Sonic Impact T-amp Review
IntroductionI received a Sonic Impact T-Amp just before Christmas as a gift for crossover work that I did for somebody. This will be a quick and short review but will reflect my opinion of the performance of this amplifier. I have tested it with 8 AA batteries and a 4 amp 12.5V DC very stable power supply and noticed very little difference, maybe a little bit in the bass department but not much although it clipped sooner with the batteries.
Initial Un-modified ComparisonWhen comparing amps, I use a relay switchbox between two amps to do an instantaneous switch between them. I compared the T-amp to my Yamaha A-700 100 W/ch integrated amplifier which is currently my favorite amp. The next best amp that I have heard relative to my Yamaha is my friend's McIntosh MC240 tube amp which is 40 W/ch. After both amps warmed up and I put my Yamaha in "Auto Class A" mode and you could barely tell the difference between my Yamaha and his McIntosh tube amp. The main difference was that the bass was a bit warmer and spacious with his tube amp while mine was more detailed and defined. After that comparison I felt much better about my amp and felt no need to upgrade in the near future.
I used the relay switchbox to compare the Yamaha to the T-amp with the batteries and with the power supply. With either comparison it wasn't real easy to distinguish between the two amps but in a blind comparison I could almost always pick out which amp I was listening to. If I had to generalize my comments on the differences I would say that the Yamaha sounds more "tube-like" than the T-amp. The T-amp has more detail in the midrange and frequencies above that. The bass is also a little bit better defined. The Yamaha has a smoother midrange and bass sound with a little less definition in the bass. These are the exact same things I usually hear when comparing a tube amp to a transistor amp. Now you must remember that my Yamaha inherently sounds more tube like especially since it sounds so similar to the McIntosh. With the 4 amp power supply the bass of the T-amp seems like it is just as strong as the Yamaha although it may be a little bit weaker at times in some frequency ranges. With batteries the bass is a bit weaker but only noticeable when doing a direct comparison with a more powerful amp. The imaging and soundstage characteristics were no different between the two amps.
I've read all kinds of recommendations on what type of power supply to use with the T-amp so I did an experiment. I hooked the T-amp up to my 4 amp power supply with an ammeter in series with the connection. I played the T-amp very loud until I could hear it clipping. The maximum current rating that I got was a short peak of 700 mA (0.7 A). So based on that measurement I think that a 1,000 mA (1 A) 12V power supply would be more than adequate to power this amp. I actually had it running distortion free at lower levels with a 200 mA supply but I don't recommend that you do this for longer listening sessions.
At $30 the Sonic Impact T-amp is a tremendous value. If it can compete with an amplifier worth several hundred dollars and hold its own that is really saying something. The only downside to the amp is the low power at around 10 W max into 8 ohms (15 W max into 4 ohms). Despite the low power I was able to get nice clean sound at around 80 dB from my listening position 2 meters away with 85 dB sensitive speakers and could go a bit louder without any distortion. To sum up my impressions I would say that this amp gives you more of a transistor amp sound with added detail and definition while my Yamaha sounds more like a tube amp with a smoother and very slightly less defined presentation.
The Sonic Impact T-Amp can be found at several vendor sites including Parts Express and Amazon for around $30. A 12V DC, 1000 mA "wall wart" type power supply can be found for less than $10 from several sources including Parts Express.
UPDATE:After listening a bit more, the attenuated bass of the T-amp is a bit more noticeable especially at higher levels and lower frequencies. I would say that most of the attenuation above 50 Hz isn't very apparent but below this point it becomes more severe. When I pushed the T-amp to its limits it wasn't nearly as smooth as my Yamaha and the bass attenuation was much more noticeable but at lower listening levels (closer to what I usually listen at) the differences aren't as apparent. Perhaps replacing the input stage capacitors and possibly the supply cap might improve the bass response but I'm not quite ready to do that just yet.
Modifications Performed and Initial ImpressionsI went ahead and replaced the power supply filter cap and input coupling capacitors. The stock supply cap is a 330uF, 25V value which I replaced with a 1,000uF, 35V value that I got for $1.59 at Radio Shack. I paralleled the existing input coupling capacitors with some 2.2uF value caps that I had in my parts stockpile. The surgery went smoothly but you must be careful when soldering to the ends of the SMD caps on the board (I used a 550 degree F soldering iron temp to be safe and not damage the caps or the board).
