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Author Topic: Tascam DR-70D 4-channel audio recorder (Part 4)  (Read 48008 times)

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Offline leehookem

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Tascam DR-70D 4-channel audio recorder (Part 4)
« on: July 17, 2015, 10:35:57 PM »
Here's Part 1
Here's Part 2
Here's Part 3

Tom Duffy from TASCAM, "site rep"

And thanks to voltronic, for putting together a FAQ page with recommended settings.

http://tascam.com/product/dr-70d/overview/

-Compact, professional-grade audio recorder designed to be used in combination with a DSLR camera
    -Uses an SD/SDHC/SDXC card as recording medium (up to 128 GB)
    -High-quality recording inputs through Tascam original High Definition Discrete Architecture (HDDA) microphone preamps
    -NE5532 operational amplifiers for even higher audio performance (also used on DA-3000)
    -In addition to ordinary stereo recording, simultaneous recording of up to four channels is possible
    -Four channels can be mixed down to a stereo signal
    -Recording levels can be adjusted independently for inputs 1–4
    -Dual recording function allows two files to be recorded simultaneously at different levels
    -Recording at 44.1/48/96 kHz, 16/24-bit, linear PCM (WAV format)
    -Broadcast Wave Format (BWF) supported as WAV recording format
    -Two built-in omnidirectional microphones
    -Four XLR/TRS combo inputs can provide phantom power (+24V/+48V)
    -+24 dBu maximum input level (20 dB headroom)
    -Additional unbalanced input for channels 1 and 2 (stereo mini jack) supports mics that require plug-in power, allowing the input of video mics and other high-output mics
    -Switchable low-cut filter conveniently reduces low-frequency noise (40 Hz, 80 Hz, 120 Hz)
    -Switchable limiter to prevent clipping
    -High-quality audio can be output to a DSLR camera for recording
    -Camera input enables convenient monitoring of audio from a DSLR camera
    -Selectable mid-side decoding for use with MS microphone setups
    -Slate tone functions (automatic/manual) to simplify synchronization of video files when editing
    -Pre-recording function allows the unit to record the two seconds of sound before recording is activated

    -Auto recording function to start start and stop recording by input level
    -A new file can be created during recording (manually or by file size)
    -Self-timer function to start recording after a set period of time
    -Jump-back function allows the last several seconds of the currently played file to be replayed again by simply pressing a button
    -Selectable delay to eliminate time lags caused by differences in the distances of two input sources
    -QUICK button allows easy access to various functions
    -Mark function convenient for moving to specific locations
    -Equalizers for playback, and level alignment function to enhance the perceived overall sound pressure
    -File name format can be set to use a user-defined word or the date
    -Resume function to memorize the playback position before the unit is turned off
    -Line output and headphones output with individual level controls (3.5-mm jack)
    -Dedicated remote control jack for use with RC-10 and RC-3F (sold separately)
    -Hold switch to prevent accidental operation
    -Low-noise buttons
    -128 x 64 pixel LC display with backlight
    -USB 2.0 port
    -Stand adapter (¼ inch) on bottom side to attach the unit to a tripod
    -DSLR bracket for easy camera attachment and removal
    -Hot shoe mount (accessible when not using the DSLR bracket)
    -Handles on the front left and right sides protect the screen and can be used to attach a shoulder belt
    -Operates on four AA batteries, an AC adapter (sold separately: TASCAM PS-P515U), external battery pack (sold separately: TASCAM BP-6AA) or USB bus power






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Offline tim in jersey

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Re: Tascam DR-70D 4-channel audio recorder (Part 4)
« Reply #1 on: July 18, 2015, 01:15:48 AM »
.

Offline voltronic

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Re: Tascam DR-70D 4-channel audio recorder (Part 4)
« Reply #2 on: July 18, 2015, 11:22:58 AM »
Re: poly film cap mod, a "phantom blocking" cap is an audio path cap, not a filter cap.  If phantom noise was an issue, those wouldn't do anything about that.  They are added under the theory tested on pg. 13 of that Bateman article, which found they did reduce distortion a bit but not very much.  They have been part of the "gospel" of audio mods for a long time, but not too many people have tested as rigorously as Bateman did.  I know Williams has an Audio Precision (high resolution test gear), so he ought to be able to provide pre/post specs.

I posted on GS a while back asking for measurements and he didn't seem too interested.  If I recall, he didn't measure his unit before it was modified but I could be wrong about that.  Maybe I'll email him and ask again.

