How to get started in amplifier repair/design?

dman535

Member
2007-12-29 11:37 pm
How does one begin the path to being able to repair/build solid state amplifiers? What tools are required?

I have done some minor electronics repair - but nothing as big as tracking down a serious fault in an electronic component. Would be curious to hear the groups thoughts on how to get started and aside from a sottering iron and a DVM what other tools would be needed.

Thanks

Derek.-
 
IMO, one learns to fix things by fixing them. You'll need some basic test equipment, and buying it on eBay, discovering it has major problems not alluded to in the description, then fixing it, is a pretty good way to go.

You need some references. I'd suggest The Art of Electronics by Horowitz and Hill, the several compilations by Jim Williams and Bob Pease, a general circuits book like Circuit Analysis by Barnstead (buy used textbooks- they're cheaper), and some on-line reading. Any of the Jim Williams pieces published in EDN are good, and usually on-line. IMO, anybody intending to design amplifiers, or even fix them, should get a copy of Doug Self's book on amplifier design. Even if you don't' subscribe to every word he says, acquiring the same information on your own would take decades. Unfortunately, books are expensive these days. Find some good used book shops and frequent them. Old copies of Timbie and Bush EE books are useful, as are books on Electronic Measurements (Stout, Farmer, Harris, Terman). Speaking of Terman, pick up a copy of his Radio Engineering book. Much of it applies to everything, not just radio. Search by the authors, as they have various titles, none of which I probably have exactly correct. Good Luck & Have Fun!

(on equipment, start with a simple but quality analog scope, an audio signal generator, and a decent DVM with a diode check feature)
 
A big chicken and egg problem!

It depends on how you learn: by trying and making (perhaps costly!) mistakes or cautiously with lots of theory from books.

If the former, try building some very inexpensive kits (you will destroy a few on the way), if the latter, get some good books (eg H&H) and do a lot of internet searches and reading of DIY sites.

A mixture of both is probably best.

As for tools, I don't know how anyone does ANYTHING without a 'scope. Being able to see why the DVM reading is all over the place and the chip is getting hot (it is oscillating at 10MHz!) is priceless.

Eventually you will need a signal generator, power-supply and 'scope. A PC with appropriate software has become extremely useful.

Keep asking questions!
 
Hi Derek -
This is a good web site for starting out - good basic info for no charge! http://www.bcae1.com/ Fixing electronic gear is different from designing electronic gear (duh) and the skill sets and approach are different. In either designing or repairing you do need to have an understanding of what the various components are and what they do when working - and what sort of indications they present when they go bad (shorted - open etc.) Good troubleshooting theory is most useful when fixing things - good electronics theory when designing or fixing. I would suggest start out building a couple of kits and fixing some things. Having good technical information at hand (ie service manual) is important. You can always feel free to PM me. :cheers:
 
Fixing is almost like building something... if you know how to build something fixing it becomes easy, as you learn to know the diffirent components and their interactions...

This is as much true for fixing a chair as for electronics

Even building some of the simplest projects can teach you more than a year's worth of reading threads.

As you build something you become aware of functional blocks of components within your circiut, and learn to spot diffirences and similarities in other circuits...

Then it is much like fixing a car... check for spark, check for petrol, scratch head, phone mechanic... just like real life...
 
LOL Nordic!

Sounds like my story! That's why I am losing my hair...Too much scratching!:scratch1:

Derek, I just started in April. These guys gave me the same advice. It is all true! Go with some progressively bigger and more complicated kits. They will each challenge you more and you will need different equipment with each step. Applying what you learned with the kit and equipment before to the new kit and equipment and adjusting/problem solving, concretizes what you learned. Then keep moving up the ladder.

In a short time you can take your experience and understanding to repairs and then designing (each is exponentially bigger than the previous steps). More tools and problem solving and the hook gets set even deeper. Evetually there will be no hope for you and you will live here like the rest of us! Even if you escape, you will always come back and visit often!

Troll the threads for others like you and me and you will learn about which equipment and software and web-sites that can help you with each step. There are always great guys here to help as well but they always appreciate it when you do your "Due Diligence" first!

I have a few threads about helpful sites here as I found them for other beginners like me.

