Yamaha Stagepas 250M

In its mono form, the system is suitable for school and college applications, smaller events, stage monitoring and so on. It could also be used as a keyboard amp or as a small full-range system to handle a guitar synth. And, of course, it works fine as a small PA system for those smaller pub gigs where they expect you to set up in a corner with no space at all for a conventional PA.

As with previous Stagepas systems, the 250M is based around a small powered mixer that slots into a recess in the back of the speaker for transport and can also be used in situ if required. Its obvious benefits are portability, ease of setup and weight, which at 13kg is very manageable. To remove the mixer from the speaker, you need to rotate two slotted catches using a coin or screwdriver, so don't ask your drummer to do this, as they seldom possess either.

When a second powered speaker is plugged into the mixer's ST Link Out R jack, the existing speaker functions as the left channel, with the new speaker handling the right. If nothing is plugged into the extension jack, then the existing speaker receives a mono mix of everything fed through the mixer. While Yamaha's MSR250 powered speaker gives the best match to the original, any similarly sized powered speaker will work, providing you adjust the input gain to get the correct left/right balance. Note that the mixer won't drive a second passive speaker, as the existing speaker already presents a load of 4Ω.

Though the mixer is very small and light, it has some features that you might not expect on such an apparently basic product. For example, channels 1 and 2 (the mono mic/line channels) have built-in compression or limiting, as selected by push-switches. There are no controls, so the compressor action is dependent on the input signal level, but it works surprisingly well in levelling out the sound as long as you are aware that using compression increases the risk of feedback in a live situation where you're using microphones. Switching to Limit works more as a safety net to stop signal peaks running into clipping distortion. You have to select Comp or Limit, as there's no bypass option. Similarly, you can switch on reverb for channels 1 and 2 (separately via buttons), but the type is preset and a single master Reverb control determines the amount added.

In addition to these two mic/line channels, which also have switchable phantom power (albeit only 15V, rather than the standard 48V), there are four stereo line channels that take the input count up to 10. All the channels benefit from basic two-band high/low EQ with a +/-15dB range, plus a rotary Level control. And there's the unusual option to feed in a click track or rhythm part on channel 7/8 and have it route only to the Phones, Speaker jack and ST Link R outputs, but without going to the ST Sub (essentially a separate mixer output with its own level control). This is activated using the Click switch below the headphone level control, and could be useful when you're using the system as a monitor and feeding the FOH system from the ST Sub Out. That way, you get the click channel through the monitors, but not through the FOH feed. Channels 9/10 have RCA phono inputs in addition to the two jack inputs used on all the line channels, making it easy to connect a CD player or MP3 player.

The master section of the mixer is on the left, rather than the more usual right, and comprises the Speaker output on a plastic jack, the ST Link output for a second speaker, a quarter-inch Phones jack, and the left and right ST Sub, which carries the whole stereo mix less the input to channel 7/8 when Click is selected. An included jack lead is used to connect the mixer's speaker output to the speaker cabinet. There are level controls for Phones, Sub Out and Reverb, as well as a rotary Master Level control, plus buttons for Click and Music/Speech selection. This latter seems to apply a bit of mid-scoop EQ in the Music position, with perhaps just a hint of mid-boost in the Speech position. Metering is via a single row of five LEDs, with a further LED indicating when the limiter protecting the power amplifier operates. The light weight and small size of the mixer suggest that a switch-mode power supply is used to power the internal Class-D amplifier, but no detailed technical information is provided for this part of the circuitry.

Mechanically, the mixer comprises a metal front panel with ventilation holes punched at either end, and this sits in a box-like plastic shell housing the circuitry. A couple of threaded inserts on the back of the mixer allow an optional mic stand mount to be fitted, and a couple of chromed bar handles both help protect the knobs and provide a means of lifting the mixer out of its recess in the back of the speaker.

Though the Stagepas 250M was doing most of the work, several people commented that the sound actually improved, even though the house PA comprised a pair of hefty speakers of a well-known US provenance with 15-inch-plus horns. What's more, we had no time to move everything around, so the Stagepas 250M actually ended up being behind some of the mics, yet we still got quite a lot of level before feedback became a problem, which suggests its dispersion characteristics aren't bad either. Instruments handled by the system at this time included several acoustic guitars with pickups, two vocal mics, and a violin processed via an effects pedal unit.

You wouldn't expect to put significant levels of bass through a system of this kind, but for everything else it delivers a clean, confident sound with good coverage capabilities and a welcome absence of high-end harshness. Whilst there are louder systems around, the maximum SPL of 116dB at one metre translates to plenty of vocal/instrument level in a typical small venue. A point to bear in mind is that the phantom power is much lower than the standard 48V used by most professional microphones, so although many back-electret models will work quite happily at 15V with only a slight loss of headroom, some condenser mics may not work at all or may have their output much reduced. My LD 1011 back-electret mics worked fine.

As to the quality of the built-in reverb, it is actually extremely good and sounds very much like one of Yamaha's studio plate reverb algorithms, but I feel they've chosen an excessively long reverb time, given that it can't be adjusted. I'd estimate the decay time at 2.5 to 3 seconds. It can be effective when used very sparingly, but if you add more than just a hint, it sounds rather too cavernous for anything other than karaoke. Similarly, the compressor works well, adding density and evenness to the sound when selected, but as there is no input gain trim on this mixer, it is effectively preset for microphones of an average output level. This turned out to be about right for use with a Shure SM58 or mic of similar sensitivity, and it was OK with my LD mics too.