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PE Subwoofer Pre-Amp - Exposed

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  • Gordy
    replied
    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.

    Leave a comment:


  • Millstonemike
    replied
    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:	14
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ID:	1348199

    Last edited by Millstonemike; 10-08-2017, 02:07 PM.

    Leave a comment:


  • Millstonemike
    replied
    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

    Leave a comment:


  • Gordy
    replied
    Originally posted by Millstonemike View Post

    Remember the old dig "Am I speaking Chinese?" Maybe that's needed now

    The original pots were 50K ohms. I spec.'d 20K for the modified board but 20K pots are somewhat rare compared to others.

    LP Filter: With a 10K pot and R6 & R8 remaining at 4.7K ohms, (hard to tell colors in the PE photo), the minimum LP Fc will be 73 Hz (up from 43 Hz in my version). Maybe not so much an issue for smaller 2.1 systems. The maximum LP Fc remains the same at 228 Hz. See the green line in the graph - mod 3. Replacing R6 & R8 with 10K resistors will get you a minimum F3 of 54 Hz. But the maximum LP Fc will revert back to 107 Hz - again, not so much an issue if your looking for a lower Fc.

    Gain Stage: If R1 & R2 remain at 4.7K (hard to tell from PE photo) and the gain pot is 10K, then the maximum gain will be reduced to 2.1x; down from ~10x maximum gain. And that could be a big issue matching sub volume with the L-R speakers. Replacing R1 & R2 with 1K resistors will get the gain back up to 10x gain. But ... the HP Fc will rise from 3 Hz to 34 Hz in the band pass filter integrated in the gain stage..And trying to select values to replace R1 / R2 and C1 / C2 to compensate becomes a mess.

    Gordy, maybe you could measure R6 & R8 to confirm their values.

    Geez ... good thing I saved one more set of components to mod the original board. "The old adage :If you want something done right ..."
    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?



    Leave a comment:


  • Millstonemike
    replied
    Originally posted by Gordy View Post
    Just received the new SKU. Looks like the caps have been changed and resistor has been removed. But the pots are still A10Ks. I ordered a cheap mono amp from the Zon that should be here in a few days and hopefully will get to test it then.
    Remember the old dig "Am I speaking Chinese?" Maybe that's needed now

    The original pots were 50K ohms. I spec.'d 20K for the modified board but 20K pots are somewhat rare compared to others.

    LP Filter: With a 10K pot and R6 & R8 remaining at 4.7K ohms, (hard to tell colors in the PE photo), the minimum LP Fc will be 73 Hz (up from 43 Hz in my version). Maybe not so much an issue for smaller 2.1 systems. The maximum LP Fc remains the same at 228 Hz. See the green line in the graph - mod 3. Replacing R6 & R8 with 10K resistors will get you a minimum F3 of 54 Hz. But the maximum LP Fc will revert back to 107 Hz - again, not so much an issue if your looking for a lower Fc.

    Gain Stage: If R1 & R2 remain at 4.7K (hard to tell from PE photo) and the gain pot is 10K, then the maximum gain will be reduced to 2.1x; down from ~10x maximum gain. And that could be a big issue matching sub volume with the L-R speakers. Replacing R1 & R2 with 1K resistors will get the gain back up to 10x gain. But ... the HP Fc will rise from 3 Hz to 34 Hz in the band pass filter integrated in the gain stage..And trying to select values to replace R1 / R2 and C1 / C2 to compensate becomes a mess.

    Gordy, maybe you could measure R6 & R8 to confirm their values.

    Geez ... good thing I saved one more set of components to mod the original board. "The old adage :If you want something done right ..." Click image for larger version

Name:	10K Pot Analysis.png
Views:	10
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ID:	1348037
    Last edited by Millstonemike; 10-07-2017, 03:39 PM.

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  • Gordy
    replied
    Just received the new SKU. Looks like the caps have been changed and resistor has been removed. But the pots are still A10Ks. I ordered a cheap mono amp from the Zon that should be here in a few days and hopefully will get to test it then.

    Leave a comment:


  • tomzarbo
    replied
    Originally posted by Millstonemike View Post
    [ATTACH=CONFIG]n1347957[/ATTACH]
    Track your package Here


    Thank you Mike.
    TomZ

    Leave a comment:


  • Millstonemike
    replied
    Click image for larger version

Name:	package.jpg
Views:	10
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ID:	1347957
    Track your package Here


    Originally posted by tomzarbo View Post

    PM Sent, thanks!
    TomZ

    Leave a comment:


  • Gordy
    replied
    Originally posted by Millstonemike View Post
    You are correct. I've been making typos all day. The last one was about $40,000 off the correct figure. Shisssh.
    If it was not for spell check, I would be a mess.

    don't know how I feel about that. You put a good amount of work and time into fixing a flawed product. I think they should have least provided co-star billing in the new SKU description.

    Leave a comment:


  • Millstonemike
    replied
    Originally posted by Gordy View Post

    I think the old module is 320-670
    You are correct. I've been making typos all day. The last one was about $40,000 off the correct figure. Shisssh.

    Leave a comment:


  • tomzarbo
    replied
    Originally posted by Millstonemike View Post
    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.
    PM Sent, thanks!
    TomZ

    Leave a comment:


  • Gordy
    replied
    Originally posted by Millstonemike View Post
    Be aware that the old board with the issues outline hear (part # 320-671) is on clearance for $3.95. The updated module is part # 320-671.
    I think the old module is 320-670

    Leave a comment:


  • Millstonemike
    replied
    Corrected Post: Be aware that the old board with the issues outlined here (part # 320-670) is on clearance for $3.95. The updated module is part # 320-671.

    Be aware that the old board with the issues outline hear (part # 320-671) is on clearance for $3.95. The updated module is part # 320-671.
    Last edited by Millstonemike; 10-06-2017, 10:25 AM. Reason: corrected part # and typos

    Leave a comment:


  • Millstonemike
    replied
    Originally posted by Gordy View Post

    Out of curiosity, did PE contact you when they updated the SKU. Or did you work with PE to upate the SKU?
    I never interacted with PE on this. I did post a review on the product page.

    Leave a comment:


  • Gordy
    replied
    Originally posted by Millstonemike View Post
    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.
    Out of curiosity, did PE contact you when they updated the SKU. Or did you work with PE to upate the SKU?

    Leave a comment:

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