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Author Topic: Balancing Sound Devices 744T Potentiometer  (Read 1913 times)

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Offline Walstib62

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Re: Balancing Sound Devices 744T Potentiometer
« Reply #15 on: December 26, 2018, 07:45:46 PM »
Joel:

Can you say more about what you mean by "balance the potentiometers"?

You want to know where to set gain on the 744 when using an external preamp?
Or you're running single ended cables into the balanced XLR inputs?
Or you're having trouble getting L and R levels to match?

which do you mean?

Sorry, it's been a trying day.  I believe my pots are a little off and would like to re-balance them so they are even with their respective positions on the dial.

Because I don't use a pre-amp a lot of the time, I often do have questions regarding the settings of the pre (SD 302) in conjunction with the 744.  As I've been doing it, I am just kissing the red ("0") on the pre, and then adjusting as necessary on the 744 to get my desired peaks.  If there's another or better way, I would be interested in learning.

You might be over thinking the process just a bit. Why do you feel the need to use an external preamp with a 744? I would think it is a perfectly good stand alone recorder. Being the same OEM, the first stages of both units must be similar to the extent that the 302 would be superfluous. Field recording is challenging enough as is. Why make it harder?

Excellent question.  The answer is this:  As you are aware, the 744 is a 4-track recorder.  When I only use 2 microphones, I do not use the 302 (pre-amp).  I do like to play though and use 4 or 5 mics sometimes.  When I use more than 2 mics, I need a pre.  At the upcoming Phish shows, I plan to use 4 mics and blend them in post.  For that I need the pre.

Ah! That info was missing. Now I understand. If there is a utility in the machine for setting digital gain it likely involves the tone generator. You'd have to read the manual.

I tried that last night, but couldn't find it anywhere in the manual.  Ugh!  I will poke around again tonight.  It isn't that much off, just enough to annoy me.  It's an easy fix in post, I just like things to make sense during recording.

Can't you just match the levels with your preamp?

Offline nak700s

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Re: Balancing Sound Devices 744T Potentiometer
« Reply #16 on: December 27, 2018, 12:03:05 PM »

Can't you just match the levels with your preamp?

Of course...but with the 744, there is the ability to "correct" the left and right potentiometers if they are not "matched".  I've done this a long time ago, but I get the feeling it needs to be done again now, and forgot how.  Yes, I still balance my levels individually, but when I know they should be even, it would be nice if the dials were at the same position.
Normal: Nakamichi CM-700's >> SD 744T (or) Sony PCM-M10
Normal: Crown CM-700's >> SD 302 >> SD 744T
Fun times: 3 Crown CM-700's >> SD 302 >> SD744T + 2 Nakamichi CM-700's >> SD744T
Stealth: CA-14c >> CA 9200 >> Edirol R-09HR
Ultra stealth: AudioReality >> AudioReality battery box >> Edirol R-09HR
Simple & Sweet!

Offline DSatz

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Re: Balancing Sound Devices 744T Potentiometer
« Reply #17 on: December 27, 2018, 06:44:30 PM »
I'm not familiar with SD recorders, and have only taken a brief look at the manual for the 744T just now. So the following comment may be out of place, and if so I apologize already--but: With potentiometers--physical, continuously variable resistors, as opposed to discrete gain switches or digital gain controls with preset values--the best you can do is calibrate a "pot" at one or two points in its range of settings.

No potentiometer has an absolutely predictable resistance value at all points along its range, so there's no such thing as a ganged set of potentiometers that maintain matched resistance throughout their ranges with zero tolerance. Deviations are par for the course. They can definitely be audible where a stereo image is concerned; our ears and brains are far more sensitive to mismatches between channels than they are to nonlinearities within a given channel.

If your application requires fraction-of-a-dB control over the gain relationship among channels (e.g. acoustical measurement, Ambisonics/SoundField or double-M/S recording), you can't depend on ganged analog potentiometers to track one another closely enough. It's not in the nature of the beast. You'll need to use test tones to set and match (hmm, where's "game"?) the exact gain for each channel, either during setup or during post.

