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Author Topic:  Crate Power Block Amp = Zero Point Energy Source???
Paul Arntson


From:
Washington, USA
Post  Posted 3 Jan 2007 8:04 pm    
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First, the backgoround:
I am in the process of finding a portable practice amp.
The criteria are:
1) cheap (<$200)
2) Light (less than 32 lbs)
3) Loud (over 50 W RMS)

So far the two front runners are the Fender Deluxe 90 and the Crate GT80. Now to get to the point of this post:

Naturally I looked at the specs for the Crate Power Block.
At first I was amazed that they spec the power at 10% THD. Is this amp good for any power at all at lower distortions?

Then my hat flew off when I saw that the input is only 35 watts. Are they getting something for nothing here? Is there something that my college professors didn't tell me about power in being less than power out by a factor of 4.28?

Can this thing only maintain rated power RMS for the time it takes to discharge the filter capacitors? (A very sketchy modification of the term RMS...)

If it's really 150W RMS it should reach the threshold of pain and hold it there with a sine wave.

I mean, I know it's a class D amp and so it has to be different, but come on. What are the REAL specs?
I'll go try one out on Friday just because they are so cute, but I am seriously turned off by the phony specs.

(Legal disclaimer)The following words are copied from the Crate(c) website under Fair Use provisions for review and discussion purposes only, and shall not be construed to be unauthorized copying of copyrighted information.

"CPB150 TECHNICAL SPECIFICATIONS:
Output Power Rating Mono 150W RMS @ 10% THD @ 8 ohms
Stereo 75W RMS @ 10% THD per side @ 4 ohms"
.......

"Power Requirements 120 VAC, 60Hz, 35VA"...


Has anybody else noticed these inconsistencies and maybe has an answer to my confusion???
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Fred Shannon


From:
Rocking "S" Ranch, Comancheria, Texas, R.I.P.
Post  Posted 3 Jan 2007 8:13 pm     Blow your hat in the creek
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Paul I have two of the little critters, and I didn't pay any attention to the specs. I bought them from Musicians "Friend for 100 bucks a piece just to use for student work, but because they are so light (4 lbs) I decided to try one with a 15 inch EV speaker. I was amazed at the output power. They're not much in the equalizer business but power wise, they're darn tough. I've been using that set up when I play a few close dates (in case of a crap out I can get to my Nashville 112's quickly). The Crate hasn't failed yet, and I'm only pushing it with a Matchbox 7a and a Lexicon MPX 100 Preamp. Sounds good to the average user and listener. And at the price one can always use it for a backup PA or instrument amplifier. My .02 Cents.

Phred
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Darvin Willhoite


From:
Roxton, Tx. USA
Post  Posted 3 Jan 2007 8:20 pm    
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I agree with Fred, no matter what the specs say, this amp is loud and sounds good for a $100 amp. Even though I bought mine before they came down to $100. Sad Crying or Very sad
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Darvin Willhoite
MSA Millennium, Legend, and Studio Pro, Reese's restored Universal Direction guitar, a restored MSA Classic SS, several amps, new and old, and a Kemper Powerhead that I am really liking. Also a Zum D10, a Mullen RP, and a restored Rose S10, named the "Blue Bird". Also, I have acquired and restored the plexiglass D10 MSA Classic that was built as a demo in the early '70s. I also have a '74 lacquer P/P, with wood necks, and a showroom condition Sho-Bud Super Pro.
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Jay Ganz


From:
Out Behind The Barn
Post  Posted 3 Jan 2007 8:42 pm    
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This little amp surprised the heck outta me, I'll tell ya.
For 99 bucks, I figured I'd give it a shot.
I use it along with my PODxt & it sounds pretty darn good.
In fact, I made up a small combo amp using the CPB-150
and a lightweight neo speaker that I'll be posting about soon
along with some pics as well.
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David Mason


From:
Cambridge, MD, USA
Post  Posted 4 Jan 2007 2:07 am    
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I just played my New Year's six-string guitar gig with a Digitech Genesis 3, into the BACK stereo inputs on a Powerblock, into two Peavey 112E 12" speaker cabs. It kept up with a drummer fine. If you go into the back inputs, you bypass the front EQ and "gain" control and it's a pure switchmode power amp. The Genesis is like a poor man's POD - the only problem I have is that all the volume control comes from the Genesis too and it has a teensy little volume knob on the back (in charge of 150 watts) so I stuck a stompbox DOD compressor in front, with no compression on, just as an additional volume control.

