My experiences with the USAmps AX-TU300C...

[JimJ 5,000+ posts]

First of all, I'd like to thank Jeremy (Flakko on CA.com and TeamSSA) for giving me the opportunity to audition this amp. The DIY community really needs more companies doing this with their products, to let people know what's out there and have a good base of unbiased reviews for people to make an informed choice. I'd also like to thank Matt Mullins (vladd) and Dave Edwards for their time and ears...having a few other people around during a review session really speeds things along.

Initial Impressions:

--------------------

The build quality is good, with the amp case and plexi bottom cover having a decent fit and finish. I can't help but notice small things that could have been changed with only a little more attention to detail - the main inductor in the power supply seemed loosely wound, thermal paste was smeared on the voltage rails sloppily. None of these likely make any audible difference, but if you're showing off the amp's internals, just something to think about. Features-wise, everything seems to be there, although I've been spoiled by the easy-to-adjust knobs on my PG Tantrums //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif.

One thing that might be a potential safety hazard is the design of the amp's power/ground terminals, which are far too close to the chassis of the amp. I could barely get a screwdriver in there without it touching the case, which leads me to wonder what would happen if someone works on it with a live circuit. A little more planning in this department could save burnt components as the amp has no onboard fusing. Not to mention save cosmetic wear on the chassis...

One last thing that caught my attention right away - on every page on the manual there's a clearly-marked warning not to use ground loop isolators with the amplifier. Now, I don't use them in my setups or plan to, but is the amp relying on grounding through the interconnects? It shouldn't matter if there's a 1:1 transformer in the low level input or not in a proper design...

Smoke Test:

-----------

I installed it in the E-150, ready to do an A/B comparison with the Tantrum T500.2 that normally handles my front stage. Test material was my standard SQ fare - trying to strike a balance between laid back, ambient music and tracks that will tear your eardrums with dynamic range and transients. Orchestral, jazz, selections from the MECA and IASCA test discs, rock, all were used. Tracks included:

John Williams - Star Wars, Revenge of the Sith/Main Titles

Diana Krall - The Look of Love

Vivaldi - Flute Concerto in D

Rebecca Pigeon - Spanish Harlem

Vangelis - Abraham's Theme

KMFDM - Inane

Dream Theater - Stream of Consciousness

London Chamber Orchestra - Reflections of Earth

Eva Cassidy - Wade in the Water

The Eagles - Hotel California (HFO)

The Eagles - The Last Resort (HFO)

Dire Straits - Brothers in Arms, Romeo & Juliet

In a word, the results were disappointing. On "Spanish Harlem", Rebecca's voice was much too sibilant and overbearing compared to the upright bass. On the "Revenge of the Sith" soundtrack, at about 3 minutes into the title track there is an onslaught of kettle drums...the punch and impact was missing. It sounded, well, like a recording. "Reflections of Earth" was similar, with the ending assault of drums starting at 8 minutes sounding laid back and veiled in the soundstage. Cymbals and hi-hat were there, but "where's the beef?" "Stream of Consciousness" should rip your ears off with dynamics and punch - it was like somebody had put a sock over the speakers. The opening of Eva Cassidy's "Wade in the Water" should be haunting, as the piano gently complements the finger snapping. With the '300C, there was noticeable hash noise with the piano keys, killing this effect. Time and time again, we'd be looking for stuff to hear its faults, which is *not* what you want to have happening when reviewing something.

The preamp stage seemed to be running "hot" with far too much gain - this is a reason why I don't like 12AX7-based circuits. Six volt preamp tubes such as the 6SL7's found in the Phaze Audio/Butler tube drivers have far more potential as good preamp tubes in a hybrid. I didn't have time to order GE 5751's beforehand, but I definitely think this amplifier is a candidate for that tube. For example: http://tubestore.com/gainfactor.html switching the preamp tubes from stock to 5751-type tubes will reduce the preamp gain by 30%. I'd be willing to bet that reducing the amount of gain will quiet the hash noise I heard and tame the amp down to a point where it'd be listenable. I had a few 12AU7's, but I didn't want to damage the solid state PA by having it compensate for all that lost gain.

As kind of a last ditch effort, I bridged it and put it on subwoofer duty driving the e12a.22, where it did an OK job. But that's hardly a demanding test for an amplifier's timbre and sonic quality.

Overall Thoughts:

-----------------

I'm not thrilled at all. While it does a passable job with high frequencies, vocals are unreliable and have a bad tendency to sound artificial. The snappy, dynamic punch of a solid state power amplifier - which, after all, is the entire point of a hybrid - was missing. It almost sounded like a single ended triode amp as far as being bass-shy, but even my 8 watt per channel SET's don't distort like the TU300C did with strong piano and other tough instrumentals. Given different tubes, I think it might be worth saving. But GE 5751's aren't economical for an amp manufacturer to include as an OEM part, and I'd go so far as to say the amp is unlistenable in its stock form.

