Balanced discrete class A line input design

PRR wrote:
"And in my humble opinion, a 1-opamp line receiver is a poor compromise. If you can be discrete, you can build a fine line receiver with the same number of parts as a single op-amp. Actually simpler, because you don't want infinite gain nor universal connection."

I remember you said this long ago [that the 1 opamp receiver is poor] in another thread and forget to ask you how should this circuit look.
Do you have a schem?
Thanks.

chrissugar

[quote author="daArry"]Hey Brian...

When i said can i roll with that i meant can i just use this quad-8 config instead of the 'opamp' i posted with the ckts attached in my prior posts in the thread... It's clear i've gotta learn my shit instead of constantly asking 'will it' or 'can i', or do what i always tend to do and wing my way thru it - i need a line mixer sorted asap so will just build it - if it passes audio, is hiss and hum free I'm happy...

Whats the summing resistors used on the main and aux busses btw?

thanks for the pics :thumb:[/quote]

Yeh, if you build this as is it will work. The only thing on the posted schem that is messed up is that r43 connects to the trace right next to it, there is about 1 1/4" gap in the posted file. If its only a line mixer you need then skip the whole mic amp part, start at pins 3 and C, S20 is in the line input position on the schematic.

I haven't gotten in to the summing section, so I don't have an answer for you there.

Good luck, Brian

> Reducing to B&W makes it pretty bad so I left it color.

Try reducing to "grey scale". That is often a lot smaller than full-color, yet leaves the eye-fooling blur around the letters instead of arbitrarily slashing everything to full-white/black.

I did that on the very yellowed (almost brown) scans from my 1977 pulp-paper FET databook. Just as legible (maybe more so), and significantly smaller file (1/2, 1/3rd, like that). Much less impressive without the "color of age", but we just want the facts, not the color.

...

Thanx John!
Will give this a try as soon as my lab bench is free :thumb:

...

Nice schem John
Do you think it would work if the 2SJ74 is replaced with a 2SK170 in a constant current configuration?

chrissugar

...

Looks that http://members.aol.com/revorecording/LineInIdea.jpg is not active anymore. Any other link guys? :roll:

Moby, just looked in notes... have a 39k jpeg renamed 'line idea oboogie'... probably this one. pm me for it, i'm not sure how to post it here.[/img]

[quote author="PRR"]
Sure, any op-amp can be put inside feedback to make a line receiver. But that is not always the best way. And in my humble opinion, a 1-opamp line receiver is a poor compromise. If you can be discrete, you can build a fine line receiver with the same number of parts as a single op-amp. Actually simpler, because you don't want infinite gain nor universal connection. [/quote]

i've been digging for information on this topic recently. some of the two opamp configurations referenced on d self's site are interesting, but if there is a differential line receiver design that is similar in complexity to one opamp, i would be interested to see that. or even to be pointed in that general direction. there seems to be a good amount of info on multiple opamp topologies, but not so much on simpler discrete ideas.

[quote author="PRR"]
How do you feel about DC? Usually when you come from a jack, it might be connected to any darn thing, possibly with DC leaking out of it. DC rejection is an important design spec. Often liberating, because you don't need precision DC accuracy.[/quote]

in my case, i am assuming dc blocking caps on the input. but i would be curious to see what tradeoffs are involved in implementing effective dc rejection. which is the lesser evil?

ed