Ok, got the PS part wired up as per Wirehead's and Richard's intruction (single bridge, center tap as common ground)
Got all the connections to the VSPS 300 boards (populated with kit parts from RJM) through a 1 meter long umbilical.
Checked voltages at pins 4 and 7 for positive and negative voltages, all good.
Mounted IC1 (OPA27) on the boards
Connected the outputs to the amp, (no turntable hooked up yet)
Turn on the amp, and......
HUMMMMMMM!!!
A nice, steady, powerful, 50hz hum
Troubleshooting time:
-Checked all solder joints, cabling, nothing to declare.
-Tried moving the PS around, rearranging cables, the hum is unaffected.
-When I touch the input wires running from the RCA connectors to the boards, the hum increases, this happens for both channels when I touch their respective input wires.
-Input wires are around 10 cm long and shielded.
-Power wires are twisted positive and negative with a third loose wire for ground.
-Comm ground on board is not connected to anything yet, (everything is mounted on wood boards for testing)
***One important thing to note is that over here in Lebanon, there is no earth connection in our power outlets, it's a simple L,N outlet.
Does anyone have any idea where to start from?
Thanks
Nick
Got all the connections to the VSPS 300 boards (populated with kit parts from RJM) through a 1 meter long umbilical.
Checked voltages at pins 4 and 7 for positive and negative voltages, all good.
Mounted IC1 (OPA27) on the boards
Connected the outputs to the amp, (no turntable hooked up yet)
Turn on the amp, and......
HUMMMMMMM!!!
A nice, steady, powerful, 50hz hum
Troubleshooting time:
-Checked all solder joints, cabling, nothing to declare.
-Tried moving the PS around, rearranging cables, the hum is unaffected.
-When I touch the input wires running from the RCA connectors to the boards, the hum increases, this happens for both channels when I touch their respective input wires.
-Input wires are around 10 cm long and shielded.
-Power wires are twisted positive and negative with a third loose wire for ground.
-Comm ground on board is not connected to anything yet, (everything is mounted on wood boards for testing)
***One important thing to note is that over here in Lebanon, there is no earth connection in our power outlets, it's a simple L,N outlet.
Does anyone have any idea where to start from?
Thanks
Nick
input wires - is the shield connected at both ends?
power wires - loose ground wire? explain a bit more
comm ground - i thought that this has to be connected to the phono ground connectors or the casework.
if there is no earth wire in Lebanon then i would presume you don't connect the earth wire to the chassis.
earth and ground should not be connected to the same case and only earth to the power supply case if separate and if same case then no earth, since you don't have an earth in Lebanon then you cant earth the case and i would use 2 core rather than 3 for power.
No, not connected to anything, btw, the wires in question are from the RCA post to the boards.
loose as in not twisted with the positive and negative wires
For the time-being, no case and no turntable connected.
Thanks for the tip
Can you explain a bit more please
I'll short the inputs and report back too.
Thanks
Nick
if you only have live and neutral in Lebanon coming from the mains then there should not be an earth wire so you would use 2 core mains cable from household mains to the power supply. do not use the comm to 'earth' the supply case.
the comm should be connected to the turntable ground and phono amp case but since there is no turntable connected and no metalwork then it should not be connected as far as i know.
as far as i know shielded cable has to be terminated at one end only, but i could be wrong.
the comm should be connected to the turntable ground and phono amp case but since there is no turntable connected and no metalwork then it should not be connected as far as i know.
as far as i know shielded cable has to be terminated at one end only, but i could be wrong.
Put it in a metal case, and connect it up. You should be good to go.
Phono preamps, even MM stages like the VSPS, must be fully shielded to operate hum free. You cannot expect them to have a quiet output when open on the workbench.
I've always been told differently, in data networks, both must be connected. Otherwise it acts as an antenna.
I replaced the RCA jacks on the turntable cables with high quality ones I had lying around (the old ones were low quality, and oxidized beyond repair)
The turntable does not have a grounding cable, so while I was at it, soldered a grounding cable on a tab mounted on the turntables internal frame.
Connected everything up again, with the boards still on the workbench, and the hum was gone!
I'm waiting for the output caps to before I do any critical listening, but it already sounds better than the phono section of my yamaha receiver.
Will report back in a week or so.
Thanks everyone for the help.
Regards
Nick
The turntable does not have a grounding cable, so while I was at it, soldered a grounding cable on a tab mounted on the turntables internal frame.
Connected everything up again, with the boards still on the workbench, and the hum was gone!
I'm waiting for the output caps to before I do any critical listening, but it already sounds better than the phono section of my yamaha receiver.
Will report back in a week or so.
Thanks everyone for the help.
Regards
Nick
I've always been told differently, in data networks, both must be connected. Otherwise it acts as an antenna.
yup i used to be Cisco certed and MCSE's BSc in networking (almost) yada yada but had to give it all up.
Connected everything up again, with the boards still on the workbench, and the hum was gone!
Good. So it was the RCA connectors do you think?