Crash course in amp repair & kit building - watcha need to know?
Old 27th December 2012
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Crash course in amp repair & kit building - watcha need to know?

So this is going to be a pretty broad question. But assuming you're taking a novice to electronics, and want to teach them the bare essentials to be able to to try build a guitar amp from a kit, or repair an existing amp, what would you say they should have a firm grasp on beforehand?

I reckon you dont need to know all the ins and outs of electrical / tube theory to do repairs, or am I mistaken? Is it safe to assume its a different learning path if you want to repair / build already designed, versus wanting to design circuits from scratch?

Reason I'm asking is I want to dive into some projects this year, with the goal of being eventually being able to build amp kits.

Thoughts?
Old 27th December 2012
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Old 27th December 2012
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Here are some topics off the top of my head:
1) SAFETY! That includes wearing eye protection when soldering, drilling, etc. And that includes a healthy respect for high voltages and how to keep from electrocuting yourself. And how to ensure that what you build is safe for others to use, etc.

2) Basic electronics. But as you say this is a broad topic and I'm not sure what to recommend here.

3) Component identification, handling, usage in circuits. You will be pretty lost if you can't tell a resistor from a capacitor.

4) Schematic diagram reading and interperetation.

5) Circuit design. Maybe not to the level of being able to design something from scratch, but at least to be able to understand WHY most of the components are where they are and why they are that value, etc.

6) Soldering. Good soldering iron's aren't expensive, but a cheap lousy iron can make even an experienced engineer into a sloppy mess. Get some old discarded gear and practice soldering, removing and replacing components, etc. on point-to-point wired circuits, and on PC boards. But microscopic surface-mount components are NOT something to mess with as a beginner.
Old 27th December 2012
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Alot.

Any sort of crash course/quick fix mentality will hamper you more than help. You need to learn electronics, both the theory of how a circuit works and the application side(Soldering, drilling, probing circuits, draining power caps). It's a long old road, but a good one!
Old 27th December 2012
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If tube amps are on the menu, You need to be aware of the dangers of 300v+DC and how to deal with them.



-tINY

Old 27th December 2012
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Quote:
Originally Posted by tINY View Post

If tube amps are on the menu, You need to be aware of the dangers of 300v+DC and how to deal with them.



-tINY

discharge filter caps with your teeth while standing in a bucket of water, right?
Old 27th December 2012
  #7
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Worst I had was 300v across a bulk cap on an off-line switching regulator. The power supplies were crap, but we were making SCSI boxes at a price-point....

The switching FET was completely open. An hour after the thing was unplugged, I still got a deep burn on my fingertip between where the two leads touched my finger - smelled like burnt flesh too...



-tINY

Old 27th December 2012
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I keep an aerosol can of freon ("quick-freeze") on the bench for two purposes. First, because application of extreme heat or cold is sometimes useful for discovering circuit problems in intermittent equipment.

And second, because a quick blast of super-cold when you burn your finger on the soldering iron can greatly reduce (or even completely eliminate) pain and blistering from the burn injury. Same in the kitchen. If you burn yourself on something hot, apply ice ASAP. It works for me.
Old 27th December 2012
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Originally Posted by rcrowley View Post
I keep an aerosol can of freon ("quick-freeze") on the bench for two purposes. First, because application of extreme heat or cold is sometimes useful for discovering circuit problems in intermittent equipment.

And second, because a quick blast of super-cold when you burn your finger on the soldering iron can greatly reduce (or even completely eliminate) pain and blistering from the burn injury. Same in the kitchen. If you burn yourself on something hot, apply ice ASAP. It works for me.
Thats probably the most useful piece of advice I will gather from this thread considering how clumsy I am.
Old 27th December 2012
  #10
S21
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To build a kit you need to be able to solder and follow instructions carefully. You don't need to have a clue how the circuit works.

To fix something you have to understand how it works.
Old 27th December 2012
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But studying the circuit of the kit (and other circuits) is an excellent way to begin to learn how circuits work and why they are designed that way. Feel free to post references to circuits that you have questions about. We all learn from studying new circuits.
Old 27th December 2012
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Originally Posted by rcrowley View Post
But studying the circuit of the kit (and other circuits) is an excellent way to begin to learn how circuits work and why they are designed that way. Feel free to post references to circuits that you have questions about. We all learn from studying new circuits.
I wish I could find teaching walkthroughs of various amp circuits. Something that tells you like "the signal passes through these resistors, in order to filter such-n-such frequency" , rather than just reading a schematic and having to know such-n-such component is used to do what....
Old 28th December 2012
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Old 28th December 2012
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You have the capability of constructing a fuzz face or big muff?
Old 28th December 2012
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S21
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High voltage power supplies on valves amplifiers aren't a good place to start in electronics. This stuff can kill.
Old 28th December 2012
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Would-Be-Teaboy
 
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Quote:
Originally Posted by S21 View Post
High voltage power supplies on valves amplifiers aren't a good place to start in electronics. This stuff can kill.
Plenty of killer tones to be had!
Old 29th December 2012
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Quote:
Originally Posted by enroper View Post
Something that tells you like "the signal passes through these resistors, in order to filter such-n-such frequency" , rather than just reading a schematic and having to know such-n-such component is used to do what....
I'm not sure I understand the distinction between those two statements?

