Rack Power Amplifier

[T1bbles]

Hey guys,

I know this isn't stricly a stompbox, but I feel this is the best place to enquire.

I'm thinking of building a PAiA 'Stack-In-A-Box' kit from their site; http://www.paia.com/proddetail.asp?prod=9210KP but if I do that I'm going to need a big ol' power amp to bring it up to a decent level to drive a speaker cabinet.

I was just wondering if anyone knows of a nice linear sounding power amp circuit I could build? I'm really not sure of what wattage to go for, 50W to 100W maybe? Preferably something which I can power from a wall-wart rather than constructing an internal power supply.

Is this feasible? I'm really not clued up on power amps.

Thanks guys

EDIT:

And if it can fit inside a 1u rack case, that'd be great

[Top Top]

I don't know if you can get a wall wart with enough amperage to power a 50W or 100W amp? I am messing with a 10W amp that requires an 800mA DC power supply.

[PRR]

> really not clued up on power amps.

Yeah, you need "clue" before you get into power amps.

I've bought a lot of power-amp clues, snorted a lot of smoke, and unless this is really your life's ambition, I advise you to go buy a box at the local rock shop.

Linear POWER amps are treacherous beasts.

Switching power amps are tricky and treacherous.

Constructing a power supply is trivial compared to building a solid robust power amp

> power from a wall-wart

You ask for 50W-100W out. Assume you master switching power amps, and do as good as 80% efficiency. Your wart must be 63W to 126W, at the specific voltage and current implied by power and load relations. A 24V 1A (24 Watt) wart is BIG. The wart for my printer is much too big to hang from a wall, and is only 40 Watts (and at two very odd voltages).

Electro-Harmonix 22 Caliber Power Amp is a bit over $100, 22 Watts switcher wart-power geetar amp in a coat-pocket. Rocktron Velocity 100 is costlier at $250 but seems to be aimed exactly at what you want. $2.50/Watt seems high, but I know I could not pay myself to build that package at that cost. A too-big Crown XLS 202D can be had for a similar price, though 200W/8ohms is a bit much for small/medium-club guitar.

If you nag friends, you can probably find an "underpowered" (for PA) rack amp laying around unused and unloved, haggle to $100 and it's a deal.

[teemuk]

Some integrated circuit - e.g. one of from various choices belonging into TDA or LM series - could be the easiest solution. Comapred to what commercial power amps put out today these "chips" don't really shine out with their output power ratings, though. Bridging and parallelling is always an option but a quite tricky one too. Definitely not something recommended for beginners.

And building a high voltage, high current circuit is nowhere near as simple as building a battery-powered, low current effect. If it's your first project with amplifiers I would just start from something simpler and invest some money to a good, commercially-produced PA unit.

[petemoore]

  What's expected from this kind of amp is clean power, other features might be low noise, wide frequ response.
 These expectations can be made possible safely, generally less expnesively [if starting from scratch] when bought ready-made.
 Unless there's a particular aspect you think you can get from DIY that ready-made doesn't provide.
 

[T1bbles]

Okay, rethinking!

How about I semi-DIY it?

Could I get something like this;
http://www.maplin.co.uk/Module.aspx?ModuleNo=46467

And buy a ready made power supply for it, and then stick a nice valve guitar pre-amp before it?

Would that give me a decent bit of amplification? Or are these maplin ready-mades a bit crap?

[petemoore]

  Looks like good quality stuff, 14.95 worth.
  200w "by what units" of course.
  Power supply, and heat sinks I'd more than guess, chassis, preamp? [maybe, they said we don't know about modifications to an "EQ before it?" question].
  take a good look at that Velleman link, looks like it wants a stepped down, DC'd voltage.

[PRR]

> something like this

The "power supply" for that is JUST a transformer. (And it is not clear to me what PT they think you should use.... 40VCT-50VCT 2A would be reasonable.)

However it MUST have a BIG heatsink. They suggest their FL42V which IMHO is barely adequate for a 70W 8 ohm operation.

> DC'd voltage.

No, look again. The rectifiers and caps are on the board. Neat.

> are these maplin ready-mades a bit crap?

I'm not keen about Maplin's website.

This particular kit is Velleman. Good kits. You may wish to review the instructions?
http://www.velleman.eu/downloads/0/illustrated/illustrated_assembly_manual_k8060_rev1.pdf

They suggest this list of big parts.

• K8060 Discrete Power Amplifier 200W
• HSVM100 Heatsink For K8060
• TR8040 Toroidal Transformer 100VA 120 / 235V INPUT 2 x 25V OUTPUT

You also want case, fuse, switch, and other odd bits.

> a bit crap?

The circuit is a bit cruder than a 1971 Fisher Hi-Fi. Sound is fine, more than good enough for your needs. HOWEVER it is missing two key protection circuits which are optional in Hi-Fi use but mandatory for overdriven stage amps. You can do better.