amplifier building

[stevecrozz]

I'm completely new, but I have read a few documents. I feel like I'm ready for a first project. I'd like to do something that will prepare me for building decent 500 watt solid state bass guitar amp, but I don't think I'm quite ready for something that big yet.

Does anyone have any ideas on what would be a good first project?

[Optical]

probably start with a ready to assemble kit that comes with the parts, circuit board and instructions

there isnt any reason why you couldnt start with a big amp as long as you stick to the instructions and are aware that big power means big (potentially harmful) voltages

some confidence is necessary when working with mains electricity also, but you have to start at some stage.

here is a nice 500W amp http://sound.westhost.com/project68.htm but unless you understand what's going on then mistakes can be easy to make

http://www.jaycar.co.nz/productView....=&SUBCATID=557

this jaycar amp is pretty good! ive built a couple and they are awesome and come with excellent instructions

[stevecrozz]

couple of questions:

Why are amplifiers so expensive, which parts tend to absorb the major cost?

Do hobbyists normally trace their own circuit boards, or what do we normally use to integrate the components?

Where can I find a decent housing to place the finished project into?

Lastly, my project equipment consists of a cheap weller soldering iron, some solder and tape, and a cheap radio shack digital multimeter. Are these projects still within my reach?

--Stephen

[Enzo]

What is your idea of "expensive?" A lot of money is not the same thing as expensive. A $5000 Ferrari is cheap. But a lot of money none the less.

Look at some commercial amp and price out the parts. You have a rack mount enclosure/chassis. Power transformer, large filter caps, circuit board, a pile of power semiconductors, a substantial heat sink for them, and probably a fan, a bazillion little parts, the input and output connectors, power cord and switch, level controls, pilot/indicator lights, screws/nuts/spacers, and lots of other little stuff. It adds up.

For a guitar/bass amp, we assume it is to be transported about gig to gig, so add in a protective cabinet of some sort, things like corners, feet, handles.

A 500 watt amp is not trivial, and remember a bass amp is more than just a power amp. A little amp with a TIP142/147 pair or something is a lot simpler to do than a row of 10 TO3 power transistors.

The ESP project mentioned above looks like a nice little piece, but note the circuit is utterly basic. There is no speaker protection, there is no current limiting, and no input section. COmmercial power amps are chock full of various protections and stability enhancing circuitry. For a straight mono amp, you don't need to worry about bridging.

Your bass amp will require a preamp section as well. Of course the preamp and power amp can be separate.

If you want to do a project, I highly recommend going with a kit or at least buying a board from someone. LAyout matters, you can't just throw parts in the box and wire them together. Once you have a better handle on construction, making boards, desiging boards, designing circuits, cooling and air flow, then you can try to roll your own.

[teemuk]

Originally posted by stevecrozz
Why are amplifiers so expensive, which parts tend to absorb the major cost?

The "iron" always seems to be the most dominating factor of expense. Resistors, capacitors - basic parts - are inexpensive and can be bought by bulk amounts. Even power transistors and large capacitors are fairly cheap. The most expensive parts will be (high power) transformers, heatsinks and possibly chassis construction. Also, you will probably find out that a large number of high power transistors, big caps, trimmers, potentiometrs (+ their knobs), jacks - and other (not so bulk stuff) will add a hefty sum to the final cost.

I do not even start pricing up the time spent on building.

Do hobbyists normally trace their own circuit boards, or what do we normally use to integrate the components?

I can not speak on behalf of everybody but this is at least what i do if the circuit is fairly complex. The PCB design is always easier to check, double check, triple check etc... and assemble than other methods to integrate components (ignoring the point-to-point construction). Of course, the proper layout of the board is another issue where extreme care should be taken. For simple circuits - or simple parts of the circuit - i try to use point-to-point construction as much as possible. I also try to avoid PCB mounted jacks, switches, potentiometers etc. The reason for this is simply reliability and the further ease on fixing the equipment. Also, the high current parts are much more serviceable and reliable when not located on printed circuit board. Of course, everything is related to the skills of assembler and designer. Reliable high current PCB design is possible - but fixing it is harder than fixing point-to-point construction, it also stresses the board and copper traqcks.

Since unique, hand-built pieces of equipment never come any cheaper whether you have all parts on a PCB or just a few of them i try to use PCB only on low current parts of the circuit that are likely never to fail.

Where can I find a decent housing to place the finished project into?

What do you consider decent and how much metal/woodworking skills you have? Do you have an access to tools for metal/woodwork? You can, for example, use a cannibalized chassis, search the internet for industrial chassis manufactures and order one, buy a chasis from a shop or just simply bend a metal plate to L, U or whatever shape and stick it into a wooden enclosure. The possibilities are endless and highly depend on your skills.

Lastly, my project equipment consists of a cheap weller soldering iron, some solder and tape, and a cheap radio shack digital multimeter. Are these projects still within my reach?

If you are familiar with the equipment and the required circuit theory for such a complex project as building a power amplifier I see no reason why not. I would definitely add small spanners, screwdrivers and pliers to the list also. You will surely need them. Wood/metalwork tools plus etching equipment etc. are not mandatory but would make some things a lot faster and easier.

If you are short on circuit theory i advise you to learn a lot of it first. And if you are, do not build a 500W amplifier as your first project!!! Build a 40 to 100W amplifier instead and learn the principles of how the circuit works. After this it will be easier to focus on high power designs that require more reliable circuits and thus are more complex. It's also better do a lot of research, and i mean A LOT. Gather yourself a collection of power amplifier schematics: Always try to get as much of them as you can and study them thoroughly. The internet is full of information about circuit theory, component assembling techniques, circuit board design, biasing and thermal tracking methods etc. You have to know at least something about every aspect of building an amplifier in order to succeed in the project. Not to mention, you will always learn something new.

Teemu K