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PE Subwoofer Pre-Amp - Exposed

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  • Millstonemike
    replied
    Originally posted by tomzarbo View Post

    Thanks for looking into this Gordy,
    I'm interested in hearing about your thoughts on it. Hopefully it works as advertised and expected.

    TomZ
    Hey Tom,

    I had parts to modify another board. They're not needed now since the board has been updated. Send me your address in a PM and I'll mail them to you.

    Leave a comment:


  • tomzarbo
    replied
    Originally posted by Gordy View Post
    Looks like PE has a new board. R7 is removed and the pots look different. Also looks like the cap values changed. I have one on order to test and compare. Sure has some good mono amps I would like to test with it. I never got a chance to test the updated board but have a list of items on my bench to test in the next few weeks.

    https://www.parts-express.com/variab...ntrol--320-671
    Thanks for looking into this Gordy,
    I'm interested in hearing about your thoughts on it. Hopefully it works as advertised and expected.

    TomZ

    Leave a comment:


  • Gordy
    replied
    Looks like PE has a new board. R7 is removed and the pots look different. Also looks like the cap values changed. I have one on order to test and compare. Sure has some good mono amps I would like to test with it. I never got a chance to test the updated board but have a list of items on my bench to test in the next few weeks.

    https://www.parts-express.com/variab...ntrol--320-671

    Leave a comment:


  • Mike E
    replied
    Originally posted by tomzarbo View Post
    Gordy, did you ever get to test this out? How did it do?

    TomZ
    X2

    if it works like it is suppose to now, there is a sure amp i want to get for some a sub build.

    Leave a comment:


  • tomzarbo
    replied
    Gordy, did you ever get to test this out? How did it do?

    TomZ

    Leave a comment:


  • Millstonemike
    replied
    Originally posted by Drewdwn93 View Post
    So, I'm still leaving R8, RP2, and R6 in the signal path, right? Yes. How will the orientation of RP2 affect the circuit after removing the crossover caps and bias resistor? Theoretically, it shouldn't. But 50 K pots are prone to noise. If you like, you can jumper the pins on each of the pot's gangs making it effectively 0 ohms regardless of rotation. You can remove the pot as well with the added jumpers in place (see the pic, below). Or does it not affect it at all since it is a unity gain stage? Could I not simply pull my sub out from pin 1, rather than going through the additional unity gain stage? You'll want to use the existing sub output to take advantage of the decoupling cap, C7. This will avoid DC bias in the signal from entering the next stage / amp (though your sub amp may also have one, it's a good safety measure to keep it in the circuit). Also, I have no problem changing some of the components/values to make it work with fewer components in the signal path, if it's possible. I would leave R6 and R8 in the signal path lest the unity gain stage present a very low impedance load to the output of the variable gain stage. Also, when you say to split the sound card LF output, can I just use a jumper at LIN and RIN? Yes. Thanks for your help, In the words of the immortal Mr. Miyagi, "welcome". I'm still very new to this stuff.
    POt.jpg

    Leave a comment:


  • Drewdwn93
    replied
    So, I'm still leaving R8, RP2, and R6 in the signal path, right? How will the orientation of RP2 affect the circuit after removing the crossover caps and bias resistor? Or does it not affect it at all since it is a unity gain stage? Could I not simply pull my sub out from pin 1, rather than going through the additional unity gain stage? Also, I have no problem changing some of the components/values to make it work with fewer components in the signal path, if it's possible. Also, when you say to split the sound card LF output, can I just use a jumper at LIN and RIN? Thanks for your help, I'm still very new to this stuff.

    Leave a comment:


  • Millstonemike
    replied
    Originally posted by Drewdwn93 View Post
    Great write-up, I'm glad I found it. I was wondering if there is any way to bypass (or delete) the low pass section altogether (other than having RP2 fully clockwise)? I already have a sub pre-out on my soundcard (SB Omni). I only need the gain because the line-out on the SB Omni is too weak.

    Remove C5, C6 and R7. That will effectively make the LP stage a pass through buffer. Your sound card's LF output should be split to to drive both the L & R input channels of the pre-amp. The sound card LF output will need to drive the resulting 5K impedance load of the pre-amp's input.

    Leave a comment:


  • Drewdwn93
    replied
    Great write-up, I'm glad I found it. I was wondering if there is any way to bypass (or delete) the low pass section altogether (other than having RP2 fully clockwise)? I already have a sub pre-out on my soundcard (SB Omni). I only need the gain because the line-out on the SB Omni is too weak.

    Leave a comment:


  • tomzarbo
    replied
    Dos Post

    Leave a comment:


  • tomzarbo
    replied
    Originally posted by Millstonemike View Post
    1
    Okay. I'll give Gordy a few weeks to report back.
    Thanks again, sir.

    TomZ

    Leave a comment:


  • thekorvers
    replied
    The schematic looks pretty professional, something a manufacturer would put out. So you reverse-engineered all this. Pretty impressive. .

    Leave a comment:


  • Millstonemike
    replied
    Originally posted by thekorvers View Post
    I am talking of a time when there were no home computers or CAD (Computer Aided Designs). According to your post then, I am going by the Old style CAD symbols, probably adopted from the same symbols in earlier schematics before computers were available. I still think that the best and safest way to represent a connection is with a dot. No ambiguity.

    By the way I was not disparaging your drawing of a schematic as I assumed that this was a schematic from a manufacturer. Regardless where the schematic came from, I think you did an excellent job analyzing this and finding a solution for the problem. I commend you for it!
    It was my schematic. I agree with you on the dots, less ambiguity. They're just a PITA. It's an additional step to add each of them.

    Leave a comment:


  • thekorvers
    replied
    I am talking of a time when there were no home computers or CAD (Computer Aided Designs). According to your post then, I am going by the Old style CAD symbols, probably adopted from the same symbols in earlier schematics before computers were available. I still think that the best and safest way to represent a connection is with a dot. No ambiguity.

    By the way I was not disparaging your drawing of a schematic as I assumed that this was a schematic from a manufacturer. Regardless where the schematic came from, I think you did an excellent job analyzing this and finding a solution for the problem. I commend you for it!

    Leave a comment:


  • Millstonemike
    replied
    Originally posted by thekorvers View Post

    When I studied electrical engineering ( in Europe a long long time ago) schematic standard was when 2 lines cross without a dot at the junction, no connection is made. When 2 lines cross and there is a dot at the junction, a connection is made. The only place I see this in your schematic is to the right of C8, where it says Nominally 1/2 Vcc. So this schematic is not very consistent, something I see a lot these days.

    I miss proper protocol and standards of the old days, not only in engineering, but in life in general. Things are often done so sloppily nowadays. (I think this may be a senior citizen's rant).
    I only put a dot where a signal point is called out. From Wikipedia:


    Click image for larger version

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