After the modification I noticed that the bass was much fuller and closer to that of my Yamaha receiver. I have yet to do another head-to-head comparison but I plan to once I get my new 12V, 5A regulated power supply together. I am currently using a 12V, 1A "wall wart" type power supply (Parts Express buyout) with a 12V voltage regulator in line to provide a constant voltage. Without this regulator the 12V supply output voltage varies according to the load. You get 14.5V without a load, 13.5V with the amp at idle and 12.5V with the amp drawing 600mA so I suppose it might drop to 12V with its rated 1,000mA load. If you plan to use a "wall wart" type DC power supply then I suggest you add a voltage regulator because it ensures that you get 12V under any load less than 1A.
Modified "Wall Wart" DC SupplyIf you plan to use a "wall wart" type DC power supply I strongly suggest that you use a 12V voltage regulator or else the output voltage will vary according to the load. The highest current regulators that Parts Express carries is a 12V, 1A LM7812 regulator. This would work great with any 12-15V, 1,000mA DC wall wart power supply and would ensure that you always get 12V at the output for any load under 1A. You could shop somewhere else like Digikey and find a higher current regulator and use a higher current power supply.
For my supply I used a PE buyout 12V, 1,000mA wall wort DC supply with an LM7912 which is a -12V voltage regulator but that is all I had in my basement stock so I just reversed the output connections to get +12V (I recommend that you go with the LM7812 or a higher current version if you plan to buy them). This supply works great with a constant 12V output under any load that the T-amp presents it. Under normal listening levels the TO-220 package for the regulator barely gets warm so I didn't use a heatsink. I think this is an inexpensive way to turn a cheap DC supply into a much more stable DC voltage source.
Final ShowdownWell, I finished building my 12V, 5A regulated power supply for use with the T-amp. I hooked up my relay switchbox to compare the sound of the T-amp to my Yamaha A-700 integrated amplifier except this time the T-amp has the capacitor modifications explained above and enough current to ensure that it has plenty of headroom in that category. I'll admit that there are a lot of better amps than the Yamaha A-700 but it is still a very good amplifier and can run in pure class A mode at the power levels that match the T-amps capabilities. The Yamaha A-700 has proven that it sounds just as good (almost indistinguishable) as my friend's McIntosh MC240 stereo tube amplifier and I've read that to get an amplifier today with the same build quality you would have to spend at least $1,000. But with all that said, the reason that I am using the A-700 in this comparison is that it is the best amp that I currently own.
The comparison was made with the volume level at around 80 dB at the listening position roughly 2 meters away from the speakers. I sent the CD signal into the Yamaha and hooked the T-amp up to the headphone output of the Yamaha. To match the levels the T-amp volume control needed to be set in the 9 to 10 o'clock range. This comparison was a lot closer than the previous one due to the change in the input caps on the T-amp which previously filtered the bass output a bit. This time the bass level is very similar between the two amps. However, there is still a difference in the bass character. The T-amp bass still sounds more detailed and defined while the Yamaha bass seems fuller and more dispersed. The difference is very subtle but it still exists. In a blind comparison between the two amps I can always tell which amp is playing by listening to the midrange character. The T-amp has very good midrange definition and detail while the Yamaha sounds smoother and maybe a tad warmer. This added midrange definition also translates into slightly better imaging for the T-amp for vocals and certain instruments. The treble is very similar between the two amps and I would say that they are similar enough that you might not be able to distinguish them if only high frequency information was fed to both amps. It really is the midrange detail and clarity that distinguishes these two amps but the difference is still pretty subtle (more subtle than some of the other amp comparisons that I've made). Another primary difference between the sound of these two amps was in the soundstage but I didn't discover this until I found the right recordings to make the analysis. The soundstage from the T-amp is a bit flatter which also makes the imaging seem better defined. The Yamaha has a deeper, more three dimensional soundstage that fills the room a bit more giving it a more spacious presentation and may be part of the reason that I feel that the T-amp seems to have better definition.
I would still have to conclude that the Yamaha sounds more like a tube amp with a smoother, slightly warmer midrange sound, looser bass and a spacious soundstage while the T-amp sounds more like a transistor amp with more edge and detail in the midrange, better bass definition and a flatter soundstage. I understand that these tube/transistor generalizations don't apply to all amps but they do represent a general trend between the two types of amps based on my limited experience. Since my Asterions, which I'm using to do the comparison, already have a slightly warm midrange sound I think that I really like the sound of the T-amp because it seems cleaner overall. However, I tend to prefer the more spacious, more three-dimensional soundstage of the Yamaha so it is difficult to pick a favorite. One thing about the Yamaha is that if you were to try to approach SPL levels in the upper 80's the extra power capabilities of the Yamaha will clearly give it the edge because the T-amp will begin showing signs of harmonic distortion and get very edgy and harsh.