Crate Powerblock... horrible THD specs

[Sir H C]

Time out.  100 watts on what rails?  +-15 volts?  That could well be the problem.  Raise the rails and you get more headroom so long as the power amp chips can handle it. 

It is common to see the 10% distortion spec for car audio chips and the likes, as you can use that in a tuned bass enclosure and get reasonably good sound quality out.  Also how else can you easily claim 20 watts on a 12 volt rail? 

You can try putting a compressor in front so that you quash the peaks before you clip, also play with a graphic in front so that you can reign in some of the frequencies that are clipping.

[dosmun]

These amps sound pretty good for what they are.  No they are not a Marshall or a HI Fi  power amp but for $80 ya can't go wrong for a backup or for a sit in gig where you don't want to haul a big amp around.

[ExpAnonColin]

But putting my computer music/sampler through a guitar 2x12 would sound  even worse.  I want a solution where I can have a true stereo rig that will faithfully play back my non-guitar tunes, as well as provide a decent pre-amp for the guitar.  The powerblock was like the perfect solution, but it is indeed too good to be true.  At the end of the day, I have my classic 50 for my guitar.

-Colin

Note that it is being referred to as a guitar amp. For Hi-Fi applications, do not buy guitar gear.

Straight from the Crate homepage: "This is a 150 WATT RMS STEREO guitar amp in an amazingly compact package."

Proper research is in order when buying anything.

---------
Jimbo

You don't need to call me an idiot, I already feel like one.  That said, I'm slowly growing accustomed to the CD-IN option.  What it comes down to, is that I need to sit down and make a paia tube head and a stereo power amp wiht low THD in one box.

-Colin

[ExpAnonColin]

Time out.  100 watts on what rails?  +-15 volts?  That could well be the problem.  Raise the rails and you get more headroom so long as the power amp chips can handle it. 

It is common to see the 10% distortion spec for car audio chips and the likes, as you can use that in a tuned bass enclosure and get reasonably good sound quality out.  Also how else can you easily claim 20 watts on a 12 volt rail? 

You can try putting a compressor in front so that you quash the peaks before you clip, also play with a graphic in front so that you can reign in some of the frequencies that are clipping.

I'm not sure what the power amp chips is being powered by... guess I could open it up and test it with a multimeter to the power amp chip.

-Colin

[Elektrojänis]

Time out.  100 watts on what rails?  +-15 volts?  That could well be the problem.  Raise the rails and you get more headroom so long as the power amp chips can handle it. 

That +-15V is probably for the preamp section. Very common voltages for powering opamps...

In class D it will not need as high voltage rails as it would in class AB though.

It is common to see the 10% distortion spec for car audio chips and the likes, as you can use that in a tuned bass enclosure and get reasonably good sound quality out.

And if something is said to give 100W at 10% THD it can usually give 90W or so with less than 1% THD... In solid state gear that is... Tubes are different ofcource.

Also how else can you easily claim 20 watts on a 12 volt rail? 

Thats easy. It is called marketing. And no... I'm not joking.

This is both funny and sad at the same time: http://sound.westhost.com/power.htm

[Ge_Whiz]

Yeah, I was about to say that the 10% figure would apply to the amp when it was cranked up - and if you're really operating it at that level, the distortion is probably coming either from your monitors, or possibly your ears...

[JimRayden]

You don't need to call me an idiot, I already feel like one.

No such word or any other insult is to be found in my post. Don't feel too bad, we all make mistakes. Sometimes they're way more costly than the Powerblock though.

That said, I'm slowly growing accustomed to the CD-IN option.  What it comes down to, is that I need to sit down and make a paia tube head and a stereo power amp wiht low THD in one box.

-Colin

That's be a great idea! If you'd be in Europe, I'd be quite interested in taking the Powerblock offa your hands (i.e. buying it). (but according to the statistics of the DIY map, it's most propable you aren't.)

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Jimbo

[Johan]

Time out.  100 watts on what rails?  +-15 volts?  That could well be the problem.  Raise the rails and you get more headroom so long as the power amp chips can handle it. 

That +-15V is probably for the preamp section. Very common voltages for powering opamps...

In class D it will not need as high voltage rails as it would in class AB though.

It is common to see the 10% distortion spec for car audio chips and the likes, as you can use that in a tuned bass enclosure and get reasonably good sound quality out.

And if something is said to give 100W at 10% THD it can usually give 90W or so with less than 1% THD... In solid state gear that is... Tubes are different ofcource.

