Allo Volt+ D (Double) - DIY forums legend with horrible datasheet specs

[taisho]

With how much positive feedback this amp received on various audio forums, especially DIY forums, I decided to dig deeper. The most common praises were quality components used, general build quality, and of course the sound: "clean" and what I found alarming and contradicting the former - "warm".

The device has 2x TPA3118D2 in mono. It can be bought directly from allo.com here:
https://allo.com/sparky/volt-plus-d-amp.html

The datasheet is here:
https://www.ti.com/lit/ds/symlink/tpa3130d2.pdf?HQS=TI-null-null-alldatasheets-df-pf-SEP-wwe

Before you try to eyeball the figures on chart below:
1kHz @ 1W ========> THD+N% = 0.026 = 71.70 SINAD, not very bad for a budget amp
5kHz @ 5W,10W =====> THD+N% = 0.3 = 50.46 SINAD, uhm?

Here is another chart, this time with 3 different frequencies and full power range. 6kHz is very close to 5kHz, the worst offender from previous chart, it now peaks at 0.29 instead of 0.3 THD+N% so basically it's all the same:

Its competitor among poor man's amps TDA7498E may look relatively bad in 1kHz @1W: 65,51 vs 71,7 SINAD. However, its worst measurement at 1W, 4Ohm is 62.62 SINAD, much better than 50.46 in TPA3118D2:
https://www.st.com/resource/en/datasheet/tda7498e.pdf

Assuming that allo.com didn't pull off any engineering miracle, I think people enjoy the sound of this amp because of how it colors the sound like a tube amplifier. The distortion rises with frequency to very audible levels, what's visible on the 1st chart.

EDIT:

Thanks to @pthung for providing a link to Volt+ D manufacturer's measurements. I think that we can expect similar from Volt+ D (Double), a pity they are not provided.

Volt+ D measurements are at 20dB vs 26dB gain on the datasheet, not sure whether it can cause a significant difference. One thing is sure - for the budget, the measurements look good. Out of 1W, 5W, 10W, 15W, the worst one is 1W what I think should be the norm with a good design. SINAD below:

1W: 69.37
5W: 77.08
10W: 73.15
15W 74.42

Amir always uses 5W for reviews and FX502SPro with TPA3250 had exactly the same 5W SINAD.
However, it must be mentioned that TPA3251, the best measuring 325x (looking at THD+N), has datasheet SINAD of 84.44 @20W. Similar to other TPA datasheets, SINAD drops as the power rises due to frequencies around 6kHz, well before the clipping point. In the case of TPA3251 it's 72.77 @75W. It looks like a general problem with TPA that allo.com managed to completely eliminate. Not to mention significantly improving frequency response linearity.

The worst-case Volt+ D chart (1W):

It turns out that Allo Volt+ D (Double) has a high probability of being a good bang for the buck. On the other hand, 2 times cheaper Chinese TPA3251 without Bluetooth, for example, Aiyima should have better THD+N% at the same power and more power available. Frequency response won't probably be as flat and other problems like channel imbalance etc. are more likely to happen. The best would be Allo's implementation of TPA3251 or TPA3255, the rumor mentioned early 2020 as a release date, now it's September:
https://www.diyaudio.com/forums/ven...i-dual-lps-5v-3a-5v-1-5a-131.html#post6194765

 

[pthung]

Allo did put some measurement on their website but it's for Volt+, not Volt+D.
https://www.allo.com/sparky/volt-plus-amp.html
Volt+D is supposed to be better.

 

[sir_frigorifero]

being a dual mono version of the Volt+, Allo specified that measurements should be the same of the single board model, so Volt+ are to be considered.

i am currently using a volt+D and i should say that by now is the best budget amplifier between the ones i have tried. The sound seems similar to topping PA3 but with the lowest amount of hiss ever heard which for me is a real game changer.
another thing that may be considered for the evaluation of this amplifier is that it's big. compared to other class D chi-fi amplifiers from smsl or topping it is quite beefy, my smsl sa-50 is half the volume of the volt+D. maybe bigger board size should give better results since components are better placed to have less distorsion between them. just an hypothesis

 

[Biblob]

The Volt+D is a worthy contender to be measured by Amir, I think.

 

[al2813]

I wish we can get a good review. I bought the Volt +D based on the gloating reviews in the forums and combined with a Topping D50s, a Pi used as Roon end point and a pair of Fyne Audio F302 speakers, I am enjoying this setup a lot. A Bluesound Powernode 2i I had before was relegated by the Allo/D50s combo.

I am however looking to improve this setup. My living room setup will be on sale soon as I cannot use it for critical music listening due to many reasons. With the money I want to upgrade, but the lack of reviews is not allowing me to define an upgrade path.