UPDATE: I have built this. It works well except that the frequency is of the pulses that come from the 555 must be increased above 15KHZ or higher! I found out that if the frequency is below the upper end of the human hearing range then no amount of smoothing with capacitors will cure the problem! That is to say that if you intend to use this to feed a 12AU7 valve or other valve then you will hear a horrible noise if the frequency is not increased!!!!
Description: The 555 is set-up as an astable multivibrator with variable mark-space ratio control. The output of the 555 is fed into a MOSFET switching transistor the function of which is to dump the charge built-up in the inductor momentarily to ground. This in turn produces a massive spike in voltage which then passes through the diode. In reality I would use a Schottky diode, but the EC standard simulated diode seems to work fine here.
Once the pulses have passed through the diode, they are smoothed-out or integrated to create a pseudo DC current.
The potentiometer on the 555 allows the control of the high voltage produced by this circuit by varying the pulse width or mark-space ratio.
WARNING! Do not build this with a IRF510 MOSFET. It will blow up in your face!
I am now happily under-sampled!
EveryCircuit?
Not so accurate at lower sample rates!
EveryCircuit? Another annoyance is the need to adjust n-MOS FETs to unrealistic KP values to make a simple circuit like this work.
