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  • Diagnosis assistant

    Reading a few of the persistent drizzle of posters saying "uh, my (insert amp here) just died. What could be wrong?" made me think back to debugging, and then the solid state devil that lives on my shoulder whispered into my ear the following:
    "Most of the time, you can debug an amp by just looking at what voltages are on the tubes. Why not just read all those... but automatically?"

    The idea is of course that modern microcontrollers use so little power that they can run semi-forever from a micro-battery, the almost all include an A-D converter, and they can easily enough read voltages and make conclusions from them. The amount of conclusions to be made is really quite small. Great precision is not needed.

    I suspect that with a remarkably small set of chips - a microcontroller and a few analog MUX selectors, mostly - you could have the thing read all the tube voltages and just tell you what's wrong with an amp in 90+ percent of cases.

    Voltages are scaled to 0-5V by resistor dividers; slowed down by a small capacitor, and clamped to the logic power supply by diodes to prevent killling the logic.
    Bias can be read on a positive-only voltage scale by having the bias voltage pull down on a pull-up resistor to +5 through a largish resistor with a clamp.
    You can even sense oscillation by using ultrasonic/RF pass highpass filters that feed a rectifier and sense setup. Output is through a 2x16 LCD.
    The thing is powered by a few small NIMH batteries kept charged by the heater supply, so it works when the AC plug is pulled out of the wall, even, or if the main power fuse is blown.
    With a little work, you could have the thing tell you "AC power in, main power switch is on, but no power to transformer: Fuse is blown." as well as other stuff.
    The uCs all have EEPROM these days, so you could have it read what your amp does when it's running correctly, store it, and tell you when the operating conditions vary more than X %.
    The thing could normally do nothing, but come into action when you pressed the "diagnose" button, using the previously charged NiMH batteries to run even if the amp is stone cold dead.

    Sorry for dumping this here. I had to write it down while I thought of it.
    Amazing!! Who would ever have guessed that someone who villified the evil rich people would begin happily accepting their millions in speaking fees!

    Oh, wait! That sounds familiar, somehow.

  • #2
    Wait a sec! Are you suggesting that amps, like cars, start sporting "on-board computers"?

    Interesting idea, although one would hope that they don't result in that little yellow "engine alert" light that has been illuminated on my dashboard for some 3 years while the vehicle continues to run fine and pass emissions tests.

    Comment


    • #3
      Excellent idea, congratulations.
      PICs are great, if I only knew how to use them !!!
      Juan Manuel Fahey

      Comment


      • #4
        And a whole new generation of amp techs who will report back to the customer, "I don;t know, I can't read these codes."
        Education is what you're left with after you have forgotten what you have learned.

        Comment


        • #5
          Originally posted by Mark Hammer View Post
          Wait a sec! Are you suggesting that amps, like cars, start sporting "on-board computers"?

          Interesting idea, although one would hope that they don't result in that little yellow "engine alert" light that has been illuminated on my dashboard for some 3 years while the vehicle continues to run fine and pass emissions tests.
          LOL!

          I just read one too many posts saying "My amp just died. It won't make sound any more. Whatever in the world could it possibly be?? It's the output transformer isn't it?"

          And I hate to say this, but the dashboard light is working as designed. Unless you hook up a code reader to it and see what the problem was, then turn out the lamp, the light is designed to stay on in perpetuity. I had exactly this problem with my pickup (Texas, you know... ) and when I read the code with my brand new $39 Harbor Freight code reader, it said "misfire on cylinder 1". Light off, never came back on. So where do I mail this code reader thingie??

          But yeah, there is not a cure for management directed... er, I mean poorly executed programming.

          Oh. I had another thought. The action of latching dashboard lights may well be a US government requirement. The only thing better than management designed software is government designed software.

          And a whole new generation of amp techs who will report back to the customer, "I don;t know, I can't read these codes."
          RIGHT~!!

          Actually, in my dream-idea, I'd use a two-line LCD display. Drives really easy from uC, low power to fit the batteries thing, and cheap - about $4.
          Amazing!! Who would ever have guessed that someone who villified the evil rich people would begin happily accepting their millions in speaking fees!

          Oh, wait! That sounds familiar, somehow.

          Comment


          • #6
            Of course, this will be followed-up by the robotic repair machine.

            When I finally see the bias "idiot lights" work properly on EVERY new SVT, then perhaps I will say "yes" to this idea. Until then, live techs are still needed.
            John R. Frondelli
            dBm Pro Audio Services, New York, NY

            "Mediocre is the new 'Good' "

            Comment


            • #7
              And all these guys worring about a tenth of a milliamp setting their bias, when I see on some schematics the bias setting spec was to monitor MAINS current and set the bias for X number of watts draw from the wall by the amp.


              I used to have a 1982 Datsun 200SX, and one night about 2AM, in the middle of nothing, on the interstate, the CHECK ENGINE light comes on and glows at me. Oh my god!!! I had no idea, so I pulled over, couldn;t find anything wrong, car seemed to be running OK, so I gingerly continued on to my home. I'm no dummy, I had the service manual for the car. I got out the schematic for the car, and traced the light back to its control.