Good luck!

Regards//Keith
 

karelc

Member
2008-01-03 11:35 pm
I agree that you should start with Horowitz and Hill and Doug Self's books, or similar.

It is important to know how the different types of transistors work, as individual components, but you must also know how they can be put together as functional units, e.g. current mirror, Darlington, long-tailed pairs and so on. More than that, you must also learn where, why, and if to use these building blocks.

After reading about the basics, why not try getting a design for a decent, well-known amplifier and trying to make a "copy"? Once built and working, take some measurements at various points under no-signal and signal conditions and see if you can work out why those measurements are correct for the conditions. Change compnent values and see what happens. This will help your understanding. Then look at other designs. Look for similarities and differences. A pattern of common building blocks and esoteric differences may soon emerge.

Good luck - it's not as easy as it sounds, but it certainly ain't rocket science. (I seem to recall that early ads for, or articles about, NAIM indicated that Julian Vereker studied electronics for a whole year so that he could build his first amp. Hmmm.... )

Karel
 
dman535 said:
... Would be curious to hear the groups thoughts on how to get started and aside from a sottering iron and a DVM what other tools would be needed.

Thanks
Derek.-

Aside from the very good advice already given, it will also be for your own good to know the correct spelling of that tool to connect all the electronic parts...which is "soldering" iron. "Solder" is that thing we melt. I just hope you take this in a good way...;)
 

anatech

Administrator
Paid Member
2004-06-06 8:31 pm
Georgetown, On
Hi Derek,
An important idea.

" The more you know, the more you understand what you don't know". Always keep an open mind and examine all your information.

Use common sense. Accept your own failings and you will find your own mistakes faster.

To design well and service well, you must understand the characteristics of each component type. This comes with time if you pay attention and read. Understand heat and the troubles it can cause. Engineers are getting better on this one.

App notes from component manufacturers are a great source of information. Even the one from Motorola that tells you how to mount power devices. I wish more people would read that one.

Take your time and try not to skip ahead when you are learning. There is a lifetime of learning waiting for you, so learn the basics well.

-Chris
 
Test Equipment?
I'd start with a CD player and speakers. I can tell more from the sound than from an Oscilloscope and sound generator. A small amp is needed for working with other than amp products. I also use a cheap analog voltmeter.

Of course, you'll want good test equipment when you can, but for me, I usually used them after the repair for final tuning/adjustments.

A 'patchpanel' is good to simplify interconnecting. Watch the grounding!
 

d3imlay

Member
2004-09-09 11:34 pm
Ohio
From the test equipment standpoint, if the budget is tight, you may want to look into PC based gear. I have a USB based scope I use for live training classes on uninterruptible power supplies. http://www.usb-instruments.com/oscillo_stingray.html

This device measures RMS voltage, peak, average etc. One must be careful of ground loops. I use isolation amplifier probes but an isolated USB hub works also. I understand that there is software for a low distortion generator but I've not used any. Consider buying a good quality voltmeter such as a Fluke and a soldering iron ASAP. Quality gear pays for itself if your going to do this for a while.

I can hear problems with an amplifer, but a scope tells me a lot more about what's wrong. I'm not sure I would be able to hear an amp that is down 2db at 20Hz because of a failing feedback cap. The scope will certainly tell me that.
 

anatech

Administrator
Paid Member
2004-06-06 8:31 pm
Georgetown, On
Hi d3imlay,
I have to agree with you on that score. Listening to an amp that is misbehaving is part of the troubleshooting process. It will not come close to telling yuo everything you need to know all the time. Not using an oscilloscope is just plain silly.

Hi Derek,
As d3imlay mentioned, good basic equipment is a must have. If you use a hand held meter, you can't go wrong with a Fluke. Stay away from the 80xx series as they are very long in the tooth. Escort makes decent meters (not nearly as good as a Fluke) and the new Agilent ones will be very good too. For bench meters (if you go that way), Agilent is my #1 choice followed by Fluke, then Escort and others. Stay completely away from Extech products.

