Valve Itch phono

[merlin el mago]

Salas I have hum with the PSU attached.

 

[Salas]

Must try more resistance I guess (if its not a ground loop hum)

 

[merlin el mago]

If I use more resistance SSHV2 can't regulate to 300VDC.

 

[Salas]

How much more R in the CRC it takes to go 310-320V raw with your transfo? Maybe having a choke in hand to try there instead? Or lower the CCS setting a little.

 

[merlin el mago]

47 ohms for 320V, I don't have any choke at hand.

 

[Salas]

Tight voltage space excludes a bigger R choice. Having any low DCR choke to test?

 

[merlin el mago]

No.

 

[Salas]

Is there 100Hz ripple on the phono rail that can be seen on the scope?

 

[merlin el mago]

I have to check, let me a little of time, what sets have I to do at the scope to see the 100Hz ripple?

 

[Salas]

AC scope input, probe 1/10, 1mS scan, should do.

 

[merlin el mago]

OK thanks.

 

[merlin el mago]

Salas real load or dummy load?

 

[merlin el mago]

For dummy load I have near 7K5 for 300V 40mA, 6K8 and 8.K2

 

[Salas]

Real load

 

[merlin el mago]

ok

 

[merlin el mago]

Warm up the Itch before to make measurements.

 

[merlin el mago]

I don't see nothing!

Scope set probe 1X10 5mV/cm 1ms.

 

[Salas]

So not power related. No ripple. If you got some harmonic noise its a ground loop or an interference.

But you were not talking about that noise last time you reworked it to lower the input capacitance very successfully.

What changed?

 

[merlin el mago]

Possible the 22uF in parallel with 1uF at the SSHV2 input?

 

[Salas]

But nothing bad passes in the rail. Unless there is something very high in frequency. Sweep the timescale.