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Re: Radio reception problem

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8/19/1999 9:58 AM
AMZ	Re: Radio reception problem >>I suspect my power supply too (it's an old-fashioned transistor-with-zener-diode thing. I had forgotten to put a cap at the beginning of it). Do you have a cap across the zener? Try something like a 0.01uF and see if that helps any. regards, Jack

8/19/1999 5:19 PM

I have made a new Doctor Q. I've changed some things
- I've put a cap across the zener
- I've plugged my amp in a power outlet *with earth*
in my basement

And there is still this #@&?#! radio ! Even with input to ground.
My power supply seems not very good. I still hear a loud 60 Hz hum thing though the Doctor Q doesn't amplify very much. Here is how I do it:
an AC adapter gives me an almost-continuous 12V. I filter it through a RC low pass filter (R=47ohms C=1000uF). The filtered signal is connected to the collector of a 2N1711. I do the zener thing. I filter the resulting signal on the emittor with a 220uF.

I've tried to search it on my hi-fi and I've only found it on FM band ! EH has found out a new kind of PLL !

I've also tried to put a capacitor to ground everywhere: input, output. Doesn't change anything.

Don't know what to do ...

8/20/1999 1:25 PM

a) is it in a metal box?

b) it might be better to put an electro cap from the base of the 2N1711 to ground than on the emitter

c) try a 100 ohm resistor in series with the input and a 50pF capacitor to grround at the input

d) use an ohmmeter to ensure that all of your ground connections are sturdy and low resistance

e) check your lead dress; if you have long, looping wires onto and off the board, they form perfect radio loop antennas. Wires should be short and direct, ideally shielded or twisted with a ground wire if they are not inside a grounded metal box.

Extraneous signal pickup is one of the plagues of breaboarding. I just ignore RF, hum, flourescent light buzz, etc. when I have something breadboarded, assuming that it will simply be that way, and don't worry about it until I put things on a PCB inside a box.

8/20/1999 8:02 PM
Arnaud	Thank you R.G. ! I'm going to try all these things

8/21/1999 2:41 PM

Problem solved !

While testing all my wires to check if one of them was broken, I noticed that the ground of the circuit was not connected to the ground of the output jack.

And..hum... how could I say this... I had ..hum.. swapped the 2 wires of my jacks making the shield of my jack the hot wire. And a wonderful antenna !

Think I'm the great DIYer of the month ...

Whatever, thank you to all the people who helped me.

Even if it was not the problem, this discussion improved my power supply.

8/22/1999 1:39 PM
paul perry	Well Amaud, you aren't the first to do this.. I had a box of 1/4 jacks and only found out the hard way that a couple were built 'slightly' differently.. worst was that everything seemed OK on the bench, but it sure hummed on stage!

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