Input of mic preamp ???

Archived from groups: rec.audio.pro (More info?)

David Barras wrote:

> Hi
>
> I would like to know which solution is better for a professionnal system
> regarding the input of mic preamp for an analog-to-digital device converter:
> - transformer coupling or
> - electronically balanced system
> I guess the bottlneck is the common mode rejectio ratio (CMRR), especially
> at higher frequencies. Does a system like electronically balanced input
> provide a sufficient CMRR to cope with "pin 1" problem or ground loop issue.
> What about the inlfluence on sound quality for a transformer solution, some
> say that transformer coupling could bring "accidents" or the frequency
> curve...
> Does anybody has expertise in this domain ?

If either were *better* that would fix a lot of discussion about mic pres !

I can confidently say that CMRR shouldn't be a problem with well designed
electronically balanced inputs though.

Transformers have issues all of their own.


Graham

Archived from groups: rec.audio.pro (More info?)

Arny Krueger wrote:

> "Pooh Bear" <rabbitsfriendsandrelations@hotmail.com> wrote in message
> news:41881406.3DC10664@hotmail.com
> > David Barras wrote:
> >
> >> Hi
> >>
> >> I would like to know which solution is better for a professionnal
> >> system regarding the input of mic preamp for an analog-to-digital
> >> device converter:
> >> - transformer coupling or
> >> - electronically balanced system
> >> I guess the bottlneck is the common mode rejectio ratio (CMRR),
> >> especially at higher frequencies. Does a system like electronically
> >> balanced input provide a sufficient CMRR to cope with "pin 1"
> >> problem or ground loop issue. What about the inlfluence on sound
> >> quality for a transformer solution, some say that transformer
> >> coupling could bring "accidents" or the frequency curve...
> >> Does anybody has expertise in this domain ?
> >
> > If either were *better* that would fix a lot of discussion about mic
> > pres !
> >
> > I can confidently say that CMRR shouldn't be a problem with well
> > designed electronically balanced inputs though.
>
> However, Common Mode dynamic range can be an inssue with an
> electronically-balanced input.

Yeah, I guess if there's bucketloads of it !


> > Transformers have issues all of their own.
>
> Agreed.

Graham

Archived from groups: rec.audio.pro (More info?)

David Barras <david.barras@hispeed.ch> wrote:
>I would like to know which solution is better for a professionnal system
>regarding the input of mic preamp for an analog-to-digital device converter:
>- transformer coupling or
>- electronically balanced system
>I guess the bottlneck is the common mode rejectio ratio (CMRR), especially
>at higher frequencies. Does a system like electronically balanced input
>provide a sufficient CMRR to cope with "pin 1" problem or ground loop issue.
>What about the inlfluence on sound quality for a transformer solution, some
>say that transformer coupling could bring "accidents" or the frequency
>curve...

This is a religious issue. This is as much as religious issue as the
digital vs. analogue or catholic vs. protestant issues.

I tend to be in the transformerless camp, but sometimes I am in the
transformer camp, especially when there is an AM broadcast transmitter
in the room.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

Archived from groups: rec.audio.pro (More info?)

Ty,

Actually I was speaking about input stage of a mic pre which drives ADC and
I
intend to use such a device in not very friendly environments, I mean not
equipped with good grounding: my goal was to build a mobile (portable)
multitrack recording system for live performance, for example. This system
should be plugged easily to an already installed live system.
Basically, since not every mixers is equipped with pre-fade direct output,
and in order to be very "flexible" (i.e. to cope with every -bad-
situations), the signal from the main system has to
be splitted and here questions:
- active or passive splitting, and transformer decoupled or not ?
I thought that a transformer decoupled system was more robust in this case.
Secondly, what's happen when the signal is already splitted for a monitor
mixer or a
broadcast system, does a third passive split harm the overall signal quality
? Three input impedances from mixers may at least reduce equivalently the
signal strength in the best case (if all three input impedances are the
same, if purely resistive, which is not the case with long cable,...)
Too many "if" for me... Or do I need to use active splitting as a first
stage to feed monitoring and recording device ?

By "accidents" I meant some peaks and valley in the the frequency response
(inductance of transformer + capacitance of cable=resonances).

Thanks a lot for your comment

Dave

"Ty Ford" <tyreeford@comcast.net> schrieb im Newsbeitrag
news:xuGdnXgydqq_ixTcRVn-ig@comcast.com...
> On Tue, 2 Nov 2004 15:30:56 -0500, David Barras wrote
> (in article <cm8qq1$i4g$1@newshispeed.ch> ):
>
> > Hi
> >
> > I would like to know which solution is better for a professionnal system
> > regarding the input of mic preamp for an analog-to-digital device
converter:
> > - transformer coupling or
> > - electronically balanced system
> > I guess the bottlneck is the common mode rejectio ratio (CMRR),
especially
> > at higher frequencies. Does a system like electronically balanced input
> > provide a sufficient CMRR to cope with "pin 1" problem or ground loop
issue.
> > What about the inlfluence on sound quality for a transformer solution,
some
> > say that transformer coupling could bring "accidents" or the frequency
> > curve...
> > Does anybody has expertise in this domain ?
> >
> > Thanks for your comment
> >
> > Dave
>
> Dave,
>
> That would be the output of the preamp into an A/D converter.
>
> I don't understand your reference to "bottleneck." Common mode rejection
is
> generally recognized as a good thing.
>
> The quality and circuit design variations in electronic versus transformer
> outputs are more significant than simply transformer versus electronically
> balanced topologies. There are electronic outputs that are fully balanced
> (double ended) and those that aren't.
>
> Ground loops are another issue and have more to do with how a circuit has
> been designed, how it uses or misuses the ground and how the AC powering
to
> the studio has been designed. Studios without a starground system are far
> more prone to ground loop issues.
>
> What sort of accidents do you refer to?
>
> Regards,
>
> Ty Ford
>
>
>
>
>
> -- Ty Ford's equipment reviews, audio samples, rates and other
audiocentric
> stuff are at www.tyford.com
>