General question on big and old analog circuits designs

Discussion in 'General Electronics Chat' started by Blue_Electronx, Jun 13, 2019.

  1. Blue_Electronx

    Thread Starter New Member

    Jun 10, 2019
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    My question is about circuits like the one attached. I actually don't know what it is, and it's not my intention to know it for now. I actually refer to those big and old circuit diagrams which have thousands of opamps, transistors, and analog components in general. For a digital/microcontroller guy (like me), this might take a longer time to understand it all compared to an analog designer with a vast experience. As I said, my question is not to understand this circuit, but to know if nowadays these circuits are being significantly reduced using microcontrollers or special ICs. Let's say you're given one of these big diagrams with obsolete parts and you have to redesign it from scratch. I would like to hear people who have had the experience of redesigning an old circuit. What would your approach be? Of course, the first step would be to understand the application of the circuit.
     
  2. Berzerker

    Active Member

    Jul 29, 2018
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    Not to mention logging all the components that are in it, trading them for updated or replacing obsolete components.
    Brzrkr
     
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  3. CharlesWMcDonald

    Member

    May 16, 2019
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    This is for a device called "Boss CE 300 Analog Chorus" from the 1980's. Don't know exactly what it does but you can get a used one on EBay here.
    Since this is for audio, you couldn't replace much of it with a microprocessor but modern analog components would simplify it considerably.
     
  4. OBW0549

    Distinguished Member

    Mar 2, 2015
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    Yes, that's certainly the first step, to find out as much about the application as possible.

    Next, I'd try to "de-jumble" the schematic: identify the various functional blocks in the diagram, and re-draw the schematic on multiple sheets, with only one or two of the functional blocks on each sheet to make it easier to figure out. Trying to work with a schematic like the example you posted is apt to lead to difficulties, and taking the time to put it in more readable form is well worth the effort.

    Beyond that, I'd say it's best to do the re-design at the highest level possible to take maximum advantage of simplifications possible with modern components. Try to re-design entire functional blocks, or groups of functional blocks, and simplify them rather than searching (probably in vain) for direct substitutes for the obsolete parts in the original design.

    I've been through this sort of thing a few times, and the above is the approach I took.
     
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  5. CharlesWMcDonald

    Member

    May 16, 2019
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    I wouldn't attempt to reverse engineer the device, if I could generate a set of requirements for functionality then I would design a new one from the ground up.
     
  6. BobTPH

    Senior Member

    Jun 5, 2013
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    Seriously? Where have you been for the last 30 years?

    From Wikipedia:
    Bob
     
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  7. WBahn

    Moderator

    Mar 31, 2012
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    As you say, the first step is to understand what the circuit is supposed to do, in detail. Ideally, either find or back out a set of performance specifications if you can. If you have to back it out, then welcome to the joys of reverse engineering. While that schematic is pretty dense, it also seems reasonably well laid out in terms of functional groups and provides quite a few clues with the various labels here and there. Then you are in a much better position to decide how much of the functionality can be implemented in, say, a digital signal processor.

    Since this is clearly an audio application you can almost certainly reduce it significantly using modern digital technology. But you are also trading one headache for another in that you are still going to have to figure out, one way or another, an acceptable set of performance specifications and required functionality in order to develop your code and your user interface.
     
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  8. RPLaJeunesse

    New Member

    Jul 29, 2018
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    One approach is the "black box" approach. Define what goes in, what gets done with that, and what comes out. Assuming you know what gets done, the choice of how depends on many factors, one of which is soft vs. hard tooling. An all-analog design like the example requires a lot of tooling, that costs money and is difficult to modify if changes are needed. Soft tooling isn't necessarily cheaper, but it is often easy to modify - good if you are attempting something new and not 100% certain of what really needs to be done. Soft tooling is often in the form of microprocessor code, or code for an FPGA or other (re)programmable device. Nowadays the circuit above is minimized by the use of a DSP core surrounded with ADC and DAC and the few needed analog input & output signal conditioning circuits. Or maybe an ARM CPU with the necessary analog support. Personally I've looked at the Orange Pi Zero for a multi-drop group intercom function, just needs the added controls & connectors.
     
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  9. AnalogKid

    AAC Fanatic!

    Aug 1, 2013
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    It's not a bad design at all; each functional block is pretty tight in its component count and design stability (the ability of 100 assemblies to perform exactly the same with a minimum of calibration adjustments). As above, it is an audio effects processor based on a delay line called a BBD (bucket-brigade device). The delayed audio is recombined with the direct audio to make a single voice sound more full, or one voice to sound like many singing together ("chorus").

    ALL of this can be done inside one digital signal processor, which is how someone aiming for the low to medium quality market would do it. Someone aiming for the golden-eared retro audio crazies might go all analog, but that BBD part is going to be hard to find. As a compromise, you could put a digital delay line in the middle of all analog input and output processing.

    I've done some old circuit redesign (called technical refresh). Most of the time there is a good reason for keeping at least some of the analog stuff. Digital is different Almost anything that was a state machine can be replaced with a microcontroller, and pages of very fast random logic can fit in a single CPLD. FPGA's are all the rage, but for the vast majority of this kind of retrofit their unique characteristics are not required.

    ak
     
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  10. CharlesWMcDonald

    Member

    May 16, 2019
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  11. BobTPH

    Senior Member

    Jun 5, 2013
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    And some people say the earth is flat.

    Bob
     
  12. AnalogKid

    AAC Fanatic!

    Aug 1, 2013
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    Flat-Earth eclipse:

    upload_2019-6-13_23-56-15.jpeg

    ak
     
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