So, I did a gig on Friday at the lovely La Mesa Wine Works. A quick thank you to them. They are a great venue staffed with great folks.
In lieu of the usual gig report (it went well) I wanted to drop a review of TC's dirt-cheap BQ500 "Thrust" bass head, as I bought one as a backup and wanted to see how well (or poorly) it worked outside the bedroom, live and in front of people. The other two threads I could find on the amp weren't that helpful, and a lot of folks got wrapped around the axle with the "active/passive" switch issue and some other stuff that, while, really annoying, was not germane to the essential question of "is this a gig-worthy bass head or not?"
The answer to that question, by the way, is "yes".
The partial answer to the second question that everyone will ask is that, on my amplifier, the "active/passive" switch is wired properly and does the gain drop that you expect it to. I did say partial answer as there are some other issues surrounding the gain stage and I'll try to address them as best I can.
Pros:
$199.
Loud enough to bury a volume-crazed guitar player and a drummer who should use nunchaku instead of sticks.
Pretty simple to operate.
100-240V power, worldwide operation (literally all micro amps should be able to do this, most don't).
Cons:
Not 500 watts as you and I know the term.
Some really questionable build decisions.
Heavy! This is a five-pound amp, my GK with double the power weighs far less. And is smaller.
The name. "Thrust". C'mon, guys.
EXPLANATIONS:
Power: advertised as "500 WATTS PEAK!". Using the old radio guy's rule that RMS should be .707 of the peak power, using PEAK*.707=RMS gives me an RMS of 353W@4 ohms. 175-200W@8 ohms. I think that's reasonably close to reality. It stays clean forever, I could not get ANY dirt out of this amp one way or another. Since I don't do dirt, that was fine.
The "really questionable build decisions": First, a signal flow diagram...
View attachment 3421412
Some of you will notice that not everything is where you'd think it should be.
Input: self-explanatory.
Gain LED: plugged in, cranked it, got a bit of light on peaks. OK, good. Turned it all the way down. Still lighting on peaks. Cranked it all the way up, still only lighting on peaks. Repeated with buddy's active Warwick. Mostly solid light on zero, half, and full gain. Only explanation:
the circuit controlling the gain LED is BEFORE the Gain control. Which renders it quite useless. You'll have to do it by ear.
Gain control: Did it by ear. Can't make this amp clip the input stage with anything I have (my basses are all pretty low output). I ended up running it cranked up to about 3 o'clock on the knob. Did not try with the Warwick bass (we were in the middle of a gig!) This amp wants to be clean. Probably great with pedals.
Thrust LED: on when "thrust" compressor is on. Off when it is off. The "lights on triggering threshold" thing they talk about in the manual may have been their intent, but that's not how it works. More on "Thrust" later.
EQ: Works as expected, I don't like the EQ points. Bass is great. Low mids - too high (400HZ). Hi-mids also too high (1.6KHz)- really annoying. Treble - at 10KHz and up, this is literally a "hiss" control. I run it at about 10 o'clock. Just enough for some zing. I might add that this amp is one of the quietest micros I've ever run across.
"Thrust" control: again, the name! Try some class, TC.
With that complaint out of the way, this is an interesting knob. Because of where (so far as I can tell) the compressor is in the circuit, everything affects "thrust" and "thrust" affects everything. Change gain, it changes the compression (that's expected). Change EQ, it changes the compression, and that is NOT expected behavior at all. The good part is that you can get very different sounds out of this head with little experimentation. The bad news is that it's almost impossible to replicate those sounds, small movements with lots of compression make huge changes in the sound. The only way you're going to replicate sounds is just don't use the compressor at all.
CONCLUSIONS:
Suggestions for TC: ditch the Gain light and ditch (or put it pre-EQ) the "Thrust" compressor. A $199 no BS micro head that puts out enough power to legitimately gig with should have you guys owning the market, but you've made this amp too complicated and committed the unpardonable sin of giving rookie users an instruction manual that really does not bear much resemblance to the product that it was written for.
For me: It's a good amp. I may well keep it.
While I agree that 5 lbs isn't heavy, I will also say that I was a little surprised at the heft of this lil bugger, given its size. It IS a dense little amp. I've had other class D amps that are more powerful and bigger in size, but similar and even lighter in total weight than the BQ500. It's not heavy, but it IS heavier than expected, given its competition. 
