So, I guess my input is:a) make sure that your preamp is fully reverse polarity protected (you mentioned output diodes, so I guess you have that covered???), Yes, I have protection diodes on the DC input jack to protect against reverse polarity.
(Not to be confused with the diode protection I also have at the output XLRs, which is meant to protect my pre when for example you plugged the outputs of my pre to the inputs of another pre/console by mistake and turned on 48V phantom on the other pre, which then goes to my pre via the backend. Of course, this scenario wouldn't happen to tapers but more likely for someone in a studio.)
(And not to be confused also with the input diodes on my pre, meant to clamp down high input voltages (example: 48V discharge) that may damage the pre.)I just did a quick check with my bench PSU powering the preamp both with correct and reverse polarity voltages, and going back to correct polarity.
No problems. Dead as a doornail when reverse polarity powered.
Comes back to life when correct polarity is applied.
Just don't apply a reverse polarity greater than 400VDC. Otherwise, all bets are off. That's the max. limit.
b) make the design respond passively if reverse polarity _IS_ applied. Yeah the fuse might be an additional form of protection, but now that it blew, I still have a dead preamp that's gonna cost me $100 to get fixed by Apogee, so from my perspective, I'm not sure what's been saved with this design.You know of course with my DC input protection, I'm losing $100 everytime someone applied reverse polarity and NOTHING happens to my pre.
A fuse is not meant for polarity protection but for current overload protection. If the current flowing exceeds the rating of the fuse, the fuse opens up. For example, there is a short inside the unit, you apply power, instead of the external PSU being damaged because of a short in the load, the unit fuse opens up. It's not a form of reverse polarity protection. A fuse doesn't care which way the current goes.
final case design should indicate in the cover artwork at the power input what are the polarity and voltage requirements are...surprisingly, a good number of my electrical gadgets don't give polarity requirements at the jack.From a cost standpoint, (remember, I'm a very tiny small operation not a huge manufacturer with deep pockets)... that's one more expense for silkscreening or engraving the backplate. Maybe I'll put a metal sticker.
A second input on the case design is that I REALLY like the idea of standoffs at the rear of the unit,You mean the bracket I installed in the back?
If the user is using straight XLRs, they do not get in the way. But the straight XLR is still longer than the bracket. So the bracket is useless.
If I put in a rear bracket, and somebody tries to use a right angle XLR, the brackets get in the way... and again, the right angle XLR is still taller than the brackets so the XLRs provide stress relief for the DC plug. So the bracket is kinda useless.
The only time the rear brackets provide stress relief is if you don't have XLR jacks plugged into the back, and only the DC plug. But who uses a unit like that? i.e. DC plugged in, but the XLR jacks not plugged in?
I will be using DC locking jacks, so there is no danger of the DC plug falling out. And if you use straight or rt-angle XLR jacks, they will provide stress relief to the DC plug. Somebody also mentioned locking right-angle DC plugs. That would be even better.
I hope you still plan on using the vintage dial type knobs instead of the black ones in the pics at the top of this page. It wouldn't be a big deal if they ended up being the blackies, but those vintage knobs are COOOL!Yes, I agree! They are cool looking. I like them. Either way, the knobs will be easy to replace. I could offer both styles as an option.
Thanks for your inputs. Much appreciated.