Rediscovery of TEAC as a serious audiophile brand was one of my highlights of 2024. The moderately affordable VRDS-701 Preamp/DAC/CD Player (the actual name is longer, so I have shortened it) and accompanying CG-10M-X Master Clock Generator set a new standard in preamplification and CD playback in my system and opened my eyes to the advancements taking place in the industry. Trickle down is real, and over a period of perhaps ten years, the audiophile can holistically upgrade their sound for a fraction of what it cost the previous decade. I bought both of those products after the review, and I have not regretted it one second! They have been anchoring systems with several genres of speakers – hybrid horn (Colibri C2), hybrid array (Legacy Audio Wisper DSW Clarity Edition), dipole (Kingsound King III), and concentric (PureAudioProject Trio15 10” Coaxial) all to good effect. I strongly recommend that if you have been churning a separates system in the hopes of hitting the right combo, check out the TEAC 700 series line.
I had not bought the AP-701B amplifiers that I reviewed because they were quite like the Legacy Audio i.V4 Ultra Amplifiers, which also are class D, but higher power. The Legacy amps are on loan, so it would be redundant to purchase class D amps for similar purposes. I did wish to follow up, however, by handling the smaller form factor that is the TEAC AP-507 amplifiers, chiefly because they use the newer Hypex NCOREx power module. It is a new generation product, which has superior resolution and is said by TEAC to confer, “an immersive, three-dimensional soundstage and a more expansive spatial presence.”
The NCOREx amplifier module is “tuned” for TEAC. It offers 95wpc into 8 Ohms in either the stereo or Biamp mode, and 350wpc into 8 Ohms in the BTL (Bridge Tied Load; effectively switched to Mono internally) mode. The Owner’s Manual points out that the stereo or bi-amp modes are suitable for speakers with a nominal impedance of 4-16 Ohms, and BTL mode is suitable for speakers with nominal impedance of 8-16 Ohms. TEAC doesn’t recommend running the amp into a 4 Ohms load in BTL mode.
As a reminder, never join external channels of a Class D amp to achieve mono operation. Any Class D amp that offers the equivalent of mono operation, usually referred to as BTL, will indicate that operation in the Owner’s Manual and typically will show the connections for it. TEAC offers very clear directions how to hook up the amp singly, or a pair of the amps in Bi-amp mode or BTL mode.
Unusual methods
TEAC is not afraid to try unorthodox designs to improve sound quality. One of the more unusual features of the AP-507 is that it has a “semi-floating aluminum top plate.” In other words, the top plate is not screwed down. When I opened the box and heard jangling metal, I was concerned that something had broken in transit. I thought that odd considering the robust packaging and apparent lack of damage. Upon investigation I learned that it was intentional as a design feature to aid the sound quality.
I’m not convinced the loose top plate does much of anything sonically. While a loose plate may assist marginally in heat dissipation over an anchored lid, previous testing with footers and weights atop components had no discernible impact on the sound as opposed to components without such trappings. I suggest potential buyers of the AP-507 focus on the topology of the component and system configuration to achieve excellent results. Through the decades of testing such things informally, changes outside of the power and signal pathways have been insipient to cause significant sound improvement. The amplifier’s 3-point Stress-Less Isolation Foot system along with the semi-floating lid are said to create a more open and natural listening experience. They did not seem to hurt the sound quality, so I treat them as neutral design features. Be aware that the thin rubber discs that the owner applies to the metal footers can leave residue if the TEAC components are placed atop other components. I suggest that you place a barrier, a piece of cloth or leather, etc., between the footers and the surface they rest upon.
Aesthetics and features
TEAC’s entire current lineup hearkens back to the glory days of the 60’s and 70’s, with black cases and large meters on the amps. Tidy toggle switches and handles resembling those found on professional gear are used across the line. Tiny, low contrast lettering on the front makes the name of each button or switch practically hidden from middle-aged eyes. TEAC needs to address that shortcoming. Making the lettering either larger or more contrasting to the chassis would help.
The Mellow-Yellow, Dual Pointer VU Meters are a welcome change from the worn-out blue meters McIntosh uses. Please don’t hate on me for saying so; the look of McIntosh is at once classic and tedious, like Harley Davidson motorcycles. Meters don’t make components sound better, so TEAC could eliminate them, but why? It’s fun to see needles dancing with the music! If the company was making OK sounding gear, I might suggest they allocate resources to the circuitry, but they are rocking class D sound, so I’m not going to give them a hard time for including them.
