Results 1 to 19 of 19

Thread: Fender Princeton 112 Plus power switch pop

  1. #1
    Twobie
    Join Date
    Feb 2019
    Location
    Alabama
    Posts
    5
    Thumbs Up/Down
    Received: 0/0
    Given: 4/0
    Rep Power
    0

    Fender Princeton 112 Plus power switch pop

    I recently purchased a used and sightly abused Fender Princeton 112 Plus that had a few issues such as a reverb control with a loose shaft and missing knobs. I have it functional but when the power switch is turned there is a loud pop from the speaker. I am worried about damaging the speaker if this is not repaired. Any suggestions? Thanks in advance.

    0 Not allowed! Not allowed!

  2. #2
    Stray Cap DrGonz78's Avatar
    Join Date
    Oct 2011
    Location
    Scottsdale, AZ
    Posts
    2,043
    Blog Entries
    1
    Thumbs Up/Down
    Received: 271/5
    Given: 183/0
    Rep Power
    10
    The pop won't damage the speaker. Try the test of plugging the power cord in while the power switch is on and reverse that by turning it off by unplugging the power cord. This will tell us if the power switch is arcing which could make a popping noise at turn on/off. Then again many amps pop when turned on/off. Start with that test and report back to let us know the results.

    2 Not allowed! Not allowed!
    When the going gets weird... The weird turn pro!

  3. #3
    Twobie
    Join Date
    Feb 2019
    Location
    Alabama
    Posts
    5
    Thumbs Up/Down
    Received: 0/0
    Given: 4/0
    Rep Power
    0

    Fender Princeton 112 Plus power switch pop

    Quote Originally Posted by Kirby02 View Post
    I recently purchased a used and sightly abused Fender Princeton 112 Plus that had a few issues such as a reverb control with a loose shaft and missing knobs. I have it functional but when the power switch is turned there is a loud pop from the speaker. I am worried about damaging the speaker if this is not repaired. Any suggestions? Thanks in advance.
    The pop at turn on is not nearly as loud as at turn off. The pop is the same volume if the amp turned off with the switch or unplugged from the power.

    0 Not allowed! Not allowed!

  4. #4
    Supporting Member Jazz P Bass's Avatar
    Join Date
    Dec 2008
    Location
    Wernersville, PA
    Posts
    12,788
    Thumbs Up/Down
    Received: 428/2
    Given: 224/0
    Rep Power
    25
    To see if it is a preamp or a power amp issue, insert a plug into the Return jack.

    That plug will isolate the preamp from the power amp.

    1 Not allowed! Not allowed!

  5. #5
    Twobie
    Join Date
    Feb 2019
    Location
    Alabama
    Posts
    5
    Thumbs Up/Down
    Received: 0/0
    Given: 4/0
    Rep Power
    0

    Fender Princeton 112 Plus power switch pop

    Quote Originally Posted by Jazz P Bass View Post
    To see if it is a preamp or a power amp issue, insert a plug into the Return jack.

    That plug will isolate the preamp from the power amp.
    When I insert a plug into the Power Amp In jack the amp is quiet while I turn it off.

    0 Not allowed! Not allowed!

  6. #6
    Old Timer
    Join Date
    Jun 2007
    Posts
    5,080
    Thumbs Up/Down
    Received: 77/0
    Given: 49/0
    Rep Power
    19
    Schematic?

    Does that amp pop when there is no guitar cord plugged into the regular input?

    1 Not allowed! Not allowed!

  7. #7
    Senior Member nevetslab's Avatar
    Join Date
    Apr 2010
    Location
    Burbank, CA
    Posts
    1,652
    Thumbs Up/Down
    Received: 563/1
    Given: 1,299/1
    Rep Power
    11

    Princeton 112 Plus Service Manual attached

    Quote Originally Posted by 52 Bill View Post
    Schematic?

    Does that amp pop when there is no guitar cord plugged into the regular input?
    Ah....solid state amp. That begins to suggest things.

    Princeton_112_Plus_Service_Manual.pdf

    So, breaking the signal between the Preamp Out (at the Send) by inserting plug (or guitar) into the Return jack eliminates the Turn-Off pop. Does it do the same at turn-on?

    A brief look at the schematic shows a 22uF coupling cap at the preamp output (C32) ahead of the Send Jack, while following the Return jack there's just a 470nF cap (C34). Nothing large in stage-to-stage coupling upstream in the preamp circuits. And, in the power amp, there's the bootstrap cap C40 that can also produce a pop at turn-on, while everything is charging up all at the same time.

