Yamaha XS350 Power Amp

Whatever happened to that "good old country doctor" amplifier that could do a little bit of everything well at a reasonable price? It seems to have reappeared in the form of the Yamaha XS350.
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Much like medical practitioners, power amps are becoming more specialized by the day. Just as there are neurosurgeons, orthopedists and podiatrists, there are now amps for use with reference monitors, lightweight amps for touring companies and even amps with different topologies on each channel, to work in biamp scenarios. Whatever happened to that "good old country doctor" amplifier that could do a little bit of everything well at a reasonable price? It seems to have reappeared in the form of the Yamaha XS350.
Product PointsApplications: Live sound; installations

Key Features: Key Features: 230 W/channel at 8 ohms, 350 W/channel at 4 ohms; 25 Hz to 150 Hz high-pass filters; 40 Hz low-pass filter for subwoofer use

Price: $699

Contact: Yamaha at 714-522-9011


+ Simple operation

+ Selectable high- and low-pass filters

+ Flexible enough for a wide range of uses


- Heavier than switching power supply amps

The Score: An affordable and flexible all-in-one power amp; especially attractive for contractor and fixed installation use.

The XS350 ($699) measures 3 RU high, 12.44" deep and 19" wide and weighs in at a hefty 44.08 lb. The XS350's front panel is simply adorned. It has a power switch, a pair of three-stage signal LEDs (signal, clip and protection), a power LED and an air intake port. The signal LEDs glow when signal exceeds 2 Vrms, the clip indicators illuminate when signal distortion exceeds 1% and the protect lights come on if the amp is overheated or DC voltage is present. The protection also engages during start-up to prevent speaker damage.

The front of the amp is so sparse looking that a client pointed to the XS350 in my amp rack and sarcastically stated, "That sure looks complicated; I could never figure out how to use it." He found it rather amusing that the amp had only a power switch while the outboard gear and the console were littered with controls that were baffling to him.

The back panel of the XS350 has a pair of XLR balanced inputs, barrier strip balanced inputs, binding post and barrier-type speaker outputs, a mode switch (stereo/ bridge/mono), two volume controls, and a nifty filter section. This filter section has a pair of three position switches and corresponding frequency selectors. The switches can be set to off, subwoofer or low cut.

As you would expect, when the switch is in the off position, the amp operates at full range. When the selector is moved to the subwoofer position, this engages a fixed frequency (40 Hz/6 dB) low-pass filter, allowing the XS350 to act as a subwoofer amp without the need for an external crossover. When the low-cut function is selected, the frequency knobs determine the points at which the high-pass filter operates. The range of this filter goes from 25 Hz to 150 Hz.

The XS350 is a Class AB amp that has a power output rating of 230 Watts per channel into 8 ohms and 350 Watts per channel into 4 ohms (20 Hz to 20 kHz, THD+N=0.1%). In addition, the XS350 has a THD rating of 0.05% (20 Hz to 20 kHz, half power), a signal-to-noise ratio of 100 dB, a damping factor of greater than or equal to 100 (8 ohms, f=1 kHz), and a slew rate of +/-30 V per microsecond. The XS350's exhaust ports are located on both the sides and the back of the chassis.

In use

My first impression of the XS350 was recorded prior to any sonic exploration. This amp is really heavy by current standards. Putting several of them in an amp rack would require a muscular assistant. Seriously, at 44 lb. it is nearly double the weight of amps using switching power supplies. Although Yamaha touts the XS350 as suitable for sound reinforcement, the fact that the amp weighs as much as it does, and has all the controls on the back, would lead me to view the amp as more suited to fixed installation duty.

I used the XS350 on a number of sound reinforcement jobs to drive monitors and FOH speakers. It did a marvelous job powering two 8-ohm wedges. The monitor mixes were rich and punchy. When I introduced a 4-ohm load (two 8-ohm wedges per channel), the amp seemed a bit underpowered when trying to reach moderately loud stage volumes.

The XS performed well for FOH duty too. I used it to power a pair of full range cabinets for both speech and full band functions. The low cut was a handy feature. I used it to engage a 30 Hz rolloff, so as not to overburden the woofer when there were no subs present. When used in a biamp system, I sent the XS350 a mid/high signal (150 Hz and above) and it worked flawlessly. The amp produced great representation and was not stressed powering two 250-Watt, 8 ohm cabinets.

I didn't use the XS to power subwoofers, as I think its power output is a tad short for club applications. Perhaps in a smaller club with lots of ambience, it could be used to power subwoofers. Although it adds flexibility, the subwoofer function would be more appropriate on an amp that had a more substantial power rating.

In general, I found the moveable low cut to be a handy feature, especially when a system is limited to just full-range speakers. In the interest of added flexibility, I would like to have seen combination input connectors that accept both XLR and 1/4" balanced connectors.


The XS350 is an amazingly affordable amp that is good sounding, moderately powered and can be used for sound reinforcement or fixed installations. With its low price, it would be perfect for a band or venue on a tight budget. Due to its weight, I would not really recommend the amp for traveling systems. It does have reasonable input and output connections, making it ideal for contractors who want something inexpensive to offer their clients. It is attractive and would look great in most corporate or institutional settings. Admittedly, it must be hard to design an amp to cover all the bases. The XS350 comes close to being an all-purpose amp, and with such a low price, you should have enough cash left over to buy a decent external crossover.