The J-Box III Review
The J-box is a device that I’ve often looked at on AliExpress, but I don’t see much or any talk about it really on DIY forums, not English speaking ones anyway. It looked quite interesting to me as an all-in-one measurement system; the poor man’s alternative to a Clio Pocket.
Thanks to tktran for the donation to help make this review possible.
The J-box is effectively a USB audio interface with a built-in dual channel configuration for measuring impedance as well as providing a timing reference for acoustic measurements. It provides a small built-in amplifier as well, so it can avoid a lot of the clutter of wiring up a USB audio interface to a measurement jig to a power amp. It’s perfectly functional for any measurement system like REW or ARTA, and is plug and play on both Windows or Linux systems (probably Mac too, but I don’t have one to confirm).
What’s in the box?
The J-box is available in 3 different bundles. One includes just the device and power supply, not case or microphone. It can also be purchased with a case, and with a case and calibrated electret microphone. For testing, I have the full kit with case and microphone.
It comes with a reference resistor, mine was labeled as “9.976 ohm”, I don’t have an accurate enough meter to verify that, my Fluke 179 reads 10.0. The power supply unfortunately has a very short cable, only 3 ft, so you may find yourself wanting to take on a DIY project to extend the cable length. It also comes with a RCA cable for the mic about 3m long which is decent, as well as some alligator clip leads for impedance measurements, and a USB A to B cable. There is also a USB stick, which contains nothing more than the mic calibration file.
The microphone came with a serial number hand written on the foam insert in it’s case, and the serial number is hand etched on the mic body. The mic itself is a simple electret mic capsule inserted in a brass tube. It came with a 3D printed camera mount. Unfortunately I don’t have a camera mount, so I 3D printed a mount to fit a 20mm mic clip.
The I/O
For audio output it includes a selector switch for 1.41V, 2.83V, or 4.9V. Output can be connected directly to a speaker via the "PORBE" binding posts, or used as a line level output via the “aux” RCA connector. The Aux output is labelled “0.5x” and will be precisely that, 0.5 x the output on the speaker binding posts, so maximum output on the aux connector can be 0.5x 4.9V = 2.45VRMS max line out.
For input there is an RCA mic input and a XLR mic input, and an adjustable input gain control. Note that the RCA mic input is powered for ~6VDC for electret microphones, and the XLR/TRS combo input is powered with 48VDC phantom power for condenser mics. Unfortunately there is no switch to turn off the phantom power, and it is powered on both the XLR and TRS pins, so this is a “condenser mic only” input.
The J-box included no documentation whatsoever, however there are fairly clear diagrams on the AliExpress sales pages for the device.
The “cal” selection is simply a loopback connection on both channels, for “soundcard calibration” in REW. The “Z” selection operates the same as my dual channel measurement jig, but with a 12 ohm sense resistor. The SPL selection uses the Left channel as the mic input, and the right channel as the feedback loop, for a dual channel measurement. Unfortunately, because the loopback is built-in, there is not an opportunity to inject things like a high pass filter capacitor in the feedback loop, but it’s still great to have a good timing reference with no additional effort required.
What’s Inside?
Inside the J-box there are two TDA2050A amplifier ICs, which I found curious as this is a mono device. After staring at the circuit board for a few minutes, I determined that the second TDA2050A chip is being used to generate the split voltage rails. The J-Box receives 24VDC from the external power supply, which it then splits into +/-12VDC rails using a TDA2050A. Like this:
The second TDA2050A is the audio amplifier. A trim pot next to it can be used to fine adjust the gain setting. The rightmost trimpot adjusts the aux level output. 4 more trimpots to grouped together at the bottom for the voltage dividers for the loopback operation. At the mic input, there is an NE5532 and a OP1662. I believe the NE5532 is for the RCA mic input, and the OP1662 is for the XLR input. The USB and audio functions are all built into a single SSS1701B “USB Headset / Line-In Controller”. This chip combines the USB connectivity as well as DAC and ADC functions. I found it’s datasheet here for those interested:
SSS1700B1_USB-Headset-Line-in-Controller-Datasheet_v1.pdf
The J-box is a device that I’ve often looked at on AliExpress, but I don’t see much or any talk about it really on DIY forums, not English speaking ones anyway. It looked quite interesting to me as an all-in-one measurement system; the poor man’s alternative to a Clio Pocket.
