Kamis, 08 Juli 2010

DIY resistor for DAC current to voltage conversion

June this year is my zero writing month. Don't want to skip July so here it is another DIY audio adventure.
My tweak darling, the Sony CDP950 is almost weekly being changed. I used it for learning both digital & analogue wise. At DIYAudio I came across a strange resistor made by John a.k.a EC Design. It is quite complex to be made- although fully doable in my workshop. Here is my 'dream' Ri/v - the resistor that convert current out of the DAC to voltage that goes to the tube grids. In my case its valued 33ohm.

A beauty isn't? (hopes John wouldn't mind I use his pic.). Why all the troubles? well this DIY resistor promises low capacitance - non inductance - and high wattage. All good for tiny current out DAC.

What I can not get are a coated resistance wires & patience for winding it.  Being a naughty DIYer like me,  I have once hammered several of those white bricks, just to see what's inside :). It turned out that for low R value the R is wire wound. Higher value some kind of carbon film. Hmm..this brings me to an idea..

So, armed only with double tapes and 2 pairs of white bricks 39R/5W here we go :

The tools are 1 hammer, 2 pliers, cello-tape, double tapes (thick & thin semi transparent), scissor or a cutter, a tweezer.teflon tape...thats it.

Take care not to break the wire from the end cap. Tape the wire to the cap & legs for strength

Thick double tape both end stripped & glued to the table and start making zig-zag pattern of the first wire lay up about half of total wire length (my case 28cm ~ 1ft). plan for the double tape length.

Cover the first lay up with thin double tape, next lay up

The first lay up is now 'insulated'. Start now with a second layer, now you know why I need a semi transparent tape :).

Measurement shows a lower R value than the original 39ohm. This happen once you unwind the wire from the ceramic center piece. Not to worry & its closer to my 30ohm target :).

Cut both ends, add another thin double tape, peel wax paper on both sides & start rolling

Two DIY Resistors :)

Rolling & teflon taping. measurement shows quite acceptable 'tolerance'. After rolling the tapes the R value goes higher a bit.

In action :)

The sound? well the 'cocoon' beats my Philips metal film for sure, and about a 'tie' with the pink Takman's, not yet decided though ;). Highs of this DIY Ri/v are quite breath taking...

But...hold your horses, recent discussions on DIYAudio with EC reveals that this DIY Ri/v is not completely non inductance yet. But it can be made non inductance, using a so called Ayrton-Perry_winding and for this I need to insulate the wires using a proper lacquer. Not so hard to do compared with 5m long EC's wire :).

So ..my adventure is to be continued...thanks John..