Ultra High Gain Preamp - Valve Wizard’s

[kuDo]

N.B.:
Hum at the power line frequency (that is, 50Hz or 60Hz) is caused by the mains leaking into the audio path. This can be poor grounding, capaictive coupling, magnetic field coupling AC wall socket ground or neutral shifting, that kind of thing.
Hum at twice the power line frequency (100 or 120Hz) is caused by the rectifiers. There is always 2x power line frequency in full wave rectification. This forms the classical sawtooth ripple voltage on the B+, but is also part of the hum caused by ground blips caused by poor grounding of the first filter cap. It's possible, but very rare to get capacitive leakage of the ripple voltage coupled into very high gain stages as well.
Hum at three times the power line frequency (150 or 180Hz) is caused by something clipping the AC mains sine wave. This can come from magnetic saturation of the incoming AC mains in the power transformer being coupled magnetically into the signal path.
Technically, rectification produces 2x, 3x, 4x, 5x, ... hum components, but it's unusual to see much beyond the first few components as the size of the harmonic decreases very rapidly.
A buzzy sounding hum is usually caused by pulses happening at 1X or 2x the power line frequency. These are most commonly from fluorescent lights or dimmer hash being coupled through the AC power lines, but can sometimes be caused by the "slam off" nature of silicon solid state rectifiers. The cure for this last cause is snubbing the rectifiers or changing to soft recovery diodes. I notice that the schematic includes "UF..." specced diodes, which is good; changing to 1N... diodes could cause rectifier buzz, so be sure to use the UF ones.

Thanks for this summary.

[martin manning]

It is due to the fact that I picked a standard transformer, which might not entirely match my calculations. The output voltage of the transformer winding for the heaters might have lowered a little.

The input voltage won't matter much at all unless it is so low that there isn't enough headroom for the regulator.

[bepone]

It is due to the fact that I picked a standard transformer, which might not entirely match my calculations. The output voltage of the transformer winding for the heaters might have lowered a little.
A thing I need to get use to is that in practice things just might be a little different from my basic calculations
Maybe I should have used a variable resistor.

transformer is perfect to make hum free heaters circuit, you have too much space for it. first think , why you need current regulated heater? heaters are, just heaters.

and what did you make to prepare little bit better dirty voltage before the regulator? nothing. and why not?

lets use simple 7812. and make perfect humm free circuit.

use rectified 20VDC. it is also perfect. more voltage is better. why? think little bit out of the box. also 25V is even better?
looks worst, but how is better??

to make humm free 7812 output, you need at least 14.5V-15V with 230V network tolerance-.
insert cheap RC-RC elements before 7812. you get 2 bonuses. all the heat (IMPORTANT) is taken by series resistors, and you have better filtering BEFORE regulator. two filters will already be too much for good heater reg.
how to calc. value of R?
deduce drop of the voltage, 20-15V divide by heater current. 5/0.3=16.6 ohms power? i*i*R=1,44W. use 5-7W resistor total resistance 15-16ohms.

after 7812 you will have straight line, and also 7812 would need only small heater, compared to first solution (drop 20V -12VDC without any R, only by regulator)

[kuDo]

Thanks bepone, but I am fine like it is.

I just need to adjust de LM317 a little and it’ll be perfect.
It already works like a charm.

[bepone]

ok
here is draft for the next time, and principle you can copy to all the sensitive power supplies (phono, DAC etc). regulator alone has limited range of filtering.

dr.png

[kuDo]

Maybe, I give it a try next time!
Thanks for the schematic