If the max level is +20dBu as Speff mentioned, the balanced input is only
4Vrms on each line. 25Vpp is exactly +21.14dBu or 8.8Vrms, that is just 10% higher. So how much CMRR do you get from your opamp and a few Rs? And if 1.70$ is expensive for a dual differential amp, I wonder what kind of opamps you use. Already the precision resistors needed(0.01%) will cost more.-- ciao Ban Bordighera, Italy
Except that +20dBu limited outputs are normally / invariably 'single ended' or 'unbalanced'. Hence there are *NO* volts on the 'other line' at all.
You need to consider that every output is driven by an op-amp supplied from a
+/- 15 ~ 18 V DC supply.
Simple. It depends on the R match ! Just about *every* pro-audio manufacturer finds 1% tolerance Rs acceptable in this application ( some actually find 5% suitable ! ). Bear in minfd that 1% Rs are actually typically withinn 0.3% of value and are often better matched withina batch !
You're wasting money on unnecessary specs. Even Neve never used resistors that accurate ! I was a project leader there for some years btw so I kinda know !
I pay about USD 0.2 for a pair of balanced inputs. That's 8.5 x less than you suggest. I put the money into the areas where it actually *counts for something* !
Graham
oops, I'm paying that for a single MKT input capacitor, and I use 4. Those opamps you use must be really cheap. I have worked on Neve desks and they had transformers. :-( hardly any cheaper. BTW you do not work for Behringer, do you?
-- ciao Ban Bordighera, Italy
No- I'm not one of Uli's guys but I have to work to the same constraints.
A couple of guides here. Don't use input coupling caps if they're not needed. Normally they're not for a line level stage.
*never* use transformers unless you have an Arab (oil rich ) sheikh as your customer !Neve entirely dropped transformers on the legendary V Series version 3 on.....
Graham
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