RX-V2500 Benchmark Tests - Part 2

Figure 1. Line Level Attenuation vs Frequency Response

Before measuring amplifier performance, I thought it was good practice to first sweep the preamp section of the RX-V2500. As you can see, the RX-V2500 frequency response via the line level outputs into a 10kohm test load was 20Hz to 20kHz +0 / -0.1dB. This is a very good response and indicates the RX-V2500 would serve as a great preamp / processor to those wishing to use separate power amplifiers.

Figure 2. Amplifier Output Impedance vs Frequency at 1 Watt

The RX-V2500 has relatively low output impedance when driving an 8 ohm load. The rising impedance with frequency could be attributed to zobel compensation and/or series inductance after the feedback path for added stability which is normal practice in many receivers and power amps and especially not an issue for a receiver in this price range.

Figure 3. Damping Factor vs Frequency Response @ 1 Watt into 8 Ohms

The RX-V2500 had sufficient damping factor as per Damping Factor – Effects on System into an 8 ohm load. Yamaha does specify a damping factor of 140, but don’t really say how exactly it was measured and at what power levels and frequencies.

Figure 4. Attenuation vs Frequency Response @ 1 Watt 8 Ohms

The Yamaha RX-V2500 exhibited good frequency response into an 8ohm load at 1 watt as indicated by our measurement of: 20Hz to 20kHz +0 / - 0.15dB. Note that this does not factor in losses due to cable impedance and stray inductance from the test load. In reality I would suspect the loss at 20kHz would be more like - 0.1dB, just like the preamp line level path I previously measured.

Figure 5. Damping Factor vs Frequency Response @ Full Power

This test is most interesting as it shows the RX-V2500 has excellent damping factor into an 8 ohm load, but goes to a meager average range of 5 when driving a 4 ohm load at full power. I suspect the damping factor may be slightly better than measured here as the cable impedance is certainly coming into effect here. This does demonstrate the amplifier is not acting like an ideal voltage source (even very few dedicate amps do) and is getting loaded down by the low impedance. What is also likely is the limiting circuitry is raising the output impedance to limit delivered power to the low impedance load. This however, is not surprising or disappointing for a receiver in this price class, especially since it is not specified to drive 4 ohm loads but as you will see below, does a commendable job doing so.

Figure 6. Maximum Unclipped Power vs Frequency

The Yamaha RX-V2500 does a bang up job in power delivery into 8 ohms. While it is specified to deliver 130wpc into 8 ohms, I actually measured a whopping 148wpc with one channel driven and 135wpc into 8 ohms with 2 channels driven unclipped!

What’s even more impressive is that it did so with only 0.05dB additional attenuation at 20kHz when compared to the 1 watt frequency response test. What this demonstrates is excellent frequency response uniformity at all power levels. Kudos to a receiver that delivers all the latest bells and whistle with a free 7CH amp thrown in!

Driving 4 ohm loads is certainly not the RX-V2500’s forte, but it did a commendable job considering. It was able to deliver 200wpc with one channel driven and about 110wpc with 2 channels driven unclipped. Initially I cranked more power out under these test conditions from 20Hz to about 15kHz but then found major slew induced distortion at higher frequencies followed by a rapid shut down of the receiver. This is very good news actually since the amplifier automatically shuts down once bandwidth uniformity has been compromised for being driven too hard and is a good preventative measure for protecting both the amplifiers and the loudspeakers. This shouldn’t be a real world problem because at high frequencies very little power is being delivered to the speaker system since music is mostly harmonic in nature above 13kHz or so. The real power demand is in the bass and in most home theater systems a dedicated subwoofer or two is used to alleviate this problem.

Considering this, I backed off on the Yammie until I had a pristine unclipped waveform at 20kHz to come up with the measurements published herein. It should also be noted that anytime I drove 4 ohm loads at full power, the fan came on shortly after. I caution those using 4 ohm speakers to make sure you have plenty of ventilation and airflow.

Recommendations

The Yamaha RX-V2500 has respectable amplifier performance for a receiver in its price class and should serve most home theater environments quite well. I advise against using low efficient 4 ohm speakers in environments where you like to play your music loudly and your room dimensions exceed 2000 ft^3. For best results, my advice is to use reasonably efficient (88dB or higher) 6-8 ohm speakers (4 ohm may be used if their efficiency is 90dB or greater and you provide adequate ventilation) and apply bass management to all channels and route the power hungry bass information to a dedicated subwoofer or two. If you find you need more power in the future, simply preamp out to a dedicated amp and you have yourself a great processor with all the latest surround formats on board.