What I gather the 744 most likely has is dual, concentric potentiometers behind each of the front panel controls, and the way that they're employed in the circuit then depends on a switch setting. But that's two (!) ganged pairs of electrically and physically separate potentiometers. In the relationships among channels controlled by "pots", the worst-case tolerances can very well add up (e.g. the gain set by one pot may be 1 dB lower than its scale indicates, while the gain for the pot on another channel may be 1 dB higher than its scale value, for a total of 2 dB difference, etc.).

Also, depending on the circuit and the "taper" of the pot, the tolerances can very well be wider at one end of the scale, often the lower-gain end (the attached photo shows the gain pots on a Nagra IV-S, which could be ganged via a little clutch on the red part of the left pot; these were very high-quality pots costing more than an entire recorder might cost today, but they had all the problems that I've mentioned).

--best regards
« Last Edit: December 27, 2018, 07:04:53 PM by DSatz »
music > microphones > a recorder of some sort

Offline Walstib62

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Re: Balancing Sound Devices 744T Potentiometer
« Reply #18 on: December 27, 2018, 06:55:55 PM »

Can't you just match the levels with your preamp?

Of course...but with the 744, there is the ability to "correct" the left and right potentiometers if they are not "matched".  I've done this a long time ago, but I get the feeling it needs to be done again now, and forgot how.  Yes, I still balance my levels individually, but when I know they should be even, it would be nice if the dials were at the same position.

It would be the exception to the rule that you would have perfectly matched input signal amplitudes between channels. I would never expect all gain pots to be at exactly the same position in a real world situation. They are usually close to the same, but I don't see how that matters much. Again, you can easily get caught up in overthinking something that makes little or no difference in the end result.   

Offline noahbickart

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Re: Balancing Sound Devices 744T Potentiometer
« Reply #19 on: December 27, 2018, 11:40:15 PM »
all of which adds up to, "set your levels conservatively and don't touch them at all during the show. Then fix all L/R and M/S balancing in post."
Recording:
Capsules: Schoeps mk41v (x2), mk4v (x2), mk22 (x2), mk3 (x2), mk21 & mk8
Cables: 2x nbob KCY, 1 pair nbob actives, Darktrain 2 and 4 channel KCY extensions:
Preamps:    Schoeps VMS 02iub, Naiant Littlebox, Naiant IPA, Sound Devices Mixpre6
Recorders: Sound Devices Mixpre6, Sony PCM m10

Home Playback: Mytek DSD 192> McIntosh MC162> Eminent Tech LFT-16; Musical Fidelity xCan v2> Hifiman HE-4XX / Beyerdynamic DT880

Office Playback: Grace m903> AKG k701 / Hifiman HE-400

Offline jcable77

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Re: Balancing Sound Devices 744T Potentiometer
« Reply #20 on: December 28, 2018, 01:55:42 AM »
Not sure if this helps, But have you tried using the 1k tone generator at the far upper right of the 302? Says mic/1k. Run that tone into your 744 and set your levels to match. Im guessing if one channel on the 744 is off then adjust accordingly. Then just use the 302 input pots to adjust when in the field. I cant remember if theres a difference of dbu on the 302 to dbfs on the 744 but I think this might be a good start maybe just to see if your pots are a little off on the 744 and by how much.

Offline nak700s

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Re: Balancing Sound Devices 744T Potentiometer
« Reply #21 on: January 03, 2019, 01:08:00 PM »
Not sure if this helps, But have you tried using the 1k tone generator at the far upper right of the 302? Says mic/1k. Run that tone into your 744 and set your levels to match. Im guessing if one channel on the 744 is off then adjust accordingly. Then just use the 302 input pots to adjust when in the field. I cant remember if theres a difference of dbu on the 302 to dbfs on the 744 but I think this might be a good start maybe just to see if your pots are a little off on the 744 and by how much.

