Paul McGowan writes:
I’m not sure how this thread morphed into a How I built this about volume controls but things have a tendency to just drift in a certain direction. But, I ramble on.
In yesterday’s post, I told the story of boiling the innards of a volume control down to nothing more than a single high-quality resistor. It was the best we’d heard but it still had a signature that wasn’t appreciated. How could it get better than a single, simple, component? By eliminating even that one device.
Preamplifiers are impractical designs. They consist of three things: input switches, volume control, output amplifier. With the volume control turned on high so no attenuation happens, preamps put out far more signal than needed to clip an amplifier. Which means volume control always attenuate—reduce signal level—to match the gain of the output amplifier. Seems rather counter-intuitive. We are forced to throw away signal to compensate for the amplifier’s gain.
Then, a light bulb went off in my head. Why suffer the added distortion of a volume control when it could be eliminated entirely by changing the output stage gain. Thus, a variable gain preamplifier is reduced from the tradition of three parts to two: input switching, variable gain output stage.
The first iteration of this technology we called the Gain Cell, which appeared nearly a decade ago in the GC Series. Today, it’s what is also inside the Stellar Gain Cell DAC/Preamp. But, we didn’t stop there. Bascom H. King (BHK) realized the same thing. Volume controls are the Achille’s heel of preamplifiers and, using entirely different techniques, he too varies the vacuum tube gain of the BHK Signature preamplifier in place of a traditional volume control.
Both preamp offerings of the company are based upon the perfect volume control. No volume control.
And that is how you make a better volume control.
Nothing is best.