We were rather excited to take a look at the Accento Dynamica Hybrid Stereo amplifier, provided by The LoudSpeaker Kit. The hybrid amplifier includes a valve pre-amp stage, with a transistor power amplifier stage. This combination has proven popular for instrument amps to retain the warmth of the analogue age, and it appears to be equally as engaging in this application.
We give it a good listen, paired with a pair of 6.5" Dayton Audio bookshelf speakers.
The short version? Thoroughly impressive.
ADHA24BT Accento Dynamica Hybrid Stereo Amplifier
Photographs will do the ADHA24BT far more justice than words. The amplifier is presented in a black anodised, brushed aluminium case, with clear acrylic finger guards for the protruding valves. Three layers of acrylic are supported and spaced by stainless-finished metal posts, and visually partner well with the blue LEDs below the valves which shine up through the valves and glass.
This modern aesthetic coupled with modern features allows us to really enjoy what this amplifier has to offer. While it's not overly cumbersome, it still packs quite a punch.
"This is great for streaming music from a Raspberry Pi, or any other Bluetooth source."
12W RMS @ 4Ω, per Channel, 2 × Channels
THD < 0.1% at 12W
20Hz - 20kHz
Signal to Noise Ratio:
Greater than 80dB
Valve Pre-amp, Transistor Power Amp
USB, Bluetooth, 2 × Auxiliary Inputs
Front Panel Controls for USB Memory Device
Internal Power Supply
Separate Headphone Amp
Output for Active Subwoofer
One of the most curious features of the ADHA24BT is that it utilises a linear power supply. Not just a linear front end on a switch mode power unit, but entirely linear. This eliminates any possibility of switching noise contaminating the preamplifier power rails, and seemed to do a good job of avoiding any noise from the incoming power, something that can be a problem with all the switch mode gear plugged in on the DIYODE workbench, and with the generally noisy mains grid in our area.
The preamplification is handled by a valve stage using 6F2 valves. This section links to a separate headphone amplifier, delivering 15mW into 600Ω loads, dropping to 5.6mW into 16Ω loads. Distortion figures for the headphone amplifier is less than 1% at 1kHz.
Using headphones will disengage the audio path to the power amplifier, including the subwoofer output, meaning that you have to choose between headphones or speakers, but that's fairly standard and expected operation.
The power amplifier stage is entirely transistor-based, and is a class AB. Rated for 12WRMS for each of its two channels into 4Ω loads, this stage boasts Total Harmonic Distortion of 0.1% at full power. While some audiophiles may see this as poor, preferring amplifiers with claims of 0.001%, the reality is that audible difference is negligible.
Depending on your preference of audio source, most streaming services and MP3s etc won't reach the full potential that this amplifier provides anyway. So let's not get too caught up on the numbers specifically.
AROUND THE AMPLIFIER
The top face of the unit features two control knobs. One is the usual volume control, which is a 270° rotating potentiometer, rather than a rotary encoder found on many current amplifiers. Again, this means the elimination of interference in the audio signal.
To the right of this is a four-position rotary switch, the selection control for the four inputs: USB, Bluetooth, Auxiliary 1, and Auxiliary 2. In front of this are four small, black pushbuttons. These are the play/pause, previous, next, and stop buttons for the USB source, the socket for which is to the left in front of the volume control, and is slightly recessed into the face. We occasionally fumble with these simple controls, but expect most of us will use Bluetooth from a smartphone, or use a Raspberry Pi as a media centre with Kodi or similar suitable operating system.
The back panel of the amplifier contains all of the inputs and outputs. At the left is the antenna for Bluetooth. This is an unusual feature on consumer devices, which usually have an internal PCB trace antenna. The external antenna improves reception and is a quality touch. Next to this are the RCA connections for both Auxiliary inputs. No 3.5mm Stereo input is featured. There is a 3.5mm socket to the right of the RCAs, but it belongs to the headphones output. Below this is a single yellow RCA socket for connecting an active subwoofer.
Next to this section is the speaker output panel. This features four small 4mm binding posts, which take both banana plugs, and screw-down wires. The holes to insert the wires when using screw-down mode are vertical, not offset to the side, so wires have to be inserted from above for positive, and below for negative. There is, however, enough room to avoid bending these wires too sharply when they reach the shelf or floor. Next along are a power switch and fused IEC socket.
Underneath, the unit has substantial feet made of semi-soft plastic, which allow air to flow to the vented powder-coated sheet steel underside. It is important to ensure enough air flow to this area, so the ADHA24BT would be best situated on a shelf rather than an enclosed cabinet, unless other airflow arrangements are made.
BLUETOOTH AND USB
The built-in USB socket takes regular USB memory sticks, and reads MP3, WAV, APE, and FLAC files. No mention is made in the documentation of WMA, OGG, or AAC, and no success was achieved with testing, but this isn't really surprising.
The USB socket does not stream audio however (such as from a connected iPod), it's designed for reading files. Certain Android devices which can present as a USB drive may be suitable, however we have not tested the functionality. Instead, Bluetooth is better for streaming.
The Bluetooth is version 4.2, which should make it compatible with anything with a Bluetooth capability. We gave this a run and no device in the office had trouble pairing with the ADHA24BT. The use of an external Bluetooth antenna proves beneficial. Quite an uncommon feature, this was found to improve the range of the Bluetooth reception. Normally limited to around ten metres range, the Bluetooth link tested here dropped out at twenty-two metres which is impressive and definitely provides some user benefits.
5-40WRMS, 75W Peak
70Hz - 20 kHz
AMT with Kapton Diaphragm
B652-AIR Dayton Audio 6.5” Bookshelf Speakers
The LoudSpeaker Kit sent a pair of Dayton Audio 6.5” bookshelf speakers with the amplifier, which are their recommended pairing. The B652-AIR speakers feature 6.5” polypropylene woofers, and something called an ‘Air Motion Transformer’ tweeter. This technology is beyond the scope of this review, but the summary is that AMT tweeters respond very rapidly for their cost, giving sharp sound that is claimed to be comparable to much more expensive technologies. While those claims are hard to verify, we were certainly happy with the sound these speakers provide.
The internal crossovers are first-order, level-matched, high-pass, which means that there should be no volume difference between the high and low frequencies. The manual includes a detailed note about power ratings, distortion, and clipping. The maximum stated power is 40WRMS, with 75W peaks tolerated.
The speakers are presented in vinyl-coated chipboard enclosures with black cloth-coated grills. On the back, the speakers have spring terminals for wire connection, rather than binding posts. Despite assertions to the contrary from some quarters, this is perfectly adequate for speakers of this power, even if they were to be driven at 40W. Also on the back is a keyhole mounting bracket of reasonably thick pressed steel, screwed firmly into the chipboard with screws that can happily carry the weight of the speakers. Having said that, the manual cautions to ensure any anchors reach wood or masonry, not plaster or other linings. That’s just good practice anyway.
The combination of the Accento Dynamica ADHA24BT Hybrid amplifier and Dayton Audio B652-AIR bookshelf speakers performed satisfactorily and easily met expectations. The sound was clean and full, with plenty of depth and clarity. We tested a variety of music from metal to orchestral, Bach and Beethoven to Bad English and The Beatles, and were pleased with all of it. If you want something beyond the ordinary range of consumer-quality, made-for-TV audio systems, but don’t want to spend a fortune on high-end gear, then this is a happy combination.
Amplifier & Speaker available at The Loudspeaker Kit: https://theloudspeakerkit.com