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Group Build: Dynafet


luvdunhill
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Well, Team Spain's package is mailed, along with digger945.

All that is left is Team j4cbo, and looks like the remaining parts will arrive on Wednesday.

I'm planning on starting a build thread at some point. Until then, feel free to ask any questions in this thread. Hopefully we will have a chance to come up with stable value recommendations for a few gain settings by then.

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I need a show of hands for who wants to buy the passive parts kit for standard DynaFet board. Finalizing the BOM right now with Marc.

I will be offering a standard and boutique option (most resistors and some caps).

Getting the number of buyers will help me scope out the final cost per kit.

I would like to get this info ASAP so we can finalize the order.

Name ## of board kits

Better yet PM that info to me.

Thanks

Pete

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Finalizing the BOM right now with Marc.

Sorry Pete, I'm so slammed this week I haven't had a chance to look at your BOM. Here are a few quick comments, but shouldn't be considered exhaustive.

A lot of part choices in the previous BOM was due to using a more restrictive E-series of resistor, to allow all the 1/4W resistors to be PRP.

I am planning on using a Wima for C2 so all the film caps are red (yes, seriously). The 0.47uF value is correct.

All the electrolytic caps are 18mm diameter now.

The OPA445 is recommended.

C11-C14,C31 are correct on your BOM. The only important value is the 220pF. The others are just bypasses. Use something nice here.

I'm planning on not using TR1 and TR2, per Kevin's original schematic. Some people may use them, but I didn't see a reason to do so in the Dynahi and not really here either. I can see most people wanting to use them, so YMMV.

My recommendation was R17, R18 = 10K and a 20K pot with a 3.3K series resistor. The two 5K resistors at the feedback point are also changed to 2K. I plan on trying this and going from there. I think digger945 should be the authority on this recommendation, especially since I'm going to be running mine at considerably more current than anyone else, AFAIK.

Jacob asked about how to bond the TO-92 devices together. I'm planning a tutorial at some point, just haven't gotten around to it, as there are a few tricks I've learned having done this so many times. You want to use a small particulate metal epoxy. There are several out there, but the easiest to get in small quantities is Arctic Silver Thermal Adhesive. Note the adhesive part.

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<snip>

Jacob asked about how to bond the TO-92 devices together. I'm planning a tutorial at some point, just haven't gotten around to it, as there are a few tricks I've learned having done this so many times. You want to use a small particulate metal epoxy. There are several out there, but the easiest to get in small quantities is Arctic Silver Thermal Adhesive. Note the adhesive part.

This is even with the heatsink thingies from diyaudio group buy? I figured you could just slip them on and that would be that :palm:

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