    1 Not allowed! Not allowed!
    Logic is an organized way of going wrong with confidence

  8. #8
    Twobie
    Join Date
    Feb 2019
    Location
    Alabama
    Posts
    5
    Thumbs Up/Down
    Received: 0/0
    Given: 4/0
    Rep Power
    0

    Fender Princeton 112 Plus power switch pop

    Quote Originally Posted by 52 Bill View Post
    Schematic?

    Does that amp pop when there is no guitar cord plugged into the regular input?
    Yes it does but not as loud as when the guitar is plugged in. If I can't find a fix this will be the shut off procedure I will be using.

    0 Not allowed! Not allowed!

  9. #9
    Twobie
    Join Date
    Feb 2019
    Location
    Alabama
    Posts
    5
    Thumbs Up/Down
    Received: 0/0
    Given: 4/0
    Rep Power
    0
    Quote Originally Posted by nevetslab View Post
    Ah....solid state amp. That begins to suggest things.

    Princeton_112_Plus_Service_Manual.pdf

    So, breaking the signal between the Preamp Out (at the Send) by inserting plug (or guitar) into the Return jack eliminates the Turn-Off pop. Does it do the same at turn-on?

    A brief look at the schematic shows a 22uF coupling cap at the preamp output (C32) ahead of the Send Jack, while following the Return jack there's just a 470nF cap (C34). Nothing large in stage-to-stage coupling upstream in the preamp circuits. And, in the power amp, there's the bootstrap cap C40 that can also produce a pop at turn-on, while everything is charging up all at the same time.
    Wow, Thank you so much for the service manual with schematic. This will give me a starting point to trouble shoot this issue. I will check the caps you suggested. I contacted Fender about a schematic and received a vague answer about their system being down for upgrades.

    0 Not allowed! Not allowed!

  10. #10
    Senior Member nevetslab's Avatar
    Join Date
    Apr 2010
    Location
    Burbank, CA
    Posts
    1,652
    Thumbs Up/Down
    Received: 563/1
    Given: 1,299/1
    Rep Power
    11
    Quote Originally Posted by Kirby02 View Post
    Yes it does but not as loud as when the guitar is plugged in. If I can't find a fix this will be the shut off procedure I will be using.
    Here's a simple solution. Plug in an open circuit TRS 1/4" plug into the headphone jack. That disconnects the speaker from the amp, and turn it on and off with the plug in place. There is room on the rear panel to put a Speaker On/Off switch, in lieu of having to mess with a dummy plug.

    Click image for larger version. 

Name:	Princeton 112 Plus Chassis open-1.jpg 
Views:	105 
Size:	68.1 KB 
ID:	52388

    0 Not allowed! Not allowed!
    Logic is an organized way of going wrong with confidence

  11. #11
    Old Timer
    Join Date
    Jun 2007
    Posts
    5,080
    Thumbs Up/Down
    Received: 77/0
    Given: 49/0
    Rep Power
    19
    Some of these have mutes that turn off the signal into the power amp when there is nothing plugged into the amp. This one seems to have a mute that turns off the reverb only when there is nothing plugged in.

    1 Not allowed! Not allowed!

  12. #12
    Lifetime Member Enzo's Avatar
    Join Date
    May 2006
    Location
    Lansing, Michigan, USA
    Posts
    31,626
    Thumbs Up/Down
    Received: 1,514/7
    Given: 0/0
    Rep Power
    54
    SO the preamp is picking up the pop. Probably a spark in the power switch.

    Try this, leave the power switch on, and just pull the power plug from the wall outlet. Does it still pop? You might need nothing more than a cap across the power switch.

    In my shop we do not consider pops a problem, it will not hurt your speaker.

    0 Not allowed! Not allowed!
    Education is what you're left with after you have forgotten what you have learned.

  13. #13
    Senior Member
    Join Date
    Aug 2017
    Location
    Portland, OR
    Posts
    570
    Thumbs Up/Down
    Received: 174/1
    Given: 87/2
    Rep Power
    2
    I think every Fender solid state amp I have had of this vintage has this same pop sound, worse at turn off. It is annoying, but something I just learn to live with.

    2 Not allowed! Not allowed!

  14. #14
    Lifetime Member Enzo's Avatar
    Join Date
    May 2006
    Location
    Lansing, Michigan, USA
    Posts
    31,626
    Thumbs Up/Down
    Received: 1,514/7
    Given: 0/0
    Rep Power
    54
    Most players do not turn it off during a performance.

    0 Not allowed! Not allowed!
    Education is what you're left with after you have forgotten what you have learned.

  15. #15
    Stray Cap DrGonz78's Avatar
    Join Date
    Oct 2011
    Location
    Scottsdale, AZ
    Posts
    2,043
    Blog Entries
    1
    Thumbs Up/Down
    Received: 271/5
    Given: 183/0
    Rep Power
    10
    I only try to fix these solid state Fender on/off popping noises when they are really bad. Most times it is just little pops but only worth investigation when it seems excessive.

