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Analog guitar amp with digital meter

Discussion in 'General Electronics Discussion' started by Still buildin, Dec 28, 2018.

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  1. Still buildin

    Still buildin

    14
    4
    Dec 28, 2018
    Hi all.....in the process of completing an old school tube amp. It's sounding great and I want to add a digital hour meter into the circuitry (for tube changes and other maintenance). My problem is that the only pcb style meter I have on hand is a used Curtis unit. It is a non reset version and I want to reset it to zero. I'm good with analog circuitry but out of my depth in digital. I've attached a couple pics of the unit I have here.

    Is there a way via eeprom/ pc link? to get inside the ic and reset there? Thanks.....any help would be appreciated!
     

    Attached Files:

  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,490
    2,831
    Jan 21, 2010
    1. Note the number of hours currently on the meter.
    2. Calculate the number of hours until the next service interval.
    3. Add these numbers together.
    4. Get a small piece of clean white paper and a non-erasable pen.
    5. Write on the paper "service at xxxx hours", where xxxx is the number calculated in step 3.
    6. Afix the paper near the hour meter.
    Repeat this process after each service.

    I hope it's a class A amplifier or servicing after a fixed number of hours will mean even less than it would for a class A amplifier.

    And presumably you're measuring hours of HT applied to the tubes.
     
  3. Still buildin

    Still buildin

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    Dec 28, 2018
    Thanks.....I think. I appreciate the time you've taken in responding to my enquiry - although I'm sensing some holier-than-thou sarcasm. You probably realised that someone capable of building their own tube amp is likely smart enough to have already thought of suggestions 1 thru 6 - detailing a convoluted Pen and Paper scheme.

    I'll leave the post up in case anyone can actually provide any useful answer to my query.

    Thanks again....
     
  4. Audioguru

    Audioguru

    3,247
    702
    Sep 24, 2016
    Tubes in this day and age??
    Many bands replace the worn out antique tubes after each show. Then a timer was not needed for them to produce the muffled and distorted old sounds.
     
  5. Still buildin

    Still buildin

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    4
    Dec 28, 2018
    Yep, tubes.....all the way. Still the only thing that really sounds good. Don't take my word for it though: ask any performing guitarist.

    A little background may alleviate confusion here......my amp build is a hybrid circuit. Between an old David Gilmour favorite, the HiWatt and another called the "Trainwreck" - originally designed and built (mad scientist style) by the late great Ken Fischer. The Trainwreck elements are deliberately built close to the edge of instability and oscillation.......hence the name. Running a circuit so hot could still be done reliably when built by a genius like Ken. My efforts are not as reliable but have achieved the sweet harmonic overdriven feedback on demand - which his circuits were famous for. There are a number of regular maintenance issues I have to watch.......

    Thanks!
     
  6. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,490
    2,831
    Jan 21, 2010
    No, I'm just suggesting how these things are typically used. If you have a resetable device there is always a question as to whether it has been inadvertently (or not) reset, and it removes the capability of having a series of service intervals (replace output tubes every 200 hours, phase splitters after 1900 hours, and rectifier tubes after 9000 hours).

    Also, my major point was that time may not be the best indicator of need to replace the tubes.

    @Audioguru suggests 2 different methods:
    1. After each use (for a guarantee of freshness)
    2. On condition (for a guarantee of utility)
    Changing on a set schedule guarantees either a schedule or an income -- it is typically set very conservatively (see aircraft maintenance schedules) -- to try to limit the probability of failure, but you don't know if you're changing out an almost failed component or one that is almost in new condition.

    Consider oil changes on a vehicle. Most of these are done on a mileage basis (because cars don't have hour meters). Tyres are typically changes "on condition" (i.e. when they are nearing the minimum legal tread depth). In some cases safety equipment is changed on an event basis (e.g. seatbelts may be removed and replaced after a serious accident).

    On cars you don't reset the odometer after each oil change. On our laser cutter we don't reset the hour meter after each tube change. Resetting these meters is an exception (e.g. trip meter in a car) rather than the rule.

    You mean distortion. You know you can do the same with a single jfet in a solid state preamp, don't you?

    I understand still using tubes. It is a very lucrative business. And changing valves after a set number of hours is a great way to ensure the money keeps rolling in. Congratulations.
     
  7. Still buildin

    Still buildin

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    Dec 28, 2018
    Are you really going to try to turn my simple request into a tube vs chip amp bitchfest? Perhaps one of the oldest and most tired internet arguments of all time. I'm going to take a chance here and guess that you are not a guitarist. Those that play (and can play), almost all prefer to play through analog tube amps. But I'm not going to waste any more time going through what is already obvious to recording and performing guitarists.

