[LAU] Galvanic isolation (was: Re: pianos with built in recorders?)

[Len Ovens]

On Thu, 24 Dec 2015, Bob van der Poel wrote:

> I believe that the MIDI spec
> 
> http://www.midi.org/techspecs/electrispec.php
> 
> says that you must have a opto-isolator. Devices without one are probably not
> compliment ... don't know about direct usb connections.

Yes that is the spec. However, that spec also gives a part number for that 
iso-isolator. If builders are already using other opto-isolators which are 
outside the spec but are concidered ok if "it works", then if "it works" 
without any opto-isolator and by the way costs less, are you surprised 
that there are a lot of MIDI interfaces that are not to spec, but still 
work. How many buyers know the spec? How many of the buyers who know the 
spec measure to be certain? How many of those people take it back and 
demand a refund? (this MIDI interface is broken because there is an 
electrical path from the input pin(s) to the USB pin(s)) I think that any 
manufacture who got a lot of returns because they built something 
incorrectly would change but I don't think that will happen here.

If you still have a PCI slot... find an old AI with a game port. It's 
better than a USB MIDI adapter. Keyboard controller (no audio out) USB 
direct is potentially better (higher speed), but may not be.

Ground loops with computer audio can be a real pain. So far I have not had 
any problem with my PCI AI. USB has been a different story. I have been ok 
with a mic and an amplifier that is double insulated power (two prongs on 
the power plug). But as soon as I plug it into an amp that is grounded... 
every mouse move is heard... oh, that was a network transfer... and 
that was the sound of the screen saver. My PCI (D66) IF is plugged into a 
mixer that is grounded, but no problem. I have tried external power for 
the USB AI (no help) I need to try balanced cabling to see if that helps 
too... My d66 also has balanced i/o but I am not using/needing it :)

Isolation boxes would work I am sure, but add up quickly costwise.


--
Len Ovens
www.ovenwerks.net