Crystal cMoy Freeform Headphone Amp

Interesting, I was longer curious how to do that. Bookmarked.

Would it be safe to do with with a class A headphone amp or would it produce too much heat?
 

you could probably bias those opamps to run in class A mode a-la tangentsoft's tutorial but I think you will want to check max heat output of the specific opamp you are using when it is configured that way and also the thermal properties of the resin you want to use.

 

 

Probably best to organize it with a heatsink and arrange the heatsink to stick out into the air. My guess is that the resin is too good a thermal insulator to allow much dissipation in the interior. Resins usually have things added to them when thermal conductivity is required, aluminium shot, alumina, metal filings or chips...

 

Most silicon devices expire at about 150 degrees C, which you can probably get to without too much trouble, and the resin may start to decompose too.

 

w

Would heatsinking really be necessary if it's being biased in the same way pimetas are biased?  These JFETs are only pulling a few mA.

 

Pimeta is class-AB. 

 

Most people don't say class-A until the output devices are idling at more than 20mA.

 

I would trade RF shielding for looks any day....

 

Maybe no, but maybe yes. You can find out for the rest of us if you like. Since the amp is working (for the moment) a certain amount of dissipation is evidently tolerable.

 

Remember that if you are pulling current out of an opamp with a ccs then the opamps dissipation is the single-sided voltage rail times the current, and the ccs's dissipation is the same. If you're only pulling a few mA then the amp drops out of class A the minute the phones demand current in excess of the bias, what have you really gained? The critical factor is the thermal insulation anyway. My guess is that it's pretty good, and that you could use that stuff to make a handle on a cooking pot without much risk of burning yourself.

 

Most plastics are pretty good insulators, certainly compared with metals, that's why they put extra heatsinking pads on AD8397's and TPA6120's, to get the heat out into some copper with a big surface area. Unless you can get figures or you actually try it, however, what I said previously remains a guess, other than that a heatsink is rarely a bad idea. 

 

w