    Regarding maintenance in my rig - it is also not simply about changing tubes.

    If anyone can actually tell me how to access the meter chip and reset it somehow, I would really appreciate it.

    Thanks
     
    Last edited by a moderator: Dec 29, 2018
  8. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,490
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    Jan 21, 2010
    No, but the vocalists and other musicians (mostly guitarists) who have expressed interest in my tube preamp seem to think the same way as you.

    I'm happy to sell them what they want. I was simply congratulating you for figuring a way to extract more of their money. Unfortunately the musicians I deal with are typically stretched for cash.

    And my solution for resetting the counter is "don't bother". It's cheap and easy.

    If you want someone without specific knowledge of the unnamed part you're using to answer your question then you'll need to supply more details. Perhaps the model number, a schematic, or perhaps you could disassemble it enough to identify the EPROM or microcontroller it uses. If it's an EPROM, maybe it's possible to desolder it, reprogram it, and resolder it back in place each time you want to reset it.

    Do you just want to reset it once, or each time you change the tubes?
     
  9. AnalogKid

    AnalogKid

    2,497
    718
    Jun 10, 2015
    Modifying the hour meter you have is not possible. Under the LCD is a small microcontroller that does the counting and display management. There are no unpopulated pads that might be an in-circuit programming port, so even if you had the original program code to modify, you couldn't reprogram the device.

    The meter is keeping the last count in non-volatile flash or e-squared memory so it powers up with the last value intact. Unless there is a secret handshake to trigger a reset function, you're cooked.

    ak
     
    (*steve*) likes this.
  10. Still buildin

    Still buildin

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    4
    Dec 28, 2018
    Ok thanks, I appreciate that advice and information. I'd like to convert the meter into a resettable unit if possible.

    It is a Curtis pcb hour meter, model 701.....probably 15 years old.

    As previously stated, I'm a bit out of my depth here.......the board is small and I don't even know where to look for the right chip. I read online that these units do contain eeprom chips.

    I guess the pics in my post don't help - I'll try some disassembly.......

    Thanks
     
    (*steve*) likes this.
  11. Still buildin

    Still buildin

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    Dec 28, 2018
    Oh...ok thanks. Much appreciated!
     
    (*steve*) likes this.
  12. Audioguru

    Audioguru

    3,247
    702
    Sep 24, 2016
    Electric guitarists are deaf to high audio frequencies and do not hear the awful distorted fuzz that people with normal hearing hear.
    Old age also kills the ability to hear the awful fuzz. My new hearing aids make my hearing young again to hear then turn off the awful fuzz.
     
  13. 73's de Edd

    73's de Edd

    3,085
    1,302
    Aug 21, 2015
    Sir . . . .(are you ?) . . . .Still buildin


    Refer to the submitted CURTIS INSTRUMENTS sheet and its PARAGRAPH 4 of pages 14 and 15.
    There you have the model 700 resettable unit and the model 701 unsresettable (supposedly) unit.
    Ignore the following 703 model, as its just being a unit counter.

    Now, one of your photos Identifies its 701 heritage.

    This would be easy to ascertain if you had one of each 700 and 701 type to physically compare against.
    In my analyzing the manner of construction / design you can see that there is being the running time aspect of the unit and the ADDITIONAL need of an EAROM family of memory add on for the incorporation of the data retention of the time count.

    Now you read the instructions and procedure.

    Then you inspect the counter . . . en toto . . . and there I am seeing 4 corner wire supports and connections and down inside the module proper, I am seeing 4 gold flashed pads. There are fine wires coming up and being soldered to them.
    We can figure that two connections are going to be a given . . . . for being power connections, the others are referred to in instructions.

    Now I ab-so-root-ley can't see them making TWO custom chips, when just one could suffice for being a non resettable and resettable function.
    Just think of them not having installed the reset function wire connection / or / pcb foil wiring path for the non resettable function . . . . on the 701 series of meter.

    On yet another of your photos . . . made of the bottom of the unit . . .

    I perceive J1 as being Positive power connection ?
    J2 as Negative power connection ?
    J3 I . . .as Input ?
    And probably the most significant . . . .
    J4 as R . . .eset ?
    and then there is R2 lead being just over immediately to the side.

    Check out the other side of the PCB of J4 stake to see if there is being any connection that is made into it on the other side.
    IF NOT . . . . . can we then be concluding, that the 700----701 product difference is being that short foil interconnect between R2 and J4 ?


    (Also check out the gold pads and see if one is being without connection.)

    Fill us in with your observations . . . . . .


