OT: Amplifiers

[Hydesg]

Hi
there seem to be only schematics for tube guitar amps
are there any solid state but decent guitar amp that can produce at least 20w online?

my marshall mg15cdr just doesnt sound nice at all
and very noisy on the dirty channel

[jimmy]

yeah theres schems out there, but your way better off getting a power amp IC (check TI, //www.texasinstruments.com for about 20 or 30 watts, and put your favourite distortion circuit and tonestack on the front. some people are doing this with the ROG amp emulators, sounds good to me. i actually tore my BOSS MG-10 amp apart coz the preamp section SUCKS, and am planning to put a thunderchief in there.

good luck
Jim

[Ballz]

Hmm...you mean you want to build a SS amp for, say, 50W? My gut feeling tells me it will be a lot cheaper to buy an amp of that kind.

Not to discourage you, by all means - I am sure there are DIY 50W, 100W and 200W amp schematics out there. Let us know what features you need and what you play - guitars, music style etc.

My money is still on a store-bought amp, new or used - you get all the bells & whistles, and at a *very good* watt per dollar rate, compared to DIY.

Cheers /Richard

[petemoore]

Yupp why build when you can just buy...could be one of the reasons we're not seeing a plethora of SS amp Schematics around.
 Chip amps with doctored [added input stages like the Amp Sims or Dist] inputs can do a fine job for cheep tho. The little 386 amps [I have two 2w Gem types with buffered inputs].
 Quite astounding how 2w can drive a 10'' speaker, and I'm using 'lowly' LM386-1's [with homey heat sink].

[al3151]

http://sound.westhost.com/site-map.htm

[Peter Snowberg]

http://sound.westhost.com/project19.htm 50W into 8 ohms

[Mark Hammer]

If you look at a lot of the "also-rans" from the golden era of amps, a great many of them had the making of decent amps.  However, they fell by the wayside because the folks making them had not been terribly thoughtful.  

How had they not thought things through?  Sometimes it would happen by way of badly designed/conceived cabinets that would fail to bring out the best in the speakers.  Sometimes the speakers themselves were poorly chosen and a bad complement to the amp and preamp.  Sometimes it was a matter of selecting a lousy tonestack, or a less than optimal supply/plate voltage.  And so on.  Basically, whenever companies would try to hitch a ride on a trend as latecomers, they would have to figure out a way to cut corners on production costs so that their pricepoint would enable them to compete with the companies first out of the chute.

Marshall, for all their tradition, reputation, and such, are stuck in that same set of circumstances.  So how do they make a practice amp, with precious little in the way of possible profit margin, for the price they do, and deliver features that make it attractive to those with shallow pockets such as yourself?

The first thing that goes is the cabinet.  I can't see the back of the amp from the Marshall website, but the front picture indicates that it is about as small as is possible and still house an 8" speaker.  I'll wager it is fairly shallow and open back.  An open-back cab saves wood, covering material, and most importantly shipping costs.  You can do the math yourself, but just calculate, based on height/width, what it would add in the way of material costs to just make the cabinet an inch deeper and closed-back.  Sadly, with shallower cabs and open backs, the tonal balance, and particularly the "muscle" one is accustomed to from larger amps, goes missing.  The EQ-ing *may* be able to offset that, but usually not.  So, you can very often take a crappy little amp, marry it to a better/bigger speaker in a cab with a different resonance/efficiency and get something much more pleasing.  Ask yourself how often people have commented that their 386-based amp or their Firefly or something akin to a ZVex Nanohead sounds fabulous going into their 4 x 12 celestion cab?

Of course, this leads to the next point, and that is that while an 8" speaker is nice and bright, and certainly easy to carry around, it will not move as much air, and will have clear shortcomings if you and your buddies try to compare your recent 7-string acquisitions.  Plug in an octave-down box, and you won't be all that thrilled either.

All of this points to you considering simply buying yourself a nice 10" or 12" speaker and making a cabinet that will bring out the best in the amp.  When you play in your home you can use the extra cab instead of the onboard speaker, and when you want convenience and an easier bus ride, you can just go with the amp as is.  The bottom line is there may be tons of tone in that amp that lies unexploited/untapped.

While I don't doubt that the R&D people put in sincere amounts of time into developing such products, at that pricepoint, the product is more guided by "Does it have enough bells and whistles to lure customers and retailers, while providing a reasonable profit margin?" than by "Does it sound amazing, given what's in it?".  For that reason, attention to details in preamp design may fall by the wayside, and designers may simply resort to the tried and true because they know it will work.  So, the tonestack may not be voiced to complement that speaker but a standard configuration simply borrowed from elsewhere, the distortion may be the usual back-to back diode pair, with no consideration for asymmetrical clipping or defizzing of any kind, or strategic cascading of gain stages, and so on.  I'm not saying they are ALL like this, but even the manufacturers with the best reputations can't devote hundreds of development hours to a product they'll make a buck or two on with every unit shipped for a total product lifespan of maybe 3 years before it gets redesigned.

Finally, 15W is actually a lot of power.  You would easily need 4-5 times that much power to make an appreciable difference in maximum volume.  The rule of thumb is that audible volume doubles with every tenfold increase in power to the same speakers.  So, hypothetically, 150W going into a cab that could take it, would only sound twice as loud as a 15W amp.  Of course where people get confused is that wattage is usually accompanied by both cabinet and speaker size as well as speaker number.  What gets attributed to wattage is generally more attributable to both cab size and speaker efficiency/size.  Just about the only exception to that I can think of are those older Gallien-Krueger amps that used a pair of 6.5" speakers to deliver 100W or something like that.

Personally, before building a totally different amp (because the one you have has some nice features), try it out with a different cab and see how you like that first.

[Hydesg]

hi thankyou guys for ur advices

after much thought
perhaps buying a tube amp is more feasible for me
right here, it's very hard for me to get cabinets with 12" speakers done
and i think the cost of DIY would perhaps buy me a better commercial made amp.

the guitar community here in singapore is very small
and i suppose there are less than 10 people here that DIYs their own stuffs

the distortion channel on my marshall is very noisy

is it because of the dirtiness in the power supplies?
i was thinking of modding it
replacing the pre amp part with a blackfire or thunderchief and changing the power supply inside
as it might just improve the tone by alot and quietness of the amp

would open it up tonight to have a look at it.

and post some pictures for you guys to see the internals

[tcobretti]

The easiest way to solve your problem is to build a ROG emulator pedal, run your marshall amp as clean as you can with all the eq knobs at 10.  Your amp will basically be acting as a power amp while your ROG pedal will be the preamp.  

I have a "First Act" amp that is honestly the worst sounding amp I've ever heard (it was free).  I built an English Channel and it makes the First Act sound incredible.  

You could even just sell the marshall and buy a cheap power amp.  Use a ROG pedal as a preamp and you're in business. But then you'd have to dig up a speaker cabinet as well.

The absolute first thing you should do is build a ROG pedal and see how it sounds with your amp.  It may sound awesome.

[Gilles C]

And if you ever really want to build something, check this site, my favorite for discrete circuits designs...

http://www.redcircuits.com/Music.htm

more audio not guitar related designs, but good for ideas

http://www.redcircuits.com/#Audio