    0 Not allowed! Not allowed!

  16. #16
    Don't forget the joker g1's Avatar
    Join Date
    Feb 2010
    Location
    Canada, somewhere north of Fargo
    Posts
    11,406
    Thumbs Up/Down
    Received: 1,351/21
    Given: 3,343/8
    Rep Power
    22
    The tendency is for the user to worry that the pop will cause damage.
    Don't worry, although it seems loud, it is not as loud as the amp is capable of. So the speaker will be dealing safely with bigger transients when being played at high volumes.

    0 Not allowed! Not allowed!
    Just because they don't have tubes doesn't mean they don't have feelings! - glebert

  17. #17
    Old Timer J M Fahey's Avatar
    Join Date
    Oct 2007
    Location
    Buenos Aires, Argentina
    Posts
    11,365
    Thumbs Up/Down
    Received: 1,557/18
    Given: 1,195/28
    Rep Power
    26
    As many said above, it is not a damaging problem, at all, just an annoyance.

    Most amps do it naturally, a few donīt.

    Many include some kind of mute at power amp input, shorting across input for half a second, this one does not.

    3 possible solutions:

    1) donīt turn amp on/off during performance, amp wonīt be hurt by having it on a few minutes (or an hour) before playing, same at turn off. Already suggested above.

    2) add anti pop capacitors across opening-closing switch contacts.

    Click image for larger version. 

Name:	Antipop caps.jpg 
Views:	34 
Size:	28.9 KB 
ID:	52422

    anything from .01 to .047uF but they must be rated for 250V AC
    DC rating is irrelevant here, these are caps specially designed for that duty.

    3) add a "Standby Switch" which is nothing more than a switch in series with speaker out.
    Starting with Mains and "Standby" OFF (like on Tube amps),you first turn Mains ON, waity a few seconds and only then turn Standby on.
    Reverse procedure for turn OFF .
    100% guarantee no popping.

    2 Not allowed! Not allowed!
    Juan Manuel Fahey

  18. #18
    Senior Member
    Join Date
    Aug 2017
    Location
    Portland, OR
    Posts
    570
    Thumbs Up/Down
    Received: 174/1
    Given: 87/2
    Rep Power
    2
    Quote Originally Posted by J M Fahey View Post
    3) add a "Standby Switch" which is nothing more than a switch in series with speaker out.
    Starting with Mains and "Standby" OFF (like on Tube amps),you first turn Mains ON, waity a few seconds and only then turn Standby on.
    Reverse procedure for turn OFF .
    100% guarantee no popping.
    And you were giving me grief for my Plush amp which is tube but looks like a Kustom, and now you want to add a Standby to a solid state amp? What's next, some tiny incandescent bulbs to add some "heater glow?" Just kidding

    1 Not allowed! Not allowed!

  19. #19
    Old Timer J M Fahey's Avatar
    Join Date
    Oct 2007
    Location
    Buenos Aires, Argentina
    Posts
    11,365
    Thumbs Up/Down
    Received: 1,557/18
    Given: 1,195/28
    Rep Power
    26
    Your Honour!!! Your Honour!!!! please donīt shoot me (yet) !!!!
    My defense is that respected Thomas Vox already added standby switches to SS amplifiers in the 60's!!!! (and most probably for the exact same reason)

    Click image for larger version. 

Name:	VOX Beatle V1143 Standby.jpg 
Views:	24 
Size:	25.2 KB 
ID:	52423


    2 Not allowed! Not allowed!
    Juan Manuel Fahey

Thread Information

Users Browsing this Thread

There are currently 1 users browsing this thread. (0 members and 1 guests)

Similar Threads

  1. Fender Princeton Chorus- switch pop?
    By drewl in forum Maintenance, Troubleshooting & Repair
    Replies: 7
    Last Post: 06-15-2018, 08:36 PM
  2. Fender Twin Reverb Silverface power transformer voltage selector switch wiring
    By beatnik in forum Maintenance, Troubleshooting & Repair
    Replies: 13
    Last Post: 03-31-2014, 09:17 PM
  3. Replies: 15
    Last Post: 03-07-2014, 04:35 PM
  4. Arch from power switch on Fender SS amp
    By DrGonz78 in forum Maintenance, Troubleshooting & Repair
    Replies: 10
    Last Post: 08-09-2012, 11:16 PM
  5. Fender Roc-Pro pops when power is switch off.
    By pbdog in forum Maintenance, Troubleshooting & Repair
    Replies: 2
    Last Post: 01-13-2008, 01:04 AM

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •