mediatechnology wrote:Correct. There are no mods. Just off-board power devices and jumping around the balanced input using the level control connector if the balanced input is not needed.
Ok, thanks. That makes doing my own boards seem a little unnecessary... Hmmm. Re. balanced inputs; I don't see this as essential - my pro audio days are (likely) behind me, and yes, I do realise that means I'm probably in the wrong forum!
My workshop soundcard does have balanced outputs though, so it's not completely without merit. While I no longer deal with long cable runs, the interference rejection could be valuable in an (electrically) noisy environment...
mediatechnology wrote:I mounted the emitter resistors standing off the board not only due to lead spacing but to give them and the board some "air." Flying leads to the power devices is probably more reliable since the transistor to PC solder bond isn't thermally stressed.
Yep, I understand that those resistors need some cooling, and will take that into account. Is it preferable that these are a non-inductive type? What power handling would be required for the 10W design? And re. the output devices - mounting them off-board would be the only option if I was to use the headphone amp boards, and even if I made my own layout I'd prefer them off-board, to make it easier to fit the amp into some off-the-shelf case and to allow for different transistor case types. The thermal stress is also a good point, and it would also move the main heat source away from the input stage etc. Would it be ok to use screw terminals for this, or is soldered connections preferable? How long do you think the leads can be before they start causing problems?
mediatechnology wrote:If you do use a stepped attenuator go for the Goldpoint and build your own custom. In the "Self" "shared gain" configuration you ideally want to use a make-before-break switch which the Goldpoint/Elmas are.
Thank you, that's a valuable tip, and exactly the kind of thing I would be likely to overlook. The prices even of unpopulated Goldpoint switches is shocking though; over $150 for a 2-pole model! Hopefully I'll be able to find something cheaper... Am I right in thinking that with a variable gain stage (as opposed to an attenuated input) I'd only need a two pole switch (or 2x one pole switches) since it would be switching the voltage to the gain stage rather than the signal itself? Should it still be a "shorting" type?
mediatechnology wrote:Why don't you use a conventional heatsink and add bling by having it thermally pump a Lava Lamp?
Hehe, that's a fun idea
I've thought about water-cooling, but that would only make sense for much bigger amps - water is a great medium for dumping heat into, as high-end PC builders know... But having the heated water perform some kind of "work" is a novel idea! TBH though, I think something like the case below (311 x 260 x 70mm, or 12 1/4 x 10 1/4 x 2 3/4 inches, costs ~$50) is the way to go, and leave the crazy cooling ideas for later - I think I'll have enough on my hands just to get the amp itself working, and the money saved could be spent having the front-panel professionally engraved instead. Does it look to you as if the heatsinks on that case are substantial enough for this amp? Unsurprisingly the manufacturer(s) say nothing about the thermal conductivity...