    CURTIS INFO . . . . .
    https://cdn.curtisinstruments.com/products/manuals/700_manual_en.pdf




    73's de Edd . . . . .
    . . . . . . . . . . .


    One third of Americans can't do math . . . . . and as for the other three-quarters . . . . . they just don't care.
     
    Last edited: Dec 29, 2018
    (*steve*) likes this.
  14. Still buildin

    Still buildin

    14
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    Dec 28, 2018
    Lol yes - it's because they're playing solid state amps.....
     
    Richard9025 likes this.
  15. Still buildin

    Still buildin

    14
    4
    Dec 28, 2018
    Wow! That's brilliant......thanks!

    Yes, I noticed in the data sheet at Part 4, page 15: Operation - it mentions that reset (on resettable units) is achieved by applying power to pin 4, while the same power is applied to pins 1 (V+) and 2 (V-). These are exactly as you thought, and Pin 3 is Input (labelled Enable in the PDF).

    I opened the unit up a little and folded the screen display back to expose the other side. Pics here......Pin 4 is the longest, top left - does this help? Sorry, I didn't understand which gold pads you meant for me to examine....
     

    Attached Files:

  16. Still buildin

    Still buildin

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    4
    Dec 28, 2018
    Ok on further inspection I see that Pin J4 is foil connected only to Lead R2. No connections I can see on back side of pcb re pin 4. Lead R2 appears to be connected to nothing else.......
     
  17. Still buildin

    Still buildin

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    4
    Dec 28, 2018
    So are you thinking that I should break the connection between J4 and R2, then try resetting? Or add a connection from R2 to somewhere else, and then try to reset?

    Thanks again!
     
  18. Still buildin

    Still buildin

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    4
    Dec 28, 2018
    Ok this might all be academic now........I touched power to the lead adjacent to Lead 2 (while the unit was powered). The display went blank and won't come back on, no digits at all......I guess I cooked it.

    Thanks to everyone for your help and input anyway!
     
  19. 73's de Edd

    73's de Edd

    3,085
    1,302
    Aug 21, 2015
    Sir Still buildin . . . . .


    Kudos ! . . . .on your photo support / supplifications . . . with them being just what is now needed..

    Now after some squaring up . . .resizing to scale . . .paralllax correction . . . (triple lll is when its reallly bad). . . we then come up with the supplied photo referencing.below.
    (But don't really believe it . . .as it is actually just being an optical collusion ! )

    The RED line referencing to the installed xtal 1 connections confirms final board to board side relationships correctness..

    READING THE BOARD . . . .

    Bottom left corner we see the PINK CIRCLE J2 connector is connecting to a large ground plane foil (X3) and connects to up at the top with a gold flash via that passes thru the board at the PURPLE CIRCLE with a making of connection to the other side of the board. At the top photo you see that PURPLE via on that side connecting to the negative lead of C1, a 22 motherfarad unit, it being THE main dry tantalum E-capacitor .

    Back to the bottom photo, slightly off right center.
    There is another YELLOW CIRCLE gold via that has a green foil path to the left that then enters the black epoxy dome of the COB's astronomicaly large and complex logic factory . . . yet , its being microscopically, small, physically sized.
    Top picture of that same YELLOW CIRCLE via , we see a branch off foil routing to the top pad of the R3 resistor.
    A second foil branches off the YELLOW CIRCLE via to route under the 5100 ohm R8 resistor, to end up at the right upper BLUE CIRCLE via and a connected square pad to its right.

    OBSERVATION . . .
    Of the bottom photo . . . looks like that same BLUE CIRCLE via also connects to a round gold flashed contact and some gold flashed artwork resides to its bottom left.
    Possibly related to a potential future or past utilization, in the manner of contacts associated with an adjunct
    silicone dome with an internal graphite influxed conductive pad, that sits atop the contacts creating a simplified .
    PRESS to reset.
    HOWEVER . . . that might have already been used . . . .but with potential recurring situations coming up of:

    Delmer Pee Dumbnuttz . . . . observes and sez . . . .( I wunners whuts this-a- hears thang duz ?) . . .PUNCH !

    With such ease of accidental / unexpected data dump they might have opted for the more involved RESET procedure.

    BACK ON TOPIC . . . .

    MEMORY REFRESH . . . .

    A second foil branches off the YELLOW CIRCLE via to route under the 5100 ohm R8 resistor, to end up at the right upper BLUE CIRCLE via and a connected square pad to its right.
    Seems like there should be a logic family value of SM resistor (10K...4.7K ) mounted between the BLUE CIRCLE's neighboring pad and the upper R2 (its missing) pad.

