Transmission Lines as Applied to Audio

[J-ROB]

Walt,

Flat "card wound" non-inductive resistors are a better geometry than cylindrical bobbins. More ideal cancellation and lower inductance using Ayrton-Perry or pi windings if the former is flat. Flat coils are lousy inductors.

They are bobbin resistors just on different shaped bobbins. Early card wound resistors were found on flat cards of mica or asbestos, for your carcinogenic snorting pleasure.

Surely there are mechanical advantages to cylindrical steatite bobbins and that is how most were later made. From the 50s on, most were dipped or molded in resin. Precision WWs are are somewhat mechanically fragile due to the fine wire employed, usually Nichrome on high value Rs and manganin on low value.

The early Daven stepped attenuators and pads were enclosed in metal cans and they used card wounds. Card wounds take up less space so there is an advantage if you are doing a 30 step H attenuator (5 element) in a small can.

Late model Daven and Shallco attenuators (still made, I think) used Dale metal films...boring!

I almost finished an EAR 834 clone using (mostly) all non inductive wirewounds. Never used mostly WWs before so curious how that would sound. I have used them in the past for phono input and the like. If you look around (or get in touch with Wiggins) there are higher dissipation (1-3W) precision wirewounds to be had. I have a collection here as well.

[SoundMods]

You make them from flexible resistor cards.

I just happen to have a stack in my shop -- NOT!

[J-ROB]

flexible resistor cards.

Yeah, there are wirewounds on flexible braided fiberglass (?) formers with a glass braid tube on the outside.

I can't say I have seen a stack but then they are very hard to keep stacked, being so flexible.

[Roscoe Primrose]

I've got a whole bunch of these: http://www.surplussales.com/Resistors/C ... 200_L.html except that they're BX193-N, I assume the -N is for non-inductive. Unfortunately, I only have 2 or three different values, one of which is 130k...

Roscoe

[Roscoe Primrose]

I almost finished an EAR 834 clone using (mostly) all non inductive wirewounds.

I'm getting the parts together to build something Siren Song-esque in the near future. Maybe I'll have to try some WWs in there...

Roscoe

[J-ROB]

Let me know the values and I'll see what I have. Also check with Paul Wiggins.

I'll trade towards future smoked brisket (or pork.)

[SoundMods]

flexible resistor cards.

Yeah, there are wirewounds on flexible braided fiberglass (?) formers with a glass braid tube on the outside.

I can't say I have seen a stack but then they are very hard to keep stacked, being so flexible.

Shallcross is (or was) a major manufacturer of bobbins. YUM!

[SoundMods]

I forgot to include photos. Sometimes implementation of an idea is not as easy as it sounds. The adapters were not a big deal. The 36S DAC had no room on the PC boards to insert the 250-ohm bobbins at the summing point of the differential amplifiers. The XLR output connectors provided the placement needed to pull it off.

Attachments

[J-ROB]

Precision WW resistors come in very small packages, down to the size of 1/4 or 1/8W resistors, if you decide to build that thing in.

Putting it in an XLR shell is a good solution though.

[SoundMods]

Precision WW resistors come in very small packages, down to the size of 1/4 or 1/8W resistors, if you decide to build that thing in.

Putting it in an XLR shell is a good solution though.

They are really not classified as wire-wound resistors as most people know them to be. They are quite different from wire-wounds whether non-inductive or not.

They are classified as Bobbin resistors because of the back-to-back copper bobbins. They especially measure better than the best non-inductive WWs with self-inductance in the low uH range. Then -- being fabricated with copper wire as opposed to the typical WW Nichrome wire they serve the music in ways the Vishay guys can only dream about.

As far as building the Bobbins into my BAT pre-amp -- that would be cool if there was a way to do it. To make it permanent I would want switched resistance selections kind of like a MC phono stage. Unfortunately, the BAT has 10# of crap in a 5# case. It would take some serious butchering to pull it off. So -- high quality XLRs get the job done. At least it's a permanent DAC improvement.