Thanks again for those articles.  The Bateman one I think I actually understood most of, at least the principles of it.  The other one went overt my head fairly quickly.
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Offline Chomps

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Re: Tascam DR-70D 4-channel audio recorder (Part 4)
« Reply #3 on: July 18, 2015, 04:23:24 PM »
following  ;D
Microtech Gefell m200/M20/M21/nBob Actives>PFA
AKG 414 XLII
Telefunken M60/M61/M62
AT853
nBox Elite(4 Channel) /Sound Devices MP2/Edirol UA5 Busman B2+MOD
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Offline Colin Liston

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Re: Tascam DR-70D 4-channel audio recorder (Part 4)
« Reply #4 on: July 19, 2015, 02:32:10 PM »
Just marking thread
Occasionally....music mics record

Offline Sonus Captor

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Re: Tascam DR-70D 4-channel audio recorder (Part 4)
« Reply #5 on: July 20, 2015, 12:56:11 PM »
Re: poly film cap mod, a "phantom blocking" cap is an audio path cap, not a filter cap.  If phantom noise was an issue, those wouldn't do anything about that.  They are added under the theory tested on pg. 13 of that Bateman article, which found they did reduce distortion a bit but not very much.  They have been part of the "gospel" of audio mods for a long time, but not too many people have tested as rigorously as Bateman did.  I know Williams has an Audio Precision (high resolution test gear), so he ought to be able to provide pre/post specs.


Speaking of the JW mod and capacitors in the signal path:
In 'Speaker Builder' 3/1996 there was an article 'Capacitors: Why they matter'.

Among other parameters the THD and DA of various kinds of (mostly) 2.2uF caps for use in speaker crossover networks were measured.
All MKP caps had <0.001% THD, the bipolar electrolytics 0.003–0.012% THD, an ordinary 'lytic (normally not used in the signal path) had 0.025%.

Same thing with dielectric absorption which, as stated in the article, has an important influence on the sound.
All MKP caps had a DA of ≤0.01%, the bipolar 'lytics a highish 0.63-3.3% which is clearly inferior.

A friend of mine, an electronics technician who used to service musical and audio equipment told me that the difference between an electroytic input cap with or without a HQ bypass cap is measurable.

Tony Gee wrote about the positive effects of bypass caps in speaker crossover networks in his capacitor test: http://www.humblehomemadehifi.com/Cap.html

Of course, mic preamp input stages and crossover networks are different animals. But in both cases you want low distortion.

So bypassing the DR-70's input electrolytics with film capacitors makes sense to me.

In case I get the JW mod done I'll let you know about the results.

Offline Sonus Captor

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Re: Tascam DR-70D 4-channel audio recorder (Part 4)
« Reply #6 on: July 20, 2015, 02:40:19 PM »

I did not find a single measurement in the article you linked; unless I missed it that article was an entirely subjective analysis of listening tests conducted across a very long period of time.

Hi Jon,

no, there aren't any measurements in Tony Gee's capacitor test. It's entirely based on listening:
''The subjective results of this test are meant to give you a basic idea of the sonic differences between capacitors when used in loudspeaker filters.''

In a tiny device like the DR-70 there's certainly no room for capacious polys or even bigger paper-in-oil caps. We have to live with the electrolytics.
If bypass caps improve things a bit, I wouldn't grumble.

All the best, SC

Offline groovon

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Re: Tascam DR-70D 4-channel audio recorder (Part 4)
« Reply #7 on: July 20, 2015, 03:11:24 PM »
Re: poly film cap mod, a "phantom blocking" cap is an audio path cap, not a filter cap.  If phantom noise was an issue, those wouldn't do anything about that.  They are added under the theory tested on pg. 13 of that Bateman article, which found they did reduce distortion a bit but not very much.  They have been part of the "gospel" of audio mods for a long time, but not too many people have tested as rigorously as Bateman did.  I know Williams has an Audio Precision (high resolution test gear), so he ought to be able to provide pre/post specs.


Speaking of the JW mod and capacitors in the signal path:
In 'Speaker Builder' 3/1996 there was an article 'Capacitors: Why they matter'.

Among other parameters the THD and DA of various kinds of (mostly) 2.2uF caps for use in speaker crossover networks were measured.
All MKP caps had <0.001% THD, the bipolar electrolytics 0.003–0.012% THD, an ordinary 'lytic (normally not used in the signal path) had 0.025%.

