djgardner.com DIY Audio • Dynahi (1999) • HD‑800S • External PSU • CPC Harness

Dan “djgardner” Gardner — DIY Audio Archive & Projects

Reviving the 1999‑era DIY site: the Kevin Gilmore Dynahi (quad‑mono, balanced), the external Condor ±30 V PSU via CPC harness, and modern notes on HD‑800S balanced cabling. A living record of group‑buy culture, schematics, BOMs, and photos.

Site is being rebuilt. If you have an old bookmark to djgardner.com, you’re in the right place — the archives are coming back online.

About

In the late ’90s and early 2000s, I coordinated group buys and built reference‑grade headphone amplifiers under the handle djgardner. This site documents that work — especially the balanced Dynahi — and connects it to what I build today.

1999: Balanced Dynahi

Four single‑ended amp boards forming two differential bridges (L+/L−, R+/R−), with a 4‑gang DACT stepped attenuator and dual 3‑pin XLR outputs per channel.

Front panel: LMB Heeger blue Unipac, dual XLR‑M/F per channel.

External Condor PSU

Four linear Condor supplies (±30 V rails) in a separate chassis, connected via a CPC circular harness — isolating heat and hum from the amp.

True dual‑mono power isolation.

HD‑800S Balanced Cables

Modern notes on dual‑mono cabling for Sennheiser HD‑800S: dual 3‑pin XLR, 4‑pin XLR, and 4.4 mm Pentaconn options; pinouts and builder briefs.

Period‑correct pinout: XLR Pin 2 = hot, Pin 3 = cold, Pin 1 = chassis/shield.

Dynahi (Balanced) — Build Notes

Topology: XLR in → DACT 4‑gang → L+ / L− / R+ / R− boards → dual 3‑pin XLR outs (per channel)

BOM & Parts

  • 2SK389 / 2SJ109 dual‑JFETs — matched pairs (historical Toshiba parts).
  • Output BJTs: 2SC3421 / 2SA1358 (complementary banks).
  • Driver/VAS: 2SA1145 / 2SC2705, 2SC3381 / 2SA1349 (per rev).
  • DACT stepped attenuator (4‑pole) for balanced operation.
  • Neutrik XLR3 panel connectors (M/F per channel).

Download BOM (XLS) (archive)

Pinout (Outputs)

  • XLR‑3 Pin 2 → Hot (+)
  • XLR‑3 Pin 3 → Cold (−)
  • XLR‑3 Pin 1 → Chassis / shield (not to driver)

No shared returns; headphone driver sees only the differential pair.

Dynahi front panel with dual XLRs and DACT Four mono amp boards inside chassis Internal wiring and star grounds

External Power — Condor Linear Supplies

Four independent Condor linear supplies provide ±30 V rails to each mono board. The PSU lives in its own chassis with ventilation and proper earthing; power routes to the amp via a CPC circular connector harness.

Block Diagram

Download block diagram (SVG)

IEC earth → chassis → XLR Pin 1 at jack. Signal grounds remain isolated from headphone returns.

Service Notes

  • Recap aging electrolytics on Condor modules as preventive maintenance.
  • Inspect CPC pins for oxidation; clean and re‑seat if needed.
  • Verify DC offset (few mV) across each differential output before use.

HD‑800S Balanced Cables

Builder Brief

Spec for a dual 3‑pin XLR balanced cable for the Sennheiser HD‑800S.

  • Headphone: HD800/HD800S keyed 2‑pin connectors (L/R specific).
  • Amp: two male XLR‑3 (Left, Right), Pin 2=+, Pin 3=−, Pin 1=shield→chassis only.
  • Conductor: OCC copper Litz or high‑grade OFC; 22–24 AWG per leg; supple jacket.
  • Length: 1.8–2.0 m; low microphonics; robust strain relief.

Download printable brief (PDF)

Suppliers

  • Hart Audio Cables
  • Norne Audio
  • Arctic Cables
  • Corpse Cable
  • Double Helix Cables

Ask for dual‑mono terminations; provide the brief above.

Archive

Snapshots and documents from the original djgardner.com (1999–2005). As I recover more files, they’ll appear here.

Downloads

If any file belongs to an original author and you’d like it removed or re‑attributed, please contact me.

Contact

Email: dan@djgardner.com

For historical corrections or contributions to the archive, feel free to reach out.