DI FAQ
Q: What transformer is used in your direct boxes?
A: Jensen JT-DB considered by many (including us) to be the best audio transformer for direct box applications. This is the single most expensive part in our direct boxes and are worth the cost.
Q: Does the transformer limit low frequencies?
A: The transformer is -0.25dB at 20Hz (which is approximately E0 (20.6Hz). the theoretical lower limit of human hearing, low B is approximately 30.9Hz) so it effectively does not limit the low frequencies In addition, the distortion is very low at 20Hz at max signal input where most audio transformers struggle. The data sheet for the transformer is available on the TDI page with more detailed information.
Q: How well does the TDI handle a low B string when tuning?
A: The tuner is +/-1cent down to E0 and I went to a lot of trouble making sure the tuning algorithm could handle a low F# string on extended range basses, so yes it tracks a low B very well in my humble opinion. You can see a video demonstration of its behavior on the TDI page.
Q: Tell me about the quality of the design
A: Over a year and a half of design and development went into both the TDI and MDI. All of the components are top notch and went through a rigorous evaluation period. Many of the initial parts didn’t make the selection for the final products. Numerous circuit and thousands of lines of microprocessor code (in the case of the TDI) were made to optimize the design. Several vendors and parts were traded to reach the design goals of audio quality, durability and aesthetics, to name a few. The printed circuit boards are purchased from US companies (and made in the USA depending on availability) and use through-hole parts for excellent solder penetration from both sides of the board, use gold plating and have extra large ground planes. Steps were taken to reduce stress on the circuit boards and parts when the enclosure experiences physical shock. All jacks and switches are panel mounted to allow the enclosure to bear the brunt of mechanical impact as opposed to the circuit boards. Metal ¼ jacks were used to improve durability. A recessed XLR jack with gold plated contacts was used for a secure and pure audio connection. Several proprietary circuits were developed to quietly extract power from the mixing board and are pending Patents. The audio signal path is fully analog, passive (transformer based) and is as pristine as possible. The circuit board traces are short, isolated from unrelated signals and shielded from multiple dimensions in at least two levels. The digital circuitry is physically separated from the analog signal path during “play mode”.
Q: Why would I want the TDI when I can just combine a tuner with a direct box?
A: I had done this for years, but here is why the TDI is a superior solution:
- You don’t have to worry about a battery dying for the tuner as the TDI runs off of the mixing board’s phantom power. The TDI will be more durable as its tuner and DI interconnects are fixed inside the unit and protected by a sturdy metal enclosure (as opposed to external plugs/cables connecting a DI and a tuner which can come loose or have intermittent contacts due to vibrations).
- Alternatively, you don’t have to worry about finding an outlet to power the tuner
- The setup time for the TDI is much shorter and you only have one unit as opposed to three (tuner, DI and interconnect cable) to locate. When stages are setup and torn down multiple times a week, this is a big benefit.
Q: My amplifier has an active direct output, why would I want to use an external DI unit?
A: I have found on my amplifiers that using a SNE DI (TDI or MDI) in conjunction with the amplifier (either in front of or in the effects loop) was a superior approach because:
- Hands free control of muting the signal
- I can turn off the amplifier without causing a loud “pop” going to the mixing board
- The dynamic range of the SNE direct boxes are generally MUCH higher than active equivalents. Even when the dynamic range limit is reached, distortion is gradual and more “tube like” in its behavior for the SNE DIs as opposed to harsh and “digital” for the active equivalents.
- Many amplifiers have noisy fans which are often desired to be turned off when the music stops so that the fan isn’t heard over the other audio (such as a speech, sermon, act in a play, etc)
- The audio quality and hum elimination are superior even if the outlet power is interrupted for the amplifier, the signal to the mixing board would remain intact if placed before the amplifier the show will go on in that case
- In some venues I found the active DI from an amplifier would not kill a ground loop. A transformer based solution like in the TDI/MDI was the only way to achieve this.
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- The lower frequencies in general were transmitted clearer with the SNE direct box and the high frequencies weren’t corrupted by hiss.
- You may find that bringing your amplifier to a gig is unnecessary as the TDI/MDI provides all you need – saving time, energy and your back
Q: Why is there a gain reduction from input to output?
A: DIs with transformers, in general, attenuate the input signal. There are many technical reasons for this all of which revolve around the specialized audio transformer needed for this application. Sonic Nuance DIs use the Jensen JT-DB transformer which is a 12:1 step down which gives approximately -22dB of gain.
