“Shiny Eyes” Tube active crossover, my implementation of Pete Millett’s design

“Shiny Eyes” Tube active crossover

My implementation of Pete Millett’s design

Back to work on a different type of project. I needed a 4 pole that rolls at 24dB/octave. I also needed 2 frequency crossover options: first around 100Hz and second around 700Hz. I like Pete Millett’s design at http://www.pmillett.com/tube_active_crossover.htm. He also had some boards left which was awesome. I want to thank Pete for all his support.

The PSU is a little different that Pete’s. For the high voltage, I use a quasi choke input and two sets of chokes. the last capacitors are low ESR Vishay MKP at 100uF. The PSUD2 results show a low output ripple of about 0.6mVrms.

PSU2 HV

The low voltage supply uses two LT1084 set at 6.3V output and feed each channel’s vacuum tube’s filaments. The layout of this crossover is very simple: left side, and far away from the PCB is the PSU: right side is the PCB with switches and RCA jacks. The enclosure is made of high quality Brazilian cherry top coated with light oil and urethane. The inside of the wooden enclosure is screened using a high purity 5 mil. copper sheet. I also used a screened FR4 board inside the box, between the PSU and the PCB.

top inside psu

The hard part was to figure out the switches at a decent cost. I found a guitar store that had 6 positions 4 pole rotary switches. I used four of the them, one for each 2 pole filter ( two 2 pole filters per channel). I used RN55 1% Vishay for all filters, and not only.

PCB inside

Tubes are E88CC/6922 Jan Phillips low noise from thetubestore.com.

The sound is transparent and there is no noticeable hum or noise.

Measurements, all tubes are biased at 8mA. B+/B- at 95V.

HF outputs:

HF-THD HF-600Hz cutoff HF 90Hz cutoff HF Harm H2 H3

LF outputs:

LF Thd LF FR at 90Hz cutoff LF FR 600Hz cutoff LF THD H2 H3 cutoff 600Hz

And last but not least some pictures:

top overview overview top right top left 00 top right case and plate

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