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Building a DOA SeNNator Headphone Amp

Posted 3rd January 2017 at 04:56 AM by disfunctionalshadow
Updated 3rd January 2017 at 04:26 AM by disfunctionalshadow

In a search to replace a modified SMSL headphone amp that I use at work, I decided to build a DOA SeNNator, a variant of the filtering headphone amp for the Sennheiser HD 650, published by Solderdude over at - diyaudioheaven along with measurements of the HD650's responses.

It's based on the "HD 650 SeNNator" and "SeNNator build tips" pdfs. In adapting the design, DOAs were used. An upgrade to the filtering caps from polyster to polypropylene. To the original circuit, circuits and design ideas from:

  • Sam Groner - +/-30mv DC offset adjust and DC bypass cap.
  • Layout idea lifted from Jeff Steiger's CAPI-2 Line Stage Amp, from Capi-gear.
  • DC filter from Collective Cases, reducing the numerous different electrolytic caps and upgrading the linear regs. from LM217/337 to LT1963/3015.

Minimized mechanical assembly, using the default PWBs available in Kicad, each channel and the DC filter/regulator boards are in a Euro card form factor - 160mm x 50mm. That allows using a Hammond 1455 series chassis where the boards slide in the chassis slots. They are held in place by friction - a single M3 screw and 5mm hex spacer braces the center of each board.

The input RF filter, input jacks, 10K switched attenuator, and input capacitors are hardwired to the front panel.

The power supply is a switched external supply from Collective Cases that provides +/-16V and +48V.

In the first version, I neglected to verify some of the holes sizes for the 0.1uF polypropylene caps and had to fall back to Nichicon QX series, along with the wrong footprint for the protection diodes.

The second version I thought to lower the capacitor cost and used WIMA FKP series polypropylenes. While that worked, even after 400 hrs of use, the sound seemed to have a light veil to it. The lower rev boards were put back in, in which the highs were better, with more 3D detail.

In working on the third version, Rel Cap PPT Thetas were used. For the pair of 0.1uFd caps directly in the audio path, Rel Cap TFT (teflon) caps.

Amtrans AMCH series were used for the smaller caps. The resistors, in the audio path, had the layout changed to accommodate 1/2W and 1W resistors.

The power supply filter caps - for the DOAs and the offset adj. were changed to polymer caps to increase life and lower impedance. Changing the DC bypass cap from ELNA RFS SilmicII to Nichicon MUSE ES doesn't seem to have made any difference.

The filtering works very well! It removes the darkness (mid-bass hump) from the HD 650s. The sound is much like quality speakers (if one ignores the imaging issue) - very flat, deep bass, extended highs, non-fatiguing sound. The one thing that surprised me was the highs with the teflon capacitors - silky. While used to the sound changing over the 100 to 400 hours it takes to burn in film capacitors, there was almost no burn in required for the highs, only a tightness in the bass.

Attached is a pdf with the schematic for the PWB that allows for tuning HD650s - old cups vs. newer, old drivers vs. new and allows for the HD600 with proper changes per Solderdude.

Also attached are photos of the current headphone amp and the test output of THD-N at 97mv out.
Attached Thumbnails
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Attached Images
File Type: jpg DOA_SeNNator_HD6500003a.jpg (100.4 KB, 71 views)
File Type: jpg DOA_SeNNator_HD6500005a.jpg (105.4 KB, 70 views)
Attached Files
File Type: pdf DOA_SeNNator_V1.5p.pdf (43.5 KB, 77 views)
Posted in Headphone Amp
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