Directly heated triodes like the 2A3 output tubes used in the Stereomour II amplifier are exceptionally linear, which contributes to a DHT amp’s great sense of realism. One of the challenges of designing a fully capable DHT amp is to make the preceding driver stage as close as possible to the output stage in terms of linearity without sacrificing gain. We use a couple of different means to optimize the performance of the driver stage.
The stock Stereomour II amplifier uses our well know Camille Cascode Constant Current Source (C4S) to regulate current through the 12AT7 driver tubes. This gives the first amplification stage exceptional isolation from power supply ripple for low noise, and creates a very high impedance load on the tube to elicit the maximum gain from the driver stage while keeping the tube in a linear operating condition to higher input signal levels than a typical resistor loaded driver stage.
The Stereomour shunt regulator upgrade kit adds shunt voltage regulation to the C4S loaded driver stage with the application of the same hybrid shunt regulator circuit used in our premium Kaiju 300B amplifier, BeePre 300B preamplifier, and Mainline headphone amplifier kits. This hybrid tube/solid state regulator tightly controls the supply voltage to the C4S current source loading the driver tube, creating a sense of greater bandwidth and better dynamic performance.
Please note that this upgrade is only to be installed in the Stereomour II. The original Stereomour uses a different tube configuration that is not compatible with this upgrade.
“I have about 6 hrs on the SR upgrade. This is amazing! Doc’s description of the circuit’s effect, increases bandwith and dynamics, is too modest. I get the bandwidth part; the amp does now have greater range. The really impressive part is the control of the image. Voices and instruments are now more discretely placed and the SII seems to have a deathgrip on those woofers. How is that possible? Well, at any rate, for those with SIIs or those considering one, this is a must have!”
“Installed the shunt kit today (after DC Filament and volume pot upgrades). The other upgrades were cool, especially the DC supply, but the Shunt regulation! Good grief! Fired up right after the voltage checks, and with about an hour or two warm up, the amp is sounding absolutely stellar. I mean whole new ballpark, stellar. I thought the amp sounded good previously. Not quite up to the level of my KT88 SE monoblocks, but hey, each of those weigh more than the Stereomour. Now they’re punching in the same class!
Good job you all, and thanks for apparently saving the best for last.”