The Heretical Preamp, p6

The Proof of the Pudding This is a plot of the spectrum from a 2VRMS 1kHz sine wave measured using an Audigy 2ZS soundcard and RMAA software in a noisy environment. The green plot is a straight wire loop from input to output. The white plot is the same but with the...

The Heretical Preamp, p5

In earlier parts, we considered a unity gain preamp with an ECC88 at its heart. The design was mostly conventional, but withal, a good performer, a unit that will not be the limitation in any reasonable system. Now it’s time to get unreasonable. And,...

The Heretical Preamp, p4

Plate Job With solid raw supply in hand, we move on to the next two inter-related problems- attaining the proper DC level and getting rid of the ripple and noise. This will require some regulators, or at the very least, more filtration. Let’s start with the anode...

The Heretical Preamp, p3

To review, in Part 2, we considered a very basic transformer-coupled input, capacitor-coupled output unity-gain preamp. That circuit is, as it stands, an excellent performer. We do need to power it and to build it, so those circuits and options will be considered...

The Heretical Preamp, p2

Third step: Design details Looking at the plate curves for the ECC88, we see that with 90V on the plate, a cathode-to-grid voltage of 1.7V will give us the desired 10mA minimum current. The significance of this choice will be clear later. Nonetheless, this is a common...