I think a 18K steel guitar pickup straight into the front of a Powerblock could easily overwhelm their preamp circuit, but if you can get your steel output down to a preamp signal somehow and go into the back inputs, it will work fine. This switchmode stuff is going to revolutionize live amplification, along with the neodymium speakers. (World, Stewart and the new Fender Jazzmaster are all switchmode amps too). The switchmode circuits don't follow the "normal" rules of amplification, so I'm not sure if you can evaluate them using tube-oriented concepts? - I'm pretty sure it doesn't even have filter caps.... It's loud as heck, that's good enough for me! It's also dirt-cheap, and constructed by workers who may have been making lawnmowers or towel racks (or jet-fighter parts Shocked) yesterday, so a backup does seem prudent.


Last edited by David Mason on 4 Jan 2007 2:52 am; edited 1 time in total
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Jack Stoner


From:
Kansas City, MO
Post  Posted 4 Jan 2007 2:43 am    
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I used mine New Years Eve, with a POD XT (into the power amp in jacks) and two 12", 8 ohm (not 4 ohm) speakers. It held it's own and was a helluva lot lighter than my rack preamp/effects processor/power amp. I had to double on lead, with my Tele, and steel and wanted more than the Nashville 112 for lead.

I was debating on the rack or the POD XT/Crate and decided to try the Crate. It surprised me.

BTW, I was in the local (Tampa) Guitar Center and the salesman had a stack of the Crate Power Blocks and I asked him for a price and it was "$79.00 out the door".
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Kevin Ruddell

 

From:
Toledo Ohio USA
Post  Posted 4 Jan 2007 2:56 am     crate
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I got one from MF to try and my Tech 21 preamp overdrove the input no matter the settings. I've used the Tech 21 with many units and never had this mismatch problem . The uncolored sound of the power block was pretty bad to my ears . I returned it
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Len Amaral

 

From:
Rehoboth,MA 02769
Post  Posted 4 Jan 2007 9:17 am     Power Block
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I use the Power Block for small gigs and practice with a Goodrich LDR volume pedal and a few Boss reverb and delay pedals and a one 1501-4 speaker. The specs say not to use a 4 ohm speaker but it operates fine with no problems and plenty of power.

To add a monky wrench to this mix, you every have an amp setup in the house and you think its sounds great only to get to the gig and be somewhat disappointed? I was not excited how the Power Block sounded in the house only to very surprised with the power and tone this little thing put out at a gig.

For a $100.00 with a padded gig bag it's a good deal.
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David Doggett


From:
Bawl'mer, MD (formerly of MS, Nawluns, Gnashville, Knocksville, Lost Angeles, Bahsten. and Philly)
Post  Posted 4 Jan 2007 11:11 am    
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Paul, to address your original question, the output "watts" and the power requirement "watts" are completely different measures, even though they have the same name. The output watts are a measure of the nominal sound coming from a speaker of the specified impedance. It is not really an electrical measure, but rather a sound pressure measurement. The power requirement watts is the standard electrical measurement of the power draw from the outlet - the same as the rating on a light bulb. The 10% harmonic distortion I believe is measured at the maximum output of 150 watts mono. It indicates some fairly serious clipping at that output. There is probably much less distortion at lower outputs.
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Fred Justice


From:
Mesa, Arizona
Post  Posted 4 Jan 2007 12:06 pm    
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My buddy Danny Sneed plays thru two power blocks, one thru a 12" LV and the other one thru a 15" BW, both thru a RV-3, GREAT TONE.
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Mike Wheeler


From:
Delaware, Ohio, USA
Post  Posted 4 Jan 2007 12:10 pm    
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Dave, with respect, I need to clarify the watts question.

It is, indeed, an electrical measurement taken at the speaker terminals with an appropriate load (speaker or dummy load) attached. P=E^2/R, Power equals output voltage squared divided by the load resistance.

The 150 watts, according to the specs, would be the output power at the point where the waveform exhibits 10% distortion. At 10% distortion in a solid state amp, you would just begin to hear some harshness, possibly a buzzing, in the sound. (thus Peaveys DDT compression circuit) In a tube amp, it would be heard as a sort of compression effect in the sound. (very desireable for the tube guys)

The sound pressure is a measure of the acoustical output of the speaker taken with a sound pressure meter.

edit: Dave, you are quite correct about the confusion in the two "watts" references on amps.
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Mike
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David Doggett


From:
Bawl'mer, MD (formerly of MS, Nawluns, Gnashville, Knocksville, Lost Angeles, Bahsten. and Philly)
Post  Posted 4 Jan 2007 3:15 pm    
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I defer to Mike's correction. I suspected I was a little wrong on that. The sound pressure generated by a given power output would depend on the speaker efficiency, and so be different with different speakers. So it makes sense to measure that as the raw electrical power at the speaker terminal, rather than the sound pressure.

