How to get to know amplifier?

[dunnoguit]

Hi guys, first post here. I bought a second hand amplifier recently. It sounds so good and this purchase made me be massively interested in electronics. Just wondering how should I start to learn and master the skills to be confident in manipulating amplifier like repair, recap etc. I have basic soldering skills, made couple of rca xlr interconnects before. Cheers.

 

[indianajo]

You get more of an education from a broken amplifier.
However, a working one gives you something to listen to while educating yourself.
Get a copy of Thomas Floyd Electronic Devices, the Electron Flow Version 2nd ed or a similar community college or trade school 2nd year text. Read it, Get a dvm and do some of the power supply experiments with transformer, capacitor, resistor. If you buy a 24 vct transformer (center tap) you are ready for an experiment. 36 vct or 48 VCT allows an even more powerful experiment.
Get some perf board, or a sheet of NEMA CE 1/16" laminate and a yankee drill & #48 bit. Drill some holes. Get a steel box like a recipe card file, and some binder posts for output and RCA jacks for input. Buy some transistors, like MPSA06 and 56, BD139 and 140, MJL4302 and 4281. Get a few 1n4003 and some capacitors and resistors. Get some heat sinks for TO220 and TO247, some insulator material, some heat sink compound, some 24 ga wire in two or 3 colors. Get a WP35 iron, some tin/lead rosin core solder, some diagonal cutters, strippers, 5 way screwdriver, safety glasses. Build an amp. I like the Apex AX6, I'm building one right now on NEMA board, 3.5"x5". Or you can buy a kit from diyaudio store with the parts all included. The writeup of the Honey Badger is very instructive for the names and functions of all the parts.
Does the new amp sound better than the one you bought? Try some difficult material, say a Telearc or similar high quality piano CD. Compare the sound to a real grand piano. Is your new or old amp better? Are your speakers good enough where you can tell any difference? Does the reproduced music sound anything like a real grand piano? Usually not, took me 40 years to find speakers I could afford that sounded anything like real. Is the sound different between headphones (often good at the $25 level) and speakers (usually bad).
Have fun with the hobby.

 

[dunnoguit]

You get more of an education from a broken amplifier.
However, a working one gives you something to listen to while educating yourself.
Get a copy of Thomas Floyd Electronic Devices, the Electron Flow Version 2nd ed or a similar community college or trade school 2nd year text. Read it, Get a dvm and do some of the power supply experiments with transformer, capacitor, resistor. If you buy a 24 vct transformer (center tap) you are ready for an experiment. 36 vct or 48 VCT allows an even more powerful experiment.
Get some perf board, or a sheet of NEMA CE 1/16" laminate and a yankee drill & #48 bit. Drill some holes. Get a steel box like a recipe card file, and some binder posts for output and RCA jacks for input. Buy some transistors, like MPSA06 and 56, BD139 and 140, MJL4302 and 4281. Get a few 1n4003 and some capacitors and resistors. Get some heat sinks for TO220 and TO247, some insulator material, some heat sink compound, some 24 ga wire in two or 3 colors. Get a WP35 iron, some tin/lead rosin core solder, some diagonal cutters, strippers, 5 way screwdriver, safety glasses. Build an amp. I like the Apex AX6, I'm building one right now on NEMA board, 3.5"x5". Or you can buy a kit from diyaudio store with the parts all included. The writeup of the Honey Badger is very instructive for the names and functions of all the parts.
Does the new amp sound better than the one you bought? Try some difficult material, say a Telearc or similar high quality piano CD. Compare the sound to a real grand piano. Is your new or old amp better? Are your speakers good enough where you can tell any difference? Does the reproduced music sound anything like a real grand piano? Usually not, took me 40 years to find speakers I could afford that sounded anything like real. Is the sound different between headphones (often good at the $25 level) and speakers (usually bad).
Have fun with the hobby.

Thanks for such a detailed reply. Wow, looks like a lot to learn, probably will grab a book on amazon as a start.

 

[Jay]

looks like a lot to learn, probably will grab a book on amazon as a start.

Learning is an important topics. Knowing how to learn is critical. I believe that once we have a sufficient IQ (and discipline to do the work), what we need is a good teacher. Here, to some extent it can be replaced with a good tutorial or book.

Everyone has different knowledge. Some knowledge may be required to gain another knowledge. I don't know your background to know what you already know. But focus on searching a specific "keyword" such as "Power Amplifier Design" or even "Power Amplifier Design for Dummies".

You should get several books, such as from Douglass Self or Bob Cordell, or several PDFs, or several PPTs, or you may get a youtube tutorial video (Youtube/video learning is a big advantage for many people).

Just for knowing the concept and design a working amplifier, you can read literature (in my case, the result was so awful), but to really design a good amplifier you may need LTSpice. Unfortunately, it is not easy to learn to use the software (It took me one year to really "click" with the software).

 

[anatech]

Hi dunnoguit,
Welcome to our place!

There is a ton of stuff to know, and the great thing about this hobby is that you never stop learning. But before beginning this repair, I would implore you to get and read the books from Doug Self and Bob Cordell. Then read the chapters again when you are running up against a problem.

It takes years to become a good repair person, you'll see that once you get started. It is more than worth pursuing this as a hobby. Just don't rush things.