Also how else can you easily claim 20 watts on a 12 volt rail? 

Thats easy. It is called marketing. And no... I'm not joking.

This is both funny and sad at the same time: http://sound.westhost.com/power.htm

..the sad part is that people who should know better, actually believe it too...on an other forum where I hang out, a vintage VW beetle forum, people are talking about installing 700+ watt systems in their 6volt cars  ..there isnt even an alternator in these..its a generator, yes, a dynamo..capable of dellivering  maximum 180 watts. and that is supposed to run the engine AND charge the battery AND running the head lights ( 2x45W )...so how can anyone really believe they will get 700watts of sound out of that car ( and how can the expect to survive inside if they actually did?)
..but car audio amps are usually bridged amps to take maximum advantage of the small voltage that is availible and also rated at low Z, too make the figures look better...

johan

[Elektrojänis]

..but car audio amps are usually bridged amps to take maximum advantage of the small voltage that is availible and also rated at low Z, too make the figures look better...

Most of the more powerfull car "hifi" amps use switch mode powersuplies to pump up the voltage. I'm not sure if there are models for 6V systems though... Probably not. But anyway... no matter what is used , the amp cannot pump more juice to the speakers than it can get from the battery, battery loader or whatever it is that is providing the power. 700W from 180W doesn't seem likely to happen... If it does, they just might have solved all energy problems on earth. 

[ExpAnonColin]

That's be a great idea! If you'd be in Europe, I'd be quite interested in taking the Powerblock offa your hands (i.e. buying it). (but according to the statistics of the DIY map, it's most propable you aren't.)

----------
Jimbo

No, I'm afraid I'm in America.

Here's what the guy said from Crate:

CD inputs are definitely the best place to plug a CD player into the
Power Block, if that's what you're asking.  CD players output a -10dB
consumer level signal, which is also the input spec for the RCA tape
inputs on the Power Block.  If you have a variable level control on the
output of your CD player, you should be able to set it at or near its
max volume in order to create the best gain structure for your signal.
The CD inputs are designed to accept the typical line output max of a CD
player.

That said, THD is basically an output spec for everything coming out of
the amp, regardless of what you plug in.  AS THD is the ratio of the sum
of all harmonic components to the power of the fundamental, 10% is
probably a fairly accurate representation for the CD inputs as well as
the instrument input simply based on the construction of guitar amps
verses pro audio and/or home stereo amps.

Hope this helps!

That is interesting, and perhaps not true?  Based on the block diagram at least...  But it is fairly bluntly put here that it's a guitar amp through and through, power amp and all, I guess.

-Colin

[aloupos]

Hey Colin --

I also bought this little amp, and although it's problably not so great for your home theatre, it is a good little guitar head. 

I've been using it in rehearsals, with a Dr. Boogie and The English Channel, in series with a presonus blue tube, into the return of the effect chanel (bypassing the tone stack and gain controls).  I get a really nice warm tone out of it in this configuration.  The blue tube really helped to warm it up and put some mids in there. 

Plenty of volume as well.  I will use this to gig with for small shows in NYC as well.  No lugging my JCM900 !  woo hoo

[ExpAnonColin]

More info... (or less)

I don't have any spec info that's not in the manual.  Because the input preamp is being bypassed (see the block diagram here: http://www.crateamps.com/product/manuals/CPB150.pdf) it's quite possible that the spec is a little bit lower for -10dB signals, but I have no way of getting an exact number for you.  My spec sheets are the same ones available on the web, so despite my willingness to help, I don't have a way of getting an exact number, if that's what you're looking for.  The greater likelihood is that the 10% spec was generated with the preamp inline, however, so I would suspect some of the THD is generated therein, making your guess as good as mine as to what the line and headphone amps are actually putting out with CD-in only.

A strange observation, too:

My soundcraft mixer's monitor outputs give decent levels, but also distort at lower volumes.  The THD on the monitor out shouldn't be horrible.  So, what it might come down to is simply getting a 150 watt per channel power amp.  Does anyone know of any smaller ones that might be viable for rehousing?

-Colin

[Sir H C]

If you could figure out the chips they are using for the class D output that could help.  If you see what the manufacturer claims the part as the you can get a better feel for the power driving it can do. 

In general these class D amps can have crappy THD at lower inputs as it is a case of how fine can they get the PWMing going.  Sort of like an ADC, you have a much worse SNR if you always run at -12 at the inputs.