Being an electrical moron, I am still a little puzzled by the fact that no matter how many watts an amp outputs, you don't seem be get shocked when holding the speaker wires. But if you hold wires coming directly out of an outlet, you are lucky if you live throught it (a lesson from my childhood). Question
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Mike Wheeler


From:
Delaware, Ohio, USA
Post  Posted 4 Jan 2007 5:44 pm    
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Dave, The amp only generates voltage and current, and thusly, power when a signal is driven thru it...no signal, no power. I have been shocked by speaker connections...it ain't much fun!
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Mike
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Paul Arntson


From:
Washington, USA
Post  Posted 4 Jan 2007 8:37 pm     My conclusions on this subject...
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I apologize before hand for this long post.

Dave, thanks for pointing me in the right direction.
Here's what I've concluded:

There is no consistent definition of output "watts" as used by guitar amp spec writers. If anybody can cite a technical publication that disproves this, please tell me and I will go get educated. I would need to see actual math before I could be convinced, however.

The "watt" is usually pretty inflated when it describes amp output. (Often by 200%, not as often 400% as in the case with the crate).

I called Crate tech info and had a long conversation that actually wound up with the tech guy saying (and I quote):
"There is no relation between watts in and watts out." That says it all. He was nice about it even though I crowded him pretty hard. That confirms the inflation scenario, if you credit the source with knowing the full implications of his statement.

My interpretation is that the high efficiency of the class D amplifier design contributes to the higher apparent inflation, as does the high THD distortion rating. Doesn't account for all of it, but at least the arithmetic goes in the right direction.

Thanks also to all the other folks who chimed in saying that they are happy with their power blocks. I need to put down the calculator and just go plug into one.

Here are the references I read:

An article on the (lack of) definition of RMS power in audio amps:
http://www.hifi-writer.com/he/misc/rmspower.htm

This is real close to the traditional power guy's definition of RMS:
http://www.tpi-thevalueleader.com/rms.html

Here is the wikipedia article:
http://en.wikipedia.org/wiki/Audio_power

Some duplication. Read the last paragraph:
http://www.answers.com/topic/audio-power
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Bo Borland


From:
South Jersey -
Post  Posted 5 Jan 2007 4:14 am    
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The Crate power block amp was advertised yesterday @ Guitar Center for $69.00 ... sounds like a grate deal ..
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Bo Borland
Rittenberry SD10 , Derby D-10, Quilter TT12, Peavey Session 400 w/ JBL, NV112, Fender Blues Jr. , 1974 Dobro 60N squareneck, Rickenbacher NS lapsteel, 1973 Telecaster Thinline, 1979 blonde/black Frankenstrat
Currently picking with
Mason Dixon Band masondixonband.net
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Mike Wheeler


From:
Delaware, Ohio, USA
Post  Posted 5 Jan 2007 6:04 am    
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Paul, the "RMS Power" rating actually is a standard measure used in instrument amplifiers. The audiophile world debates these power rating theories ad nauseum. While there is a basis for the debate, the RMS method is an accepted, and useful, standard when taken in the context of it's purpose.

The RMS method was devised to level the playing field for consumers when comparing one amp with another. Previous to that, amp ratings were all over the place and were totally meaningless to a buyer. In fact, marketing writeups were downright lying to consumers. After some lengthy court battles, where it was shown that many manufacturers couldn't provide any proof for their wattage claims, this RMS method was imposed on the industry. The intent here was to force some basic method of measurement that was easily reproduceable, and applicable to all audio amplifiers, and that would provide consumers a simple means for comparison.

No, it doesn't take many important audio factors into consideration, but then, it wasn't intended to. Speaker efficiency, transient response, power supply reserve power, etc., etc. aren't accounted for at all.

So, when you hear that an amp produces 100 watts RMS, and the other one puts out 50 watts RMS, you are able to make a basic comparison as to it's suitability for your application. Beyond that, the other specs, a listening test, and a good return policy, are your best friends.

As to a "publication", I can't give you a reference. But, by applying the RMS method of measurement to any guitar amp, you'll find the wattage is nominally correct when compared to the published specs. So, why does a Fender 100 watt Twin only put out 85 watts? Because the "100" was the design engineer's "idealized" output rating. As is often the case, in production the component values are changed, or "adjusted" for the sake of cost reduction. Though electronic designs can be very precise on paper, they rarely end up that way in the end product.