The front of the amp is clean, with the Power toggle switch on the left of the meters and a dual function button to control the Dimmer for the meters and a Meter Gain adjustment for sensitivity to the input signal. I like the +2-dB setting as the meters show more movement. It reminds me of the old days when meters in my system were pegged, reaching the red zone, or the signal pushing LED meters from green to yellow to red. I do not play music at live or concert levels, so I can keep them on a more sensitive setting without them being plastered to the upper end of the range.
The back of the unit is organized similarly to the AP-701, with the Left/Right channel inputs, 12V Trigger functions (In and Through), Input Selector (RCA or XLR), and Output Mode (Stereo, Bi-amp, and BTL). There is also a Micro USB port which is reserved strictly for maintenance access by TEAC. while another marked off area contains the Left inputs, The switches for Input Selector and Output Mode are tiny and placed near the bottom of the backside. They are small and it takes little pressure to slide the switch entirely to the other side.
One must exercise gentleness to find each setting to be sure of the mode the amp. I had to use a flashlight and peer intently right at the indicator to be sure that it was on the preferred setting. The offset speaker posts with BTL mode using the top two is good design. The offset placement of the posts is especially beneficial for longer stiff leads on speaker cables. The amplifier takes a typical 15A IEC plug. The amp is sensitive to switching power cords, and I recommend the owner may wish to explore aftermarket cords for all equipment, amps included.
Also, the 12V trigger causes an unintended effect when used with the VRDS701. There is no soft shut down, but the amp is turned off at the same time as the VRDS-701. Consequently, there is a pop associated with the amp’s powering off heard through the speakers. It doesn’t hurt the speakers, but it is annoying. Typically, the power amplifier is to be turned off prior to the preamp, not simultaneously. Turning off the amplifier prior to the preamp causes a slight surge to the speakers that results in an unpleasant popping sound. Perhaps TEAC can put a second or two delay in the circuit such that the amps do not cause the popping sound when shutting down.
The AP-507 does not have an external fuse, but it does have a built-in protection circuit. If the protection circuit activates, perhaps due to an excessive load due to cables being shorted from improper connections or high temperature (the unit runs cool, even after hours of use), the Level Meter lights will blink. The unit is to be set to Standby for several minutes and then powered on. I never had power interruption with the AP-507.
The AP-507 has fully balanced circuitry and is said to ensure ultra-low signal to noise ratio. However, I found that in my room it emitted a noticeable electronic noise, especially with higher efficiency speakers. With lower efficiency speakers such as the Legacy Audio Whisper, the noise is reduced quite a bit to the point of being negligible. When the amp was used in Stereo mode, the noise level was tolerable with speakers like the Colibri C2, but it jumped when the amp was used in BTL mode, as the power was doubled to 350wpc. With a hybrid horn like the Colibri C2 I could not ignore the level of the electronic noise during quiet passages. That was a shame, because the amps are distinctly clean and revealing, which would accommodate the openness of the Colibri C2. I recommend those who have higher efficiency speakers try out the AP-507 in their system to see if it will work well.
Was the noise the result of my room’s electrical supply? I have two sets of dimming lights in my room, and there have been occasions when components have been particularly sensitive to them. If the lights are on fully or off, the noise is all but eliminated, but if the lights are dimmed, then the noise can intrude. However, I found that even turning the lights off entirely did not eliminate the noise. One solution I tried was insertion of cheater plugs (3 to 2 prong adapters) for the power cords, and that reduced the noise by a perceived 50%, but it did not eliminate it altogether.
Other components such as the Heaven 11 Billie Amp Mk2, which is a tube hybrid class D integrated amplifier, or the PS Audio Stellar Strata Mk2 Integrated Amplifier have never had noise issues. Conversely, the Legacy i.V4 Ultra Amplifier at times has been a bit noisy like the AP-507, but not as loudly. All this took place while using the TEAC VRDS-701 and CG-10M-X upstream, so using a full TEAC system is not a fix for the potential of the AP-507 exhibiting noise. The simplest solution is to use these amplifiers with less efficient speakers and if necessary, insert an adapter plug.
I cannot say definitively what was causing the noise, but it is less likely to be an issue for people who have less efficient speakers. As I worked through my collection of speakers from the most efficient (Colibri C2) to least (Kingsound King III electrostatic), the noise receded until it was a nonissue.
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