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July 99
A Common Cathode Line Stage (Part Two)
Here is a line stage amplifier that has a very low input capacitance and low output impedance and does not invert the phase at the output.
June 99
A Common Cathode Line Stage
Here is a line stage amplifier that has a very low input capacitance and low output impedance and does not invert the phase at the output.
May 99
Auto Bias (Part Two)
Auto-bias means never having to worry about the correct current adjustment for an amplifier. As the output tubes age or are replaced with fresh new tubes, the bias current will remain constant. This month's circuits use active grid voltage adjustments to set the current bias for the output tubes.
April 99
Auto Bias
Auto-bias means never having to worry about the correct current adjustment for an amplifier. As the output tubes age or are replaced with fresh new tubes, the bias current will remain constant. This month's circuits use active grid voltage adjustments to set the current bias for the output tubes.
March 99
Easy Cathode Followers
Just how little is required to make a working ground level Cathode Follower? Two resistors and a triode is the answer. One resistor to bias the grid to 0 volts and one cathode resistor is all it takes. More can be added, but at the cost of simplicity.
February 99
High Voltage Regulator
With many audio devices what is needed is a voltage regulator that can shield the audio portion of the circuit from the noise originating from the power supply and the wall receptacle, while not generating any noise of its own. This high voltage regulator is quiet enough to use with an MC pre-preamp.
January 99
Tube Crossover
An active crossover must divide the full audio signal bandwidth presented at its input into sub-bandwidths for each of the four speaker drivers so that their summed output equals a flat frequency response. Two crossover versions: 6 and 18 dB per octave. The 6 dB circuit has been pared down to the essentials only. The 18 dB version is carefully designed to eliminate as many signal path capacitors as possible. 18 dB Schematic 6 dB Schematic
December 98
Tube Headphone Amplifier
This month's circuit is a small, single-ended, OTL amplifier for driving dynamic headphones. Some excellent sounding headphones can be had from Beyerdymanic, Grado, and Sennheiser. This amplifier can power all of them, even down to the 32 ohm Grado. Schematic
November 98
Phase Selection &
Zero Gain Line Stage Amplifier
More no gain, no pain. This month's circuit offers inversion of the signal's phase and a low impedance, zero gain, buffered output. Furthermore, the circuit has been optimized to reject power supply noise at its output. Schematic
October 98
Zero Gain Line Stage Amplifier
No gain, no pain. Many audiophiles prefer to use passive attenuators, which have zero gain. However, there are circumstances that demand the use of a high current line stage. So here is the design goal: no voltage gain, but a healthy output current delivery. Schematic
September 98
Medium Gain Line Stage Amplifier
This line stage uses the Constant Current Draw Grounded Cathode (CCDGC) amplifier topology. A Grounded Cathode amplifier cascaded into a Cathode Follower...what could be more obvious? Here is where the twist comes in: the Cathode Follower's output is not taken directly at its cathode. Schematic
July 98
Medium Gain Phono Stage for MM Cartridges
The objective is a two stage phono preamplifier that uses interstage passive RIAA equalization for use with medium output moving magnet cartridges. Schematic
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