Sorry for the long post.
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Best regards,
Mike
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Mike Wheeler


From:
Delaware, Ohio, USA
Post  Posted 5 Jan 2007 6:18 am    
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One more thing....

The A/C input voltage power rating, as previously stated, is the power consumption of the amp. There is no direct correlation between A/C input power and the audio output power. In this case, the amp, apparently, uses a class D configuration which is very efficient, as one of your references states. That's why the output wattage seems high compared to the A/C input wattage. It's what's inside the box that determines how efficiently the electricity is used.
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Mike
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Darvin Willhoite


From:
Roxton, Tx. USA
Post  Posted 5 Jan 2007 7:03 am    
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All of the online retailers seem to be out of these, and show that they have been discontinued. Some stores may still have them available, but probably only for a short time. I was going to sell mine, but now I think I'll hang on to it.
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Darvin Willhoite
MSA Millennium, Legend, and Studio Pro, Reese's restored Universal Direction guitar, a restored MSA Classic SS, several amps, new and old, and a Kemper Powerhead that I am really liking. Also a Zum D10, a Mullen RP, and a restored Rose S10, named the "Blue Bird". Also, I have acquired and restored the plexiglass D10 MSA Classic that was built as a demo in the early '70s. I also have a '74 lacquer P/P, with wood necks, and a showroom condition Sho-Bud Super Pro.
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David Mason


From:
Cambridge, MD, USA
Post  Posted 6 Jan 2007 5:36 am    
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If anybody lives near a Guitar Center and can pick one up for me, I want a backup one. I will pay the "MF" price shipped, you could make a few bucks - it's always nice to tell the wife how well steel guitar pays... Rolling Eyes See "Want To Buy" or E-mail me. Thanks!
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Len Amaral

 

From:
Rehoboth,MA 02769
Post  Posted 6 Jan 2007 7:52 am     Power Block
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A friend contacted me yesterday and said Guitar Center has the Power Block advertised at $80.00. YIKES!
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Jack Stoner


From:
Kansas City, MO
Post  Posted 6 Jan 2007 8:02 am    
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Len, see my earlier post on this thread about the Guitar Center price for the power blocks.
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Paul Arntson


From:
Washington, USA
Post  Posted 6 Jan 2007 11:15 am     Thanks to all ...
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I appreciate everybody's input on this. Man this was a great discussion. It really got me thinking.


I wound up buying a used Fender Deluxe 90. My opinion is that it was louder than the crate GT80 or the power block, and the tone was a bit brighter and cleaner. I know it made my ears hurt more. Didn't have near the bottom end, though. Definitely cheaper by the time I would have had to buy a speaker cab to go with the power block.


The Crate Power BLock amp is an amazing feat of miniaturization, regardless of my obsession with the ratings. The distortion was a little high for my taste, but it was plenty loud and you certainly can't argue about the price. It is ->not<- louder than a twin reverb, however. The things are amazingly efficient. The power block consumes 1/10 the power from the wall compared to my Fender Deluxe 90, and is almost as loud. That is amazing to me.

Will we be seeing these things go for a lot on the used market?? Maybe somebody will buy the few remaining ones and scalp them?? (Just kidding...)

.....
Mike -
What do you think about the following link?
I agree exactly with what it is saying, and it applies exactly to the Crate situation. Same numbers even. It even explains where the factor of 4 comes from.

http://www.electronixwarehouse.com/education/amplifiers/power-ratings.htm

Another thought occurred to me also:
Also, if RMS voltage = 0.707 peak sine wave voltage
and RMS current = 0.707 peak sine wave current,
then shouldn't RMS wattage = RMS voltage x RMS current ??
And Peak Wattage = peak voltage x peak current.
I use the term peak here to mean the top of the sine wave crest, not a transient music value, just to keep things consistent.

Calculating 0.707 x 0.707 = 0.5 exactly.
(0.707 being shorthand for [sqrt2]/2).
So RMS wattage is one half of peak wattage. Exact definition.
I found this makes a lot of sense if you graph out sin(wt)
and sin(wt)*sin(wt) on the same scale. The second one is twice the frequency and is entirely above the zero line. That puts the integral of the power function at amplitude 0.5.

Amp manufacturers have been using peak wattage for many years to rate their outputs because it is a bigger number. They don't call it rms wattage, they call it some other label, like peak music power.

Continuing the logic from the above paragraph, Crate's advertising copy writers were taking their math lessons from Art Bell's guests who claim over-unity power generation. My opinion is that you can't get more out than you put in. My only point should have been that they shouldn't call it RMS watts, because it isn't. They should call it some other name. Returning to the original point of my original post, if they claim RMS watts output, they can't output more rms watts than the available input rms watts coming from the wall.
.......


Again, thanks to everybody who chimed in. I know more now than when I started, and that's the point of the forum.
I think I should go practice music now and get off the computer.
-Paul
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Mike Wheeler


From:
Delaware, Ohio, USA
Post  Posted 6 Jan 2007 12:23 pm    
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Paul,

You are correct in that ErmsXIrms=Prms...of course that's the hard way to do the measurement in real life. A better way is Erms^2/Rload=Prms.

I suggest you read up on Class D amplifiers. They are a switch mode design...which means the output devices are operated like switches where the power supply is applied fully to each half of the output stage....thus the very high efficiency of about 95%.

Of course, Crate could be lying, but I don't think they are. No company would risk their credibility in such a foolish way. By stating RMS as their measurement method, they are saying this can be easily verified by anyone with the right test equipment.

As far as output watts exceeding input watts...what do you mean? Are you familiar with switch mode power supplies? Maybe the 35VA spec is a misprint?
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Mike
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David Mason


From:
Cambridge, MD, USA
Post  Posted 7 Jan 2007 1:39 am    
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We were fooling around with it yesterday plugging it into a PA cabinet with a 15" JBL and a horn, and feeding the back inputs with a five-string bass (low B string) through a tube preamp. I'm not sure if the 10% distortion is measuring the noisy front preamp, or the back power section? I had it turned up to "6" or so and I couldn't hear any raspiness or crackling or tincan noise, but our fillings were rattling and stuff was falling off the walls so we had to stop there. One of my student's parents have an antique store with a loft above it they've set up as a practice space - boy, nothing makes a 14-year-old happier than knocking stuff off the walls! (Well maybe one thing Shocked)
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Paul Arntson


From:
Washington, USA
Post  Posted 7 Jan 2007 3:41 pm    
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My kids still like to knock stuff off the walls and they are all grown up.

I agree they are plenty loud. (The amps that is, although my sons are plenty loud, too.) Without regard to what the spec says, they are plenty loud. I think if you sat it down next to a twin reverb it would not move as much furniture, but neither does it weigh 80+ lbs nor cost $800.

Mike - with regard to watts and watts, I'm not meaning anything obscure. Just if you put a power measuring instrument of some kind on the power supply input and a similar instrument on the audio output and do a power measurement however you want, >>using the same definition of the word watt<< for both measurements, you can't get more out the output than you supply at the power supply. Conservation of energy. Physics 101 stuff. The same thing that makes it impossible to produce a perpetual motion machine, but that's another thread.

My problem was with the definition of the word "watt" being different at the input and the output. I'm pretty rigid in my thinking sometimes. I have trouble doing math with poorly defined units.

That was supposed to be the semi humorous portion of the initial post. Too obscure I guess. I should have said over unity instead of zero point. A coast to coast Art Bell sort of joke.

And yes, thanks for the tip, I do know a little about switching amplifier design and switching power supply design. I've never designed and built one from the ground up, but I use digital servo amplifiers for motion control and switchers for powering them in my work. I did study the theory of switching power supply design in one of my college classes briefly. I know the math OK. It's the conventions used in commercial audio amplifier electronic specs that elude me. I'm mainly an industrial type of guy when it comes to tech stuff, and I rely on the good folks on this forum to educate me as to the fine points of consumer electronics in the real world. Including yours and Dave's excellent comments which put me on the trail of figuring out what is what.

My mistake, the back of the power block says 45 volt amperes not 35. Same difference. Spec is misrepresentative. I am confident of that now, and I am confident that if I tested the crate pb on a bench it would fail to perform at 150 Watts RMS output. Still a fine sounding really loud amp. Just not more powerful than a Twin Reverb. I wonder if Crate is blowing them out GC because they want them all to go away before this mistake gets them in trouble. (Probably not - they are just too radical and they weren't selling...)

It's all good. Thanks for a rousing discussion to everyone about this interesting little amp. I also really appreciate the good manners and courtesy displayed by everyone on this thread. It is wonderful to go anywhere on this steel guitar forum and have 99.999% of the discussions be so informative and civilized.

Best to all -
-- Paul
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