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PE Subwoofer Pre-Amp - Exposed

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  • #46
    Originally posted by Gordy View Post

    A starting frequency of 73hz is a real downer. It seems that if they would have just used 20k pots this would be a non issue. The 10k on the gain really looks like a mess. R values below

    R1 = 10k
    R2 = 10K
    R3 = 10K
    R4 = 10K
    R5 = Missing
    R6 = 4.7k
    R7 = MIssing
    R8 = 4.7K
    R9 = 10k
    R10 = 215

    Going back over your initial notes, I don't see anything about removing R5. How does this impact?



    R5 was the base resistor for the voltage divider network to provide 1/2 Vcc. Without it, the signal is biased at Vcc. So you'll only get the negative portion of the signal through the module.

    With R1 & R2 at 10K and a 10K pot, the maximum gain is now 1x. And at that gain, there is a 1st order LP at ~48 Hz in the gain stage addition to the LP filter stage.

    A step back in functionality I think. Better save the module I sent to you. And I'm glad PE didn't associate me with the updated module.

    Anyone know where to get Mandarin lessons

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    • #47
      The is my fault - the issues with the updated module. I was analyzing using the standard engineering progression of 1, 2, 5, 10, 20, 50, .. I should have used commonly available pots - 10K, 25K and 50k.

      The use of the same pot for both the gain stage and LP stage could have been anticipated: fewer parts list and simpler assembly - qa common approach for these low cost modules. In fact, with a 25K pot, the adjustment range is the best option by a small margin (see the graph "Mod 4" in brown). And with a 25K pot in the gain stage, you would have had ~5x gain available. Though there's not much I could have done about the additional missing resistor, R5.
      Click image for larger version

Name:	25k Pot.png
Views:	1
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ID:	1348199


      Last edited by Millstonemike; 10-08-2017, 12:07 PM.

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      • #48
        Originally posted by Millstonemike View Post
        The is my fault - the issues with the updated module. I was analyzing using the standard engineering progression of 1, 2, 5, 10, 20, 50, .. I should have used commonly available pots - 10K, 25K and 50k.

        The use of the same pot for both the gain stage and LP stage could have been anticipated: fewer parts list and simpler assembly - qa common approach for these low cost modules. In fact, with a 25K pot, the adjustment range is the best option by a small margin (see the graph "Mod 4" in brown). And with a 25K pot in the gain stage, you would have had ~5x gain available. Though there's not much I could have done about the additional missing resistor, R5.
        [ATTACH=CONFIG]n1348199[/ATTACH]
        Please dont blame yourself. Your work and expertise is much appreciated. now if I could learn a better way to desolder Than buying an expensive electric solder sucker. I also looked on Mouser (because it is 3 hours away) and could not find 25k pots. I think 20's will be just fine. I need to order some single gang 10k's and will throw a few in that order and 10k resistors.
        "A dirty shop is an unsafe shop, if you injure yourself in a clean shop you are just stupid" - Coach Kupchinsky

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        • #49
          Originally posted by Gordy View Post

          Please dont blame yourself. Your work and expertise is much appreciated. now if I could learn a better way to desolder Than buying an expensive electric solder sucker. I also looked on Mouser (because it is 3 hours away) and could not find 25k pots. I think 20's will be just fine. I need to order some single gang 10k's and will throw a few in that order and 10k resistors.
          Never cared much for the solder suckers, even the expensive ones. I prefer to use the simple inexpensive copper braid. Try that. It wicks the solder right out:

          https://www.parts-express.com/nte-sw...-5-ft--341-556

          https://www.parts-express.com/nte-sw...-5-ft--341-550
          Don't worry, if your parachute fails, you have the rest of your life to fix it.

          If we all did the things we are capable of doing, we would literally ASTOUND ourselves - Thomas A. Edison

          Some people collect stamps, Imelda Marcos collected shoes. I collect speakers.:D

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          • #50
            Originally posted by thekorvers View Post

            Never cared much for the solder suckers, even the expensive ones. I prefer to use the simple inexpensive copper braid. Try that. It wicks the solder right out:

            https://www.parts-express.com/nte-sw...-5-ft--341-556

            https://www.parts-express.com/nte-sw...-5-ft--341-550
            You know, I never tried copper braid. I'll have to give it a go. I used a $1.79 solder sucker from Fleabay when I modified Gordy's board. though it required some finesse and experience.

