Topic: 722 Line In Comments

[wboswell]

Just an FYI-
I remember discussion about the 722 and its line in functionality, specifically the stepped attenuation and how those with fixed gain pre's were concerned:
1) it doesn't really matter b/c of the low gain feature on the mic input.  It runs from 10-55dbs, so for those running an oade m148, you're going to need at least 10 in most situations.  At least that was my experience running  the m148 in front of the V3 the 5 or so times I ran that combo.
2) the stepped attenuation is very smoothe at .1 increments.  I ran out of the sbd for Tim O'brien last night and rode the levels up and down until I got comfortable.  On playback, its not noticeable, though I haven't listened on headphones nor have I given it and extremely critical listen.  But my first impression is that its pretty smoothe.

[Tim]

good info

[Lil Kim Jong-Il]

I had the same experience with the levels.  I can't hear steps, just smooth adjustments.

About running line vs mic in when fronting with soemthing else, why run something else if you are going go through the 722 mic stage anyway? 

[wboswell]

I had the same experience with the levels.  I can't hear steps, just smooth adjustments.

About running line vs mic in when fronting with soemthing else, why run something else if you are going go through the 722 mic stage anyway? 

I chose to run the m148 in front of the V3 when I was looking to color the sound a bit.  I was very happy with the results of the added warmth the m148 gave to hypers.

[Tim]

I had the same experience with the levels. I can't hear steps, just smooth adjustments.

About running line vs mic in when fronting with soemthing else, why run something else if you are going go through the 722 mic stage anyway?

line in... mic in... it's the same gain stage

[Lil Kim Jong-Il]

I chose to run the m148 in front of the V3 when I was looking to color the sound a bit.  I was very happy with the results of the added warmth the m148 gave to hypers.

I was thinking that with chained mic preamps, you get the summed sonic effects of both.  So it really isn't a m148 sound but m148 + something else.  Which may be a good thing. 

If you tried both mic and line in with the m148, did you notice a difference in the 722's bass response between the two settings?

BTW, what hypers are you using in front of the m148?

line in... mic in... it's the same gain stage

Is it?  I wasn't thinking that in line mode they route the signal around the mic-pre stage, but you may be right. 

If they are using the same complete signal path in both modes, then why bother with a line/mic selection switch when they could have just allowed the gain pots to adjust down to 0db?

If it is the same complete signal path in line and mic, then that would simplify the lineage documentation.  Also, I guess there would be no point putting something like the V2 in front of the 722 - something that I wanted to try.

[Tim]

Todd R has explained this linein/mic in issue in depth a few times... I may be wrong but from my understanding it's the same signal path just a different amount of gain is applied

as for m148/v3... that was easily my favorite combo out of V3, m148/modsbm1, m148/minime, v2/minime... smooth, yet detailed.

[Lil Kim Jong-Il]

Todd R has explained this linein/mic in issue in depth a few times...

I never read (or I don't recall) any of those posts.

If that's the case, I have to wonder why they consumed panel space for a mic/line selection switch instead of just providing a 0db gain setting.

[Tim]

Todd R has explained this linein/mic in issue in depth a few times...

I never read (or I don't recall) any of those posts.

If that's the case, I have to wonder why they consumed panel space for a mic/line selection switch instead of just providing a 0db gain setting.

I'll see what I can find.

perhaps the sd boxes are designed differently.

[Tim]

here's the first one I could find... he has made several posts about this, we should stick it in the archival forum

http://taperssection.com/index.php?topic=10860.msg132251#msg132251

People should really exorcise themselves of this notion of being forced through "the preamp circuitry".  A preamp stage is nothing but a gain stage, though configured to allow for the possibility of higher levels of gain required for microphoes.  Here's the important thing:  all a/d converters will have a gain stage, to get the right signal level for the a/d converter chip.  This holds true for all in one boxes like the MMe, V3, AD1000, UA5 whatever, but also holds true for line-in only boxes like the AD500, the AD2k+, the ADC20, etc.

People act like since they cannot bypass "the preamp circuitry" of an all-in-one box, it means the box was designed poorly and if it had only been designed correctly it would sound better if someone wanted to run an external pre in front of it.  THIS IS NOT TRUE.  That you must go through "the preamp circuitry" of an all-in-one box even when running an external preamp is a design feature that makes for a better product.  It means the box only has one gain stage, rather than two, which is definitely a good thing.

The difficulty is that people keep calling it "the preamp circuitry" and not the gain stage, or else they fail to realize that a gain stage will always come before the a/d circuitry, even in line-in only (non all-in-one boxes).  You must have this gain stage, all-in-one boxes simply allow the gain stage to do double duty for the needs of mic preamplification and line-level gain adjustments prior to entering the a/d circuitry.  If you use two boxes, you get two stages of gain, period.  Same if you go V2>ad2k+, or m148>AD500e, or if you go V3>MMe, m148>V3, or psp2>MMe.