Good idea to check to see how dramatic the imbalance actually is.  I will try that...but when I normally use the 302 with a multi-microphone set-up, I run it into the line in, not the mic/line in.  Still, that's a good idea of how to check.  I know the pots aren't off by much, I only want to balance them because it's annoying.  As pointed out by so many, of course it doesn't matter if the pots are not exactly balanced, but since I have the ability to balance them, why wouldn't I?  Naturally, it's an easy fix in post...
It just bugs me that I've done this a long time ago, but forgot how and can't seem to find it in the manual.
Normal: Nakamichi CM-700's >> SD 744T (or) Sony PCM-M10
Normal: Crown CM-700's >> SD 302 >> SD 744T
Fun times: 3 Crown CM-700's >> SD 302 >> SD744T + 2 Nakamichi CM-700's >> SD744T
Stealth: CA-14c >> CA 9200 >> Edirol R-09HR
Ultra stealth: AudioReality >> AudioReality battery box >> Edirol R-09HR
Simple & Sweet!

Offline Ronmac

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Re: Balancing Sound Devices 744T Potentiometer
« Reply #22 on: January 03, 2019, 04:28:34 PM »
Perhaps a quick call to their customer service department will answer your question.


Offline nak700s

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Re: Balancing Sound Devices 744T Potentiometer
« Reply #23 on: January 03, 2019, 04:29:51 PM »
Perhaps a quick call to their customer service department will answer your question.

I try to avoid that, but you are right, it's probably my best bet at this point.
Normal: Nakamichi CM-700's >> SD 744T (or) Sony PCM-M10
Normal: Crown CM-700's >> SD 302 >> SD 744T
Fun times: 3 Crown CM-700's >> SD 302 >> SD744T + 2 Nakamichi CM-700's >> SD744T
Stealth: CA-14c >> CA 9200 >> Edirol R-09HR
Ultra stealth: AudioReality >> AudioReality battery box >> Edirol R-09HR
Simple & Sweet!

Offline noahbickart

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Re: Balancing Sound Devices 744T Potentiometer
« Reply #24 on: January 04, 2019, 09:39:21 AM »


As pointed out by so many, of course it doesn't matter if the pots are not exactly balanced, but since I have the ability to balance them, why wouldn't I?  Naturally, it's an easy fix in post....

Read Dsatz’s post again, he’s saying that even if you could figure out how to “balance” the pots you could only do so at one point in their range.

Just fix in post. Your microphones are guaranteed to be more off than your pots.
Recording:
Capsules: Schoeps mk41v (x2), mk4v (x2), mk22 (x2), mk3 (x2), mk21 & mk8
Cables: 2x nbob KCY, 1 pair nbob actives, Darktrain 2 and 4 channel KCY extensions:
Preamps:    Schoeps VMS 02iub, Naiant Littlebox, Naiant IPA, Sound Devices Mixpre6
Recorders: Sound Devices Mixpre6, Sony PCM m10

Home Playback: Mytek DSD 192> McIntosh MC162> Eminent Tech LFT-16; Musical Fidelity xCan v2> Hifiman HE-4XX / Beyerdynamic DT880

Office Playback: Grace m903> AKG k701 / Hifiman HE-400

Offline nak700s

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Re: Balancing Sound Devices 744T Potentiometer
« Reply #25 on: January 04, 2019, 02:19:46 PM »


As pointed out by so many, of course it doesn't matter if the pots are not exactly balanced, but since I have the ability to balance them, why wouldn't I?  Naturally, it's an easy fix in post....

Read Dsatz’s post again, he’s saying that even if you could figure out how to “balance” the pots you could only do so at one point in their range.

Just fix in post. Your microphones are guaranteed to be more off than your pots.

Correct...but, what Jcable77 pointed out (which was a smart observation that eluded me), I can use the tone on the 302 to balance with.  Sure, it could still be off, but would be pretty darn close.  They didn't seem off much at the Phish shows, and my post work balancing the channels are minimal if at all.
Normal: Nakamichi CM-700's >> SD 744T (or) Sony PCM-M10
Normal: Crown CM-700's >> SD 302 >> SD 744T
Fun times: 3 Crown CM-700's >> SD 302 >> SD744T + 2 Nakamichi CM-700's >> SD744T
Stealth: CA-14c >> CA 9200 >> Edirol R-09HR
Ultra stealth: AudioReality >> AudioReality battery box >> Edirol R-09HR
Simple & Sweet!

 

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