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            • #51
              Ignoring that the particular implementation of these crossover boards may have problems...assuming there was a board with correct implementation...if I wanted to run two subwoofers, could I run the signal from pre-amp to a single variable crossover board, then split the RCA out with a Y-adapter and run the signal to the two subs separately? That way I know I have the same crossover and gain rather than implementing two separate boards?

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              • #52
                Originally posted by a4eaudio View Post
                Ignoring that the particular implementation of these crossover boards may have problems...assuming there was a board with correct implementation...if I wanted to run two subwoofers, could I run the signal from pre-amp to a single variable crossover board, then split the RCA out with a Y-adapter and run the signal to the two subs separately? That way I know I have the same crossover and gain rather than implementing two separate boards?
                The output impedance of the pre-amp module is 200 ohms. That is low enough to drive the line level inputs on two sub amps (barring some unusually low input impedance).

                But, however, take notice ...

                The original module is no longer available to mod as originally posted. And the new version has more issues than the original - totally useless. I just received a third party module and will be evaluating soon.

                Tune in next week, same Bat time, same Bat channel ...

                Sub Pre Amp.jpg

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                • #53
                  I've tested the Sanwu 2.1 pre-amp module in this thread. It suffers from the same issues of the original version of the PE sub-woofer pre-amp

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                  • #54
                    Originally posted by Millstonemike View Post
                    Correct. If its not connected, I use a "c" like shape to denote a connection doesn't touch another. Is that really old school? With R7 removed, the schematic looks like this:

                    [ATTACH=CONFIG]n1320222[/ATTACH]
                    I've recreated this schematic, but I seem to have a big problem with significant over-driven signal. The signal is able to pass through the circuit, but is heavily distorted and is still "full-range," if that makes sense. The distortion is so bad that it just sounds like garbage.

                    I've tried upping the resistor values for R1 and R2, as well as putting in a resistor in parallel with pins 1&3 of RP1A.

                    Any thoughts on how to remedy this issue?

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                    • #55
                      Originally posted by bolson2011 View Post

                      I've recreated this schematic, but I seem to have a big problem with significant over-driven signal. The signal is able to pass through the circuit, but is heavily distorted and is still "full-range," if that makes sense. The distortion is so bad that it just sounds like garbage.

                      I've tried upping the resistor values for R1 and R2, as well as putting in a resistor in parallel with pins 1&3 of RP1A.

                      Any thoughts on how to remedy this issue?
                      What is the PS voltage you are using for the module?

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                      • #56
                        I'm using a 12v DC power supply, 2A output.

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                        • #57
                          Originally posted by bolson2011 View Post
                          I'm using a 12v DC power supply, 2A output.
                          That's plenty. Which version of the pre-amp do you have? Please post the exact PE part number.

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                          • #58
                            The original part #320-670

                            But I recreated the schematic that you linked in the original post in the picture attached.

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                            • #59
                              Originally posted by bolson2011 View Post
                              The original part #320-670

                              But I recreated the schematic that you linked in the original post in the picture attached.
                              There really wasn't a problem with the input resistors R1 & R2 or a resistor required across RP1.

                              Are you trying to modify the module according to my original recommendations? Be aware, circa post #28 there are suggested mods for a totally different application and do not apply to the original mods..

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                              • #60
                                Originally posted by Millstonemike View Post
                                There really wasn't a problem with the input resistors R1 & R2 or a resistor required across RP1.

                                Are you trying to modify the module according to my original recommendations? Be aware, circa post #28 there are suggested mods for a totally different application and do not apply to the original mods..
                                I haven't modified the original module, I recreated (or at least tried to) it based on your recommendations and the schematic provided, with the changes in place. Essentially, I'm trying to make it work as a variable high pass filter, leaving only ~80-120hz and below pass through that particular filter.

                                I guess I should say that I haven't purchased the original module, or the update to it.

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