Orange Squeezer problem

[joakimkarlthomas]

Hi!

Have a problem with my Orange Squeezer Im building, the pbc etc is from generalguitargadgets.com.

There's a high frequency tone when on, here is a soundcloud link:
https://soundcloud.com/joakim-johansson-13/orange-sqeezer-fel/s-qBUMG

Anyone experienced the same or may know what can be wrong?

/J

[GGBB]

Welcome to the forum.

Is it in a metal enclosure? What kind of power supply are you using?

[joakimkarlthomas]

Thanks.

Yes, its in a metal box. I use a 9v dc, 650 mA. Its a multi/adjustable.
Also tries 9v battery, same thing, but different tone/frequency.

[Cozybuilder]

It sounds like oscillation. You might try putting a couple of small alligator clips on a small capacitor and clip it in parallel with R9 (220K). I'd try 51 to 100pF and see if that helps.

[joakimkarlthomas]

Thanks, will try that. So does parallel mean that I put the cap on the same solder joints as R9?

[Cozybuilder]

Yes. Look at the schematic, this adds a small capacitance in the feedback loop.

[joakimkarlthomas]

Thanks a lot! I tried it, didn't have anything between 51 - 100 pf, but used a 10 pf and it got a tiny bit better. Also tried with 470 pf which helped a lot with the noise even if it didn't completely disappear. But the 470 pf also caused too much of a lack of treble tone of the guitar.

Will buy a couple of caps 51 -100 pf and try that aswell and see what i think.

Is there anything else I can try to do about it?

[induction]

That GGG pcb doesn't appear to have any power filtering. Try placing a 100u cap across the power rails and see if it helps. A small series resistor (100R) on the +V rail before the cap might help even more. Something like this:





If this takes care of the oscillation, you can leave out the feedback cap on the op-amp, and leave your high frequency response intact.

[joakimkarlthomas]

Thanks! I'm a novice at this.. Do I put the caps + between the + pin on the dc socket and the 9 V input on the pcb? And then the - of the cap between input jackets sleeve and the GND of the dc socket?

Or am I completely lost?

[Cozybuilder]

The low-pass filter on the 9V supply described above is for reducing noise induced by the power supply. This is always a good idea. However, since you tried a 9V battery, this is as clean of a DC supply as you are going to find, and yet this build still had the same noise (OK- a shift in frequency). This indicates the problem is in the circuit, not the supply.

Since you don't have caps in the suggested range of 51-100pF, you could parallel a few 10pF caps until you get to 50 - 100pF total capacitance, and try the different values obtained. This could be done on a breadboard and the leads attached to the 220K resistor by jumpers as described. Not perfect, but it should let you know if the 51-100pF fix will do the job.

[induction]

The way I understand it, a lack of power supply decoupling can cause oscillation even with a battery. Am I wrong?

[joakimkarlthomas]

Thank you all for your kindness! Actually, I tried with the battery again and now for some reason the noise is gone when using the battery.

So I gued the power filter thing is a good idea to try after all. Do i insert it like I described above?

[GGBB]

Do i insert it like I described above?

Yes.

[PRR]

> lack of power supply decoupling can cause oscillation even with a battery. Am I wrong?

With a modern fresh batt, decoupling won't be essential unless the circuit is wickedly vicious and eager to howl.

As the battery gets old, problems increase. Several dozen ++ uFd across the batt is a wise precaution in case the wedding gig goes on and on and on and your battery gets as tired as your feet.

[joakimkarlthomas]

Thanks everyone. Inserted a 200uf and 200 ohm power filter (didn't have a 100ohm resistor at home) and the noise is gone!

[Cozybuilder]

Heres a tool that will help you select appropriate RC values in the future. Personally I like using 47R and 100uF, but there are many combinations that will work fine.

http://www.learningaboutelectronics.com/Articles/Low-pass-filter-calculator.php