Camcorder XLR Audio Adapter/Mixers: TechTalk

This section elaborates on the feature set, and compiles answers to some frequently asked questions for the juicedLink family of Camcorder XLR Audio Adapter/Mixer/Preamps.

The User Manual is full of additional information.

• WHY DOESN’T IT HAVE A “G1/G2” SWITCH LIKE MANY PASSIVE XLR CAMCORDER AUDIO ADAPTERS?

• I have a separate page devoted to the juicedLink Grounding Strategy.

• PREAMPLIFIERS IC UTILIZED:

• If you want to geek-out on the preamp used, it's a THAT1512. It's a real pro-audio preamp, with a spec for Total Harmonic Distortion + Noise (THD+N) of 0.005%.

• Do you want to learn why I started this business? I bought a Beachtek DXA-8 Camcorder XLR Audio Adapter. At the time, it was advertised as the “Ultimate Adapter” and it set me back probably around $450. I got it, and I was so unhappy with its performance. I could not tolerate the noise or “hiss” that it generated. I though there must be something wrong with it, so I took it apart to see what the problem was (I am an engineer, after all). It uses a SSM2166 preamp, which has a THD+N spec of ~0.11% (I believe that the Beachtek DXA-FX Camcorder XLR Audio Adapter uses the same amp, since the specs with the Beachtek DXA-8 Camcorder XLR Audio Adapter are the same). That’s something that I would have designed into consumer applications like telephones, not as the front-end preamp for a camcorder. The preamp IC in the juicedLink XLR Camcorder Audio Adapters is nearly 20x better in THD+N. I felt I could bring a better solution to customers at a reasonable price … business opportunity!

• WHY DO YOU COMPARE TO THE BEACHTEK DEVICES, BUT NOT OTHERS LIKE THE PROMIX, ENG44, OR MIXPRE/FP24?

• The Promix, ENG44, MixPre/FP24 are a slightly different class of devices, even though they also have low-noise preamplifiers. They were designed to drive high signal levels through their XLR outputs to devices like mixing boards or expensive line-level recorders. You will notice in their specifications that their output drive capability and maximum gain are completely un-necessary (and counter productive) for use with camcorder mic inputs. I designed the juicedLink devices, specifically to interface to the microphone input jacks on camcorders. Eliminating the requirement to drive line levels has allowed me to miniaturize the system, enabling a 4 channel mixer small enough to mount under a camcorder. Additionally, focusing the design on this application has allowed me to fine-tune the gain lineup to optimize the device’s low-noise performance with camcorder mic inputs. Remember, you don’t want too much gain, otherwise you will overload the camcorder. You want just enough gain, so you can throttle back the camcorder’s noisy amplifiers.

• Although many of the Beachtek XLR Camcorder Audio Adapters use a different architecture and do not use low-noise preamps, the market they target the same as the juicedLink target market: XLR Camcorder Audio Adapters for use with the microphone inputs on camcorders.

• A PASSIVE ADAPTER ADDS NO NOISE. HOW CAN AN ACTIVE ADAPTER HAVE BETTER NOISE PERFORMACE?

• You can’t compare the specs of the XLR Camcorder Audio Adapter alone. You need to consider the overall system performance. Camcorder preamps are fairly noisy. Using a professional low-noise preamp allows you to throttle back the gain in the camcorder, so you hear less of noise generated by the camcorder. Passive XLR Camcorder Audio Adapters have no gain, so it requires you to crank up the gain of the noisy camcorder amplifiers. You can see some measurements made comparing a Beachtek DXA-6 with juicedLink XLR Camcorder Audio Adapters using a Canon GL2 on the SNR page. You can also hear a comparison in the difference in noise performance on the Video Demo page.

• WHY IS IT SO IMPORTANT TO BE CONCERNED WITH LOW-NOISE PERFORMANCE WITH LOW-LEVEL SIGNALS?

• The ability to have low-noise performance while recording low-level signals is important for the videographer. It is at the times when you are trying to pick up fine detail, when you want your best low-noise performance. Otherwise, the noise will mask the fine detail that you are attempting to pick up. In addition to picking up fine detail, you may encounter low level signals for a number of reasons: 1) use of dynamic mics, 2) not all condensers produce high output voltage/Pascal (lavs, older shotguns, some wireless receivers, etc), 3) sometimes, you can't get the optimal mic placement and need to crank up the gain.

• WHY WON’T ANY OLD PREAMP YIELD THE SAME RESULTS WITH MY CAMCORDER?