It will do an acceptable job on your subwoofers provided they aren't too power hungry, but why spend that kind of money on a 300W monoblock when you can't hear the primary reason for getting it?

Skip this one.

~ Jim

--------------------------------------

Other equipment used for this review:

Alpine 9835 source unit

Memphis MSync6 6.5" components

PG T1200.1

eD e12a.22 in 1.5 cF @ 27Hz

--------------------------------------

Click to read more...

 

[JimJ 5,000+ posts]

Pictures are at the top of this gallery:

http://www.carstereos.org/gallery/browseimages.php?c=188

 

[flakko 5,000+ posts]

^^^ thanks for your review jimmy //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif even tho its a negative one, im glad its unbiased. kinda makes me want to try the AX600 see what the difference sounds like.

 

[Johnny Drama 5,000+ posts]

And this is an excellent example of how all reviews should be written.

 

[Beat_Dominator 5,000+ posts]

JimJ fancy's himself a young Jim Atkins //content.invisioncic.com/y282845/emoticons/tongue.gif.6130eb82179565f6db8d26d6001dcd24.gif

 

[zachzchw 5,000+ posts]

And this is an excellent example of how all reviews should be written.

X2.

Very well written and indepth review. Jim should make a career out of reviewing products.

Im suprised by the results, as I thought this line was supposed to bring Us Amps back to the forefront of SQ amps.

Props to Flakko as well, for not going the usual route of dogging a negative review of a company he is tied to.

 

[flakko 5,000+ posts]

actually the solid states have amazing sq capabilities as well. My AX2000 moves and controls my sub like no other amp i have used in the past

remember this is only one review. people have different tastes in the way the music is being produced. at first for me, thought the TU's sounded funky, but the longer i listened. the better it sounded. sean holland who used to work with usamps back in FL, still uses these tube amps in sq comps and wins.

 

[CBFryman2 5,000+ posts]

Even though this is a few days late. I will ask.

Instead of dropping the preamp gain by 30% which would effect the over all output of the amp and possibly over work the solid state part (correct?), could you use a much higher quality tube with less noise? Just an idea. I am thinking about buying a TU-4300 second hand and would not have a problem buying a pair of $20 tubes to improve the sound quality if I was not satisfied.

Also, how well will they hold up to 150dB? //content.invisioncic.com/y282845/emoticons/laugh.gif.48439b2acf2cfca21620f01e7f77d1e4.gif

 

[JimJ 5,000+ posts]

Good idea, but something tells me you could find the lowest-noise, most microphonic-resistant tubes out there and it would still sound like shit.

I'm not a big fan of 12AX7's for hi-fi, and this amp is the best reason I've ever heard for why...guitar amps that routinely go into clipping are another story.

 

[smd4life 5,000+ posts]

good review...

 

[CBFryman2 5,000+ posts]

Good idea, but something tells me you could find the lowest-noise, most microphonic-resistant tubes out there and it would still sound like shit.
I'm not a big fan of 12AX7's for hi-fi, and this amp is the best reason I've ever heard for why...guitar amps that routinely go into clipping are another story.

So do you think I should just steer clear of it unless someone reliable can throw some different tubes in and see how the amp responds? Or do you think my semi-untrained ear wont notice much of a difference over my IS2080? We share some of the same music intrests and vocals are rather important to me.

 

[SQBubble 10+ year member]

Pictures are at the top of this gallery:
http://www.carstereos.org/gallery/browseimages.php?c=188

hey man do u have the link of the worklog of that fiberglass work, the 2 12" mag with the hifonics amp, i remember i saw it long time ago??

 

[JimJ 5,000+ posts]

SQBubble - Do a user search for NDMStang65, he did the work //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

So do you think I should just steer clear of it unless someone reliable can throw some different tubes in and see how the amp responds? Or do you think my semi-untrained ear wont notice much of a difference over my IS2080?

It shouldn't need to have this done to it, but yes, NOS 5751's might be a hope for salvaging it. You certainly would be able to tell a difference...

 

[SQBubble 10+ year member]

SQBubble - Do a user search for NDMStang65, he did the work //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

It shouldn't need to have this done to it, but yes, NOS 5751's might be a hope for salvaging it. You certainly would be able to tell a difference...

thx found it.

 

[flakko 5,000+ posts]

So do you think I should just steer clear of it unless someone reliable can throw some different tubes in and see how the amp responds? Or do you think my semi-untrained ear wont notice much of a difference over my IS2080? We share some of the same music intrests and vocals are rather important to me.

i definitely noticed a difference between an MD41 and and the TU300C. at first, it sounded funky, but then i liked it //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif