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This topic has been moved to Performance and Measurements.

https://analog-precision.com/forum/performance-and-measurements-12/measurement-equipment-14/

Symmetrical clipping means the absence of 2nd harmonic distortion and dominating 3rd harmonic distortion but no higher frequency distortion artifacts which should be music to the ears of tube aficionados.

[Introduction]

Introduction

The Ultimate Pre-amplifier features a soft clipping feature which when enabled, clips in much the same way a push-pull tube amplifier does but does so more accurately and consistently since it is implemented in the digital domain.

Measurements

• Soft Clipping of 1kHz sinewave at 0dBFS.
• Soft Clipping of 1kHz sinewave at -10dBFS.
• Soft Clipping of 1kHz sinewave at -20dBFS.
• Soft Clipping of 1kHz sinewave at -30dBFS.
• Soft Clipping Sweep of THD + N vs Amplitude of 1kHz sinewave.

Conclusion

The soft clipping works extremely well and in textbook fashion according to the measurements below. In fact it works so well there are no more distortion artifacts above 3rd order so even the most ardent of tube aficionados would welcome its tube like characteristics which can be turned on or off at will.

[Scope shows even more distortion than Power Pentode as expected !]

Scope shows even more distortion than Power Pentode as expected !



Only 2nd, 3rd and 4th harmonic present ! No higher order harmonics in sight which should be music to the ears of tube aficionados

[Scope shows more distortion than Signal Tube profile !]

Scope shows more distortion than Signal Tube profile !



Only 2nd and 3rd harmonic present !

[Scope shows some distortion as expected !]

Scope shows some distortion as expected !



Only the friendly 2nd harmonic present though !



Distortion vs Amplitude Test

[Introduction]

Introduction

Whilst all of the other tests posted so far are looking for the best possible distortion and noise measurement, in this case we are going in the opposite direction and purposely trying to add distortion in the same way a tube circuit does.

Measurements

In the following tests we operate different tube profiles whilst keeping the grid bias constant. In all of these tests we are mimicking the way a tube Preamplifier behaves which is exposed to a full scale signal all of the way before the volume control which is unlike a Tube Power Amplifier where the distortion increases with increasing volume control !

• "Signal Tube" emulation mode distortion test at -3dBFS
• "Power Pentode" Tube emulation mode distortion test at -3dBFS
• "Power Triode" Tube emulation mode distortion test at -3dBFS

Conclusion

These are just three examples of what can be achieved with Tube Emulation as the grid bias control and amplifier type allows many different permutations of altering the tube linearity and hence the distortion profiles !! For tube and SET aficionados the pure 2nd harmonic distortion should be music to their ears !!

[J-test dScope III internal generator test with expanded frequency scale]

Some additional spikes here, In terms of jitter the analog generator in the dScope III is not as good as the ES9038PRO Sabre DAC in the Preamp



J-test dScope III internal generator test with expanded frequency scale

This topic has been moved to Performance and Measurements.

https://analog-precision.com/forum/index.php?topic=11.0

[No evidence of ESSTech IMD/THD hump !!]

No evidence of ESSTech IMD/THD hump !!

[Introduction:]

Introduction:

The THD+N vs Amplitude measurements are good for testing a devices linearity and noise performance and see whether there is any dependence of noise with signal level. In this test a stimulus in the form of a 1kHz sinewave is fed to the EUT (equipment under test) to see how it responds. In an ideal test what is fed into the EUT should also be present at its output in proportion and without any other frequency components or artifacts present if the EUT is perfectly linear. However in the real world some non linearity is always present and we expect to see some frequency artifacts in the form  harmonics of the original fundamental test frequency. The random uncorrelated noise is also added to this measurement.

We also use this test to show up a flaw in some Esstech Sabre DAC implementations in the form of a hump in THD measurements at a certain band of signal amplitudes.

[No Evidence of the ESS Tech IMD hump present !]

No Evidence of the ESS Tech IMD hump present !