This idea of regulating harmonic distortion really resonates with me... There was a solid state project on DIYaudio similar to this one, its called the PeeCeeBee Preamp. It has a clean signal path and a "harmonic rich" signal path. The relationship between those two can be adjusted..
Good, honest conclusion. Glad to see input potentiometers back in play. In my tests, I am always surprised at how much signal degradation potentiometers can cause. So, it’s tremendously important that potentiometers at the input be of good quality.
Not sure if you are aware of this, thought I might mention it as a valuable testing tool. You can check the frequency response between stages as well. For example, you could DC (or AC) couple the probe to the grid of a tube to see what the frequency response is at the input of a tube. Ideally, you'd want to see a flat frequency response curve from 20 to 20k for the appropriate dB. For the output of power tubes, AC couple the probe to the cathode. In this scenario (assuming you're cathode bypassed), ideally you'd only want to see noise below -50 dB. If you have anything above the noise floor, the bypass capacitor is not completely shunting AC signal at those frequencies. I use the Diligent Waveforms software to do this with the network analyzer. You can do it with Audio Analyzer as well, I just prefer the control Waveforms gives you. I'd be happy to tell you more about this if you think it would benefit your amp testing.
Interesting results. What output loading was connected? If it was only loaded with the output pot, you'll likely get different results if you put a solid state amp on it.......
I can not thank enough. it was very informative for me special the measurement of noise level relative to volume position. I can make some modification on mine. just a question, since input stage of my discrete power amp has coupling cap too (1uF), the value of output cap could be reduced for getting same frequency response? as far as I understand after some point there is no change with increasing the cap value. correct?
The interaction is between the output cap and the 10K pot on the output. You can't remove that cap, as then you would have 86V on the RCA jack. And yes at some point the change by increasing that cap extends past usefulness with audio gear.
You should also check the X10 Compensation on both your Scope probes too, since incorrect compensation can affect the accuracy of your waveform measurements.
Yeah I do check that but thanks for the reminder. At some point I may need to replace this ancient analog gear, but I have learned their quirks and what I need to look for.
@Skunkie Designs Electronics When you are talking about roll-off frequencies (upper or lower), can you give us the 3db down frequencies please? Thanks 😁
I cannot see the 3db down frequencies in the videos, which is why I asked ☹ A 3db down frequency is relevant because that's about 1/2 of the amplitude, which is relevant to engineers because what single poles are calculated at 😉
@@SkunkieDesignsElectronics Okay 😞 If you can, when you frequency sweeps in the future, please give us the upper and lower frequencies where the signals are 3db down? That would be helpful 👍 Thanks 😁
In this case the 3db down should be 2.34hz and I'm not sure this suite measures down that low. But the 3db down needs to be that low to not impact the signal at 20hz.
Besides the failure of the petentiometer , this pre does exactly what it's purpose was designed for. Keeping the harmonic content stable independant from volume output ..... Adjusting the harmonics content by adjusting the input level.... Restoring the harmony of harmonics lost by amplifiers who elimante second harmonics leaving odd harmonics , mostly due to what's happening in PP designs. it's not about the percentage of DHT but about the structure and caracter of harmonics , ......even very low distortion measured amplifiers do sound un nantural when the harmonics are out of balance , so restoring the harmonics relatioship may result in a better musical experience . We all know we don't want distortion but we also do not like and the perfect measuring amp that doesn't sound right or good ......;it's rather the nature of distortion that results in a musical experience than the sound that emerges from an out of balance relationship of the harmonic structure of music and natural sounds ! That's also why we like triodes and SET amplifiers ..........another less know advantage of this kind of amplifiers is that at very low levels below 1 watt , these can have disrtion levels lower than 0,01 % WITHOUT any usiing any NFB !..........in contrary many modern /classic amplifiers with very low announced and measured distortion levels the distortion goes up at very low level output ( Hard distortion ) before to fall down to the annnounced distortion numbers . The caracter of the distortion also changes with output and frequency to wich the ear is extremely sensitive !.................So the nature of distortion and behaviour as well as the structure of harmonics on modulation...dynamic and frequency related .........is more important than only fabulous numbers not rlated to real music and sound. Have a very nice , we all have those periods that it seems to go wrong .....but we learn and have the patience of the return of sunny days .
What you just wrote here is worthy of a whole video series exploring. And as you said, the main thing I noticed when I started listening to SE tube gear was that music still sounded very good at low volume levels, something that I haven't experienced with SS gear. And I don't feel like most PP gear has that same sweetness at low volume levels either.
