The "Freebird" ultra clean ultra simple preamp design

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trafo is 2x12V and 2,25VA per secondary winding.
capacitors are 150uF-150uF-100nF before the regulator and 100nF-220uF after.

I tested the supply with a 4,7K and later a 1K load and it worked fine, then I connected it to the preamp and one of the regulators stopped working.
they are (+ - )12V and rated to 1,5A


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Well, I had at bigger transformer earlier. 17,5V and 85mA per winding.

I went over to the local supermarket just now and bought a 9V battery. The Preamp works, thats for sure. I did however blow a pair of speakers earlier trying it with the powersupply. Cheap pieces of crap but the were useful when testing amps.
Hi again, I built a powersupply using the datasheet for the 7812-regulators and etched a new pair of Mono-yardbird PCBs. I have 47pF on the cap designated CRF and on the RG I have 0,85R since I didn't have the exact value.

My casing is made of MDF with aluminumfoil on the inside connected to ground. Internat wire is unshielded.

The problem is a buzz combined with a sparking sound that is more or less constant. What should I look after to solve this?
An update and some changes. I added 470uF between each fuse and the first capacitor.
So on the positive rail it's fuse->470uF->0,33uF->reg->0,1uF
and on the negative it's Fuse->470uF->2,2uF->reg->1,0uF

The positive, negative and common rail ends with a dual pinhead which connects to the two boards.

So the powerstarground is at the PSU-board and the signalground is as specified on the board. The signalground of each channel is separated from the common with a 0,82ohm resistor.

When the CD is connected to the poweramp directly there's no buzzing sound so it should be the pre that is the source.

Attaching a schematic of the PSU (one psu to two channels)


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No, Swedish apartmentbuildings doesn't have i mainsground in the wall-socket. It is stated in some law that when renovating a threepronged socket containing mainsearth must be installed but that is when and if thers a renovation. So no.

And I can't seem to think of a way to seperate the ground of the two channels.

Oh, one more thing. If I disconnect the ampboards from the PSU and drive one channel only with a 9V battery, when there's still buzzing.
I measured the voltage to approx 11,9V positive and negative. The layout is from the datasheet exept for the added 470uF caps, shouldn't it be good enough?

Attatched a pic of present setup, one channel disconnected.


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Is it possible you have the opamps on the solder side?
Not if you turn the paper upside-down when putting it in the UV-box :cannotbe:
I managed to etch it on the wrong side and that's why the OPs are on the copperside, they are however correct. Forgot to mention it :)

I went for a run to the nearest gasstation and I'm now in possesion of two 9V batteries. Stay tuned!
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