Allo Volt+ Speaker Amplifier (tpa3118)

  1. AudioNoob
    If there is a standout amongst assembled Tripath/Class-D boards, it has to be the Volt+. Volt and the Rpi focused audio ecosystem it belongs seem to be a hobby project of Allo, an otherwise telecom manufacturer in India.

    With a little diy (if you don't buy it preassembled), it would be the perfect amp to power bookshelf speakers from your DAC/Headphone Amp Line out for shared listening sessions. It is no frills, doesn't need warm up, and is generally not finicky.

    **Largely building on the TI reference design for the TPA3118, even including the AM avoidance dipswitch, Allo uses Würth inductors and a generous spread of Film Caps and 1% resistors on an amp circuit designed to maximize fidelity. The choice of short and symmetrical paths over all else is evident in the the quirky I/O layout with jacks flanking three sides of the board, with the volume pot ending next to the input.

    Beyond the core of the amp, In addition to the the usual bootstrap snubbers and an anti-pop filter, *The Volt+ includes a capacitance multiplier that works to reduce the ripple from switching supplies to negligible levels. * Essentially it uses a capacitor as a small power buffer to eliminate fluctuations from the PSU.

    For the ones wanting to go over the top for an amp in this price range, and since this is head-fi, Allo offers a Stepped Attenuator (available pre-built as well as separately) to further the already excellent THD performance another notch. Speaking of THD, ALLO measures their amps at various load levels and provides extensive reports downloadable on their website, something you will definitely not find on other manufacturers’ at this price level.

    Anyhow, most of this can be found on their brochures and website, but I wanted to highlight the significant differences between the ALLO, and say, a SMSL or a Lepai T amp. I'm not comparing to various other tpa311* boards because I don't have any at hand, but it's basically like getting an upgraded board with a built in power filter. On to what it translates to in practical terms:

    Firstly, the VOLT+, should be infinitely more dependable thanks to the higher end components used throughout the board. You should expect to get a well functioning amp with well matched channels and low ESR/leakage. I’d rather pay the $10-15 extra up front and not enter the cheapo capacitor lottery, or worry about channel imbalances and non-linearity of improperly used smd components down the line.

    In comparing it to other amps such as the Q5 Pro, the Origain AD250, the SA36a-pro and the Pro-ject MaiA, the Volt consistently takes things a tiny step further, even in cases where all the amps are more than good enough to enjoy without pause. The most notable difference is the low-end reproduction, the volt+ acing through flabby, roaring bass passages with impeccable control, especially notable with smaller bookshelves already limited in their low end reproduction capabilities. Transients are another point where I can consistently pick the Volt+ out in blind comparisons, the decays of high hats lasting a moment longer, breath following vocals crystalizing in a shimmer before disappearing completely.

    Having said the above, the volt+ is definitely neutral in its reproduction. The AD250 for example, though using the same chipset and despite other forgivings, has a warm, and as far as these adjectives are useful, more musical sound singature. Essentially though, this is mostly the coloration afforded by certain distortions which I feel are better left to slight, controlled EQ adjustments, for every source and speaker combination is going to behave differently.

    Putting it all together, the VOLT+ is a no brainer if you value sound quality above the convenience of having a mini-receiver, or if you have a focused system with a single input and no need for a sub out. Besides slipping it into your headphone dac+amp setup, you could pair the VOLT with the ALLO Boss + Rasberry Pi, and for under $100, have yourself a network receiver that can see you through a few speaker upgrades as it should handle most things you throw at it under $500-750 as well as anything else.

    I tried the volt+ with a higher end industrial SMPS but could not hear a difference from the one provided by Allo. I do not have a suitable linear PSU at hand, but I feel that the capacitance multiplier is working well to nullify weaknesses inherent to switching supplies.

    The seperately available power supply is 19V, but you can go up to 26V if you need to drive less sensitive speakers, and to drive them loudly. However, the chipset really does better staying under 25W(8ohm) per channel or so, and below 24V. Save for some crazy bookshelves, I can’t see the point in stressing the voltage as paired with the Dali Zensor Picos, far from a sensitivity champion at 84db, the volt provided more than ample power with the 19V supply, going louder than I could bear shortly past the one o’clock mark. Also bear in mind that defining a useful volume range where you don't quickly out your hearing, you will have more control over the volume as there is no way to set it between steps in a stepped attenuator setup. Furthermore, stepping up to 24V yields audible change in SNR in all the tpa 311* amps that I have, all reproducing lower ranges with more control around the 19-21V level. Lastly, If you do decide to go 24V and intend to use it for long hours, I would suggest adding a wide/tall heatsink.

    Where the amp falls short in comparison is convenience, and to be clear, this is not a place where the volt even bothers to try, a bit apples and oranges, comparing stereo receivers to stereo amplifiers. With something like the Q5(or the AD18), you can trade in a notch in sound quality to have multiple inputs, a built in DAC, subwoofer out, and a remote to controlling the whole setup from the cradle of your couch. I would not count on any of the others to last more than a couple years, but if your priority is to build it into your home entertainment system with budget speakers, I could see priorities balancing out in going with another solution.

    I had the Volt+ prebuilt by Allo with a stepped attenuator. It comes in a case made from laser cut acrylic with a relatively large footprint due to the pillar/stacking design they scaled up from their raspberry pi cases. As I mentioned before, there is not much to note in the interface as this is a one input one output box with only a volume pot for control. As it is a stepped attenuator, the knob clicks the assembly into position to route the signal through a fixed set of resistors, the nature of the setup makes such devices harder to turn and the volt+ would really benefit from a larger/duckbill knob to facilitate this.

    I had a couple issues with the assembly of my prebuilt unit. One issue that I had with my build was that the speaker posts were reversed, forcing you to cross the wires in the back with the left speaker posts on stage right, and the right speaker stage left. When I opened up the unit to reverse them (the speaker posts are screwed, not soldered), one of the solder points on the board failed, immediately followed by the paired cable when I tried moving the first one to see what happened. Turns out the cabling used -even at the high level stage- is a super dinky, few tinned strands in a thick jacket sort of affair. To top this, all the said cables were zip tied together, along with the DC input, running parallel below the board, with a potential for crosstalk and noise. Finally, the soldering of the cables from case mounted components to the board was a little sloppy, one signal cable almost touching the hole for the signal cable of the other channel. **Given all this, I would recommend getting the regular volt+ and building your own case, or upgrading the cabling on the allo one. Allo responded to my comment, noting that they will look into upgrading the cabling.

    It is an easy recommendation if you know what you need and find the absent conveniences an unnecessary surplus. The unyielding performance and dependability of the amp –the issues with the built version nonwithstanding– more than deserves the inconvenience even if you have to DIY some additions.

    *disclaimer, allo provided the amp, though I owe them nothing in exchange and told them from the get go that I would post an honest, if not critical, review.

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