# Audiophile Repair Knowledge — Tj's Field Notes
This is the stuff I've learned fixing high-end audio gear.
Some from my years at PS Audio, some from repair benches,
some from conversations with the best techs I know.
1. Power / Hum / Buzz — The Most Common Call I Get
Subwoofer Hum with Class D Amps
This one took me forever to figure out. Customer has a class D amp
(Stellar S300, for example) connected to a REL sub, and there's
a loud hum even with the system OFF. Ground lift doesn't work.
Floating ground doesn't work. Chassis ground doesn't work.
What actually works: An unused RCA cable as a ground reference,
or a chassis screw near the XLR jack. REL even used to send resistor
kits for this. I sent a few of those myself.
Power Plant Fuse Specs (From My Own Notes)
- P20 220-240v: 5A, 250V, Slow-blow, 5x20mm
- P20 120v: 6.3A, 250V, Slow-blow, 5x20mm
- Don't deviate from the OEM rating. I've seen too many blown PSUs from people thinking "one size up is safer."
Ground Loop Quick Diagnostic
- Try a different grounded outlet first
- Cheater plug — for DIAGNOSTIC ONLY, never as a permanent fix
- Disconnect coax (cable TV ground is a notorious hum source)
- Test with WiFi (kill the Ethernet — ground loops travel through network cables too)
- Separate audio and power cable runs
2. DAC and Digital Component Repairs
DirectStream USB Dropout
Symptom is always the same: plays fine for anywhere from 5 seconds to 2 hours,
then audio stops. Only fix is unplugging and re-plugging the USB.
What I learned: This was a macOS Catalina driver incompatibility.
The fix was either a digital board replacement or a firmware-side workaround
that I'd send to customers directly. If your customer has this issue,
start with the driver/OS compatibility before blaming the hardware.
PWD MKII Firmware Brick Recovery
Wrong firmware flashed, stuck on "Initializing," SD card won't flash.
I used to handle these personally. The fix is a custom recovery SD card image
from PS Audio support, then flashing firmware 3.0.4 from scratch.
Don't try to shortcut this — the bootloader is picky about which cards it reads.
DSD MK2 Aftermarket Mods — Watch Out
I've seen units come back from third-party mods that were completely
unrepairable. Transformer mods especially — they cause the unit to fail
nearly every bench test. If a customer brings in a modified unit, let them
know upfront: factory service may not be possible anymore.
Out-of-Warranty Repair Expectations
It's NOT a flat fee. Depends on age and parts availability.
Vintage units (15-20+ years) cost more because parts are harder to find.
Paul once asked me to look at pricing to make sure we were being fair
to the HiFi Family values.
3. Vintage Gear and Speaker Restoration
Speaker Foam Rot
This is inevitable. Every speaker over 10-15 years old will need a re-foam.
Don't patch it — replace the whole surround. Re-foam kits are cheap and
restore them to factory spec. I've done this on everything from Advents to JBLs.
Crossover Capacitors
Those original electrolytics in the crossover? They've drifted. Maybe 20%,
maybe 50%. Replace them with film caps of the same value. The speaker
will sound like it did when it was new — sometimes better.
Turntable Speed Issues
Nine times out of ten, it's the motor capacitor. That old wax/paper cap
dried out years ago. Replace with a modern film cap of the same uF rating.
On belt-drive tables, also check the belt — they stretch and slip over time.
On idler-drive, check the idler wheel for hardening.
Turntable Hum
Check the ground wire from the tonearm base. It's almost always
a broken or disconnected ground. Next check: the cartridge ground strap.
After that: phono stage issue.
4. Streaming and Network Audio
Bridge II — Tidal/Qobuz Issues
The MConnect app can be finicky. If it says "device does not support TIDAL,"
the fix is: use MConnect CONTROL (not HD), update Bridge II firmware to latest,
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