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xrk971 Pocket Class A Headamp GB

Here is the latest BOM that should be able to work with your low impedance headphones. It uses the 2200uF Nichicon KA output caps. Install the 1uF Wima bypass on the SMT side. On inputs, use just the 10uF Silmic II. Tuning for low impedance cans involves adjusting R4 to get a slightly higher bias (circa 65mA to 70mA as measured through R7). Usually a 47R or 51R value gives higher bias. However, it is at the expense of higher 3rd order HD relative to 2nd order. The other way to do it is to choose 'hot' (higher Idss JFETs). The ones I sent you should work well with a 47R value for R4. If it is too high, add a high value like 220R in parallel to lower it slightly.
I have been looking for this attachment for a long time. Well thank you xrk971


  • Pocket-Class-A-NHB-KA-Silmic-upgrade-BOM-v2.pdf
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Thank you all for this project. I had no problems getting it up and running. I also want to thank Hugh R. Dean, who deserves credit for this.


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