We’re Stereo Exchange, located in New York City. We've been in business since the 1970s and are a major high-end dealer. We have all the current top brands on display in our huge showroom.
These two MX-R TWENTY monoblock power amplifiers belonged to one of our very best customers, and they have been well cared for. They are in great shape, and come with the boxes, packing, and fabric bags for safe shipping.
They were originally sold in 2008, and the price was $18,500 for the pair.
---In November of 2015, the owner had them sent to AYRE for upgrading to the latest TWENTY version, at a cost of $11,000 for the pair.
The will come with the fabric bags, boxes, and packing. They are double boxed. They will also come with power cords, though they are not original.
The MXR amplifiers took AYRE quite a while to design. Every single aspect of both their electrical AND mechanical design was rethought, without regard to price.
This latest version, the MX-R TWENTY, takes things even further.
CHASSIS: This amplifier chassis starts as a 75-pound block of aerospace-quality aluminum. It is then machined to form the chassis structure AND heat sinking in one.
This design has several advantages. The non-magnetic aluminum chassis is immune to magnetic interference between amplifier circuits. The huge amount of metal mass means that heat is pulled away from the transistors to each far corner of the chassis for cooler circuit operation.
Obviously, the structural integrity it fantastic. Unlike other amplifiers, there are no screws that assemble the various parts of the chassis together to loosen with time. This means that we have an almost perfect grounding plane, which keeps noise levels down…way down. The low-noise of the amp will stay that way over time.
In conventional amplifier chassis, screws can loosen over time. This is due to the amp heating and cooling with each use. Loose screws mean that the ground plane and shielding of the amp becomes compromised. This simply cannot happen with the MXR.
BALANCED CIRCUITS: AYRE believes so strongly in the use of balanced circuits and cables that this top-flight model only has an XLR (balanced) input. If you use it with a preamp WITHOUT balanced outputs, adapters are available.
Not only does this amp have balanced inputs, but the signal path is completely balanced, right to the speaker terminals! Neither the positive nor the negative speaker terminal is at ground potential, which means that noise never reaches the speaker. It goes away in the main ground.
This is an unusual design, and costly, but it dramatically lowers the noise floor, which translates into much-improved low-level resolution. You can’t heat minute details in the music when the noise floor of an amp is the same volume as the music.
THERMAL-TRAK OUTPUT TRANSISTORS: Almost all transistor amplifiers are push-pull design. This means that one transistor (or set of transistors) amplifies the POSITIVE half of the wave, and the other amplifies the NEGATIVE half of the wave. This is a MUCH more efficient design than one where a transistor handles the entire wave. Greater efficiency allows for higher power, so push-pull amps are almost universal.
The only problem is that we are asking the positive transistor to “hand-off” the wave to the negative transistors at a precise time. Any lag in the hand-off creates a “notch” in the wave, and distortion.
Transistors tend to “fall asleep” while resting, which leads to this notch distortion. The solution is simple; amplifiers use DC BIAS.
BIAS is a (usually) small amount of current sent through the transistors at ALL TIMES so they are never allowed to “sleep”, reducing distortion, and making the hand-off of the signal smooth and notch-free. CLASS-B amps use just enough to reduce distortion to acceptable limits. CLASS A-B amps use more, to virtually eliminate the distortion.
F.Y.I.: CLASS-A amps never allow the transistors to rest at all, eliminating the problem, but producing huge waste energy. This means that the amplifier must have limited power, due to heat build-up.
One problem that transistors have is that as they warm up, the lower their own internal resistance, so they pull more BIAS CURRENT, which makes them warmer, which again makes them pull more current. This never-ending cycle of heating is called THERMAL RUNAWAY. Amps that thermally run away cook their own transistors and die.
To prevent this, other amplifiers have thermal sensors mounted on their heatsinks to automatically lower the bias when the transistors get warm. This work well, at least under conventional testing on a test-bench. In theory, the transistors will always get just the right amount of bias, keeping notch levels down to insignificant levels, while never overheating.
In practice, the amplifier can still notch, however. What happens is this…
You play a music passage that is loud. The transistors get warm. The heatsink gets warm. The thermal sensors tell the amp to lower the BIAS. Now the music gets QUIET, but the heatsink is still warm from before, and the amp is UNDER-BIASED and distorts.
