A recent discussion over at gearslutz opened my eyes to a major problem (for me) of my Tascam DR-680: Unacceptable phantom power noise at higher gain. I have the Busman Mod, which lowers the overall noise of the unit. However, according to a poster in that thread, the mod won’t make much of a difference until you’ve sorted out the phantom power noise problem. After reading that post, I immediately did some testing.
One thing I had noticed a while back was that some channels had more noise than others at a very high gain. The noise wasn’t uniform-sounding across all channels. Channel 4 in particular was making a far more noticeable noise.
For me, that’s a big deal. In an ambisonic recording, if one channel is putting out more noise (or a different type of noise) than the others, then it very well may show in the final decoded sound. That’s evident in the recording below.
Testing phantom power noise was as simple as turning up the gain and flicking it on and off. Of course with no mic plugged in. You can hear a stark difference when turned on and off at a HIGH GAIN.
I’m not particularly disappointed in this as compromises need to be made when designing a box like this for such a low price. You get what you pay for. And for many people, this wouldn’t be a problem at all. This problem is certainly nothing a good external phantom power box can’t fix, or a mod, as described in this thread. (forum is dead)
I had considered those two options, but first I wanted to find out just how much noise the preamps were making. I took a recent outdoor recording that needed high amounts of gain and used RX2 to remove the preamp and phantom power noise. It’s hardly scientific or conclusive, as I recorded each input with the same amount of gain and with nothing connected, and made a noise profile out of that. But it was revealing nonetheless.
Here are my unscientific recordings of both. Download the WAV files and put them in your DAW and jump back and forth between them. You can clearly hear the difference. I’ve increased the gain digitally by about 20db to illustrate. Notice the right channel has more noise than the left. That probably has to do with my extra noisy channel 4. I’m not using that channel for the moment.
DR-680 Phantom Power & Preamp Noise:
DR-680 Denoised:
Download
Tascam_DR-680_Phantom_Power_&_Preamp_Noise
Preamp Test
At this point I’ve decided I need to make a change so I can record with less noise. For a lot of what I record it won’t be a problem. But there are plenty of times when I need to bring the gain up to a higher level. I strongly considered buying a pair of Core Sound 2phant phantom power boxes. But I have no idea if these will truly solve my problem. I’m sure they’ll work great, but what if my current preamps are STILL too noisy for my taste? I don’t want to throw my money away. And the thought of opening up my DR-680 and modding it doesn’t sit well with me. So…
Maybe an external preamp (with phantom power) is the solution. The only problem is, there aren’t a heck of a lot of products out there that fit what I need: 4 Channels, Phantom Power, Stepped Gain, Battery Powered and inexpensive. Soundfield actually does make a preamp (the SMP200) designed for the SPS200, but for some wild reason it’s AC powered only.
After some searching, I’ve found the RME Quadmic. It fits the bill perfectly in every area EXCEPT stepped gain!
At its price point, I can’t overlook it. So what I decided to do is see what kind of noise I might be dealing with if I used an external preamp into the DR-680’s Line inputs. I’ve read that the Line inputs might have less noise. At any rate, sharing the gain stage could prove less noisy.
From several reviews, the Quadmic is a low noise preamp with non-noisy phantom power at high gain. I felt I could use a similar preamp that I have on hand to get an idea of what to expect. For this purpose I used my John Hardy M-1. On paper they look very similar in terms of noise. 129 dBu EIN @ 150 Ohm. Of course that’s only on paper and I could be reading everything wrong. But hey, this is just a personal test.
For my test I used a Gefell M930 inside my vocal booth into the M1 and into the DR-680’s Line in. I tried a few different gain structures to see which would yield the lowest noise. As sort of a baseline, I first recorded M930>M1>Lynx Aurora converter. I figured the noise present in this chain should be what I’m shooting for at a minimum.
Here are the different combinations I set up:
M930, M1=+60, Lynx Aurora
M930, M1=+60, DR680 Line=0
M930, M1=+30, DR680=Line+30
M930, M1=+40, DR680, Line=+20
M930, DR680=mic pres MAX
And the results… (using headphones is more revealing)
1. M930, M1=+60, Lynx Aurora
2. M930, M1=+60, DR680 Line=0
3. M930, M1=+30, DR680=Line+30
4. M930, M1=+40, DR680, Line=+20
5. M930, DR680=mic pres MAX
24bit 96k Download
Impressions
From what I’m hearing, #4 sounds like the lowest amount of noise from the group. But not much difference from #3. According to the stats in Nuendo, there’s a negligible difference.
Surprisingly, whether I use the Aurora or the DR680, there’s not much of a difference. (#1 & 2) Somehow I thought #1 would hands down be better than #2.
I threw #5 in there for fun. Not sure if it’s fair to compare Line vs Mic inputs, but the noise difference is crazy.
In conclusion, I believe adding an external preamp with the DR-680 is the way to go. (DUH!) If the Quadmic performs as well as the hype, then I should lower my noise floor considerably and at a very reasonable cost. I’ll just need to take the time to manually set the level on each channel so they are spot on. Then figure out a way to protect them so they don’t move. Another possibility I’m researching is to put stepped gain pots of the Quadmic.
Let me finally add that the above testing is for me and only me that I thought I’d share with you. I don’t have an anechoic chamber to test in and my “procedures” may be flawed. But if you’re curious what to expect out of the Tascam DR-680 with Busman mod, then this may provide some insight. Please email me with any problems you see. I’ll be happy to test again.
And that’s my disclaimer… 🙂
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Hello,
I’m in the same boat. Curious what you ended up getting as a mobile solution to this problem.
Eric
In the end I decided to build my own preamp. Drastic measures, I know. Since there’s nothing out there that’s affordable, I felt this was the best solution.
I’ll post on this after it’s finished and tested. I’m nearly there.
Interesting tests! I’ve been a bit stuck lately, I have the option to buy a two year old SD 744T for about half the price of a new one. It’s still a lot of money and for the same I could get a DR-680 (no mods as I’m in the UK) plus a very decent 2 channel preamp and a decent microphone. It’s hard to justify the extra cost for reliabilitty, especially when not working freelance or making anything back from it…
Also, and I’m aware these tests were not scientific and such, but if I remember right – to get a proper noise level for a mic input then it has to be correctly loaded, ie have something plugged in to see the correct impedance at the input. Not 100% sure though, and also unsure if this would make any difference to phantom noise (guessing not!)
Hey, sorry for the late reply. Yeah, you’re absolutely correct. To accurately determine preamp noise a mic should be connected or something to simulate the microphone load, like a 150 ohm resistor across XLR pins 2 and 3.
I was actually halfway out the door to pick up some resistors when it occurred to me that it might not make a difference for phantom power noise. I’ll admit I’m not sure though. To my ears the noise sounds the same with or without a mic plugged in.
To be fair though, I’ll give it a shot with a resistor and see if there is any difference.
And personally, I would now probably go with the Sound Devices over the Tascam if I could afford it and the channel count suited my needs. But yeah, with a good preamp in front of the Tascam, I think it will cover most needs sufficiently. Just make sure you have a good bag to protect it. It won’t survive a lot of abuse.
What ambisonic mike are you using?
I’m using a Soundfield SPS200. You don’t happen to be the same Richard who is active on groupdiy?
Wow, you just diagnosed my DR-680 noise problem. I am happy I found this page. I am unclear about one thing though: is it possible to determine what portion of the noise is from the phantom power, and what from the preamp? For example, if you were to use a Core Sound 2phant with the DR-680’s preamps? For me building my own preamp is out of the question, so either the 2phant or the RME unit looks like a good alternative. Although where I live two 2phants (for 4 channels) is about the same as one RME Quadmic.
Regards, Christine
Hi Christine,
You could beg/borrow/steal a phantom power box to see how much of the noise is from phantom power and how much from the preamps. That’s the only way I know how to do it. Though I’m sure there’s a way to do it with a multimeter or some other testing equipment.
I’ve been real busy with (paying) work and had to put the preamp project aside. Just gotta assemble the little bugger! 🙂 In the meantime, I tried out a mod I found: http://www.audiomastersforum.net/amforum/index.php/topic,8654.msg77163.html#msg77163
The original finding of the noise here:
http://www.audiomastersforum.net/amforum/index.php/topic,8551.0.html
It didn’t work for me. Not sure why. I followed to the letter. So I decided to buy a couple cheap phantom power boxes that should help knock 11db of noise off the Tascam. Search for Millenium PP2B. It’s pretty cheap but reviews seem decent enough.
Where did I get the 11db? Here: http://www.beat-net.blogspot.tw/2014/08/dr-680-phantom-power-noise.html
People seem to think the DR-680 stock preamps aren’t so bad. I’m sure the RME are better, but you’re looking to save a lot of cash if a (cheaper) phantom power box works well enough for you. BTW, what are you recording?
Depending on the mic, you can improve the noise from the phantom power by adding extra capacitors at the feed to to each XLR socket. Made a huge difference for me on an original Brahma ambisonic mic and on Oktava MK-012 mics. Both have semi-unbalanced outputs
I can’t remember where the instructions are; possibly you can get a lead from https://gearspace.com/board/remote-possibilities-in-recording-amp-production/889971-tascam-dr680-opinions-alternatives-2.html, but there used to be photos of all the steps somewhere.
Thanks for taking your time to do these tests, looking for solutions. I’m looking for a field recorder and I have my eye on the Tascam DR-680. I will be using it for films, interviews, documentaries, etc. Will the noise problem at High Gain effect me? I use ntg2′ ntg3 and various wireless lav.
No, it wouldn’t be a problem for dialog. Unless you’re planning to mic from 100 feet away. 😉 I’ve used it with a 416 to mic dialog without issue. You’d probably be fine for most ambience/room tone as well. For the rare times you need I crank it for ambience, you could always denoise it.
One other thing to consider is finding a portable battery for it. The 8 AA batteries don’t last too long. Granted, I ran 4 channels on phantom power testing those batteries. Better safe than sorry though.