JLH Headphone Amp

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#981
Yes, I made a pair of PCBs from the published artwork, but my etching skills were not great at the time (probably worse now). One worked, but I never found the fault in the other. I never built a case for them. Shortly after, I left home for my first job and don't know what happened to those original boards.
 
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#983
IMG_3923.jpeg


Another AliExpress reincarnation. Not great for low impedance headphones.
 
#985
MilesCampbell said:
From JHL to JLH

Picture List
  1. Incorrect capacitor polarity issue
  2. JHL to JLH - The PCB's side by side
  3. Component locations for change
  4. 100Hz Square wave
  5. 100Hz Square wave X10
  6. 1kHz Square wave
  7. 1kHz Square wave X10
  8. 10kHz Square wave
  9. 10kHz Square wave X10

Comments
The performance of the JHL kit was not as expected or designed by JLH and having serious reservation with regard to the PCB layout proof was required that the project should continue. The work done for this post was to improve the amplifier performance at little or no cost and to check the PCB for function.

Limitations in testing
It must be made very clear that the test regime for the amplifier is currently very basic with a number of omissions, these are
  1. Poor input test signal quality at low frequencies
  2. The full bandwidth has not been tested
  3. The input signal has been limited to a small value of 200mV peak to peak
  4. Testing at 20, 200, 2k and 20kHz would be more useful and the design improves
  5. Both sine and square testing at the above frequencies
Steps are now being taken to improve the testing setup by serval orders of magnitude.

Stage 1
These simple changes will improve the performance of the board considerably.
  1. C23, C24 Require inserting with the correct polarity. The negative electrolytic capacitor terminals should face the centre of the board. If the board has been powered up can I suggest this component is replaced.
  2. Remove the 8 (0.1uf) capacitors shown in photo 3

Stage 2
With a small number of replacement components the design takes another step forward. Using picture 3 as our guide
  1. Implement Stage 1
  2. Change 2k2 for 3k3 resistors (2 off)
  3. Remove the two 10k variable resistors and link as required
  4. Replace 4k7 with 10k (2 off)
  5. Replace 220k with 47k (2 off)
  6. Replace the Zener Diode with 3 x 1N4148 in series (6 off) - Note the polarity is opposite to that of the zener.

Please note that there is a larger offset voltage which cannot be removed with this method in the order of ±100mV.
Click to expand...
4.
  • Replace 4k7 with 10k (2 off)

hello miles and the jlh diyers
what 4k7 ? did you not want to talk about the R21, 1K of JHL ? to replace it with a 10k, to be like R3 of the JLH ?
 
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