Hybrid ZEN Amplifier + LM317 = Efficient and simple

I'm very glad you built it and can enjoy it. It is very likely that changing R5, in addition to increasing the voltage gain, will reduce the high frequency response somewhat (although only measurement or a simulation with accurate models will indicate the amount) and increase the THD somewhat. In any case, it is likely that the high frequency limitation falls well outside the audible range and the increase in distortion acts in favor depending on the speaker used (due to the statistical probability of a minimization of acoustic distortion with the consequent greater electrical distortion generated in the amplifier itself and the respective phase of certain spectral components in the distortion profile).

Would you be able to measure input signal levels to the amplifier and typical output signal quality parameters with a program such as REW, ARTA, DAQARTA, etc.?

From the description of the natural sound that you mention, it is likely that the electrical distortion thus achieved in the amplifier (with the increase of R5) is favoring your configuration of signal source + amplifier + speaker + environment + listener, in terms of acoustic distortion, which is what we finally hear.

Many thanks to you !
 
  • Like
Reactions: radumar1
I am not skilled at all in designing PCBs, the prototype was built as seen in the videos and I still have it built like that (my laziness is strong). I only focus on enjoying my constructions in terms of their operating parameters (not their constructive beauty). I wish I had the skill and patience of many here who build true beauties of circuits.

Best regards
 
  • Like
Reactions: chermann and stv
Diego, many thanks for your very detailed answer. I use a full range 30W, 13cm, paper dual cone Monacor speaker in a homebrew, 25x35cm wooden OB. I have ARTA but it would take a couple of days to make a proper setup for all measurements. What I've done so far, on my handheld oscilloscope I can clearly see a clean sine wave amp ouput, with input provided by an online generator using my mobile phone, at 5 Hz, 100 Hz, 1000 Hz, 10KHz, 18Khz. Max input RMS is about 0.4V and output RMS is around 3.7V (measured on the amp output's 5W, 8.2ohm resistor)--clean looking sine wave.

Ref PCBs, I always use this quick enough technique for them, scratching copper clad with this cutting tool.

Bests,
Radu
 

Attachments

  • 20250204_165128.jpg
    20250204_165128.jpg
    497.3 KB · Views: 110
  • 20250207_125259.jpg
    20250207_125259.jpg
    295.3 KB · Views: 118
  • Like
Reactions: diegomj1973 and stv
Hi,

I used IRFP044 instead of Diego's IRFP150, and because I've used a low output portable CD player as a source, I increased feedback resistor R5 to 6.6K from 2.2K. I mention I use a laptop smps which outputs 20.4V, and 5Watt resistors R2=1ohm and R1=1.2ohm. If it's possible, Diego, please help me: how my feedback resistor change (giving larger voltage gain) impact THD ?

Many thanks !
Hi Radu

Nice build

Both your transistors look like the size of TO-220. The IRFP044 is usually manufactured as TO-247 which is much bigger than TO-220. Could you please verify your transistors. I’m just waking up with my first coffee so hope I’m not saying vlakies.

Thanks
Eric
 
  • Like
Reactions: decramer
Piece of cake 😀
Really, itcould be done p2p, no fuss. Don't want to go off topic, but for example, I had built Frontend 2022 preamp without a PCB, look:
 

Attachments

  • Frontend2022-1.jpg
    Frontend2022-1.jpg
    97.3 KB · Views: 120
  • Frontend2022-2.jpg
    Frontend2022-2.jpg
    131.5 KB · Views: 116