I'm seriously considering the mod. If it can drop the noise floor by at least 6db's on the 4 preamps then I think it's worth it. That's about $50 (incl shipping) a channel to give you the confidence of adding 20db in post without having to stress about hiss/noise. Dropping the external preamp is a most welcome evolution in the OMB workflow.

@spacewig

I did hear an impressive example comparing the Busman modded 680 to the non-modded. The most notable difference was that the noise floor was lowered. I also felt the top end improved, but could not confirm with the short vocal clip at hand.

The pres on the 70D sound really neutral to my ears so my interest in the mod is not in improving the "top end" which is just not relevant in dialogue rcordings. Lowering noise, however, is never a bad thing as it allows you to record at safe levels (thereby bypassing the need to engage the limiter=noise) knowing you can boost your recording in post (if your gain was too low) without having to stress about the noise inherent in the signal becoming conspicuous; to draw an analogy, imagine if for $100 someone could mod your camera sensor allowing you to raise your shadows 20 ire in post without introducing any noise... I think that's a very worthy investment.

@stauffec

I've a modded 70d as of yesterday. Haven't had the chance to try it yet. Fwiw, the dslr is the weak link in that chain. You can record the real track internally in the 70d as a 24bit WAV, and send a back up signal to the dslr for syncing etc. The second most likely culprit in the chain is the mic, unless it is a particularly quiet type of mic. The stock 70d is quite good on the noise front, granted you don't use the limiter apparently.

Here is a little sample with the very quiet BP4025, with downloadable FLAC at 24bit

No limiter, low gain. No changes, other than to lift by 7.5db in post (peaking was around -12 when recorded)

https://soundcloud.com/sage-pictures/tascam-0004s12-01

Also how would the 70D compare to the new Rodelink wireless kit when using a Rode NTG2? How will the in camera recording be?

@Alexauwa, The 70D is supposed to have much better preamplifiers which should cause less noise, also, the NTG2 is not meant to be very sensitive, which means that you are going to have to amplify the sound that comes from it quite a bit. People on the internet have often complained about the NTG2 + H4 combo being noisy.

Regarding the GH4 question, google around and you'll find out that there is an issue that causes noise when combined with the 70D (some argue it is a grounding issue).

Regarding the last question, you are asking for comparisons between a recorder (70D) and a wireless system that you will use with a lavalier microphone. These are not two items that you would usually compare because they perform very different functions. This gives the impression that you are at the very, very, very beginning of learning about sound capture and spacewig's advice is solid.

I acknowledge this probably isn't the most useful post - but my GH4/DR70d noise issue has disappeared completely. The GH4 audio is now very clean with only a small amount of noise - i.e the expected noise floor of the device - the large amount of added white noise that I was experiencing before has gone.

The problem is I have no idea how I did this... I didn't change any settings/mics/cables/anything. It just stopped doing it.

Either way, it's led me to believe the noise issue lies with the GH4, not the 70d. I've also recently experienced the common audio buzz problem using other plug in mics so I decided to send it off for repair.

Back to the 70d - I have been using this for a few months now recording 40+ 3hour interviews and it hasn't dropped a beat. Fantastic device and great results. My only tips - avoid Transcend cards as they seem to give write errors (rainbow label), get a power pack for all day power (it eats batteries), use good quality cables, and update the firmware (especially using NTG2 - the mid gain level is essential).

Note that they released firmware updates some time ago

http://tascam.com/content/downloads/products/867/e_dr-70d_rn_vd.pdf

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

@Cavemandude

It can also depend on your headphones. If they are not very sensitive and hard load - such thing can happen.

I was thinking of upgrading to the 70d from 60d, but after hearing that, I think I'll wait or step up to a higher price bracket. The 70d also does things via menu the 60d does by mechanical switches. That's important for me.

 I just got the DR-70D and it seems ok. 

I do have one big issue though. I'm using it with a Sound Devices 302 as a mixer/pre amp. If I have dual record mode on my primary tracks it sounds incredible no noise, but the secondary backup up tracks are loaded with noise and hiss.

It doesn't matter how -db they set at either -1 is as bad as -12 still the same hiss! But what's worse if I turn dual record mode off my primary tracks get filled with hiss and noise!!!!

No matter what I do if DON'T use dual record everything is recorded with lots of hiss straight on to the SD card of the DR-70D. But if I leave it on my backup tracks have the hiss which them pretty lousy backups, but my main tracks sound great. Is this a software problem? Or a hardware problem?

If it was the wire, why would it be fine when I put it in dual record mode? Also it makes the hiss when nothing is connected to it at all. No hiss in dual record mode...