I'm in the process of modifying and upgrading my Midas XL200 mixing console. The small balanced input output sub PCBs truly are a bottleneck in this desk (schematic attached). They're used for the channel inserts, direct outs, etc. and can be bypassed with a switch. When the insert is engaged it really makes the audio sound kinda flat.
After researching for a bit it came down to two designs: The so called 'voltage mode' configuration which can be seen on this website in figure 1 http://sound.whsites.net/project87.htm and 'current mode' configuration as can be seen the original circuit. It can also be found in the 1176 and many other pieces of equipment. What are the differences between those two designs? And most important which one will perform and sound better? Same question with the output driver. The cross coupled circuit is supposed to offer transformer like behaviour (if one side is shorted to ground). It's often described as unstable with real world cables though I couldn't notice any problems concerning stability yet. The alternative would be a simpler circuit with a non-inverting and an inverting op amp which does not offer transformer like behaviour (figure 3A). Since 99% of my studio gear offers balanced inputs this would be worth considering.
I hope someone can share some experiences or thoughts on this issue.
After researching for a bit it came down to two designs: The so called 'voltage mode' configuration which can be seen on this website in figure 1 http://sound.whsites.net/project87.htm and 'current mode' configuration as can be seen the original circuit. It can also be found in the 1176 and many other pieces of equipment. What are the differences between those two designs? And most important which one will perform and sound better? Same question with the output driver. The cross coupled circuit is supposed to offer transformer like behaviour (if one side is shorted to ground). It's often described as unstable with real world cables though I couldn't notice any problems concerning stability yet. The alternative would be a simpler circuit with a non-inverting and an inverting op amp which does not offer transformer like behaviour (figure 3A). Since 99% of my studio gear offers balanced inputs this would be worth considering.
I hope someone can share some experiences or thoughts on this issue.