Thanks to tktran for the donation to help make this review possible.
The J-box is effectively a USB audio interface with a built-in dual channel configuration for measuring impedance as well as providing a timing reference for acoustic measurements. It provides a small built-in amplifier as well, so it can avoid a lot of the clutter of wiring up a USB audio interface to a measurement jig to a power amp. It’s perfectly functional for any measurement system like REW or ARTA, and is plug and play on both Windows or Linux systems (probably Mac too, but I don’t have one to confirm).
What’s in the box?
The J-box is available in 3 different bundles. One includes just the device and power supply, not case or microphone. It can also be purchased with a case, and with a case and calibrated electret microphone. For testing, I have the full kit with case and microphone.
It comes with a reference resistor, mine was labeled as “9.976 ohm”, I don’t have an accurate enough meter to verify that, my Fluke 179 reads 10.0. The power supply unfortunately has a very short cable, only 3 ft, so you may find yourself wanting to take on a DIY project to extend the cable length. It also comes with a RCA cable for the mic about 3m long which is decent, as well as some alligator clip leads for impedance measurements, and a USB A to B cable. There is also a USB stick, which contains nothing more than the mic calibration file.
The microphone came with a serial number hand written on the foam insert in it’s case, and the serial number is hand etched on the mic body. The mic itself is a simple electret mic capsule inserted in a brass tube. It came with a 3D printed camera mount. Unfortunately I don’t have a camera mount, so I 3D printed a mount to fit a 20mm mic clip.
The I/O
For audio output it includes a selector switch for 1.41V, 2.83V, or 4.9V. Output can be connected directly to a speaker via the "PORBE" binding posts, or used as a line level output via the “aux” RCA connector. The Aux output is labelled “0.5x” and will be precisely that, 0.5 x the output on the speaker binding posts, so maximum output on the aux connector can be 0.5x 4.9V = 2.45VRMS max line out.
For input there is an RCA mic input and a XLR mic input, and an adjustable input gain control. Note that the RCA mic input is powered for ~6VDC for electret microphones, and the XLR/TRS combo input is powered with 48VDC phantom power for condenser mics. Unfortunately there is no switch to turn off the phantom power, and it is powered on both the XLR and TRS pins, so this is a “condenser mic only” input.
The J-box included no documentation whatsoever, however there are fairly clear diagrams on the AliExpress sales pages for the device.
The “cal” selection is simply a loopback connection on both channels, for “soundcard calibration” in REW. The “Z” selection operates the same as my dual channel measurement jig, but with a 12 ohm sense resistor. The SPL selection uses the Left channel as the mic input, and the right channel as the feedback loop, for a dual channel measurement. Unfortunately, because the loopback is built-in, there is not an opportunity to inject things like a high pass filter capacitor in the feedback loop, but it’s still great to have a good timing reference with no additional effort required.
What’s Inside?
Inside the J-box there are two TDA2050A amplifier ICs, which I found curious as this is a mono device. After staring at the circuit board for a few minutes, I determined that the second TDA2050A chip is being used to generate the split voltage rails. The J-Box receives 24VDC from the external power supply, which it then splits into +/-12VDC rails using a TDA2050A. Like this:
The second TDA2050A is the audio amplifier. A trim pot next to it can be used to fine adjust the gain setting. The rightmost trimpot adjusts the aux level output. 4 more trimpots to grouped together at the bottom for the voltage dividers for the loopback operation. At the mic input, there is an NE5532 and a OP1662. I believe the NE5532 is for the RCA mic input, and the OP1662 is for the XLR input. The USB and audio functions are all built into a single SSS1701B “USB Headset / Line-In Controller”. This chip combines the USB connectivity as well as DAC and ADC functions. I found it’s datasheet here for those interested:
SSS1700B1_USB-Headset-Line-in-Controller-Datasheet_v1.pdf
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