another newbie

[heineken]

Hi all, this is my first post. I've been lurking for a couple days now. I am interested in building my own guitar amp (obviously). I am wondering what is a good starter project?
Ideally, I would like to have a 100W amp with a killer distortion channel similar to a Randall RH100 or better (warhead perhaps), but I do realize it's best to start small.
I have lots of experience in soldering and a fair amount of knowledge of electronics, but I'm by far not an expert. I'm a technician in a Honda dealership, so I do see my fair share of wires.

All input greatly appreciated.

[J M Fahey]

Start by building a Randall preamp.
Search this forum.
Mensur built an excellent one, just listen to his posted MP3s, he drives a TDA7294.
Siund is impressive.

[heineken]

it does sound quite good. should i get a power amp circuit from chipamp, or do  I need something more for that kind of power? I've looked into the LM3886 a little bit but I don't see what it's total power rating would be. Or does you're wattage rating come from the preamp? I guess I'm newer at this than I thought.

On another note, is an Opamp just an integrated circuit? Or is there more to them than that. Are they made specifically for amp design, or can I pull one out of say, a cars PCM?
just curious.

[J M Fahey]

Chipamps are good, but best of all is that they come in kits with everything needed, they are relatively simple, and since many have built them successfully, there's a pool of knowledge and help available around here.
They usually supply 50/60W each; a stereo Kit gives you 100/120W; if you become power hungry you can later build a powered box and add speakers and power indefinitely.
An Op Amp is an integrated circuit.
The excellent TL072 costs less than 1$; just buy a few and experiment.
That Randall preamp uses Fets, they are also inexpensive.

[heineken]

at the risk of asking a "dumb" question, what do you mean by a powered box?

When I look at a schematic and see four diode symbols making a diamond shape, is that just four diodes, or something I've not seen before?

Should I trust myself to use perf board to build a preamp like this, or should I look harder for a PCB?

thank you

[Dabbler1]

The diamond shape is a bridge rectifier which comes as a single component. It is made up of diodes internally though, hence the appearance.

[J M Fahey]

Hi heineken.
A powered box is simply a cabinet with a speaker, say a 12", and a power amp built-in, say a 50/70W chipamp and its power supply.
It only has a couple input jacks , an (optional) volume control, a power switch, a power cable, and little else .
The idea is this: we usually encourage members to build a not-too-complex 15W (TDA2030) to a somewhat more complex 50/70W amp, (LM3886/TDA7294), to ensure success.
Many say: good!, it sounds great!, but now I need more power/speakers.
Instead of throwing everything overboard and starting from scratch, I suggest building powered boxes, when and if needed, which allow you to go real power crazy if you want.
They are driven from the preamp output of your original amp, the parallel input jacks allow for easy daisy chaining, everybody is happy (except your neighbours).
Just imagine your original 15W amp (homemade or store bought) driving 4 70W/12" (or 15" or 2x10") boxes.
Woodstock anybody?
EDIT: forgot this:
You can use perfboard; if available use Veroboard (stripboard) which allows easier designs and neater boards.
Download the excellent DIY Layout Creator.
Use the original Windows version (unless you are a Linux/Mac guy) because there are already a lot of excellent projects there; the new Java (universal) version is not compatible with them.
Study other guy's layouts to learn.
It's good to start by building preamps on solderless protoboards; only after that you build them on permanent boards.
Good luck.
EDIT2: just an example of what can be made with DIY Layout Creator on stripboard (they also offer PCB and Perfboard options):

[heineken]

That's really cool. I'm going to go find that program now and play around a bit.
thanks for all the advice guys I really appreciate it. and look forward to lots more! lol

[heineken]

will it show you how everything hooks up on the bottom side, or do you just figure it out from the schematic?

[J M Fahey]

Hi Neken  (sorry, couldn't resist)
Start with something relatively simple, say a Screaming Bird or LPB1 or similar, just to practice.
Draw the regular schematic on a sheet of paper, then try to deploy it on "veroboard", which is simulated by square gridded paper.
Use pencil and rubber to correct layout until you like it.
Consider horizontal lines as uninterrupted horizontal tracks, joining everything soldered to them unless specifically cut somewhere.
Join tracks vertically with short pieces of wire, also draw components as long as needed to reach whatever they have to.
That's to say, the actual design is *not* automated, but brains, pencil and rubber on a sheet of paper.
Play some music you like, work preferably at night or in a quiet moment (you don't want wife/boss/kids/mother/customers/teacher/etc. interrupting ) and draw, correct, redraw, etc.
The program lets you confirm relative sizes and draw it neatly, both for you and to publish in the Net, as the above example.
Step by step draw more complex ones.

[heineken]

so when you buy the LM3886 stereo kit, you end up building you're power amp, and a clean channel preamp? is that right, or am I still confused?

thanks for all you're advice, everything is coming along nicely in my head so far.

[J M Fahey]

Hi heineken.
Almost there.
Your stereo power amp kit means you get *two* 50W LM3886 amps, don't know if on two separate boards or a single stereo one, plus a power supply board, ask the kitmaker for details.
The power transformer can either be sourced fom him or somewhere else you prefer , or pulled from some dead guitar amp.
You will have to build a preamp which will drive one or more power amps.

[heineken]

okay... so, if I were to build an amp with a clean channel, and footswitchable distortion channel, would I need two separate power amps?

what do you think of this as a power amp??
http://www.a1parts.com/newkits/amplifiers_kits.htm#DISCRETE POWER AMPLIFIER 200W-K8060

this guy has a lot of stuff to pick from on his website, and I just discovered it today, so there is probably somethng better on there. I figured if I can source my parts within the country, than at least I can save money on duty and exchange

[heineken]

that link is actually supposed to go directly to a heading of: DISCRETE POWER AMPLIFIER 200W-K8060
you have to scroll down the page about 1/3 of the way

[J M Fahey]

I had seen it a couple months ago, looks good, although somewhat more complex.
If you dare ..... go on.
I'd rather build *just one* more 3886-class chip amp before getting into the next step, a higher power, full discrete power amp, but of course, it's your project.
Good luck.