    Now is where your eagle eyes and an ohmmeter for zero ohms /continuity is needed.
    I look at the J3 corners gold flashed foil rectangle and I see no connections to it.
    I see the same rectangular gold pad foils at the J2 and J1 areas , but they are being 1/2 solder flooded.
    Now we move to my J4 areas outer inset photo, with its enhanced digitally dithered and averaged replotting.
    What i initially thought was fine wiring going to some of the gold pads is not.
    Seems like the meters frontal bezel for the unit is probably light gauge steel matte black finished and uses 4 formed tabs that pass above the cut in slots of the PCB that is just above the gold tabs.
    Then you twist them inwards upon the gold tabs surfaces and the 4 then compress the front bezel and hold it in place.
    ASIDE . . . you would expect the metal tabs to bite in and it could potentially/accidentally interconnect all 4 gold pads together.
    But it seems that the two twisted tabs bare steel metal at the J1-J2 areas pads are intentionally solder flooded . . . right ?
    Now confirm this for me . . at the J4 corners gold pad, it positively looks like there is a foil path that runs to he left
    routes under the center of R9? and then possibly zig zags over and up and direct connects to J3 stake .? ? ?
    Back to the J4 gold pad, confirm left corner has foil dropping down to the left one of two small gold vias.
    Now the real mystery is what the little zig - zag detail from the right bottom corner.
    It slants a bit at 45deg then goes right and then drops 45 again and then runs level twice the distance then STOPS.
    That last oddity precludes me from determining . . . . . if that gold tab is the left end half of a corner foil (GREEN conformally coated) that would interconnect J4 stake and the R2 resistors top pad.
    Or is that corner area devoid of foil and has a floating R2 pad and a cut / open interconnect between it and the J4 stake.
    Your last photos positively revealed that the J1I--3--4 stakes have no connections on the COB side and the J2 tieing into ground plane.

    If those are floating . . . then a RESET conversion, just might be related to a R2 install and solder connect between J4 and R2 top pad. Then follow the CURTIS reset instructions.


    Pee Ess . . On your degree of display teardown that you did . . . .if your display doesn't display upon reassembly . . . .you might then be in need of some further intelligentia enhancement on the exotic topic of "Zebra strips" .

    I see that my professional industrial sized 39 inch crystal ball was RIGHT !
    as per your final . . .just below.
    (Ready to go back to the classroom ? )

    Ok this might all be academic now........I touched power to the lead adjacent to Lead 2 (while the unit was powered). The display went blank and won't come back on, no digits at all......I guess I cooked it.
    Thanks to everyone for your help and input anyway!

    At any time after power up did you see a display, or was the pop created before you even looked at the display ?
    J2 is ground plane and possibly that gold tab beside it is also . . . so you might have just ACTUALLY grounded out your + power supply for just that instant. Which should POP.

    If you touched the + of the nearby yellow electrolytic just above that area you might have made a direct connection to power and bypassing any intermediate resistor, likely with no harm, but wouldn't POP.


    TECHNO REFERENCING . . . . .

    [​IMG]

    Thaaaaaaaaaaaaassssssssit . . .


    73's de Edd . . . . .
    . . . . . . . . . . .


    To vacillate . . . or not to vacillate . . . .that is the question . . . . or is it ?
     
    Last edited: Dec 29, 2018
    Richard9025 likes this.
  20. Still buildin

    Still buildin

    14
    4
    Dec 28, 2018
    73's de Edd......Thanks and kudos to you for all your efforts!

    You are quite right - the four gold pads are used to twist on the screen tabs and lock it into place.....the only soldered one is at J2 (V-).......ground.

    In my flawed logic and impatience I concluded that as Pin J4 is connected by small foil line to Lead 2, this meant that power applied to either is the same as power applied to both. Therefore, power had to be applied elsewhere to bridge the intentional gap (non resettable chip), left by the manufacturer. I had also noticed the short jagged foil line heading out from the gold pad near J4, then going nowhere. But, it stopped right between Lead 2 and another Lead.......

    I decided any reset connection had to be close to J4, or the manufacturing difference between resettable and non resettable would not make economic sense......

    So I applied matching V+ to two different nearby areas (separately). This was after reassembly and final checking that the display still functioned under power, and still showed the old hours count. When power was applied to the gold rectangle nearest J4, a pop and small flash was seen. This did not affect the display. I figured I had just shorted it momentarily, but without harm.

    When power was applied to the Lead next to Lead 2, (adjacent to the two small boxes labelled 512), no pop or flash was observed.....but the display went blank and now stays blank.......oops..
     
    BobK likes this.
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