One comment about your soldering equipment. You have a "heat stick" already. What you really do need is a soldering station. Some really good ones cost about $100, plus or minus a few $$. There is a make from "Pro's Kit", Solomon and others that look the same. The model number is SL-30 for many of these brands and they look similar to each other. I've had one well over 15 years now and I have rebuilt it once. It's running like new again. The soldering iron is your basic tool, it makes a big difference having a controlled temperature iron with a grounded tip (terminal on rear of iron). A similar iron from Weller will set you back over $200, and I am glad I replaced those with the SL-30 model. Tips last forever too.

-Chris

 

[indianajo]

I would implore you to get and read the books from Doug Self and Bob Cordell. Then read the chapters again when you are running up against a problem.
pursuing this as a hobby. Just don't rush things.

One comment about your soldering equipment. You have a "heat stick" already. What you really do need is a soldering station. Some really good ones cost about $100, plus or minus a few $$.

Those books, Self & Cordell are way more advanced than the one I quoted. I learned from GE transistor manual 6th edition. The Thomas Floyd book is much better.
The $100 soldering station is way more expsnsive than the one I use. I use a Weller WP35 $40 in a tin pie pan with a grocery store cellulose sponge as a tip clieaner. I don't have trouble cooking transistors with a wedge tip, but IC's are too small and require a cone tip.
Also designing amps and simming them with $70 a update Windows is way ahead of what I do.I use free LInux with a *****y simulator, GEDA
I fixed my first transistor amp before the internet with no schematic diagram, no help, just a $20 analog VOM. 7 smoked transistors, a dozen smoked resistors replaced. E-capacitors based on age. I guessed wrong on the design of the incinerated current limiter and had the ST120 amp limited to 20 watts both channels until I found a post on this website explaining how it was supposed to work.
Now I take schematic diagrams from here and build them on NEMA CE laminate. then when working I modify them. The ST120 boards are "the worst amp on earth" and require defined gain transistors I can no longer buy. I'm now building an Apex AX6. Then modify it. The AX6 looks to have a 100kohm input resistance. The PAS2 preamp I use can only drive 500kohm. So I make changes.
Have fun with your part of the hobby.

 

[anatech]

Hi indianajo,
Go for the station.

That Weller has enough AC leakage to blow the hell out of sensitive devices. I tried using one, and the lack of temperature control is a serious issue. Let's just say that you don't know what your problems are until you use something without those problems. I have used the 35 W Weller iron. Get the station.

My fixit history is similar to yours at the beginning. I learned to get as much info as possible. If only the internet was even thought of when I started!

I hate windblows. I'm running Fedora 22 right now with the Electronics Lab suite. Again, you are probably running the same thing, or close enough. I have to run windows on a couple of machines due to work. An old windows Vista laptop runs like the wind when running Fedora. A whole new machine!

Why are you fighting with an ST120? I guess it is a challenge. You can make a lot better easily.

Best, Chris

 

[indianajo]

Well, no mosfets hear this iron. This is a grounded tip WP35. Though WP35 did work a 2n7000 power up silence circuit with no problem.
Thanks for the tip on fedora electronics suite. I'm using lubuntu 12 and the electronics suite ****s. Dell recycle program is so effective here through goodwill, no used computers for sale on craigslist after pentium 4, so have to use old software. At least I can communicate on forums.
Better amp is subjective. 99.99 % of amps on here will blow your speaker sky high if one soldering joint lets go. Had that happen on the ST120, overheat, a wire let go, the $50 amp went up in ball of flame on stage, no damage to the $100 each speaker. I like the simple stupidity of capacitor coupled speaker amps. I'm trying to protect a repaired (maybe) PV1.3k with a 60 part rail disconnect FET circuit but packaging is befuddling me. That direct coupled amp will not touch my $300 each speakers until protected better than the self melting crowbar circuit which doesn't blow the breaker. Relays as amp protection strikes me as stupid, gold contacts won't allow enough current interruption capability and copper contacts corrode and quit working.
Also this ST120 took a lightning stike through the power line and blew only a shut off pop cap. Try that with new transformers. But no center tap, has to be single supply . Have a LM49810 and some TIP142-147 to try but I'm nervous about hand soldering those close together pins. Discretes, you can bend them out. Also lots of oscillation bad news on the thread about that. LM3886 has limited 7 amp current and this ST120 will put out 40 v peaks when the cannon goes off into 6.5 ohms - with NTE60 output transistors (MJ15003 white box?) I like 70 db signal/noise in the living room, dont' need the heat sinks for 200 real watts unless I'm on stage (hence the PV1.3k). Also I can tweak the AX6 design maybe to work with the PAS2 preamp which only drives 500 kohms, not 50k.
Thanks for listening.

 

[anatech]

Hi indianajo,

Go for the station. At some point you have got to get something better that doesn't hold you back. Face it, parts are smaller these days. Having said that, I tend to use the largest screwdriver tip with this station, but I can quickly change to a needle tip if I need it. When you buy a station, buy extra tips, all screwdriver types that have flat spots. Wide ones and skinny ones. You can turn the heat up for big jobs and down for little transistors. At least the tips will allow you to work on that stuff.

Relays. I like them. You shouldn't be turning amps off with signal flowing anyway. If you do, then you pay. I'll replace relays any day rather than a single woofer! Call it ... maintenance. Like brakes on your car, if something has to die, please let it be the relay. I just did my Marantz 300DC (speaker relay) after a good 10 years or so of service since the last one. That's fine by me.

-Chris