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Author Topic: Tascam DR-70D - modification discussion  (Read 20926 times)

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Re: Tascam DR-70D - modification discussion
« Reply #75 on: June 08, 2016, 06:40:36 AM »
No, I mean a service manual with all the schematics.

I doubt you'd find one for this recorder; it's not something that's meant to be field serviceable.  You could go ahead and contact Tascam to see what they say.  Just be aware that it's mostly SMT components so you have to be prepared for that sort of work.  I don't have that skill, so I bought the components and then sent mine to a shop that specializes in that kind of work.
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Re: Tascam DR-70D - modification discussion
« Reply #76 on: June 08, 2016, 10:40:19 AM »
No, I mean a service manual with all the schematics.

I doubt you'd find one for this recorder; it's not something that's meant to be field serviceable.  You could go ahead and contact Tascam to see what they say.  Just be aware that it's mostly SMT components so you have to be prepared for that sort of work.  I don't have that skill, so I bought the components and then sent mine to a shop that specializes in that kind of work.

Tom with Tascam provided me the schematics for the hs-p82 when I asked - so I would think he may be able to provide the schematics for most Tascam products
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Re: Tascam DR-70D - modification discussion
« Reply #77 on: June 08, 2016, 10:43:38 AM »
If anyone wants to run some comps with my unit at Phish this summer, get in touch!
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Re: Tascam DR-70D - modification discussion
« Reply #78 on: June 08, 2016, 01:10:35 PM »
No, I mean a service manual with all the schematics.

I doubt you'd find one for this recorder; it's not something that's meant to be field serviceable.  You could go ahead and contact Tascam to see what they say.  Just be aware that it's mostly SMT components so you have to be prepared for that sort of work.  I don't have that skill, so I bought the components and then sent mine to a shop that specializes in that kind of work.

Tom with Tascam provided me the schematics for the hs-p82 when I asked - so I would think he may be able to provide the schematics for most Tascam products

Do you have an email for him?  He has flown the coop from TS but I occasionally see him post at JWSound.
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Offline Carlos E. Martinez

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Re: Tascam DR-70D - modification discussion
« Reply #79 on: June 08, 2016, 05:08:53 PM »
From what I've seen, the components involved in the mod are not that small. The 49720 is just 5mm long, and you have just to know how to solder. The original 5532s you just cut away carefully. The caps are a breeze to add.

But what got me curious about the schematics was the comment on your page that "Limiter adds 12dB noise and should be avoided".

Some time ago I saw the 680 schematics, and the limiter was praised for its quality. so I wonder why didn't they use it on the 70.

 

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Re: Tascam DR-70D - modification discussion
« Reply #80 on: June 08, 2016, 10:33:50 PM »
From what I've seen, the components involved in the mod are not that small. The 49720 is just 5mm long, and you have just to know how to solder. The original 5532s you just cut away carefully. The caps are a breeze to add.

But what got me curious about the schematics was the comment on your page that "Limiter adds 12dB noise and should be avoided".

Some time ago I saw the 680 schematics, and the limiter was praised for its quality. so I wonder why didn't they use it on the 70.

Well, clearly you have much more experience in electronics assembly than I do, which is why I sent mine out.

As for the 680 limiter, that recorder costs twice as much as the 70D, so I'm not surprised compromises were made.  I'm fairly certain that the 680 is still a digital limiter though.
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Offline Carlos E. Martinez

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Re: Tascam DR-70D - modification discussion
« Reply #81 on: June 10, 2016, 07:16:19 PM »
I am aware of the price of the 680. But it's also a much more complete design, much larger too.

In fact it's closer in price to the DR701, which has some similar capabilities in a smaller package. Comparison tests should be in order.

The limiter is probably the same on all Tascam models, and yes, it's digital. But I wonder why it introduces noise on the 70 and not on the other models.

Now there's a 680 Mark II, but the mic preamps are probably the same HDDA types than on the 70, with 5532 chips.

Interesting the chip selected by Jim for the mod, as a much better one, lower noise could be used: the NJM2068. I've already mailed him to ask the reasons for his choice.




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Re: Tascam DR-70D - modification discussion
« Reply #82 on: June 10, 2016, 07:56:10 PM »
I am aware of the price of the 680. But it's also a much more complete design, much larger too.

In fact it's closer in price to the DR701, which has some similar capabilities in a smaller package. Comparison tests should be in order.

That's exactly my point - they had a larger size case and a larger price point in which to work, so the 680 should be a design with fewer compromises made.

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The limiter is probably the same on all Tascam models, and yes, it's digital. But I wonder why it introduces noise on the 70 and not on the other models.

Now there's a 680 Mark II, but the mic preamps are probably the same HDDA types than on the 70, with 5532 chips.

Hopefully someone with more knowledge on this will chime in here, but from my understanding the limiter on the 70D is after the ADC and at some point within there lowers the gain 12dB, then later raises it back up to the original level after applying the limiting in a way the brings the internal noisefloor up 12dB along with it.

Quote
Interesting the chip selected by Jim for the mod, as a much better one, lower noise could be used: the NJM2068. I've already mailed him to ask the reasons for his choice.

??? Are you sure you aren't looking at a different chip?  Jim's mod uses the LME49720.  THD+N is 0.00003%, vs. your recommendation of the NJM2068 at 0.001%.  The 49720 also has a much higher slew rate: 20V/us, vs. 6V/us for the 2068.  Finally, the 49720 also has nearly twice the gain bandwidth: 55 MHz vs. 27 MHz.  Now, there are many out there that say none of that really matters and that either are more than good enough for this application, but the 49720 looks like a superior part in all respects.
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Offline Carlos E. Martinez

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Re: Tascam DR-70D - modification discussion
« Reply #83 on: June 10, 2016, 09:59:06 PM »
Sorry, I mixed up the chips. The NJM ultra low noise chip is the NJM2122.

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Re: Tascam DR-70D - modification discussion
« Reply #84 on: June 10, 2016, 10:28:08 PM »
Sorry, I mixed up the chips. The NJM ultra low noise chip is the NJM2122.

Well, the NJM2122 is worse still.  Just comparing 3 of the specs:

                            LME49720           NJM2068           NJM2122

THD+N                 0.00003%           0.001%            0.003%
Slew Rate            20 V/μs                6 V/μs              2.4 V/μs
Gain Bandwidth   55 MHz                27 MHz             12 MHz
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Re: Tascam DR-70D - modification discussion
« Reply #85 on: June 10, 2016, 10:49:02 PM »
Because the input noise would be dominated by the discrete input transistors below a certain noise level for the opamp.  It's questionable whether a change from 5532 even results in lower EIN.  See posts #57-58.

I thought it was the other way around; that the input transistors were the biggest contributor of noise at high gain levels.  Maybe I misunderstood.  Either way, the highest gain setting (HIGH+) on this unit is not useful for music recording, and that hasn't changed post-mod.

Not to go through this all again, but the modification did not reduce the self-noise in any way I can detect.  What it definitely did do was improve the HF clarity / extension, but again I wonder if the added caps have more to do with that than the opamps.

Curious that TI does not list a THD spec for the 5532.
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Re: Tascam DR-70D - modification discussion
« Reply #86 on: June 11, 2016, 04:49:51 AM »
cool discussion! I have no personal experience with the modded 70D except listening to Noah's/Voltronic's modded units, and like they said, the difference is very subtle at best to me, BUT I have never heard a direct COMP between a modded and unmodded 70d! Noah and I ran on the same stand@PH MPP last year[I ran mk4>pfa>70d + mk41>VMS02IB>70d and he ran mk41v>pfa>busman modded 70d + mk22>pfa>70d], so not really a direct comp! If anyone wants links to my PH/MPP Night 2 from 2015, just LMK! I have the show on my Google Drive acct already ;)

That said Carlos, I think you should get your 70d and try it stock first, before doing the mod. But that's just my opinion :) I have run mk4>pfa>70d preamps numerous times, and I think that the 70d preamps are quite adequate for use with low-noise condenser mics like my Schoeps and many other brands, as long as you aren't using the High/High+ gain on the 70d like Voltronic said. I have only used LOW or MID for field recording[LOW being enough gain for me 90% of the time] with my Schoeps caps, with great success :) However, I would really like to hear a DIRECT COMP between the modded 70d vs. a stock 70d unit, because in the end I want to get all that I can out of my 70d's, and if that means changing some opamps/caps, then I'm all for it 8) Especially since I only paid $300 total for BOTH of my 70d's :P ;D So If its a cheap way to improve the 70d even further and extend the HF range a bit, then like I said, I'm ALL for it ;) I just don't want the HF's to be grating and fatiguing or the lowend affected AFTER the opamp/Cap mod, when it could've been avoided by leaving the 70d stock, that's all :) I guess someone just needs to do a correct COMP so we can hear for ourselves if getting the mod is "worth it" or not? :)

Noah, you still have seeders on any of your PH sources up on etree with your Busman modded 70d ??? I can provide my mk4>pfa>70d source if you can provide your mkxx>pfa>Busman modded 70d sources for Phish/MPP Night 2[8.16.2015] ;)
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Re: Tascam DR-70D - modification discussion
« Reply #87 on: June 11, 2016, 07:03:48 AM »
I agree that you should get a bunch of recordings in with the stock unit before you decide on modding it.  And you'll probably never hear the difference if you're doing amplified shows.  I notice the effect of the mod on the acoustic recording I'm doing, particularly with the attack of percussion and strings and consonants in voices, and also on the quality of the reverb in a hall with good acoustics.

2manyrocks and I tried to do a long-distance comp of self noise since we have some of the same mics, but that didn't work out.  Do do a true comp, you probably need a mic splitter box so one set of mics is feeding the two 70Ds recording the same concert.
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Offline Carlos E. Martinez

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Re: Tascam DR-70D - modification discussion
« Reply #88 on: June 14, 2016, 01:30:40 PM »
No, I won't touch my 70D until I make many recordings, some of them using the line input and external mixer or preamp.

Even so, I think the line input may not bypass the mic input, just attenuating the signal.


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Re: Tascam DR-70D - modification discussion
« Reply #89 on: June 14, 2016, 04:23:02 PM »
Even so, I think the line input may not bypass the mic input, just attenuating the signal.

I think you asked about this already, and it's likely exactly how you said.

Be advised that there are different opamps for the 1/8" line in/outs than there are for the 4 XLR-1/4" combo jacks.
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