Download Cerwin Vega Stroker 1000.1 Amp Review – part 2

Cerwin Vega Stroker 1000.1 Amp Review – part 2
Big Numbers, Small Price
by Eric Guarin, Aug 24, 2010
S1000.1 Amplifier
Now that we’ve raised expectation by declaiming its long and proud heritage, let’s see if the
Cerwin-Vega Mobile Stroker 1000.1 rises to the occasion or goes down in flames. The amp has
a fairly utilitarian look: a basic black finned heatsink with bent metal mounting feet. Things are
spruced up by the fins angling downward along the sides, which you don’t see every day. A nice
brushed satin finish and contrasting dark red brushed satin insert with the Cerwin-Vega Mobile
name give a sleek feel. Connections for power and speakers sit at one end, with audio inputs
and controls at the other end. The end panels don’t quite exactly match the shape of the
heatsink, so for next time I’d suggest the extrusion should overhang those panels and cover the
wires. For a one-channel amp, the S1000.1 has a number of features:
•Since this amp specializes in bass, the lowpass crossover always operates. You can set it from
40-250 Hz.
•A subsonic filter complements the lowpass. It seems ironic that the company which shot to
fame simulating ground tremors would nowadays be filtering out the very low frequencies-but
subsonic filtering should almost be mandated by law for typical vented box applications. For
those who don’t want it, set it down to 16 Hz to minimize effect on the sound.
•The Stroker 1000.1 also features BASS BOOST, because without it, surely the Apocalypse
would come sooner. To give credit to CVM, at least this version features adjustable frequency
and hence becomes more customizable to the customer’s taste. Or, lack of taste, for some
customers I’ve met.
Users can adjust the bass in question via a Remote Level control. How much extra is that, you
ask? Nothing, it comes in the box for free! Hey, nice one Cerwin-Vega Mobile!
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•A phase control (actually polarity) switch can help you tune the system, plus…
•For even more power you can strap two of these monoblocks together, using said polarity to
invert one of the amps. You should then get twice the power into twice the impedance-whatever
one does into 1 ohm, the pair will put out twice as many watts into 2 ohms. Just like bridging a
2-channel amp, but in separate chassis. One remote level control controls all the amps in the
chain, also very handy.
•Power and speaker connections work by sticking the wire into beefazoid circular hole
receptacles, then cranking down a screw with an Allen key. Self-installers, be aware the Allen
keys are NOT included. You need a METRIC set: don’t strip the screws on accident trying to
use American sizes! The screws seem to be made of a rather soft metal and caused us some
problems connecting everything, since I didn’t realize immediately they were metric. Also note
the speaker wire connections have the pluses and the minuses next to each other, not in pairs,
so double check that if you get no sound. (Not that that ever happens to me, ha ha…)
•Want to know why your amp isn’t playing? Could it be low voltage? Shorted Outputs? SDA
comes to your rescue! Self Diagnostic Analysis blinks the power and protection LEDs at
different rates depending on what fault occurs. A secret decoder type table in “S1000.1 White
Paper Small.pdf,” posted at Cerwin's website, lets you diagnose the problem and react to solve
it. Kudos for this clever solution to inform users without adding much cost.
•Clipping adjustments: as you’ll see later, subwoofer amps can easily be set up to clip too easily.
Again the White Paper comes to the rescue with a nicely described procedure to set the gains in
order to get high output without continuously slamming the amp into hard distortion.
•Overall size? 9.25” deep, 2.125” tall, and 15.75” in length (235x54x401mm). Not compact but
not huge. That yields 0.084 watts per square centimeter* of mounting surface. For comparison,
our test of the Phoenix Gold Ti2500.1 showed 0.202 W/cm2., albeit at a larger size and price.
(*Our assumption is that folks don’t care much about how tall this type of amp is. Do you agree?
Disagree? Comment below please.)
A Class-ier Design?
Most audio amplifiers are either the traditional Class AB, which amplifies the audio waveform
directly, or Class D. Class D acts more like a radio station and modulates a high carrier
frequency with the audio; the speaker just “sees” the audio part. Many think Class AB sounds
cleaner; Class D offers much better efficiency. Gee, wouldn’t it be nice if you could get the best
of both worlds? Of course, designers constantly try to do just that.
Military contracts often serve as big motivation, leading to Class G circa 1962.** Hitachi first
applied this class to audio with their 1977 Dynaharmony HMA 8300 power amplifier.*** Think of
Class G as a kind of stack of Class AB amplifiers with different maximum output rail voltages. If
the output power gets too big, the power supply switches to a higher voltage supply, which can
swing more power into the speaker. Pat Quilter, a founder of the mammoth pro audio company
QSC, invented a further evolution of Class G by creating an amplifier where the power supply
voltage actually tracks the signal, outputting just enough voltage to avoid clipping.
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Yeah, Yeah, What’s The Point Already?!
In a nutshell, Classes G & H aim to achieve higher efficiency than Class AB but with the same
sound quality-in particular, avoiding distortions and high frequency junk which can occur with
Class D. An example of the efficiency gain versus Class AB can be seen in this graph:
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The graph is for a particular product sold by ST Microelectronics, but the general trend applies
to any good Class H implementation. (Class G would look vaguely similar but stepped instead of
smooth). We shall see how well CVM’s implementation works in a few paragraphs. By the way,
if you noticed we only measure efficiency at full power, that’s OK. CAE commissioned a highly
scientific Gallup Poll of 12,486 car audio enthusiasts, which showed that only a measly 1.3%
ever run their sub amp at anything less than full power. All right, actually the poll really consisted
of me and a buddy chatting over a few beers, but we’re pretty sure that’s what the result would
have been. Plus, at lower power, you’re using lower power so it doesn’t matter as much.
