dc adapter adds screaming to some effects

[dj_death]

Hi i have a little problem. I have a regulated dc adapter of 12V that i modified for 9V (by changing the 7812 with a 7809). I also changed the orientation ( + -) of the jack. The problem i have is that when using it in circuits like the hornet, rocket, rangemaster, obsidian transistor version there is a screaming like sound ( i don't know how to describe it exactly maybe it's oscillation) added to the signal. When i tune the volume up this sound is more audible and it's really annoying. Of course when i use a battery there is no problem. In the other hand there is not such problem with  circuits like rat, small clone, small stone, pt80 etc. when  using the dc adapter. In all my circuits i added big supply caps but there is no improvement. I see that the circuits having this problem with my dc adapter are with bjt
transistors, ic circuits seem to work perfectly. Do you have any idea about tyhis problem?

Thanks in advance
John

[Joep]

Try adding a small cap (0,01 .. 0,1) between the input and ground, and the output and ground of the 7809.

[smoguzbenjamin]

Yeah, and add a 1000 uF cap over the power lines before the power leaves the PSU, that might help.

I had the same problem but I decided that fixing my old PSU would be much easier than fixing the new one, so I brought it back. :roll:

[gez]

Try adding a small cap (0,01 .. 0,1) between the input and ground, and the output and ground of the 7809.

I'd agree with this.  I think that what 'might' be happening is your regulator is oscillating but stops with some effects because of the filtering those circuits have.

Most regulators DON'T require huge caps at their outputs, they have low ripple at their outputs and it simply isn't necessary.  Large value caps aren't too great at filtering highs which is probably why you have a problem.

Schematics I've seen that use the 78XX series only have a 220nF cap at the output and one at the input.  Try this value, or at least wire up one in parallel with your BFC (as RG might put it!).

[Boofhead]

The first problem is the filter cap on the power supply is probably in the adaptor.  Those regulators will oscillate if the input supply capacitor is too far away, the solution is to put a 330nF poly to 10uF electro cap close to the input pins.

The second problem is the regulators can get cranky without an output cap, I use 10uF electro here.  Often a 100nF will ofte do but sometimes it's not enough.

[dj_death]

I fixed it. I read somewhere in this forum that the boss pedals use a trick in order to stop ground loops. I used in series with the (-) of the adapter a diode. This eliminated my problems immediately and the voltage is a little lower but i have not a problem  9.5-0.6=8,9V. Thanks a lot for your help.

[dan]

hi, would all those tips work work if this power suply setup is used? i made that (right now, i only have 2 jacks) but when i plug it into a zoom 505II it makes terrible squeels and hiss and hum and screaming on all the patches. and also a little hum on some other pedals.

[tomtom]

I know some things about this buzz, I have some problems too with my "only one" adaptator, a tranformerless design.
I wonder if it's less filtered than a classic design.

I have powered two circuit with it, one quad BJT disortion and a germanium fuzz.
As strange as it may seems, on the ten similar Quad BJT design, I had to put 100µ/100R to kill the buzz, but one of them still buzz...
For the Germanium, even with the 100µ/100R, I encounter buzz.

I don't know how to cure the buzz. Do I need to use twice a value for the cap? For the resistor?

I use a 1N914 for polarity protection between "+" to the circuit and "-"  for space purposes, no problems yet. Why commercial products use a bigger one (1n4007 and others) ?


One good product to use : Switchcraft sells DC adaptator, all meal like a jack, very compact and isolated even if it's metal. A bit expensive but great compact one for tightly packaged boxes.