reduce power to reduce heat from UPC1342V kit

[kozard]

Well I discovered that if I lock the REW generator to the FFT the results improve significantly. See attached.


Harmonics are now: (Only 8 Vrms output into 4 Ohm 100W aluminum cased power resistor.)

THD: 0.021 %
N: 0.054 %
THD+N: 0.058 %
2nd harmonic 0.0039%
3rd harmonic 0.020%
4th harmonic 0.00069%
5th harmonic 0.0051%
6th harmonic 0.00019%
7th harmonic 0.0032%
8th harmonic 0.00018%
9th harmonic 0.0029%


This time I setup the RTA as follows:

65536-point spectrum using Blackman-Harris 7 window and exponential averaging 0.94
Input RMS 72.6 dB, 72.6 dBC, 72.6 dBA
Distortion at 999.8 Hz, -13.9 dBFS based on 8 harmonics.




So now it is much closer to the datasheet with the exception of the 3rd harmonic and some 60 Hz pickup. I think I know the cause of the high 3rd harmonic.

 

[kozard]

If I remove the speaker line disaster fuse (fast blow) the 3rd harmonic significantly drops.

I guess I now know the answer to my question: "Do fuses in the speaker line affect distortion?" Also I now think this is a really nice kit.


See the new data, below: (Only 8 Vrms output into 4 Ohm 100W aluminum cased power resistor.)

THD: 0.0082 %
N: 0.054 %
THD+N: 0.055 %
2nd harmonic 0.0038%
3rd harmonic 0.0072%
4th harmonic 0.00080%
5th harmonic 0.00068%
6th harmonic 0.00022%
7th harmonic 0.00019%
8th harmonic 0.00019%
9th harmonic 0.00018%


REW RTA Setup:

65536-point spectrum using Blackman-Harris 7 window and exponential averaging 0.94
Input RMS 72.6 dB, 72.6 dBC, 72.6 dBA
Distortion at 999.8 Hz, -13.9 dBFS based on 8 harmonics: