Crate Powerblock... horrible THD specs

[ExpAnonColin]

Hello everyone.

I just got a crate powerblock and a pair of alesis monitor 1 MKii passives, as a plan to integrate my guitar as well as my stereo computer/sampler/synth/etc rig in one convenient, small package.  The monitors sound great, but I was careless and stupid and spent too much time looking at the block diagram to notice that the powerblock has 10% THD... ouch!  At moderate levels it starts to break up, noticeably above 300hz.  Since there is really no other solution (other than a DIY one of course) for such a small, cheap, an convenient amp, is there anything I can do internally to get the THD down?  I have not looked inside of it yet, but I feel like it is likely SMD because of the size.  Is it worth taking a look?

-Colin

[Meanderthal]

 As long as you don't mind voiding the warrenty, go ahead & open it up. If you find it's got human sized components there may be things you can do- possibly burr-brown opamps(if it has opamps in there), good film caps, etc. might make a difference. As inexpensive as these are they might not have the best quality components...
If it's a bunch of SMD stuff I'd personally leave it alone... but that's just me.

[ExpAnonColin]

As long as you don't mind voiding the warrenty, go ahead & open it up. If you find it's got human sized components there may be things you can do- possibly burr-brown opamps(if it has opamps in there), good film caps, etc. might make a difference. As inexpensive as these are they might not have the best quality components...
If it's a bunch of SMD stuff I'd personally leave it alone... but that's just me.

At this point, I really have no choice.  I just wanted some kind of confirmation that there might be something for me to do before I opened it up.  I imagine it's the power amp chips that provide the THD... right?

I just tried to open it up, I have no allen keys.  Maybe another time.

-Colin

[Meanderthal]

 I would assume the specs are for the whole amp. I'm not sure there's much you could do in the way of a simple chip replacement for the power chip though. I picture 2 of those "100 watt amp in a chip" chips bolted to a heatsink and a preamp, maybe a couple big caps, a power supply circuit, not much else... but the preamp section is where you would have the most flexibility for mods...
That really is some horrible THD, bad enough that I've never heard of a modern high power audio amp like that... the chip would be useless for anything other than a guitar amp! I really suspect most of the distortion in in the preamp section(maybe they try to make it sound 'tubey')- especially because it's a guitar amp.
There's also a possibility that it distorts deliberately...

[Connoisseur of Distortion]

i doubt that whatever is wrong cannot be modded to right. most of those power amplifier chips have extremely low THD- and the distortion they produce is nothing short of ghastly. I'm sure that a company would try to give it a softer distortion by slanting the preamp in their favor, because anyone who's overdriven one of those chips can testify that it's a foul sound.

[Gladmarr]

If you're going to use it for guitar isn't THD a good thing?  If there's one thing I can't stand it's crystal clear clean guitar.   

[ExpAnonColin]

I would assume the specs are for the whole amp. I'm not sure there's much you could do in the way of a simple chip replacement for the power chip though. I picture 2 of those "100 watt amp in a chip" chips bolted to a heatsink and a preamp, maybe a couple big caps, a power supply circuit, not much else... but the preamp section is where you would have the most flexibility for mods...
That really is some horrible THD, bad enough that I've never heard of a modern high power audio amp like that... the chip would be useless for anything other than a guitar amp! I really suspect most of the distortion in in the preamp section(maybe they try to make it sound 'tubey')- especially because it's a guitar amp.
There's also a possibility that it distorts deliberately...

i doubt that whatever is wrong cannot be modded to right. most of those power amplifier chips have extremely low THD- and the distortion they produce is nothing short of ghastly. I'm sure that a company would try to give it a softer distortion by slanting the preamp in their favor, because anyone who's overdriven one of those chips can testify that it's a foul sound.

Interesting.  I have the box open, and the preamp chip is covered with some green glue-goo, that obscures the part #.  It's a 5 pin chip, heatsinked against the wall...  but if what you say is right, it shouldn't be a big deal.  The rest of the chips I can see are 8 pin SMD.  The only two which I can really see are +/-15V voltage regulators.  The thing is, if what you say is true about the preamp, if I use the CD in's, I will bypass the preamp and thus hopefully have much less THD.  I think replacing anything in the preamp woudl be pretty difficult without a schematic, at the least, as I'd like to know which chip was doing what... there are 4 8 pin chips that I can't see, I can tell that one or two of them are for the line out buffer.  But they are buried pretty deep.  If my camera had batteries, I'd take some pictures.

If you're going to use it for guitar isn't THD a good thing?  If there's one thing I can't stand it's crystal clear clean guitar.   

If you heard this thing (with guitar) through my monitor one's you'd know what I mean... this is really not nice distortion at all.  It's not ugly, but it's annoying, and nothing nice.  I am also using the monitors for playing back music from my computer, as well as my sampler, which I don't want any added distortion on.

I guess I will see if the CD input will fix my problems.  Too bad I have it all open now...

-Colin

[tcobretti]

Please let us know how this turns out.  I have been curious about this amp.

[Paul Perry (Frostwave)]

Note that class D switch mode amplifiers are getting out into the domestic area now.
en.wikipedia.org/wiki/Switching_amplifier  If that is what you have........

[ExpAnonColin]

Note that class D switch mode amplifiers are getting out into the domestic area now.
en.wikipedia.org/wiki/Switching_amplifier  If that is what you have........

Hmmm...  that would truly suck.  What is the probability of that?  Though most of the class D chip datasheets I'm seeing are saying about 1% THD, and I haven't seen one that can do  150W (or 75W stereo)... but this car amp says it has plenty of watts and is Class D:
http://www.pricegrabber.com/rating_getprodrev.php/product_id=18659788/id_type=M/

Using the CD input, music sounds much better (maybe that is because it isn't sent through the "speaker simulator")... but I am still getting audible distortion around 200hz+.  I guess it's how the music sounds, not the test tones, though, right?

I am still not entirely pleased, but I guess you get what you pay for.  A statistic on the output THD with inputs on the guitar input, line in, and the CD input would be interesting, and useful.  I emailed crate but I doubt they will email back.

-Colin

[tcobretti]

I am pretty sure I've seen Class D amps with 50 watts, so 75 doesn't seem like such a stretch to me.

If you actually start communicating with crate, tell them they need to make a bass amp version.  If it sounds pretty good it could be the new Walter Woods but for a fraction of the cost.  Jazz guitarists and bass players (and us DIYers) would eat it up. 

[ExpAnonColin]

I am pretty sure I've seen Class D amps with 50 watts, so 75 doesn't seem like such a stretch to me.

Help me find a datasheet... then I could get an idea of what the THD is.  It would be 75W per channel.

-Colin

[tcobretti]

I am not an expert, but you could try ssguitar.com which is guys from this forum talking about DIY solid state amps.

I know that Analog Devices used to make an AD1996 that made 80w bridged, so there must be more stuff like that out there.  The google phrase you want to use is "chip amp". There a whole DIY community built around it.

[hairyandy]

Hey Colin,

Have you tried it through any other speakers?  I got one from Crate last summer and it does kinda suck, but I would think that really good speakers that aren't made to break up would make it sound extra shitty.  It's not too bad through a 4x12 or a 2x12.  It's a little too NU-Metal for me though once it does break up.  The clean sound is OK, but it sounds pretty shitty with a lot of my pedals.  SS, go figure...

Andy

[Harry Palms]

http://www.fairchildsemi.com/ds/KA/KA5M0965Q.pdf

I'm about a third of the way through the preamp section. I bought my first one and liked it so much I bought a second one to do a walkthrough of it. This amp ended my quest for a home built solid state guitar amp. It's just not worth it anymore. It sounds better than anything I've tried to build so far.

For my part, this amp was exactly what I was looking for for live playing. I set the Crate to relatively clean. I run it in a stereo rig with an EL84 based tube amp as it's compliment. Each head feeding one 8 ohm speaker in a 2 X12 cab. One high power speaker (I think it's a Red Ryder, as I recall) for the Crate and one Celestion blue for the lower powered tube amp. Right now my pedalboard is running a parallel feed to each head but that changes all the time (I'm not even close to having that thing finished). I run the Crate's line out through the PA for the house mix and mic the cab through a 2nd PA channel.

[ExpAnonColin]

Hey Colin,

Have you tried it through any other speakers?  I got one from Crate last summer and it does kinda suck, but I would think that really good speakers that aren't made to break up would make it sound extra shitty.  It's not too bad through a 4x12 or a 2x12.  It's a little too NU-Metal for me though once it does break up.  The clean sound is OK, but it sounds pretty shitty with a lot of my pedals.  SS, go figure...

Andy

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

[ExpAnonColin]

http://www.fairchildsemi.com/ds/KA/KA5M0965Q.pdf

I'm about a third of the way through the preamp section. I bought my first one and liked it so much I bought a second one to do a walkthrough of it. This amp ended my quest for a home built solid state guitar amp. It's just not worth it anymore. It sounds better than anything I've tried to build so far.

For my part, this amp was exactly what I was looking for for live playing. I set the Crate to relatively clean. I run it in a stereo rig with an EL84 based tube amp as it's compliment. Each head feeding one 8 ohm speaker in a 2 X12 cab. One high power speaker (I think it's a Red Ryder, as I recall) for the Crate and one Celestion blue for the lower powered tube amp. Right now my pedalboard is running a parallel feed to each head but that changes all the time (I'm not even close to having that thing finished). I run the Crate's line out through the PA for the house mix and mic the cab through a 2nd PA channel.

Sounds like just about the perfect application for it.  It is a completely fine sounding amp to it's credit, for guitar, especially with a guitar cab.  Are you saying you're tracing it?  Is the link you sent the power amp chip?  If so, doesn't look like much of an amp chip... but it is definitely class D then?  What are the op amps in the preamp section?

-Colin

[Meanderthal]

 Ya know, it hadn't occurred to me that there is a power amp in option... DOH! Brain fart! Yeah, in that case it's all about the power amp chip... I'm too busy thinking old school here... Sorry bout that!

That .pdf looks like it must be the 5 pin chip with goo you described... looks to me like it's just a switch... with whistles and bells.

[JimRayden]

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

[MartyMart]

Yup, that's why it sounds like "Poo" through your full range HiFi spkrs !!
The CD thing is a bit "confusing" ... I'm guessing that it's just for jammin and learning stuff ?

MM