Problem:
- Cracking sound.
- Case rusty.
Actions:
- Recap all small size capacitors.
- Clean all switches and VRs.
- Touch up hot spot solder joints.
- Add speaker protection relay.
July 17, 2026
Pioneer SA-506 repair and service
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Parasound HCA-1200 ii repair
Problem: Stay at standby LED after power on. Later found output relay poor contact, sound distorted or cutoff.
Cause: Output transistor one shorted. Negative rail fuse open.
Actions:
- Replace one transistors 2SA1386 by 2SA1186 (closest found).
- Service relay to ensure good contact (R < 0.1 ohm).
- Recap some e-caps on main board.
- Replace bias adjust VR to 10 turn 500ohm, one VR shorted.
- Rusty frame is painted with silver pen.
- Touch up some suspect cold solder joints.
- Retune all Bias for L/R channels.
- Test for output power and distortion.
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January 29, 2025
Audio Innovation L2 preamp repair
There is issue on the preamp claim by owner and cannot be used. Later find out that output has about 20-40V DC level drifting. Root cause is due to Jensen output leaking, changes to other film cap resolve the issue.
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November 6, 2016
Ekras distribution amplifier inside photo
This is Korean distribution power amp and record some photos before throw away.
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October 20, 2009
All Jfet Buffer Balance Line Amp
This is also Borbely Erno Design Jfet Buffer and I use this to make my pre-amp. I use two low noise regulator and 4 buffer module to become a full balance pre-amp. The sound is very good and distortion is also very low. I have tried to use a transistor second stage but the sound become aggressive and harsh. Thus all Jfet is my choice!
Jfet regulator Circuit *updated on Dec 23, 2009*
Jfet Buffer PCB Errors *updated on Jan 15, 2010*
FFT jfet buffer xlr log at 10V
Update on Oct 20: After redo a bit on the wiring of power supply and put a NTC from star ground to the casing, the distortion has improved to below 0.0001% at 10Vrms output balance mode. Distortion is also very low at 0.0026% at 1Vrms output. The good thing about this pre-amp is that the higher the output level, the lower distortion it will be.
Some FFT measurement after improvement:
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