How To Build An Amp

[stephen]

can anybody help me with how to build an guitar amp?

[jnewman]

I'm not going to tell you that you can't jump right in to building guitar amplifiers, because I'm not your mother, but my advice would be that you not jump right in to building guitar amplifiers if you don't have past experience with electronics.

I say this because guitar amplifiers are not the least bit beginner friendly. The quintessential guitar amplifier runs on vacuum tubes, which require DC voltages usually in excess of 300V (and sometimes over 500V!). If you are not experienced with electronics work, particularly high-voltage electronics work, you stand a good chance of zapping the hell out of yourself and possibly causing serious injury or death. Seriously! There are, of course, solid state amplifiers which run at much safer voltages (usually 12-48V), but the solid state amps that sound decent tend to have loads of parts and are pretty complicated (often even including computer modeling).

Additionally, guitar amplifiers (of both the tube and solid state varieties) can be very finicky about having things just so - and that doesn't just mean all the bits connected right. Among other things, having wires cross in the wrong place can induce annoying hums or even cause feedback that will render the amp unusable until you can figure out where the problem is. These kind of problems either require a lot of experience, a lot of painstaking, frustrating fiddling, or an oscilloscope (or some combination thereof!) to fix.

The thing to do if you are interested in learning to build guitar amplifiers is to get a multimeter and soldering iron and familiarize yourself with their use. Read a little about basic electronics on the web. Build a few low-voltage DC projects like stomp boxes, headphone amplifiers, or the 9V battery powered Ruby guitar amp (which isn't fancy, but is easy to put together). Maybe hang out at some of the amp-building forums around the web, like ax84.com and 18watt.com (which is on a brief hiatus but looks to be on its way back). Read about tube electronics and tube safety - check out the "tech info" section of www.paulrubyamps.com and the "tech info" section of www.aikenamps.com as well as some of the tube theory stuff over at AX84. When you are ready to start on a real guitar amplifier, I would strongly suggest that you go with a kit (and particularly a kit which includes a build manual - plenty of kits come as a bag of parts, a schematic, and a picture of the finished product). A few places to look for kits are www.ceriatone.com, www.tedweber.com, www.bnamps.com, www.torresengineering.com, www.tubedepot.com, or www.dobermanamps.com. I can only recommend www.ceriatone.com from personal experience. Doberman amps sells kits of the AX84 designs, one of which, the firefly, is about as simple as it gets and might be a good first amp. Another good first amp would be an 18watt lite, essentially a pared-down single channel old-school Marshall (available from a number of sources on the list).

Edited June 9, 2007 by jnewman

[Geo]

jnewman is right, you need to learn some basic things first. But I think once you have those down, you can get started on building an amp... though you should build something SIMPLE for a first project.

As to tube amp safety, you can probably search that on the web and learn everything in a few minutes--i.e., the amp is always UNPLUGGED (and the power section safely discharged) when you're working on it, or if it must be on while you're moving wires around, use something nonconductive to poke, and keep one hand behind your back, in your pocket, etc, and be aware of where the high voltage is in the circuit.

Yes, you've GOT to be able to solder correctly before you get started, or you'll have twenty cold joints on your circuit board and you'll wonder why your amp keeps crackling and farting out!

[X1TX]

That's why I'm going to start on something simple like the Altoids can amp, then maybe a Rudy. If I still enjoy doing that perhaps a tube amp. But that's a year off at least.

[-CB-]

I'm not a fan of his by any means, but if you can find a copy of Dan Torres' book, it has all the basics you need to build a single ended 5w tube amp. If you read through all the stuff contained therein, and heed the warnings... you might just do ok.

If you're building an amp, and following the design thats proven and known to work well, the most important thing you'll need to learn is how to work cleanly, make clean tidy joints, not have scraps of solder and metal shavings and such laying inside the chassis, not having excessive length of exposed leads that can short.... that sort of thing.

To me, in my way of thinking, Leo had it right when he used push back wire for the wiring in his amps, as its the easiest to work with, and makes sure you don't have any exposed leads where you don't want them. Its worth the extra $$ to get that type of wire. Its also worth the effort and expense to color code your connections on your board. That is - I make my cathode wires blue, plate wires red, grid wires yellow. All the high voltage wires are red, signal yellow. For misc connections like negative feedback and screen grids I use brown. That way, when I look at a wire, I know for sure... "ok its going to the right spot". If all your colors are the same... good luck!

For tube amp work, you need not only a meter, but a Variac is essential. You can get great ones used from auction places online and from surplus houses online as well. The surplus houses do a great job btw, since most of their stuff is lightly used university and govt equipment in prime shape. You know how the govt works "if we dont spend the money we lose it!" so they're always renewing their equipment, upgrading etc etc.

Having a buddy stand bye while you power things up is also a good idea..... just in case you have a major issue.

I've built about a dozen tube amps, and I still get the willies when I power one up for the first time... I do it slowly... on a Variac... and keep one hand in my pocket. I've had exactly ONE problem, a capacitor in backwards that went BANG!. So be careful. (btw, I now mark my boards for + and - so the caps don't do that again!)

[Mike Sulzer]

can anybody help me with how to build an guitar amp?

Look at AX84.com

[WezV]

I got the a champ head kit from these guys and it was a real pleasure to build:

http://www.stf-electronics.com/

The instructions run you through all the safety checks as you go along and i had not problems. I had wired plenty of guitars before but this was my first 'proper' electronics project.

