Hey all, I am new to the forum. I just completed my first diy stereo project, a first watt b1 preamp. It works great when connected to my Aragon 4004, but when I connect it to my Quad 303 I get a constant mid-high frequency buzz through both speakers. This does not change with volume adjustment or changing input or disconnecting all inputs. I know it's not the amplifier because it only happens with this preamp. It only occurs when power is connected to the preamp. As I said before, this is my first build and I have no experience with troubleshooting. Any thoughts? I suspect some sort of ground issue...
As you are "supposing" having a ground issue a picture of your power supply would be neat as well ... sorry to be that nitpicking guy, but the question will arise anyway
I am not familiar with that SMPS, is it an isolated one ?
How did you mount your DC jack , like in ground tied to chassis or floating ?
How did you mount your DC jack , like in ground tied to chassis or floating ?
You will have to pardon my ignorance on some of the terminology used here, I am not sure what you mean when you ask if the power supply is isolated. The DC jack is wired directly to the board and is not otherwise tied to the chassis
Power it with well filtered ideally stabilized linear power supply first, and see if you have any buzz.
I am not sure what is meant by isolated, it is only pwering the preamp if that is what you mean. The DC jack is floating, it's not tied to the chassis
I think that is actually just showing the negative connection from the DC jack. I don't see anything showing that this should be grounded to the chassis, or if that is even the problem. Unfortunately I don't have a linear power supply to try..
Two 9 volt batteries in series should power that circuit.
Have you tried connecting the case to say one of the RCA grounds, perhaps even via a low value resistor such as a 10 to 100 ohm.
Have you tried connecting the case to say one of the RCA grounds, perhaps even via a low value resistor such as a 10 to 100 ohm.
MEPER - no, the signal is not grounded to chassis, wouldI do that from the input rca grounds?.
Moody - should I connect all of the rca grounds to chassis?
Moody - should I connect all of the rca grounds to chassis?
Since it is just an rca jack powering it, wouldn't that mean the chassis has to connection to earth ground anyway?
check with ohmmeter is chassis connected to audio GND ( maybe through pcb screws?)
if not, connect chassis with thin wire to audio GND, best to same pad where PSU neg is soldered to pcb