Only after a few minutes (if you’re lucky) does the heatsink cool down and the bias returns to the proper level.
This amp has a new high-tech transistor, called THERMAL-TRAK, built by On-Semiconductor, which contains the temperature sensor INSIDE ITSELF. This reduced the reaction time for bias regulation from several minutes to a small fraction of a second!
The result of this is that the transistors are always receiving the right amount of bias, there is no “notching”, even at varying volume levels, and the heatsinks have less heat to absorb. Now the power of the amp can be increased, without the amp becoming physically very large, and without fear of any sonic compromise.
IMMUNITY TO AC NOISE: The transformer design and power supply design in general are “self cleaning” in that they strip off noise coming into your AC line without the need for any external line filtering.
HIGH CURRENT DELIVERY: The combination of a huge power supply, use of SIXTEEN output transistors, and super-efficient heatsinking means that this amplifier has no trouble with low impedances. The amplifier will deliver 300 Watts into 8-Ohm speakers and 600 Watts into 4-Ohm loads.
COMPONENT MATCHING: The super-high input impedance of 2,000,000 Ohms makes this amplifier load your preamp very “lightly”. I cannot think of any preamp ever made that would have any difficulty driving this amp, due to the high input impedance.
NO NEGATIVE FEEDBACK: Conventional amplifiers use negative feedback to keep distortion low. This involved feeding some of the output of the amp back into the input to correct distortion. Many engineers feel that, although it helps the distortion specification look impressive, negative feedback hurts the sound.
On a test bench, when producing continuous tones, negative feedback is great, since the waves repeat themselves over and over, enabling the feedback to properly correct any imperfection in the amplification process.
Music, on the other hand, is NOT continuous waves, but ever-changing sounds. This makes self-correction near impossible, resulting in MORE distortion when playing real music than without feedback.
Although the debate rages on about feedback, one thing is certain; if you can design an amplifier to have low distortion WITHOUT feedback, as AYRE has done here, then the result can only be better sound. The best signal correction is to not NEED any in the first place.
The problem is that to achieve great performance without feedback, every part must be the highest quality, and transistors must be precisely matched. All this costs money. This IS a cost-no-object amp.
LONG TERM PERFORMANCE: Since all heat producing parts are mounted to the chassis/heatsink, this amp does not need to have the usual ventilation holes where dust can get in. This should translate into longer life, since the internal parts will stay quite dust-free and are not exposed to oxidation nearly as much as usual.
SPEAKER TERMINALS: I love the speaker terminals on these amps. They clamp down with great pressure on your spade lugs for a VERY solid connection. You tighten them down (together) by turning one large knob that has a rubber ring on it so it’s easy to grasp. Once tightened, those wires are not going anywhere.
PACKAGING: These amplifiers are lavishly packaged. They even come with heavy, padded fabric bags to protect them in transit. The packing material is thick and heavy, and the box is very strong. They are also double boxed. These amplifiers will survive shipping!
SIZE: The chassis measures 11” wide x just under 4” high x about 19” deep, so it’s easy to place. In the box they each weigh about 60 pounds, so shipping will not be too costly since they can go by regular UPS.
AUDIOGON SHOWS YOU THE SHIPPING COST, BUT THAT IS FOR ONE AMPLIFIER AND WITHOUT INSURANCE.
THE ACTUAL SHIPPING COST WILL BE 2x WHAT IS SHOWN.
WE WILL BILL YOU FOR THE DIFFERENCE.
INSURANCE WILL ADD ANOTHER 1% TO THE PRICE...HIGHLY RECOMMENDED!
$15,988 a pair.
Please give them a good home.
Things to know…
These amps are used, sold with no warranty, no refunds, or exchanges.
They have been tested.
We accept PAYPAL and all major credit cards for sales to the US.
We accept Paypal ONLY for sales to Canada.
We will ship this item to the US and Canada ONLY.
We will NOT ship this item overseas.
Sales tax will be charged if the amps are shipped to / sold to within New York State, or if they are picked up at the store. Sorry…it’s the law.
The above words are the property of KZ Consulting and are NOT to be copied.