tony.
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Old 1st July 2011, 08:42 AM   #3
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Always useful to have a light bulb tester handy as well.
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Old 1st July 2011, 09:05 AM   #4
JAY X is offline JAY X  Spain
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Thank you wintermute, pinkmouse,

well, my caps are well oriented and many are NP.
I know that really nothing very bad will occur, maybe the sound of a groundloop...

I tested the summing amp circuit without power, playing a cd across the inputs and even this way i discovered some faults.

I will test it this afternoon and tell you what happens.

Thanks a lot
JAY X
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Old 1st July 2011, 12:50 PM   #5
hesener is offline hesener  Germany
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In my case, I use a lab power supply with current limiter and put it to very low setting just to see what happens when I turn up the voltage. When the current stays as expected, I check the voltages inside the circuit. That should eliminate most (destructive) problems.....
Should one of the voltages (assuming e.g. bipolar power supply) not come up as expected, somethings wrong. But what?
"stuck" at 0V - most likely a short circuit
"stuck" or strongly increasing current at 0.6V would indicate a bipolar junction the wrong way, e.g. a diode or a MOSFETs body diode (p-channel in place of an n-channel?)
oscillating currents - maybe the current limit setting is too low to properly charge the caps in your circuit, it may be beneficial to increase it a little bit and try again

works for me in 90% of the cases. just my two cents....
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Old 1st July 2011, 05:44 PM   #6
JAY X is offline JAY X  Spain
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Smile its all right now!!

Hi friends,

i tested the circuit powered it and it was ok. no noise, very silent. This means that all the grounds are ok

Now i have another problem: it doesn't work as expected. I got no sound when i power it up.

I read somewhere to not play any sound into an opamp without power... but it reffered without input resistors, because it could damage the opamp. But here i have 22k input resistors.

Without power i hear the sound that comes from the cd player into the balanced inputs. On the balanced outputs i have 2 mono jacks to a 3,5mm female jack to a pair of computer speakers.

It is a balanced summing amplifier made around a ne5532.

inputs are 22k balanced on db25
outputs on stereo jacks instead of xlr.

Normally in an xlr connector 1 is ground 2 is + and 3 is -

in an inverting amplifier the xlr polarity is inverted: 2 is - and 3 is +
Then you have to build an inverter cable xlr to jack.

But in this case i have wired a stereo jack as usual: tip + ring - sleeve ground.

Maybe i only have to pull out a little the mono jacks.. i will try again tonight. Its all about that. try try and try again.

Thank you for your help
JAY X
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Old 17th July 2011, 06:08 AM   #7
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Quote:
Originally Posted by hesener View Post
In my case, I use a lab power supply with current limiter and put it to very low setting just to see what happens when I turn up the voltage. When the current stays as expected, I check the voltages inside the circuit. That should eliminate most (destructive) problems.....
Should one of the voltages (assuming e.g. bipolar power supply) not come up as expected, somethings wrong. But what?
"stuck" at 0V - most likely a short circuit
"stuck" or strongly increasing current at 0.6V would indicate a bipolar junction the wrong way, e.g. a diode or a MOSFETs body diode (p-channel in place of an n-channel?)
oscillating currents - maybe the current limit setting is too low to properly charge the caps in your circuit, it may be beneficial to increase it a little bit and try again
works for me in 90% of the cases. just my two cents....
What voltages do you start out on the variac?
How long per step up?
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