Same thing with dielectric absorption which, as stated in the article, has an important influence on the sound.
All MKP caps had a DA of ≤0.01%, the bipolar 'lytics a highish 0.63-3.3% which is clearly inferior.

A friend of mine, an electronics technician who used to service musical and audio equipment told me that the difference between an electroytic input cap with or without a HQ bypass cap is measurable.

Tony Gee wrote about the positive effects of bypass caps in speaker crossover networks in his capacitor test: http://www.humblehomemadehifi.com/Cap.html

Of course, mic preamp input stages and crossover networks are different animals. But in both cases you want low distortion.

So bypassing the DR-70's input electrolytics with film capacitors makes sense to me.

In case I get the JW mod done I'll let you know about the results.

Found an interesting comment about this on another audio forum (link at bottom):

"... The (Bateman) capacitor tests show a hierarchy of signal quality.

But the test uses the capacitor as part of a filter.
The actual distortion levels which in some of the tests is extremely low ONLY applies when these capacitors are used as filters, i.e. when there is a large signal voltage across the capacitor.

In coupling duty, where there is virtually no audio voltage across the capacitor, the distortion drops by an enormous amount.

That is why the test does not cover coupling duty, the levels of distortion contributed by the capacitors would in general (all the back to back electrolytics and better) require a different and more sensitive measurement method to show any added distortion.

As far as I know, no one has shown distortion, or similar, measurement results for capacitors used as signal coupling when there is virtually no signal voltage across the coupling capacitor.

Back to back polar electrolytics when correctly sized to pass all the audio signal are perfectly good for coupling duty."


For the DR-70, the latter option is probably out due to the space issue. Would 'audio-grade' non-polarized electrolytics fit? If not, the 'standard' small plastic bypass caps, while maybe only of token value, are possibly the best that can be done (unless of course there's any downside--for e.g., possible HF oscillations or artifacts, etc.)

http://www.diyaudio.com/forums/solid-state/176509-replacement-ne5532-8.html

PS--Yes, believe it or not the thread linked above is titled 'Replacements for NE5534'(!) The LME49720 is even mentioned somewhere. Most, though by no means all, of the comments are by audiophiles, so best taken with a gain of salt. Countering comments by resident audio curmudgeons make it worth the reading, IMO :D

Dave
« Last Edit: July 20, 2015, 04:01:24 PM by groovon »

Offline voltronic

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Re: Tascam DR-70D 4-channel audio recorder (Part 4)
« Reply #8 on: July 20, 2015, 08:17:53 PM »
I emailed back and forth a bit more with Jim, sharing the concerns raised by Jon and others here.  I even linked him to this thread if he chose to respond directly, but he did not feel it was necessary.

While I do not speak for him, I will summarize / paraphrase a few things he said that are related to our discussion here:
  • He did not measure his 70D before or after modification.
  • Measuring noise / THD is almost impossible because the analog circuits are tied to the converters and DSP.  The outputs also run through another set of opamps and a DAC.  You're therefore measuring the entire thing as a system, and there is no reference for that.
  • The 14dB reduction in the noise floor (as reported here) is erroneous.
  • The results of the mod will be a smoother midrange and better high end detail.
  • The added poly caps are there to allow high frequency details to pass through the existing phantom blocking caps.  This is something Bateman does not address.
  • He enjoys the sound of his modified unit as do others who have done it, and that's good enough for him.  He has also made the full details of this mod available to anyone for free.

My takeaway:
  • Clearly I did not fully understand all the details of this mod, and if I misrepresented something that drove some people to certain conclusions, then I apologize for that.
  • Please stop asking for a set of measurements, unless you or someone you know know has the proper equipment and is willing to do it.  We could still do the kind of "poor man's" testing discussed previously.
  • The modded unit may not measure that differently anyway - it sounds like the change may be more audible than it is measurable.
  • I feel like there's a lot of criticism (some constructive) of this mod here simply because all of the parts used were made public.   This strikes me as a bit of no good deed going unpunished.
  • While I would have liked full before / after measurements also, is there anyone else out there that actually does this?  Many on this board have purchased mods from others builders who do not tell you much at all about what they are doing, and I find it interesting that they are not subject to the same scrutiny.
  • I am done bugging Jim about all of this over email.  If you want to debate further on the merits of his mod or any of the points posted above, I suggest you contact him directly as quite frankly the technical aspects are over my head and it's not my job to be his intermediary.  In other words, don't shoot the messenger.
  • Along the same lines, if you feel like I've wasted my money on this then you're entitled to that position.  My modded unit shipped today and I'm looking forward to using it.  Maybe I'll like what I hear; maybe I won't.  Maybe I'll be so overcome by my own confirmation bias that I'll think it's magically become a Nagra VI. ;D  If the results of the mod are that the recordings I make sound better than they did before, I'll consider my money well spent.

