• WANTED: Happy members who like to discuss audio and other topics related to our interest. Desire to learn and share knowledge of science required as is 20 years of participation in forums (not all true). Come here to have fun, be ready to be teased and not take online life too seriously. We now measure and review equipment for free! Click here for details.

Allo Volt+ D Amplifier Review

amirm

Founder/Admin
Staff Member
CFO (Chief Fun Officer)
Joined
Feb 13, 2016
Messages
35,315
Likes
134,775
Location
Seattle Area
This is a review and detailed measurements of the Allo Volt+ D class D amplifier. It was kindly sent to me by a member and costs US $129 in this "dual mono" configuration with stepped attenuator.

I am not a big fan of these clear cases but in this case, pun intended, it works!

Allo Volt+ D Class D Amplifier Audio Review.jpg


Hard to take a picture of it though without heavily accentuating dust and such that normally is not visible:

Allo Volt+ D Class D Amplifier PCB TPA3116.jpg


Dual TI TPA2116 class D amplifiers are used plus a front-end switching power supplies to generate the required plus and minus supplies.

Not that no power supply comes with this amplifier. You have a choice of what you put in there. I used my lab power supply at its max setting of 31 volts and 3 amps. It could use more than 3 amps with 4 ohm load as the power supply current limited near max power sweeps. It was fine with 8 ohm load though as that doesn't need as much current.

There is no remote control so this is really a desktop amplifier.

There is a gain switch below that switches between 19 and 26 dB. I used the default 19 dB which works well with desktop DACs that have no trouble producing near 2 volts you need for max power.

Overall the Volt+ D makes a very positive impression with respect to looks and build quality.

Amplifier Audio Measurements
As usual we start with our dashboard:

Allo Volt+ D Class D Amplifier Audio Measurements.png


This is nice! Budget class D amps routinely produce SINAD in 55 to 65 dB and here we are well above that at 84 dB:

Best audio amplifiers.png


I was also impressed with how low the noise floor was at 5 watt playback:

Allo Volt+ D Class D Amplifier SNR Audio Measurements.png


Many amplifiers fail to achieve 96 dB which is my target for this level of playback.

Crosstalk is superb, better than just about any amp I have tested recently:

Allo Volt+ D Class D Amplifier Crosstalk Audio Measurements.png


Frequency response has a tiny bit of roll off at 20 kHz:

Allo Volt+ D Class D Amplifier Frequency Response Audio Measurements.png


As I noted in the introduction, with 4 ohm load my power supply lacks enough current so I also tested with one channel driven:

Allo Volt+ D Class D Amplifier Power into 4 ohm Audio Measurements.png


So it seems that getting the 60 watt advertised power level is possible.

Taking advantage of onboard capacitors, I ran my burst test:

Allo Volt+ D Class D Amplifier Peak Power into 4 ohm Audio Measurements.png


So even in stereo you have over 60 watts, going to nearly 90 watts with one channel.

Power into 8 ohm load is naturally lower:

Allo Volt+ D Class D Amplifier Power into 8 ohm Audio Measurements.png


Notice that noise floor is very low contributing to very good response at lower power levels.

Varying the frequency gives us the following power levels and distortion:

Allo Volt+ D Class D Amplifier Power into 4 ohm vs frequency and distortion Audio Measurements.png


At or below 1 kHz response is excellent and frequency independent. Above that it varies which is typical of many class D amps.

Finally, I ran a spectrum analysis without my usual class D amp filter in the path:

Allo Volt+ D Class D Amplifier 1 kHz FFT switching Audio Measurements.png


Wow, TI put some clever filtering/design in there. Usually the switching frequency is down just 10 to 2 dB from our main tone. Here, nothing rises above -88 dB or so! TI advertises that the amp will not interfere with AM radio and it definitely won't.

Conclusions
The Allo Volt+ D amplifier is a delightful surprise. Careful design has elevated the performance of these switching "chip amplifiers" to that of mass market hifi/class AB designs. Yet, it runs cool and costs very little. Yes, you need an external power supply and that is the only flaw I see with going with this solution.

Overall, I am happy to recommend the Allo Volt+ D for its nice and elegant design and performance especially at this price.

------------
As always, questions, comments, recommendations, etc. are welcome.

Good news: my garden helper text me that he is available to come and pull the weeds. Hooray! I don't have to break my back doing that. Alas, he doesn't work for free so I need money by end of tomorrow to pay him. He makes much more than me per hour so please donate toward this good cause using: https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/
 

Doodski

Master Contributor
Forum Donor
Joined
Dec 9, 2019
Messages
8,266
Likes
7,699
Location
Canada
Nice job on the volume control. Are those voltage regulators with voltage adjustments. The blue pots.
 

restorer-john

Master Contributor
Joined
Mar 1, 2018
Messages
7,815
Likes
20,838
Location
Gold Coast, Queensland, Australia
It does. If you don't need full power though, one of those laptop power supplies could do the job.

I think most people will have some 19V supplies from old laptops lying around. Allo even list a 19V supply as an add-on. That said, the difference in power output performance will be stark.

Just for fun, you could consider running a power output test on say a 19V 60-90W typical laptop brick to give people a real world idea.
 

restorer-john

Master Contributor
Joined
Mar 1, 2018
Messages
7,815
Likes
20,838
Location
Gold Coast, Queensland, Australia
It looks like they have a bridge rectifier up front behind the DC input jack. This is usually done to allow operation no matter what polarity the DC jack has. Done to protect against people not looking at the polarity markings on their power brick. Thing is, you lose 1.2V for that convenience.
 
OP
amirm

amirm

Founder/Admin
Staff Member
CFO (Chief Fun Officer)
Joined
Feb 13, 2016
Messages
35,315
Likes
134,775
Location
Seattle Area
Nice job on the volume control. Are those voltage regulators with voltage adjustments. The blue pots.
The power transistors are Mosfets. So seems to be the output stage of the switching power supply. The pots then may be setting the voltage as you mention.
 

JohnYang1997

Master Contributor
Technical Expert
Manufacturer
Joined
Dec 28, 2018
Messages
7,005
Likes
15,741
Location
China
The power supply is the largest challenge in amplifier design. Not only it gets expensive, but also it usually degrades performance a lot in the design. Magnetic interference, leakage current you name it. And well it's simply bypassed here. I am curious to see the performance with power supply from allo or some other power supply people would actually use.
 

JohnYang1997

Master Contributor
Technical Expert
Manufacturer
Joined
Dec 28, 2018
Messages
7,005
Likes
15,741
Location
China
I didn't see description of the circuit on the web page. My guess is that it's a virtual ground/single supply design + mosfet power on/off switch. There's no reason to convert dual rail on the board. And the chip should be using BTL connection / dual mono. Hence double the voltage swing like almost all class d amp chips do.
 

Doodski

Master Contributor
Forum Donor
Joined
Dec 9, 2019
Messages
8,266
Likes
7,699
Location
Canada
I'm not sure there is tpa2116 ic in Ti portfolio?
It looks like there is not a TPA2116 made by Ti.

EDIT: Perhaps it is a discontinued model but as I mentioned Ti does not have it listed.
 
Top Bottom