Asher Guitars WD Music Products Amplified Parts Mod Kits DIY Nordstarnd Pickups Warmoth.com
Asher Guitars WD Music Products Amplified Parts Mod Kits DIY Nordstarnd Pickups Warmoth.com
Asher Guitars WD Music Products Amplified Parts Mod Kits DIY Nordstarnd Pickups Warmoth.com

Princeton Reverb Vibrato tweak!

Discussion in 'Amp Central Station' started by kosmonautmayhem, Mar 5, 2012.

  1. kosmonautmayhem

    kosmonautmayhem Tele-Meister

    432
    Jan 11, 2010
    Chicago
    So I've never been happy with the range of speeds in my 72 SFPR - way too fast. I like to have a real slow deep trem sometimes. I've heard and played other PRs that do this very well.

    I've also never been happy with the lack of depth. So I aimed to increase the intensity as well.

    In the trem circuit there are three caps in series that control the speed. Stock they are .02uf, .01uf, .01uf. I changed both ".01s" to ".02uf" and now enjoy a super great range - hypnotically slow, make-you-dizzy pulse at 1 on the dial. At 10 its still probably slightly faster than I have a use for, but its way more usable than before. Pre-mod, the speed at '10' was ridiculous. Dare I say - ludicrous speed.

    The intensity mod involves one resistor swap. I swapped a 1M for a 220k resistor. WOW! This makes the trem dangerously deep. Almost too deep. So I decided some bias adjustments to attempt to help compensate this.

    In an amp with bias-vary trem like this one, the intensity will decrease as you raise the bias of the power tubes. I went from about 18mA/ea. to 22mA and found perfection. Now the trem is still deep, but not as overwhelmingly so and I'm rocking slightly hotter 6V6s than before - win-win!

    Cheers,
    kM
     

  2. jhundt

    jhundt Poster Extraordinaire

    Age:
    63
    Mar 23, 2003
    Netherlands
    thanks; I have to check and see which mods I did to slow and deepen my PR, maybe I can learn something here.
     

  3. twintwelve

    twintwelve Tele-Afflicted

    Nov 13, 2010
    Laurel, DE
    Yeah, more info, please!!
     

  4. kosmonautmayhem

    kosmonautmayhem Tele-Meister

    432
    Jan 11, 2010
    Chicago
    jhundt, I'm curious. Can you share your mods?
     

  5. jhundt

    jhundt Poster Extraordinaire

    Age:
    63
    Mar 23, 2003
    Netherlands
    @kosmo - I will be happy to, in a couple of days. I will have to open the box to check what I did. I am waiting on some new tubes so I will have to open it to do the bias, then I will make some notes and post here.
     

  6. kosmonautmayhem

    kosmonautmayhem Tele-Meister

    432
    Jan 11, 2010
    Chicago
    Thanks jhundt. No rush, just curious is all. What kind of PR do you have? BF, SF, Ri?
     

  7. jhundt

    jhundt Poster Extraordinaire

    Age:
    63
    Mar 23, 2003
    Netherlands
    @kosmo - until I get a chance to check my mods, I will share this. These are some notes I have taken down from various sources over the years, re: modding the PR trem.

     

  8. kosmonautmayhem

    kosmonautmayhem Tele-Meister

    432
    Jan 11, 2010
    Chicago
    Very cool. Yes, this seems like the same basic idea, with some different values.

    I was actually looking to compromise between the stock 1M resistor and the 220k and do something like 450k, but I didn't have anything in that value. This is why I went ahead with 220k and raised the bias by about 3mA to help dial in the intensity I wanted.

    As for speed, I'm sure other values, like .047uf would work too with diff. results. I actually trued replacing just one of the .01uf caps with .022uf a while back and it didn't slow it down that much. This is why I went with all .022uf in the series.

