DIY Audio Analyzer with AK5397/AK5394A and AK4490

[1audio]

Originally Posted by zfe

For measuring electrostatic headphone amps I would like to increase the input attenuation.
Would it be good practice to add a, say, 900k resistor in series to the single ended input? This would make a 10:1 divider with the 100k input impedance of the RTX6001. A hight input impedance is desired for electrostatic amps anyway.

For most electrostatic headphones (Stax or similar) you will need a differential measurement. 1 Meg is a significant load and you need more like 10M or even 100 M. And you need to compensate the capacitance. Fortunately the voltage swing is on the order of 200V or more so a divide by 100 probe is not an issue and the RTX has enough gain. Stray capacitance at the probe point is also an issue since the headphones are on the order of 100pF and the stray can be significant. Also use several resistors in series to reduce the voltage and associated voltage coefficients across them.

Keep in mind 200V at 20 KHz can pack quite the punch even with limited current.

[zfe]

My idea was to measure without headphone connected and add some capacitance in parallel so simulate the headphone. This way the stray capacitance and the input capacitance of the RTX6001 could be part of that capacitive load. Are there objection on doing so?

[JensH]

The capacitance of the headphones is in the order of 100 pF, equivalent to an impedance of 160 kohm at 10 kHz, so I don't think that a balanced load impedance of 2 Mohm will be a problem.

I built a KGSS amplifier some years ago. It has output resistors of 5k11 in series with each output.