All-in-one boxes make for a BETTER signal path because they only need to go through one gain stage.  This makes it much better in terms of keeping better detail and a more accurate soundstage, and for better keeping up with changing dynamics.  Remember, a shorter signal path is always better.  You may like the coloration of a particular piece of gear, but the more pieces of gear you use, the harder it will be to maintain soundstaging, detail, etc.  You may need to add a number of boxes to get the coloration your ear prefers, but if you could somehow get that coloration with one box instead of 3, you'd be better off.

So what would be the alternative for those folks who are adamant about feeling they should not be forced to go through the "preamp circuitry" of an all-in-one box if they chose to use an external preamp?  The only solution would be to make the all-in-one box design worse by inserting two gain stages, one for mic preamplification, and one for setting the right signal level for entry into the a/d converter circuitry.  This would allow folks using external preamps to bypass that dreaded "preamp circuitry" of the all-in-one box and only go through the line-level gain stage.  So using an external preamp in this case would be better than going through the two gain stages of the newly designed all-in-one box--you'd skip the preamp gain stage and only go through the line-level gain stage.  But guess what, you'd be no better off than you are with the current design of the all-in-one box as you'd still be going through a gain stage. 

This horror over needing to go through "the preamp circuity" might also make sense if it meant that designers of all-in-one boxes need to make tradeoffs in the single gain stage to allow it to operate at the high gain needed by mics.  In other words, they had to make a worse gain stage than they would have if only they were designing a line-level box that did not need to worry about the gain needed for mics.  This is also not the case.  If anything, the need to design a gain stage that can operate at high levels of gain will make for a better gain stage.  A gain stage that is designed to sound good at high levels of gain will sound even better at lower levels of gain.  In other words, it is the opposite of what people must be assuming when they run in fear of the dreaded "preamp circuitry".  It is designers of line-in only boxes that will always be starting with a strong signal who can cut corners and make worse gain stages in their a/d converters, since they know that high levels of gain will never be needed and even cheaper gain stages will sound good at low levels of gain.  (I'm not saying line-in only converter designers are doing this, but it would be easier to get away with.)

So that's the long story.  The short story would be that the only way to satisfy the misguided folks who want to be able to bypass the "preamp circuitry" of all-in-one boxes would be to design them incorrectly with two stages of gain, preferable with a really crappy mic preamp gain stage so that these folks can feel even better about avoiding it.

-Todd

[Lil Kim Jong-Il]

Thanks.  No I didn't read that when it was originally posted.  What is written is true for units that have a line level gain stage input. 

I guess what I would want as a line input (and what most people really want when they bitch about not being able to circumvent the mic preamp) is a buffered input to the ADC that has no intervening gain stage.  In that case an outboard gain stage is the only gain stage to affect the sound of the recording. 

I don't really have a problem going though the 722 (or any) mic preamp if the gain response is flat.  But most mic preamps are not - hence the reputed coloration of different units.  I can't yet say that the 722 has a color, but I notice that the bass seems to be accentuated in the recording I made.  That may be the A/D, it may be the mic pre and it may be that the 722 is ruler flat and the other gear I've been using has not captured a true representation.

Has anyone done a comp between the 722 and minime? 


edit:
One answer to my question of why have a mic/line switch: input impedance.  Mic input input is 4K and line input is 20K.  Funny how beer made me think of that.

[Todd R]

I was thinking that with chained mic preamps, you get the summed sonic effects of both.  So it really isn't a m148 sound but m148 + something else.  Which may be a good thing. 

Well, with the m148, it is always m148 + something else, since the m148 sends out an analog signal that needs to be converted to digital.  So m148>V3, m148>MMe, m148>722 are all pretty much the same thing from a block diagram perspective.  You're right, the 722 might add its own coloration behind the m148, but so might the V3 and the MMe (or modSBM1, AD1000, etc).


As to the rest of it, I don't know if Tim is right or not, since I don't know how they implemented the 722.  The SBM1 for example does have different gain stages for the mic-pre and for the line-in.  Both are implemented (non-mod) with 4580 op amps.  So if you go mic in to the SBM1, you go mics> 4580 gain stage> 4580 gain stage> digital.  If you go line-in, it is <signal> > 4580 gain stage> digital.  The V3 on the other hand, uses just one instrumentation amp no matter if you go mic-in or line-in.  It just adds more gain at that instrumentation-amp gain stage when going mic-in compared to line-in.  Same with the Minime.

So the 722 might be configured with 2 separate gain stages, or it might make use of the same single gain stage to do both mic-in and line-in.  I really don't know how they decided to implement it.