• True, if you stick an amplified device rather than one of the passive XLR Camcorder Audio Adapters, you will be throttling back the noisy camcorder amplifiers. However, that doesn’t necessarily mean that your noise performance will be any better. The principle only holds true if the amplifier used has better noise properties than the camcorder amplifiers. I’ve used camcorder adapters with preamps from other manufacturers, and was not satisfied with the results. That is why I started this company. The preamp in the juicedLink XLR Camcorder Audio Adapters is a THAT1512, and is spec’ed at 0.005% THD+N.

• ALL THIS TALK ABOUT PREAMPS, BUT NO EIN SPEC. WHAT GIVES?

• I’m between a rock and a hard place on this spec. First, you have passive XLR Camcorder Audio Adapter manufacturers claiming that their devices are “silent” because they have no active devices. Of course, it completely ignores the fact that you then have to crank up the gain on the noisy camcorder amps. Second, I don’t like the sloppy way that a lot of manufacturers represent their specs. For instance with EIN, many don’t specify over what bandwidth, the gain setting, or the source impedance used. Third, EIN, although not unimportant, focusing on EIN misses one of the most important parameters for the camcorder XLR adapter application. Let me explain.

• EIN is measured at some gain (usually full gain). The output noise is measured, then the gain is subtracted from the result so it is referenced to the input. If the output amplifier stage (which is usually a driver stage, and not used for gain) is a little noisy, it won’t matter much (and won’t impact the EIN spec much) because the output noise will be dominated by the noise produced by the preceding gain stages (which are cranked up to full gain, producing a lot of noise).

• Now, let’s take a camcorder mic application. Let’s also consider the scenario where your mic signal is strong, and no amplification in the XLR Camcorder Audio Adapter is necessary. Actually, let’s say the mic signal is so strong that we actually need to have the gain turned down so that the XLR Camcorder Audio Adapter is providing attenuation to the mic signal. Now, that output stage whose noise was unnoticeable for the EIN situation, is VERY noisy relative to the attenuated mic signal.

• A lot of customers don’t understand this dynamic. They are comparing specifications that are not really meaningful to the application (or neglecting to compare very important specs).

• I bought a Beachtek DXA-8 XLR Camcorder Audio Adapter, for around $450. At the time, it was marketed as the “ultimate adapter”. Clearly, I don’t think the designers at Beachtek understood this principle. With no input and the potentiometer turned all the way down, the hiss through the camcorder was unbelievable. This was without any gain! I knew I could do better, and that’s why I started this company.

• An ENG mixer with gobs extra gain can overcome a noisy output stage by gaining-up the mixer and using an inline attenuator to set to the level necessary for the camcorder mic input. But, now you’re carrying an ENG mixer around your neck, have a pair of inline XLR attenuators, a pair of XLR cables, a pair of XLR to RCA converters, and a RCA to 3.5mm “Y” cable. What a mess. juicedLink takes care of everything in a nice package that fits under your camcorder. ENG mixers are great, but they are a different class of equipment whose primary purpose was not the XLR camcorder adapter application.

• The juicedLink design effort has been focused solely on optimizing the performance for the camcorder XLR Camcorder Audio Adapter application. So, instead of publishing specs that are misinterpreted for this application, or compared to specs which may be misleading provided by other manufactures, I’ve decided to produce a Demo Video, so you can hear for yourself what kind of sound you can get out of your camcorder using juicedLink.

• WHY NO LIMITER?

• Our approach is to obtain the lowest noise possible, avoiding the extra circuitry and noise that a limiter would add. When you are shooting in an environment where the signal levels are unpredictable and you need protection from overload, then you should be shooting with the camcorder automatic gain control (AGC) switched on, thus making an extra limiter in the adapter unnecessary.

• I’M HEARING A NOISE/HISS?

• Remember, turn the volume down all the way on channels that do not have any input connection. When there is no input connection, the impedance presented to the preamp is high, so the preamp yields a lot of noise. Turn down the volume all the way on a channel that does not have an input connection.

• HOW DO YOU ACHIEVE INPUT BALANCE?

• I have a separate page that describes the input balance technique.

• WHAT DO YOU MEAN BY A “TRUE BUFFERED MIXER”?

• Passive XLR Camcorder Audio Adapters, such as many offered by Beachtek, don’t provide the flexibility of right/center/left pan control. They only allow a right and left channel, or one channel to be used for mono. Additionally, they are generally not buffered. So, adjusting the volume control on one channel, effects the signal level on the other channel, further decreasing your signal and thus signal-to-noise ratio.

