Input Devices


January 23, 2019

Once again, our goal is to figure out the extreme swings of current that are possible into an external load impedance. It’s all relative, you see. My old WCF sims are a mess of lost libraries. Once again, it’s totally up to preference. Thank you, regards, Gary.

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Looking forward to building the Aikido, will send some comments when I’m done!

One of the rectifiers has been replaced by an NPN output transistor, which should result in more stable idle current, as the MJE’s Vbe voltage should remain more constant, relieved of driving the external load resistance.

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Amp Chokes, Cathode Followers, and other Maplifier Questions

Since this capacitor must usually be a large value, electrolytic types are almost universally used in spite of their poor sonic reputation. Here floating means not tied to ground. Now, with mA of idle current flowing through three output tubes above and below, the heater elements will see a voltage differential of Ideally, the top triode should see an inputs that contains the same amount of power-supply ripple as the bottom triode sees at its plate.

The idea behind the single-ended power amplifier shown below is that the MOSFET is configured as a source follower and that the 2mH inductor replaces the resistor. For example, a 6AS7 offers a low plate resistance of about ohms, while a triode-connected EL34 offers about 1.

Not all dyslexic students have trouble with math, just as not all those who suffer from dyscalculia also suffer from dyslexia. Well, if it only uses N-types, why not replace the transistors with triodes? And yet they are frowned upon by many “High End” audio builders. I’m not one fopr two stage amps, don’t like high transconductance valves, very fast and seeming to do the job of two valves, but there is a trade off.

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For if the ohm resistor experienced a larger voltage drop, the PNP MJE transistor would greatly increase its conduction, which would pull up the voltage on the 2. We watched the drive signal on a scope while it chokr playing and saw no flattening of the positive peaks whatsoever, there was an equal signwave positive and negative.

The bottom output tube gets its input chooe after the Aikido cathode follower, so its grid sees little of power-supply noise. Looking at the grid characteristics learned me that I would need to supply around 2.

Another possibility is to replace the cathode resistor with a constant-current cboke circuit. However small changes in bias and resistors bring THD up to merely “point”, and typical designs are lucky to do so well unless level and load are trivial.

If an extra ground were added, so the power supply was “grounded properly,” then there could be neither amplification nor correct biasing of the triode. Click on the image below to see the full screen capture. Well, rather than go vertical and upside-down, we can go horizontal.

With resistive loading you see followwer second, as expected, a little third, and much lower higher-order the latter may be at the limits of the simulatorthe numerical limit looking at the generator directly is at about dBr. This choice was inspired by the high current demands that I needed. The 6SN7’s cathode is referenced to the negative rail, so its grid should see the same amount of rail noise, so that the noise can null folkower its plate.


So, in the ideal setup, the top triode sees a fixed cathode and grid voltage, while its plate varies with the power-supply noise; and the bottom triode sees a fixed plate voltage, while chok grid’s voltage is varied to provoke a matching variation in current conduction. In fact, I will quote from blog.

cathode follower: why the bad rep, and when sounds good?

Stereo and mono, octal and 9-pin printed circuit boards available. Is there a known technical reason for that? Apart from the obvious bad design which makes them oscillate at RF etc. Remember that, in a cathode-follower output stage, the grid must see much larger voltage swings than the cathode will undergo.

The plate load choke also isolates the output stage from the power supply. I’m sure you could charge double and still have happy customers. Let’s now move on to the SRPP circuit and its peak current cathod. See blog numbersblog 49blog 50, blog 53and blog for more details on cathode-follower output stages.