I plan to make an "after" piano recording this weekend of the same piece I played last week, and then I'll post both here blind.  It will be a completely invalid comparison, but maybe it will be fun to listen to.
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Offline pohaku

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Re: Tascam DR-70D 4-channel audio recorder (Part 4)
« Reply #9 on: July 20, 2015, 09:51:08 PM »
A mere guess on my part, but probably because he simply doesn't care to participate in the discussion.  He has no economic axe to grind here as he isn't selling his mod.  He did the mod for himself, probably based on his experience with these kinds of devices.  He has generously shared the details without charge.  That may be the extent of his desired involvement.
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Offline voltronic

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Re: Tascam DR-70D 4-channel audio recorder (Part 4)
« Reply #10 on: July 20, 2015, 10:07:47 PM »
A mere guess on my part, but probably because he simply doesn't care to participate in the discussion.  He has no economic axe to grind here as he isn't selling his mod.  He did the mod for himself, probably based on his experience with these kinds of devices.  He has generously shared the details without charge.  That may be the extent of his desired involvement.

That's quite an excellent guess.  He basically said all of those things almost exactly in one of our email exchanges.
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Offline 2manyrocks

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Re: Tascam DR-70D 4-channel audio recorder (Part 4)
« Reply #11 on: July 20, 2015, 10:46:53 PM »
Let's just carry that a step further.  If someone does the mod and doesn't like the results or doesn't think it accomplished anything, the last thing he wants to hear is somebody complaining, "but you said it would....."  And he has no control over who actually does the mod and gets no money from the mod. 




Offline aaronji

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Re: Tascam DR-70D 4-channel audio recorder (Part 4)
« Reply #12 on: July 21, 2015, 12:22:44 AM »
  • While I would have liked full before / after measurements also, is there anyone else out there that actually does this?  Many on this board have purchased mods from others builders who do not tell you much at all about what they are doing, and I find it intereting that they are not subject to the same scrutiny.

That's not true at all. There are many threads, some quite contentious, about the value of other mods, and, particularly, why they don't provide any measurements.

You shouldn't take the debate personally.  Healthy skepticism is, well, healthy...

[Edit for typos]
« Last Edit: July 21, 2015, 01:00:38 AM by aaronji »

Offline voltronic

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Re: Tascam DR-70D 4-channel audio recorder (Part 4)
« Reply #13 on: July 21, 2015, 05:30:30 AM »
  • While I would have liked full before / after measurements also, is there anyone else out there that actually does this?  Many on this board have purchased mods from others builders who do not tell you much at all about what they are doing, and I find it intereting that they are not subject to the same scrutiny.

That's not true at all. There are many threads, some quite contentious, about the value of other mods, and, particularly, why they don't provide any measurements.

You shouldn't take the debate personally.  Healthy skepticism is, well, healthy...

[Edit for typos]

I haven't come across the threads you're talking about, but I would be interested to read them.  I'm not taking any of this personally - it's not my mod after all.  I don't even have my modded unit back yet to compare against.
« Last Edit: July 21, 2015, 06:41:27 AM by voltronic »
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Quote
I am hitting my head against the walls, but the walls are giving way.    ///    If a composer could say what he had to say in words he would not bother trying to say it in music.
- Gustav Mahler

stevetoney

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Re: Tascam DR-70D 4-channel audio recorder (Part 4)
« Reply #14 on: July 21, 2015, 08:47:10 AM »
I know it's late in the game for this suggestion, but would it be out of line to request that discussion of mods to the DR70 be moved to another thread?  Frankly this discussion only pertains to a small number of you that are either interested in the mod or have the mod.

For the 30 or 40 of us that don't have the mod or aren't interested, all this discussion is wasted space and its getting a little bit frustrating sorting through the mod discussion to find the new posts that deal with our unmodded units.

 

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