Try posting a schematic diagram (or a link to one) and ask your questions. Nothing like just diving in. Go for it.
Old 29th December 2012
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Quote:
Originally Posted by rcrowley View Post
I'm not sure I understand the distinction between those two statements?

Try posting a schematic diagram (or a link to one) and ask your questions. Nothing like just diving in. Go for it.
That's a great way to learn. I stalk threads where people discuss schematics frequently. Post questions when you don't understand, or even start a related debate. Most Audio-DIY guys are pretty cool, in my experience.
Old 29th December 2012
  #19
S21
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YouTube

The "Dumb ways to die" song includes "Do your own electrical work"

The high voltage supply on a valve amplifier is lethal. Don't start learning about electronics on gear where your first mistake could kill you.
Old 29th December 2012
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Enroper,
I started my path to electronics apprenticing for a tube amp tech and have come a long way in a year (my homework was amp building...)
Repair and builds are two different mindsets, but building is the better start.
Buy the book "The Guitar Amp Handbook" by Dave Hunter. Some guys here will dis it for valid reasons, but the first chapter completely walks you through a Tweed Princeton Circuit, which I think a beginner will really like.
Next pick out a good build amp. I am a mega fan of the 5f1 champ circuit. It's so Zen and makes a beautiful sounding amp every time. There is a great website of guys, lots just getting their feet wet, and many "been there" advisors. (Pm me if ya wanna know cause last time I mentioned, it was deleted).
Another book to buy is "A Desktop Reference of Hip Vintage Guitar Amps". The back is full of schematics and all the Fenders have a schematic and layout below, probably the easiest way to wrap your head around a schematic.
Learn resistor codes
Learn capacitor codes and conversions.
Draw the pinout for the tubes you will use (to drive it home)
Learn the difference between vintage and modern tube heater wiring.
Learn the difference between vintage and modern power ripple filtration values.

Good luck.

(This was a big post for me hope it doesn't go to waste )
(I just built a D-U87 for 1/8th Neumann's cost, and am about to make the famous compressor clones. Building will save you serious $, but be warned it is addictive...)
Old 30th December 2012
  #21
S21
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Starting with valves is like giving a kid a rattlesnake as their first pet. Better to give them a goldfish...
Old 30th December 2012
  #22
Would-Be-Teaboy
 
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Quote:
Originally Posted by S21 View Post
Starting with valves is like giving a kid a rattlesnake as their first pet. Better to give them a goldfish...
There's nothing wrong with cautiousness, but you're just being negative at this stage.

We've warned him of the dangers and any books or kits will do the same. I assume this guy isn't going to go licking mains transformers or caps. If he does something wrong it something goes wrong it'll hurt and it could be lethal, but it's often not. I imagine most people on this board have played slap and tickle with electricity and while a 9V supply is more tickle to the 240V slap, it's either been non fatal or the safety features of our electricial system have prevented us getting killed.

But pain is a really clever deterrent and it's assumed OP will actively avoid suffering. We're saying to learn the theory so he can avoid both constant frustration at problematic builds and avoid hazardous situations in the first place. Cap draining, electricaly insulated tools, common sense, fuses. What more can one do to make anything safe?

Now if OP tries to wire up an MRI machine, then I'll have objections!

Full disclosure: I'm pretty sure 50V is the largest shock I've gotten. The person I know with the record got a 100kV slap while trying to shoo a bird from his line of sight when working on an electrical line. Needless to say he was thrown out the cherry picker and broke a few ribs. He doesn't recommend it...
Old 30th December 2012
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I think you guys misunderstood me. I'm going to be starting out building pedals. My goal is within a year to have enough knowledge to work on amps. Im not way in hell starting out on amps...
Old 30th December 2012
  #24
S21
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Pedals are a great place to start. I'm not saying you need to be a rocket scientist to work with high voltage, but you need to get across some basic circuit concepts first.

Have fun. There are lots of great things to build, and a lot of satisfaction to be had from building them.
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