[Geo]

For tube amp work, you need not only a meter, but a Variac is essential.

Well, I've managed without a Variac. Just triple check the wiring esp in the power section.

Another great resource is the Hoffman forum:

http://www.el34world.com/Forum/yabb2/nph-YaBB.pl

[PunkRockerLuke]

runoffgroove.com has good amps you can build such as the little gem and ruby.

[X1TX]

Then there's always the Noisy Cricket.......

Noisy Cricket

[-CB-]

For tube amp work, you need not only a meter, but a Variac is essential.

Well, I've managed without a Variac. Just triple check the wiring esp in the power section.

Another great resource is the Hoffman forum:

http://www.el34world.com/Forum/yabb2/nph-YaBB.pl

Well..... it goes like this:

If you don't bring things up slow, you really run the risk of few different problems, from "live" chassis (that whisker wire you didn't see), or a "boom" (that cap you had in backwards), all sorts of issues.

Bringing up a SS rectified amp, I like to check the voltages when the B+ is still quite low, say in the 50 volt range. Even on a tube rectified amp, I like to throw a SS rectifier plug in there, just to bring it up with. While I'm doing that, I'll give a chopstick test to make sure everything is ok. If it all holds up, then bring it down, put the tube recto back in and bring it back up again. This is just good practice to do.

[Geo]

Well..... it goes like this:

If you don't bring things up slow, you really run the risk of few different problems, from "live" chassis (that whisker wire you didn't see), or a "boom" (that cap you had in backwards), all sorts of issues.

Bringing up a SS rectified amp, I like to check the voltages when the B+ is still quite low, say in the 50 volt range. Even on a tube rectified amp, I like to throw a SS rectifier plug in there, just to bring it up with. While I'm doing that, I'll give a chopstick test to make sure everything is ok. If it all holds up, then bring it down, put the tube recto back in and bring it back up again. This is just good practice to do.

I certainly agree that's safer... but I'm not a very safe guy.... and I'm a penny pincher. But then again, I would tend to stay away from complicated amps (the most complicated I've built is a cathode-biased Princeton Reverb w/out tremolo... woo, that amp is hot!), so there's less to screw up. I check everything several times, etc... I don't use stranded wire, so none of those invisible shorts from little strands...

"That's why I'm going to start on something simple like the Altoids can amp, then maybe a Rudy. If I still enjoy doing that perhaps a tube amp. But that's a year off at least."

Unless the supplies don't cost much, I PERSONALLY would not bother with those (I imagine they're solid state). A simple tube amp will sound a lot better. But I see your reasons for going that direction. Have fun whatever you do.

[jnewman]

You can sidestep a few of the reasons for having a variac by making a current limiting box. The way to do this is you build a box which plugs into the wall. Said box also has an outlet in it that you plug your amp into. The hot wire from the plug goes through a normal incandescent light bulb to the outlet.

If everything's fine, the light bulb will glow dimly and the amp will run a little bit brown (lower power). If you have a short or other problem that would cause the amp to draw a lot of current, then the light bulb will light up at more or less full light bulb brightness, the amp will have its current limited and you will know something is wrong.

Edited June 15, 2007 by jnewman

[X1TX]

"That's why I'm going to start on something simple like the Altoids can amp, then maybe a Rudy. If I still enjoy doing that perhaps a tube amp. But that's a year off at least."

Unless the supplies don't cost much, I PERSONALLY would not bother with those (I imagine they're solid state). A simple tube amp will sound a lot better. But I see your reasons for going that direction. Have fun whatever you do.

Well, I'm not looking to build a tube amp now because I'm not that good at soldering nor guitar playing. But over time as that changes I'll head in that direction. But a small, solid state amp might be good because it's portable and cheap to build. Good learning project. And once my skills on the frets improves to the point I can actually play something I want to hear I should be far enough along to do a tuber. I'm just not there yet.

[Geo]

Well, I'm not looking to build a tube amp now because I'm not that good at soldering nor guitar playing. But over time as that changes I'll head in that direction. But a small, solid state amp might be good because it's portable and cheap to build. Good learning project. And once my skills on the frets improves to the point I can actually play something I want to hear I should be far enough along to do a tuber. I'm just not there yet.

I know what you mean. I was kind of foolish and built an amp before I could really play guitar too well. But here's another angle... a better instrument (i.e. a good tube amp) will be more responsive and make you a better player.

If it's cheap, then go for it. If you're doing small solid state, perhaps you could build an effects pedal? I've never built anything like this, but I looked at the schematic for a fuzz face once and it's pretty simple.

Just offering some more thoughts... good luck.

[-CB-]

The current limiting box is really a must have if the Variac is not in place.

When I put up antennas, we use a thing called a polyphaser to protect the building from burning down, in case the antenna goes hot or gets hit by lightning.

My less than esteemed associate says... hey we could save time and money if we left these out.....

To which I reply - the alternative, however rare, is so absolute, so catastrophic and so complete, even at the minuscule odds, its not a risk worth taking.

I mean... when you have 400+ volts DC dancing about.... thats not the time to start saying lets pull the plug QUICK.

BTW, even solid wire will be a gotcha. It does that when its not a whisker, but just a stray end that you didn't thing was touching .... and touched, or was close enough to arc when hit with 450v. <--- have had that happen to me!