Ï have just finished the Aleph30.THD is about 0.9% ( at 1W), which is much more than Mr. Pass states in the manual. Bias ( input pair, output MOSFets) , voltages is almost the same as manual shows. Has anybody an idea why?
Sinus generator ( THD about 0.006%), professional distorsion meter. All measurements were done in the university lab by experienced man.I thing measurements are O.K.
I think distortion measurements do not show quality of sound in Pass designs.
For me,if the ear is satisfied I don't need to go on distortion measurements,I prefer to trust Nelson 😛
For me,if the ear is satisfied I don't need to go on distortion measurements,I prefer to trust Nelson 😛
Koy,
Mr. Pass raises an important point: the frequency at which you take the THD is crucial. Standard is 1 kHz, but measuring across the audio band is typical; just report a given THD at the specified frequency, along with the RMS voltage (approx 2.8 V rms with 8 ohm load = 1 W).
Also, you need to state the test load. 4 ohm measurements will be greater than 8 ohms. Further, was a capacitor added in parallel with the load for test purposes and then left during THD measurements?
Finally, if the distortion is truly greater, it could be related to your layout (grounding issues, power supply design, etc) and not inherent in the overall Aleph design.
Mr. Pass raises an important point: the frequency at which you take the THD is crucial. Standard is 1 kHz, but measuring across the audio band is typical; just report a given THD at the specified frequency, along with the RMS voltage (approx 2.8 V rms with 8 ohm load = 1 W).
Also, you need to state the test load. 4 ohm measurements will be greater than 8 ohms. Further, was a capacitor added in parallel with the load for test purposes and then left during THD measurements?
Finally, if the distortion is truly greater, it could be related to your layout (grounding issues, power supply design, etc) and not inherent in the overall Aleph design.
Distortion
What does the distortion output look like. This will tell you a great deal. Harmonics noise 60 or 120 Hz etc. The Alephs are under .1% typically at 1 KHz from 1 Watt to near clipping.
What does the distortion output look like. This will tell you a great deal. Harmonics noise 60 or 120 Hz etc. The Alephs are under .1% typically at 1 KHz from 1 Watt to near clipping.
Incorrect wiring, second choice transistors, bad capacitor, defective soldering joint in power stages or power supply can easily cause distortion as high as 1%, even at 1W....
Regards. P.Lacombe.
Regards. P.Lacombe.
RlJones, Mr. Pass: You know something about electronics?! Dont you? 🙂)) Thank you. Now I realised the trouble. THS is overall value. Counting only with 2nd ( 10mV) and 3rd ( 5.5mV) harmonics we get much better values ( 3.8V ef on output , 4 ohm load ( cca 3.6W) at 1 kHz - ie cca 0.3%.) More than you wrote but better than previous one. Is it much or not? I forgot hum form the power supply ( measurement were done in a little hurry - lunch- you know on old device. Ordinary device - Audio precision is on regullary maintaince service in Switzerland).
I count all the harmonics and the noise, unless otherwise
specified. Your figures are high, even for 4 ohm load, so
I would be interested in the breakdown when your AP
gets back.
specified. Your figures are high, even for 4 ohm load, so
I would be interested in the breakdown when your AP
gets back.
The AudioPrecision turned back but still is not avaible for me -the guy lives more than 300km away - (in Europe it is more than in US 🙂). So I took PC with sound card, soft and tried to do it my self / of course with known limitations of this solution).
The first is output from the spectrum analysis - at 1kHz, cca 8V ( ef) ( the amplitude you must multiply by 10) to the 5 ohm. Prominent is hum form the suplly ( 100Hz) and harmonics - 2nd and 3rd. THD about 0.06%.
Second picture - similar power, load, only with current mirror in the input differential pair. THD is lower, ( lower 2nd, a little higher 3rd).
What do you think about it? Is it right? How behaves the "factory" Aleph?
Sorry , i did not noticed the picture size limit. Picture no2 will follow.
The first is output from the spectrum analysis - at 1kHz, cca 8V ( ef) ( the amplitude you must multiply by 10) to the 5 ohm. Prominent is hum form the suplly ( 100Hz) and harmonics - 2nd and 3rd. THD about 0.06%.
Second picture - similar power, load, only with current mirror in the input differential pair. THD is lower, ( lower 2nd, a little higher 3rd).
What do you think about it? Is it right? How behaves the "factory" Aleph?
Sorry , i did not noticed the picture size limit. Picture no2 will follow.
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