Valve Itch phono

[merlin el mago]

I think I don't need the PTFE sleeving, attached pic: are the black cables connected to RCA.

 

[kevinkr]

Do I see two sets of cables connected to the RCA jacks? This is definitely a recipe for additional unwanted capacitance, any way to tidy up and get rid of one of those cables?

The black ones appeared to be shielded as well, not what you want when capacitance is already a problem. Provided everything is enclosed and there is no AC (other than the signal) inside the box shielded wire is not needed and just adds capacitance. If the capacitance is 20pF - 30pF per 30cm or less it's probably not a concern otherwise you might want to consider changing it.

 

[merlin el mago]

Input RCAs are down & output RCAs are up, the one big blue is ground to SLB.

 

[kevinkr]

Ok, so that is a bit clearer.. 😀

For future reference it is an excellent idea to keep power supply stuff far away from the inputs in particular.

 

[merlin el mago]

OK thanks Kevin. Phono stage in the same box with SSHV2 and heaters regulators, transformers and PSU in a separate box.

 

[Salas]

Interesting will be to see with scope and table again how much parasitic capacitance haircut Merlin will achieve after the reworks. R1 (load) directly on input pins with shortest legs possible can help?

 

[merlin el mago]

Tomorrow I will do the measurements and will post here.

 

[merlin el mago]

Ok, so that is a bit clearer.. 😀

For future reference it is an excellent idea to keep power supply stuff far away from the inputs in particular.

Better now Kevin?

 

[merlin el mago]

Salas I have a severe buzzz, see attached pic, SSHV2 loaded with a dummy load of 12K, scope set 0.1V/cm 0.5ms.

 

[Salas]

When the buzz started? After reworks?

 

[merlin el mago]

Yes.

 

[Salas]

Put a decoupling capacitor across its DC input connector. Maybe the input wires coming from raw got too long.

 

[merlin el mago]

OK I will try

 

[merlin el mago]

Works🙂, with only 1uF 400V MKP.

 

[Salas]

Good

 

[merlin el mago]

Now it's open I will do come measurements of input capacitance.

 

[Salas]

Lets see if you reduced some

 

[merlin el mago]

Now I'm arming up the Itch to adjust voltages, later the measurements.

 

[merlin el mago]

Attached pics, 1st pic probe x 1 direct to signal generator scope 50mV/cm, 3rd pic probe x 1 cathode V3 scope 1V/cm.

 

[merlin el mago]

Attached more pics, 1st signal generator to 100K soldered to RCA input, 2nd probe connected to V3 cathode.