This 12:1 step down causes the reflected impedance of a source (lets say a bass guitar) to be divided by 144 (=12*12). This gets a bit mathematical, but basically, the bass guitar instead of driving a long cable to a mixing board with a 10k ohm impedance and lots of high frequency loss due to RC losses will have 10k/144 ~= 70 ohms and be much less susceptible to both high frequency loss as well as electromagnetic signal coupling. Active direct boxes achieve the impedance transformation using active devices (amplifiers, transistors, etc) and have much more freedom in setting output level.
Some people wonder why would you want a passive DI at all due to the greater attenuation of signal. There are several benefits of a passive DI to an active DI *assuming a very good transformer like the Jensen is used*:
1) You can hit a passive DI with a TON of signal before it will distort. And when it distorts it is a pleasing “tube like” soft clipping not the hard limiting often used in active direct boxes (some tube direct boxes don’t have this issue).
2) No need for power
3) Usually (although not always) a better ground isolation for killing ground loops
4) Inherently low noise since no active circuitry causing thermal noise (although this may be a wash in terms of signal to noise since the signal is attenuated)
a) designing for low noise using active circuitry inherently means burning current. Since most active DI’s get their current from the phantom power source, they are limited to 10mA max due to IEC specifications. The preamps in mixing boards do not have this limitation and are therefore often very low noise. Thus many times the resultant ratio of signal to noise is often better with a passive DI than an active DI when the effect of the mixer is included.
Q: I use a wireless system with my instrument, how could I benefit from an SNE direct boxes?
A: As long as the wireless signal does not go directly to the sound man/mixing board (as in the case of many wireless microphones), all the issues addressed for non wireless systems apply.
Q: I use a digital snake, does the TDI/MDI work?
A: Yes, the analog to digital converters are generally located on stage (or very close to it) and far from the mixing console for these systems. Thus the signal from the instrument going to the input of the digital snake is still analog and phantom power able. Thus the issues are all the same as with a fully analog snake and all of the benefits of the TDI/MDI apply.
Q: Can I use an SNE direct box for recording?
A: Yes, that is a perfect scenario to use the SNE direct box.
Q: I have a passive instrument, can I use the SNE direct box since the audio path is passive? I keep seeing the rule of thumb “if you have a passive instrument, use an active direct box”
A: Yes you can use the SNE direct box with a passive instrument. Here is why: the load seen by the passive instrument will be a very high impedance assuming a typical 1k ohm mixing board input impedance. For example, a passive bass driving a TDI/MDI would “see” about 140k ohms at the DI input due to the audio transformer’s turns ratio. Typical passive pickup output impedances hover around 10k ohms max. Using output impedance as a rough guide, this means approximately 140k/150k=93% of the instrument signal goes to the DI box. For an active instrument, assuming 100ohm output impedance, the voltage transfer would be about 140k/140.1K = 99.9%. It is true that a larger percentage of the instruments signal would go to the DI if the instrument was active, but we aren’t concerned with approximately -7% (-0.32dB) voltage gain gain difference as the mixing board will make up for it and it is not perceptible by the human ear anyway. (Subjectively, a 2-3dB change in sound is considered barely perceptible).
Q: I notice a warning label on the DI’s top. What happens if I (un)plug the XLR when the TDI is on?
A: The DI will not be damaged but the proprietary circuitry will not be able to do its job in reducing the audible transient that could go to the audio system the DI is connected to. It is generally a good idea to plug and unplug the DI when the audio system is muted. This is no different than other active circuitry powered with phantom power.
Q: When in mute mode there is an occasional slight “click” when I connect my acoustic guitar to the DI.
A: This should not happen at all with passive instruments. Most active preamps in instruments disconnect their battery power when the 1/4″ plug is disconnected from them. This is accomplished with a stereo jack that open circuit’s the preamp’s power when disconnected. When connecting the 1/4″ plug, the tip of the plug (depending on the preamp’s design) can contact ground first and then the “hot” output. This is why there is usually a loud “pop” with connecting/disconnecting an active instrument to an amplifier. Most, but not all, preamps remove the dc voltage on the preamp’s output with a blocking capacitor to prevent this. However, there still may still be a residual voltage potential on the output due to capacitor leakage. Whether the dc voltage is intentionally blocked or not, what you may be hearing is the sudden charging/discharging of the capacitance of the preamp and/or the charging/discharging of the audio transformer’s primary coils in the DI. Even with a sudden charging/discharging using 9V battery on the 1/4″ cable going into the DI, the resultant output signal will be barely audible. There will NOT be a large POP that would occur if this was done in “play” mode. You may find putting the ground lift in a different position removes this click altogether.
