AKG WMS40 Mini Instrumental Wireless Set US25B 537.900 MHz Bodypack

AKG WMS40 Mini Instrumental Set US25B: One Channel Now, a Second Channel Later

The AKG WMS40 Mini Instrumental Set on band US25B is an analog UHF plug-and-play single-channel wireless system operating on one fixed carrier at 537.900 MHz, supplied with a PT40 Mini bodypack, an MKG L instrument cable, a BC400 belt clip and an SR40 Mini receiver. Single-channel is the phrase that shapes everything about this product, and it is worth being precise about what it means: the receiver decodes one carrier and one transmitter, so the set covers exactly one performer or one instrument, and a second microphone means a second complete system rather than a second transmitter. That is a perfectly sound way to build a small rig, and often the better one, but it comes with a rule about band letters that has to be understood before the second purchase rather than after it. Audio runs 40 Hz to 20,000 Hz with a 105 dB-A signal-to-noise ratio, and one AA size cell lasts up to 30 hours. This page is about the arithmetic of growing from one channel to two.

What Single Channel Really Means on a Fixed-Frequency System

Single channel here means one carrier, one transmitter and one output, and because the carrier is fixed rather than tunable there is no way to reassign it. On a tunable system, two receivers can be moved onto different frequencies at setup and a coordination problem is solved with a menu; on a fixed-carrier system the frequency is a property of the hardware you bought, printed on the box as a band letter, and the only way to change it is to buy a different band. The consequence is simple and absolute: two systems carrying the same US25 letter will transmit on the same frequency, interfere with each other, and produce a channel that squeals or drops rather than two working microphones. A community theatre adding a second radio microphone for a two-hander therefore has to check the letter before ordering, not on the get-in day.

Choosing a Non-Colliding Second Band

AKG documents four single carriers in this group, US25A at 537.500 MHz, US25B at 537.900 MHz, US25C at 539.300 MHz and US25D at 540.400 MHz, and it also documents which of them it supplies together. Coordinated dual sets exist only as US25A with US25C and as US25B with US25D, and that is the most useful piece of information a buyer of this set can have, because it means the manufacturer has already established that those two pairs sit far enough apart to run side by side; the pairing is not arbitrary, since two carriers only 400 kHz apart, as US25A and US25B are, sit far closer together than two roughly 2.5 MHz apart. So for anyone who owns this US25B set, the intended companion is US25D. A school building a rig one channel per year, or a village hall adding a second microphone for a user group, has a clear answer rather than a guess.

Two Single Receivers or One Dual Receiver

There is a genuine decision to make once a second channel is needed, because the same two carriers can be delivered either as two single-channel systems or as one dual-channel system with a two-channel receiver. Two singles give two independent boxes, two mains supplies and two outputs, which is flexible because either half can travel alone, be lent out, or be replaced without disturbing the other; a dual system consolidates both channels into one receiver with one supply and two outputs, which saves a mains socket, a shelf and a cable, and arrives already paired on a coordinated band combination. Neither is wrong, and the choice usually follows how the equipment is used rather than how it performs. A theatre that lends a microphone to a rehearsal room wants two singles; a fixed chapel installation with one shelf wants the dual.

Fixed Frequency as a Feature for Volunteer Operators

Removing the ability to change frequency also removes the ability to change it wrongly, and in a great many venues that is a straightforward advantage. Plug-and-play here means no scan to run, no infrared pairing handshake to perform, no channel number to write on a whiteboard and no menu in which a well-meaning helper can leave the receiver on a channel the transmitter is not using; switching on both halves is the entire procedure, and it produces the same result every time regardless of who does it. The trade for that simplicity is exactly the band-letter discipline described above, settled once at the point of order rather than every week. For a community theatre, a school drama studio or a village hall handed between user groups, a system nobody can misconfigure is worth more than a system with more options.

Where the US25B Instrumental Set Fits

Community theatres adding wireless channels one at a time are the archetypal buyer, along with small churches that know a second microphone is coming, schools building an inventory across several planning cycles, drama studios needing two performers miked separately, and village halls whose equipment is shared between groups. Rental stock is another regular home, because two single systems on documented partner bands are more flexible to hire out than one dual receiver. The set arrives complete for instrument use with the MKG L cable and the BC400 belt clip in the box, and the bodypack input also accepts headset microphones and instrument pickups, so the same channel can change role between productions. Order it knowing its carrier is 537.900 MHz on band US25B, and that its documented partner for a future second channel is US25D.