You can use your sound card for an audio generator. They also make PC based function generators (expensive but extremely flexible). Also, look for older HP (Agilent now) 65x series oscillators. They have an output meter (lovely!) and good attenuators. The 654A is especially good in that regard. The 200 series generators are okay, but they cost more than the 65x series. One thing you will need to do is take the frequency tune knob and shaft out, clean and relubricate them. Do not attempt to turn it if it's stuck. You will break a nylon coupler if you do. Switch cleaning is a normal thing with almost everything that is old. I find the outboard oscillator much more useful than a sound card. These go up to 600 KHz also.

I have been playing with USB 'scopes. Right now I have a "DSO-2150 USB". That's the same one you see on the internet and Ebay. It comes with good probes and works very well. Perfect - no, but the performance is much higher than the $200 and change it cost me. These often do rudimentary FFT also. Cool!

Soldering Iron. Get a good temperature controlled model. I can say that the far east models work great. I used to use Weller, the far east ones work better and last longer. No contest as they are also much cheaper than Weller or Ungar. Buy a good assortment of tips. The wide ones are my favorite for a lot of work.

-Chris
 
I would say you want the following:

1) Soldering iron
2) DVM
3) Bench PSU - really useful to power something that is part built or to replace a fulty PSU
4) Scope. The various USB scopes are fine, but a second hand conventional one on e-Bay or through a second hand dealer can be cheap and good. I like the cheap Hitachi scopes - bright clear screen, easy to use, and last for ages. Older Tektronix scopes are good too, but I never liked HP ones.
5) Signal generator. A CD player and test disc will do at a pinch, but is very limited in frequency range. Same problem applies to soundcard in computer.

If you start working on amplifiers, a dummy 8Ohm load is really useful for testing.

The book suggestions above are excellent. One other source to look at, which I found interesting when I was getting started many years ago, was the Radio Amateurs handbook - don't buy it, but your local library might have a copy.
 
As an addition to those mentioned above:
- A various set of screwdrivers and Allen wrenches. Aside a basic screwdriver that has a tip that allows changing various head bits in buy at least one extra long and thin screwdriver with a “Philips” head and one extremely small, plastic “flathead” one.
- Cable stripping tool and a set of pliers
- Few alternative probe ends for the DMM: Regular probes, alligator clips etc.
- Light bulb current limiter (priceless!)
- Capacitor discharging tool (probe-end->wire->resistor->alligator clip)
- Schematics, service manuals and more schematics. Study them extensively.
 

dman535

Member
2007-12-29 11:37 pm
Thanks to all for the great information.

I have been building pc's, installing car stereo and building engines for years. So that basic mechanical stuff is a no brainer. I will definitley pick up some of the books and additional tools to round out my collection.

Do any of you feel that something like a basic community college type course is beneficial? Most of the stuff I have done to date has been self taught - just thought it might be an added plus to learn a few things in a classroom setting.

Thanks again !

Derek.-
 
dman535 said:
Thanks to all for the great information.

I have been building pc's, installing car stereo and building engines for years. So that basic mechanical stuff is a no brainer. I will definitley pick up some of the books and additional tools to round out my collection.

Do any of you feel that something like a basic community college type course is beneficial? Most of the stuff I have done to date has been self taught - just thought it might be an added plus to learn a few things in a classroom setting.

Thanks again !

Derek.-


Hi Derek - you sound just like me!
I too have been:

building pc's, installing car stereo and building engines for years
and,
like you, I have been wondering about a community college EE course.

I already own Randy Sloans books and will eventually get Self's, but I realize that I need a better grip of the basics. For whatever reason, this stuff fascinates me.
My dad was a TV repair man when I was young and I barely paid attention when he tried to explain stuff. I sure wish I could ask him questions these days.

As someone already stated, there is a lifetime of learning in this field.
 
dman535 said:
Do any of you feel that something like a basic community college type course is beneficial? Most of the stuff I have done to date has been self taught - just thought it might be an added plus to learn a few things in a classroom setting.

Absolutely. Having direct, hands on access to people who know what they're doing is really important.

Another thing that hasn't been mentioned is simulations. Install one of the free spice simulators, like LTspice, and have a play. You can work through lots of different ideas extremely quickly using a simulator. Even better, when something doesn't work, you don't burn your fingers on it.