Hi guys, ive spun my own pcb of rod elliots very popular p06 preamp and i gotta admit my layout was far from optimal with tracks being too long and crossing over one another where they shouldnt. Also i decided to split the dual opamp into singles which probably further messed up my chance of success with this project. And the pcb as it is hums terribly. Rca open is when its loudest. Turntable connected its quiter. Inputs shorted is even quieter but it still hums. If i float the input to the opamp, with the 47k ohm loading resistor still connected, there is almost no hum. However now my woofers start rumbling. It plays the music fine so i know it isnt from miswiring. Also the psu im using for it should be dead quiet. How should i troubleshoot this? Or is this oscillation and should i scap the pcb altogether?
Have you ruled out a hum loop .
Also on Rods pcb i can see 3 electrolytic and 2 ceramic capacitors not included in the schematic , these are probably rail decoupling capacitors .
Also on Rods pcb i can see 3 electrolytic and 2 ceramic capacitors not included in the schematic , these are probably rail decoupling capacitors .
So i deadbugged a simpler circuit onto the emptied out pcb and also followed the ground scheme posted by rod elliott and now the phono amp is dead silent... by itself. It still hums when the turntable is connected. But the table is old and so is the cartridge. If i disconnect the cartridge there is no hum and im now thinking the issue is with the cartridge because its rusted at the corners and the sound that comes out of it is also distorted...
Is it a possibiliy that a damaged cartridge can cause hum?
Is it a possibiliy that a damaged cartridge can cause hum?
Well it looks like the thing still hums with any kind of input. Tried it with my phone and a dac with same results. Im guessing its an issue with the input grounding?
Well it looks like the thing still hums with any kind of input. Tried it with my phone and a dac with same results. Im guessing its an issue with the input grounding?
Firstly hum is not oscillation unless its motor-boating, its probably a grounding issue.
No bulk decoupling on the supply rails? That needs fixing anyhow if its missing.
NE5532's need high frequency decoupling, 100nF ceramic between V+ and V- close to the chip, to get full datasheet performance for distortion.
Why R2L?, it directly adds some Johnson noise but I can't see any benefit to it to make up for this.
The impedance of the feedback network on the first stage is high, adding more Johnson noise.
Together these resistances on the inputs are adding about 11nV/√Hz (more than the opamp itself), so there's definite scope for some improvement. Ironically the 2nd stage is quieter (although by that point the damage is done).
No bulk decoupling on the supply rails? That needs fixing anyhow if its missing.
NE5532's need high frequency decoupling, 100nF ceramic between V+ and V- close to the chip, to get full datasheet performance for distortion.
Why R2L?, it directly adds some Johnson noise but I can't see any benefit to it to make up for this.
The impedance of the feedback network on the first stage is high, adding more Johnson noise.
Together these resistances on the inputs are adding about 11nV/√Hz (more than the opamp itself), so there's definite scope for some improvement. Ironically the 2nd stage is quieter (although by that point the damage is done).