Practice Amp Suggestions?

[J M Fahey]

Yes.
People tend to service relatively expensive stuff, but discard without warning "cheap" stuff.

For good reason, considering average Tech bench hour rate or minimum charge is around U$60 in USA and reaches U$120 in expensive to live New York, a lot of stuff whose used proce falls below that is simply junked.

If you have at least basic troubleshooting skills you have nothing to lose checking such stuff yourself; I´d say 30 to 50% of the time is not an electronic problem but a "mechanical": bad/rusty/dirty jack, pot or switch.

In Buenos Aires there used to be a Tech which everybody nicknamed "the digital guy"  because he accepted stuff which nobody else would touch with a 20 ft pole, (specially keyboards butalso Studio stuff) because of absolute lack of schematics, spare parts, etc.

This was over 20 years ago, where you could not ask for some PDF service manual over the Net.

He had a small rented office, with a front desk to receive stuff, and a back room Lab.

Once I got invited to that secret place, after swearing over 10 Bibles not to tell (at least inside Argentina ) what I was about to see.

I expected a ton of NASA type gear, digital stream analyzers, the latest Scope money could buy, etc.

Fact is he had only an *analog* multimeter (with a slightly bent needle, a battle scar from some wrong scale measurement) , a good set of jeweller´s screwdrivers, torx bits, a couple cans of cleaners, degreasers, etc. , some cotton, isopropyl alcohol , a few spare fuses, a jeweler´s loupe ... and not much else.

I was *amazed*.

He told me: "I test-by-use and dissassemble stuff, pull and reseat flat ribbon connectors, pull, wipe clean and reset PCB edge connectors, clean and work end to end: pots, switches and jacks, flex and test MIDI cables, check for cracked solder, specially at external access points, etc. That alone solves 30/50% of problems. Besides, I check (with the bent needle meter) that power rails are available and reach all boards (+/-15 and +5V)".

Just with that he repaired (and charged for) over 50% of the stuff .
For the rest, he tested them until he found which was the bad board, pulled it and had his beautiful girlfriend (an Airline hostess) bring it to USA to have the original Factory repair it for a fixed amount.
Of course, he charged double that.

And yes, way back then "good" stuff was still made in the USA (think UREI, Gain Brain, Mackie, Ashley, JBL, Eventide, Shure, Ampex, etc.) or had strong presence, specially servicing (Yamaha, Tascam, etc.)

Today that is impossible, because most stuff (Behringer, etc.) is disposable.

[BrianS]

Oh No harm done, Lets hope BrianS understands we are all human and even the best of us make mistakes

Indeed, and I do.  I also greatly appreciate the fact that guys like JM take the time to share their knowledge with everyone here. 

I guess I did feel a bit insulted by the tone of the response, and that feeling was multiplied by the fact that the comments were placed directly into my post.  ANYWAY...I'm over it.  Again, my apologies to the OP for the thread derail...

[phatt]

Hey I like Brian already,,A group hug all round. <3)
Now what was that Q,,, oh yeah which amp to disect thing.

He is my little story.

Long before an old bugga like me even understood "press any key to continue"
Let alone internet I started pulling old transistor junk apart, no make that anything electrical I could lay my hands on that looked like it might make music.
I back engineered old radio grams by following the tracks on those old single sided boards. My first schematic drawing where close to unreadable but at least I understood what they meant.
I read heaps of old EA magazines I'd find at book stores and other like places.

My first breakthrough was a good friend who changed direction at Uni handed me a pile of Elec Eng books (those expensive ones university students have to pay for)
One was Art of Electronics and many others, some old including Valve equipment.

Much reading went on until things started to sink in.

** Please note I urge anyone wishing to learn this art to start at the basics like magnetism/rectification/ all the basic AC DC concepts as it will speed up the process a lot. (The net now makes that even easier) And please don't forget the most important one **SAFETY**
My rules of thumb are; Don't touch anything you can't outrun,,, and Never assume it's dead. :trouble

My next breakthrough was a chap handed me a copy of a basic El simulation program.
So between that and books and now the net I feel I'm at least much more able to pick out what might work and what is just another boring old fuzz box.
Ok I've melted quite a few perfectly good components in the past ~30 years and added to landfill with many disaster circuits I've built but it's par for the course of being a hobby geek trying to get your head around all the tecky stuff. :cheesy:

Coming from that perspective I see the fastest way to get ahead is a bread board, a couple of decent multimeters and simulation software.
In your particular situation *as J.M. Fahey noted* get those little Amps and just back engineer it then simulate to see what happens inside then start modding.

Take the time to follow the tracks on the pcb note all the pins of transistors and chips, refer to data sheets for pinouts.
OK you maybe rolling your eyes by now and YES it will be slow at first but will go a long way to get in touch with circuit design and how to layout a board.

The beauty of sims for me is that I can change a value on the sim then look at how it effects the result (A visual plot on the screen) all in a few clicks of a mouse then do it on a working breadboard circuit and HEAR the resulting sound.  That way you quickly learn to identify the sonic result of that visual graph or plot. This makes for a very fast process and negates the shed full of test gear to find the same result. (cheaper also)

I've worn out 4 of those little bread boards making all sorts of music related circuits. So out of hundreds of failures I've designed about 4 I'm really proud of and most of those circuits are posted here on SS guitar.

One other point to make Which Jaun pointed out beautifully way back;
Once you start modding unknown pcb's it's easy to stuff up the pcb and render the whole thing useless and not repairable. (Hey I'm also guilty of that silly mistake)

You are far better off starting at the breadboard and *COPY* the Amp circuit you wish to understand then when you find the sweet spot transfer those changes to the original amp thereby lessening the chance of destroying the PCB.
The Pcb is the hardest part to replace and likely impossible to replace with some gear.
Phil.

[J M Fahey]

Agree

For me "parts is parts"  and can be bought over the counter (or by mail) at some place or another, or often substituted by some equivalent, but the PCB **is the amp** , it's what arranges all those individual part to be that particular amp and not other, and can not be bought anywhere.
In fact, once he finished the production run, not even the Manufacturer has them for his own use.

There are very few exceptions , counted with one hand's fingers, such as :
manufacturers of very expensive very high power , professionally abused amps (touring PA systems) such as Crown, which can send , say, Guns and Roses playing in Kuala Lumpur a couple stuffed power boards to replace those blown in Sydney 4 days earlier , or Marshall sending new production boards for DSL2000 to replace a bad batch of conductive boards or Hartke sending new boards (minus the outpuut transistors)  to amps in warranty because for them that is cheaper than moving a heavy amp both ways, but those are the exceptions.

For *any*  amp consider damaging the PCB beyond a couple pads or tracks a complete loss situation.