The Cavalli-Kan Kumisa III Stereo Headphone Amplifier

Specifications and benchmarks

All measurements were done with an CK²III amplifier with the following configuration (except where noted):

Test conditions
Output stage quiescent current set to 30mA on both channels
Output dummy load 33Ω 5W resistor between each stereo channel to output ground
Volume control50KΩ Alps RK27112A set to maximum
Parts selection As specified in the parts list

The tests were conducted using the following equipment:
  1. Wavetek 188 4MHz sweep function generator
  2. Tektronix TDS2014B 100MHz quad trace digital storage oscilloscope
  3. Protek 6510 100MHz analog dual trace oscilloscope
  4. Fluke 95 50MHz digital dual trace ScopeMeter
  5. Fluke 187 digital multimeter
  6. Toshiba Satellite A65 laptop computer with Celeron 2.8GHz CPU and 768MB RAM
  7. M-Audio Firewire Audiophile mobile interface
  8. RightMark Audio Analyzer 5.5 software
  9. dummy loads 330Ω/33Ω/none
  10. other custom test jigs, cables and software

Here are the measured results:

Measured results
Input impedance 47.6KΩ
Output impedance less than 0.5Ω
Maximum output voltage
per channel, 1KHz, prior to onset of clipping		 20Vp-p (7.07Vrms)
Power output 1.4Wrms into 33Ω
0.15W into 330Ω
Frequency response at 0dBV output:
10Hz - 1.6MHz, +0dB -3dB
0.4Hz - 1.6MHz, +1.3dB -3dB
Rise time 100KHz square wave, at maximum output, 10% to 90%:
220nS
Slew rate 100KHz square wave, at maximum output:
70V/µS
Noise level
Dynamic range
Total harmonic distortion
Intermodulation distortion
Stereo crosstalk		 see RMAA test results below

RMAA test results



Several tests were performed, one with the M-Audio Firewire Audiophile mobile interface running in loopback mode to establish the baseline (lowest limit of measurement resolution), and anothers with the CK²III amplifier added to the chain with 330Ω or 33Ω dummy loads connected to the CK²III's output.

The CK²III's volume control knob is set to within 3dB of maximum for these tests. This is worthy of mention because many others test their amplifiers with the volume set lower, which would give artificially low noise and distortion results.

Click on the following links to see the results.

Comments on the RMAA test results

The measured performance, notably the low THD and IMD results, are very good for an amplifier without the aid of global negative feedback.

The slight rolloff at the low end in the frequency response graph is due to the M-Audio's coupling capacitor. The CK²III's actual frequency response extends down to well less than 1Hz. Likewise, the high-end rolloff in the graph is due to the M-Audio's anti-aliasing filters. CK²III's actual response extends to beyond 1.6MHz (-3dB) in the tested configuration.

The small spike at 120Hz in the CK²III's noise graph is most likely rectifier diode noise, but its amplitude is only slightly above the noise floor, and is thus negligible.

The CK²III's RMAA results remain essentially unchanged whether its outputs are loaded with 330Ω or 33Ω. The 3rd-order harmonic distortion is slightly higher with 33Ω load than with 330Ω load. The stereo crosstalk in the high frequency range is a little higher with 33Ω load, but still excellent. Many amplifiers' distortion performance deteriorate significantly with lower impedance loads, there is no such problem here.

Oscilloscope waveforms

The oscillogram waveforms of the CK²III amplifier are shown below. All input waveforms are produced by a Wavetek 188 4MHz sweep function generator.

The following is the 100KHz square wave response as tested with a Tektronix TDS2014B 100MHz digital storage oscilloscope. The top trace is the input and the bottom trace is the output. The rise and fall times as well as the peak-to-peak output amplitude is shown on the right hand side of the display.



Below are additional waveforms as measured with a Protek 6510 100MHz analog oscilloscope. In all graphs except the Lissajous waveform, the top trace is the input and the bottom is the output.

The 100KHz square wave graphs show that there is slight slowing and rounding of the leading and falling edges, but there is no overshoot or ringing. The lissajous (X-Y) graph shows a slight phase shift at 100KHz. However there is no measurable phase shift within the audio band.



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