Low Power Tests
Speaking of low power, we ran our usual battery of tests. After running the low power tests, the
amp remained cool enough to hold your bare palm on. That’s better than many other amps,
which after a while of just being on get too hot to touch. Results can be seen in this chart:
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Lest anyone think we forgot some testing, remember this is a MONO amp. We therefore
adjusted the frequencies for:
Distortion & Noise
Certainly the low distortion claims for Class G/H are realized in this implementation. The
S1000.1 indeed shows maybe an order of magnitude less distortion versus Class D amps we
have measured. Likewise, the residual noise levels are way below one watt, indicating a very
clean amp. Distortion and noise are much less audible at subwoofer frequencies, but it’s still
nice to know this amp applies a very clean signal to your speakers.
Gain
Gain matching between channels does not apply, but we did check the gain range: maximum
output can be achieved with inputs ranging from a bit over 4 volts to less than 0.1 volts (bass
boost set flat, subsonic to 16 Hz, lowpass to 250 Hz). At the maximum gain setting, if you
additionally maxed out the bass boost, you could conceivably clip the amp with just 2 millivolts.
Yike! Good thing the S1000.1 has clipping indication for setup. But subwoofers need a lot of
gain in some systems, so it’s nice to have it available in case you need it.
Frequency Response
All the power won’t be much use if the amp doesn’t respond at low frequencies. So we checked
out the bass-ic response curves. If the frequency response seem narrow, that’s because-it is!
Subwoofers cover a pretty narrow range of frequencies. The low cutoff measures more like 20
Hz than the indicated 16 Hz-probably interaction with the lowpass shifts the frequency. For
instance:
•Setting the subsonic to the halfway position does give a -3 dB point about 60 Hz as expectedbut you have to use the original 0 dB as a reference.
•Changing the lowpass to halfway results in -9.3 dB at 125 Hz instead of -3 as you would think.
That’s not a mislabeling problem or unit defect. Rather, we can see a very good illustration of
how the different circuits interact:
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That interaction also becomes apparent in the Vega Bass boost curves. Instead of the smooth
mountains you might expect, the curves look like a bunny with ears or Batman or something.
Again, this is because the boost circuit has been affected by the highpass and lowpass, skewing
the bass boost asymmetrically:
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While the results may look odd, they merely reflect the reality of what happens when you are
both boosting and filtering near the same frequencies. And, all the curves look smooth, without
any weird bumps that show up in some competitors’ products. Weird bumps tend to indicate
weird acoustic phase, though not necessarily a problem you can hear.
Power!
OK, enough of the small stuff, on to the big numbers. Let’s see just how big they are:
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Big Bang Theory
CVM exceeds the big 1000! As you can see from the chart, the S1000.1 power output droops
somewhat into low impedances, but nevertheless exceeds rated power even at 50 Hz into 1
ohm. We use 50 Hz specifically because it’s tough on power supplies, and some amps unstably
clip more and more and more. The S1000.1 remained stable during this test, to CVM’s credit.
Bang For The Buck Theory
If your personal theory relies on the most watts for your dollar, the Stroker 1000.1 amp definitely
contends for your attention. At their published retail price, you get a lot of boom for your buck,
and some street pricing can be seen even lower. On the other hand, if you don’t believe all watts
are the same, and your wallet feels too heavy, you might be more comfortable with the
aforementioned Phoenix Gold 2500.1 monoblock. That amp exhibited almost no droop and had
a more extended low end. Then again, the price and size both come in rather larger than this
CVM; you could almost strap a pair of S1000.1s together for a similar package. Such as the
tradeoffs to consider in car audio-but how wonderful that we have so much choice! As for the
dollar-per-decibel ratio? Well, that’s just a tool to remind you that power works logarithmically:
double the power gives a bit more maximum loudness. Ten times the power sounds only “twice
as loud.”
Stroker 1000.1, Is Thy Name Efficiency?
After all the explanation about Class G/H, we can see the bottom line: the S1000.1 uses more
current than Class D units we’ve measured. That’s not an inherent feature of Class G/H, as you
could see in the graph shown earlier. The particular implementation and parts used by CVM
yield this level of efficiency. Their white paper shows slightly better numbers than we got, but
under somewhat different measurement conditions. Regardless, this Stroker uses significantly
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less current per watt than a Class AB amp and in a more compact package. Readers who don’t
like “Class D sound,” rejoice at this alternative!
Conclusion
Although I never met him, I somehow feel Gene Czerwinski would have approved of this amp:
good performance, good price, definitely different, all business. Nice to see Cerwin-Vega Mobile
appears to still embody their founder’s values. Next up, we’ll see what they’ve done with an amp
that has “no output devices.” Actually, there are output devices, but they’re inside a chip. Tell ya
all about it next time.
*Special thanks to daughter Connie Czerwinski and former employee Ken Koga for anecdotes
and photos.
**From the interesting looking book THE live sound manual, by Ben Duncan. (from music book
publisher www.Backbeatbooks.com, San Francisco, 2002, ISBN 0-87930-699-8)
***From QSC Audio’s very handy Glossary of Audio Terms:
http://www.qscaudio.com/support/glossary/!
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