• The juicedLink XLR Camcorder Audio Adapter/Mixers provide for right/center/left pan control for each input channel. Additionally, they are buffered, so adjusting the gain or volume on one channel does not impact adjacent channels.

• I NEED TO CONNECT A WIRELESS MIC RECEIVER (OR OTHER UNBALANCED SIGNAL):

• The juicedLink inputs are balanced. That is to say that the signal is present on pins 2 (hot) and 3 (cold), and ground is connected through pin 1. To use with unbalanced sources, you will need to have a cable that connects pins 1 and 3 together, while the unbalance signal remains on pin 2.

• It’s easy enough to do if you are handy with a soldering iron.

• I’ve also had Markertek make some up for me. Here is a quote request and the actual quote that I worked out with them. It cost me ~$12.

• The Rode VXLR is a neat little package. Be careful and check your plug. Looking at the VXLR schematic, it shows the 1/8” plug having the ring and tip positions connected together. Some mono 1/8” plugs have ground in the ring position, so the VXLR would short out your signal with that type of plug.

• USING A RECORDER INSTEAD OF A CAMCORDER:

• I designed the gain lineup and padding, specifically for the mic input of camcorders, to yield the lowest noise performance. That said, I've used the juicedLink mixers with the input jack on my computer and a MicroTrack 24/96 recorder with great results. The combination of juicedLink and MicroTrack gain was sufficient for the MicroTrack's A/D's (for what I was recording and mic used). I have not done enough interoperability testing with enough miniature recorders yet, to make claims on performance.

• WHAT ARE YOUR THOUGHTS ON DYNAMIC VERSUS CONDENSER MICS?

• Condensers will have higher open circuit output voltage per Pascal (more sensitive), and will have a flatter freq response. Dynamics are more durable and pick up less handling noise. My general guideline is condensers for shotguns, booms, and lavs (either lapel worn, or placed in acoustic guitar hole - note: in many cases, these are not hugely sensitive as other condensers). Dynamics for anything being handled (singer, interview), or a loud source on stage (guitar amp, PA, which may also get kicked around). Studios will pretty much use condensers for everything. But dynamics are still often used for vocals (since the vocal freq range is generally well within the dynamic bandwidth).

• Obviously, dynamics don't require a power source, where condensers do. Some condensers require external phantom power. Some can be powered from an internal battery (eliminating the need for external phantom power). Some condensers require 48V, while others only require 12V (which can considerably extend battery life).

• BATTERY LIFE AND PHANTOM POWER:

• First, estimating battery life is always dependent on numerous factors (battery freshness, current consumption, threshold voltage, temperature).

• The current consumption with phantom powering will depend on the type of condenser used, and the number of them powered. So, for all of the cases, these are always estimates.

• The battery life calculation for a juicedLink without phantom is fairly straightforward, because the current consumption is fairly constant. So, you basically look up the life time off of the battery manufacturer's chart for a given current. These battery life estimates are provided on the individual product pages.

• For phantom power, the use of switching power supplies is required to step up the voltage from the 9V battery to the phantom voltage. The penalty in doing this is current, and the current consumption is not linear with battery voltage. That is to say that the switching power supply needs to consume more current to maintain the phantom voltage as the battery voltage drops.

• What does all this mean? Well, the best I can do for you is to give you an empirical example. For instance, using a CX471 (4-channel mixer with phantom) powering a single AT875R condenser with 48V phantom will run from a fresh battery until the low-battery indicator illuminates for about 3 hours continuous (metering only on occasion ... this is another variable). Note, if you are not running it continuously, you could get another 0.5-1 hours out of it. The AT875R condenser is capable of running from 12V phantom, and doing so will give you roughly another 2 hours of use. In the juicedLink product line, the CX471 is capable of both 48V and 12V phantom. This compares with ~7-8hours operation when no phantom is used.

• RECHARGABLE BATTERIES:

• There are some new high-capacity 9V Lithium-polymer rechargeable batteries on the market from iPowerUS. I’ve used them on a wireless project I was working on, and I thought they were pretty nice. Unfortunately, a different battery chemistry will mess up the low-battery indicator threshold voltage. Fortunately, I made that adjustable and accessible from the outside of the aluminum enclosure (thinking ahead). I haven't had a chance to experiment yet on threshold levels with the different batteries to put instructions on how to adjust it in the User Manual yet. If you go that route, then I can tell you what you need to do.

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