              It seems the CHECK ENGINE light on that car was turned on by a switch on the odometer. I had just passed 50,000 milesw on the highway, and the little odo 50,000 mile switch turned on the light. A little research revealed the light was just a reminder to take the car in for its 50,000 mile checkup. The official procedure for turning out the light was in the manual too: remove the bulb. Sheesh...
              Education is what you're left with after you have forgotten what you have learned.

              Comment


              • #8
                Hi all!
                It's funny R.G., because not much time ago I was thinking to implement something similar inside an amp, only, I thought about the "thing" as some kind of AI primarily dedicated to channel/function switching, the "diagnostic" functions being only a side benefit/possibility.

                The idea I had in mind ( don't light your flamethrowers yet, please ) was to integrate a small PLC within the amp's architecture. Such things are very cheap nowadays (in the 100USD "retail price" range), they can deal with both analog and digital signals, they're easy to wire and program ( ladder logic ) so you don't have to be a C++ Software Engineer to write a fully functioning program ( including software multiplexing of the inputs, if needed ) and most of them also sport an "user configurable" text display for state messages/alarms and the like.

                PLCs are far more reliable than PCs, they're built to operate in industrial environments, so, operating under far easier conditions, the possibility of a failure is practically non-existent.

                JM2CW

                Best regards

                Bob
                Hoc unum scio: me nihil scire.

                Comment


                • #9
                  Excellent idea! I can think of some other features too.

                  *Alcohol fume sensor and volume limiter to stop you playing too loud when you're drunk.

                  *Anti-Stairway algorithm: prevents anyone playing Stairway To Heaven through the amp except Jimmy Page himself. (Denied!)

                  *D/A converter for automatic rendition of Free Bird, you can leave the stage and get yourself a beer.

                  *Dispenser for putting dimes into starving amp tech's begging bowl.


                  If I wanted to improve tube amp reliability, my first step would be to get rid of the tubes.
                  "Enzo, I see that you replied parasitic oscillations. Is that a hypothesis? Or is that your amazing metal band I should check out?"

                  Comment


                  • #10
                    Originally posted by Steve Conner View Post
                    Excellent idea! I can think of some other features too.

                    *Alcohol fume sensor ...
                    *Anti-Stairway algorithm: ...
                    *...automatic rendition of Free Bird...
                    *...dimes into starving amp tech's begging bowl...
                    And how about them built-in effects? Like the now-infamous
                    - Talent booster
                    - Ego-plex
                    - Blame shifter
                    ...
                    Amazing!! Who would ever have guessed that someone who villified the evil rich people would begin happily accepting their millions in speaking fees!

                    Oh, wait! That sounds familiar, somehow.

                    Comment


                    • #11
                      Originally posted by Enzo View Post


                      I used to have a 1982 Datsun 200SX, and one night about 2AM, in the middle of nothing, on the interstate, the CHECK ENGINE light comes on and glows at me. Oh my god!!! I had no idea, so I pulled over, couldn;t find anything wrong, car seemed to be running OK, so I gingerly continued on to my home. I'm no dummy, I had the service manual for the car. I got out the schematic for the car, and traced the light back to its control.

                      It seems the CHECK ENGINE light on that car was turned on by a switch on the odometer. I had just passed 50,000 milesw on the highway, and the little odo 50,000 mile switch turned on the light. A little research revealed the light was just a reminder to take the car in for its 50,000 mile checkup. The official procedure for turning out the light was in the manual too: remove the bulb. Sheesh...
                      Same deal on my Mitsubishi pickup.

                      Comment


                      • #12
                        Originally posted by Mark Hammer View Post
                        Wait a sec! Are you suggesting that amps, like cars, start sporting "on-board computers"?
                        Yes. I am wondering if this couldn't lead to "Sudden Unintended Amplification" among amp users. I would hate to see R.G. in front of Congress explaining how he can't replicate the trouble.

                        Comment


                        • #13
                          I'm deathly afraid that one of you techies will install a 'suck-o-meter' on the front of my amp, so that even the drunks will know how badly I play.

                          "Here's the big guitar solo.... My God! The Suck-O-Meter is going off like a strobe light! Pull the plug! Pull the plug!"

                          Comment


                          • #14
                            Let's face it. This idea CAN actually be implemented. The questions are: will people pay for it, and what will they do with it?

                            Use this scenario as an analogy: your "check engine" light comes on and the car is running a little rough. You borrow a buddy's code reader and plug it in. It tells you that you have a bad oxygen sensor.

                            "Geez, where is it and how do I change it?"

                            Get it?

                            There was and always will be practical reasons for technicians in every field. The diagnostic tool cannot change the bad parts, nor does it have eyes, ears and hands to detect and suss-out other problems that may be in the works for which there is no digital detection method.
                            John R. Frondelli
                            dBm Pro Audio Services, New York, NY

                            "Mediocre is the new 'Good' "

                            Comment


                            • #15
                              I agree with John, tech will always be needed. The consumer is not necessarily going to DO much in many cases - except know when he or she is out of their depth.

                              I used my Actron code reader to see that my wife's car has a bad water-level sensor in the radiator overflow reservoir.

                              Asking the mechanic how much to fix - $150. Looking up part online (you have to replace the whole reservoir) - $47. Using the Actron to delete the trouble code and waiting to see if it pops up again - priceless.

                              Wife is off my case. I won't have to fool with it again until it really breaks - then we'll go to the shop, because I don't want to spend the time under the hood.

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