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Group Build: Dynafet


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So, gathering interest for collaboration on KG's Dynafet.

The way this would work is quite simple. There would be a group buy on parts as well as the boards. The parts would be supplied by myself and we'd work a deal out for people contributing in the matching efforts and various aspects of specing and acquiring parts.

The boards would be the Hitachi version with external heat sinks, using KG's latest board files.

Front end would be constructed from devices matched from a pool of 500 2SJ74BL and 500 2SK170BL matched to 20uA accuracy. All devices were pulled from original Toshiba packaging. Actually matched to 10uA with +/- 20uA measurement uncertainty added on top. The will be bonded together using couplers made on a CNC wire-cut machine. See attachment. I think the performance will exceed the single substrate versions due to the better matching characteristics.

I also have 50 pairs of 2SJ79/2SK216 that will be need to be matched as well. These sell for around $10 a pair these days. Mine are all from the same batch code purchased in original Renesas packaging.

I'm thinking there would be an upfront deposit of $75 per stereo set ($150 balanced) for the devices and matching efforts and a similar arrangement (probably $40 stereo and $80 balanced) for boards.

Group buy participation is requisite on some member here "vouching" for you as well as an agreement that this isn't going to happen overnight and there is a lot of work that needs to be done to do this right. Everyone will have some sort of job to do, as this is really a group effort.

So, anyone interested? :)


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I'm very interested in the edm cut heatsinks... Did not even think of using

an edm that way. Have a brand new edm that i'm going to have to learn.

Those don't look edm'd though, unless they were anodized afterwards.

Yes, via edm. Wire cut aluminum then anodized with appropriate tolerances to leave 0.1mm gap for silver epoxy. One side is missing fins so two can be coupled together for a complementary quad / differential input pair (my use would be BT clone). Handy huh? 0.1mm wasn't chosen at random. Thinner than that adhesion is lost, thicker and there is higher thermal resistance.

Another interesting point is you can run V grade devices at full dissipation without any drift. Yeah Kevin, I had a problem with this and that circuit I showed you.

Edited by luvdunhill
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What is the cost to do it wire EDM? Looks perfect for a small extrusion which would then be cut to length. Or maybe laser cut out of a giant sheet if they do 1/4" thick aluminum

I haven't found a place that will do custom extrusions for less than a 1 ton order. I have a feeling that EDM is more accurate than laser cut, as it goes down to ~5um tolerances. Perhaps not needed here, but certainly doesn't hurt.

I don't see any reason Kevin you should have to pay for them if this deal gets off the ground, the only issue is the fact that I have limited quantities :)

Of course, a modified Dynafet board would be super cool, but it seems like it would be too hard to do... Specs attached just in case though!


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If any member of the HC constructors' club wants to build one of these puppies for fun, or educational purposes, or whatever it is that does motivate you solder sniffers -- but doesn't particularly want to front the cost or keep it for the long haul -- shoot me a PM and we can probably work something out. :)

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ok, so next step is to estimate the number of channels that will be built so I can get enough parts for everyone. Also, if you are a DIYer, indicate how many channels you'd be willing to build. I think we can accommodate everyone in this thread, including the non-DIYers.

Just quote the following list and add your info:

name - # channels willing/able to build - # channels wanted to have and hold

luvdunhill - 8 - 4

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I don't suppose anyone would be willing to build a Dynafet for me? I'll pay for parts of course, and labor too.

How much will one cost?

This looks like a job for Super Rockhopper. I'm sure that Stephen will get right on it after he finished putting together a part list for a source selector for me. ;D

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How much will one cost?

If you have to ask, this probably isn't the project for you :) I have no desire to calculate the rough cost honestly. Obviously things will be done in mass in order to keep the cost down, but the idea is to get things done in parallel and when possible just build them all identical with maybe one or two options. That's my vision at least.

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