“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.
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.
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.
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.
And last but not least some pictures:
The Tube active crossover looks awesome. Thank you for posting such detailed photographs of the project during construction. The photograph of the 5 mil copper sheet used to line the inside of the Brazilian cherry chassis is especially nice. How do you laminate the 5 mil copper sheet to the surface of the wood — do you use a contact adhesive? Do you have a recommended supplier for both the high purity 5 mil copper sheet?
Thank you very much.
I buy the copper sheet from Basic copper and found their quality excellent.
In the past I’ve used a marine all purpose glue,
But I switched to a stronger fast glue Rapid Fuse than can be found in any Home Depot .
It is relatively easy to work with a 5 mil sheet. All you need is to precut it, fit it inside the box , then remove it, apply the glue and place it inside the box again. Then I use a piece of hardwood and pres and slide against the sheet so it will make contact with the glue.
Allow time to a complete dry and cure, and then solder all the seams. In the end I use a stranded copper wire to connect it to the top plate.
Hope thank helps.