    Interestingly enough, I'm also working on my CVR which I believe uses .033uf caps for the trem. Its very deep and can get super slow...much like the results of last nite's experiment. :)
     

  9. jhundt

    jhundt Poster Extraordinaire

    Age:
    63
    Mar 23, 2003
    Netherlands
    you know I think I might have used a .033 in mine, that rings a bell. I'll check soon.

    Hey, shall we do an experiment? Why don't we set our trems on the slowest, deepest setting and then count the pulses in one minute - like when the doctor checks to see if you're still alive!

    I just tried mine and got 138 beats-per-minute.
     

  10. kosmonautmayhem

    kosmonautmayhem Tele-Meister

    432
    Jan 11, 2010
    Chicago
    Thats an excellent idea! I plan on testing the amp tonite when I get home from work. I'll see how many BPM I get and report back.

    It will be neat to see the differences based on cap values. Sure its not perfectly flawless, since all caps will have variation and are at least 10% +/- but will still prove interesting.

    Did you just count out loud and set a stop-watch. I was probably just going to set up my iphone, since it has a stop-watch function.
     

  11. jhundt

    jhundt Poster Extraordinaire

    Age:
    63
    Mar 23, 2003
    Netherlands
    i set a little kitchen timer (shaped like a chicken) to 1:00. I plugged in a guitar cable and held it in my hand so it would make a nice buzz. Set the intensity on 10 and the speed on 1, and counted 'til the chicken-timer went off.

    There is another difference, too, besides cap values. I have modded my amp some and am currently running 6L6s biased at around 40 mA. I don't yet understand the relation between bias voltage/current and the trem function, so I don't know what - if any - change might happen to the speed with 6V6 tubes. I think the bias voltage affects the depth, not the speed - but I am not certain.

    Mine is an 80's pull-boost Princeton Reverb with the Blackface control panel. Circuitry is almost identical to an AA1164 amp; I have removed the pull-boost stuff. I switched out the power transformer for a Deluxe Reverb part; I also dropped in an Allen TO-26 output transformer, replaced the old filter-cap can so the first stage now has 40 mF, and put in TAD 6L6's and a 12" Jensen Neo speaker. That little amp is almost as loud and clean as a Twin and sounds great... but I am considering going back to the original 6V6 setup just to compare.

    I look forward to hearing your results. Right now mine sounds pretty slow at 138 bpm, but I wouldn't mind going even lower. Your description "hypnotically slow, make-you-dizzy pulse at 1 on the dial" sounded so good - that's what got me interested in this thread!
     

  12. kosmonautmayhem

    kosmonautmayhem Tele-Meister

    432
    Jan 11, 2010
    Chicago
    Very cool. Didn't expect to read you had 6L6s! Theoretically, I don't believe the 6L6s vs. 6V6s matter much in terms of depth or intensity. Moreso it matter how they're biased. I do know, in my experience I like to bias my power tubes on the cool side so I have the best trem intensity. Perhaps someone with a bit more knowledge could help enlighten if I missed anything or if 6L6s make much of a difference. I'm going to assume no, since my CVR is a 6L6 amp with the same bias-vary trem and it acts exactly like the PRs trem.

    Speed, I believe, has mostly to do with the caps in series...not your power tubes.

    It sounds like you have a very loud and clean PR. :)
    Mine is a '72 SFPR. Circuit is true to AA1164, with a Weber 10F150 / 50W / light dope.

    If you're interested I'll have to get around to doing a sound clip of the mod results. Perhaps I can get that out this week...then you can hear if my words accurately describe the dizzying hypnosis of this trem.

    Cheers,
    kM
     

  13. SoK66

    SoK66 Tele-Afflicted

    Oct 2, 2007
    Four Corners USA
    That's an old mod that works on any vintage style Fender amp. You can just add a .01 cap in paralell with any of the ones in the three-cap array and see where you like the speed. Remember that as you slow it down on the lower settings, you're also slowing down the fast settings. Fun to fool with these.
     

  14. jhundt

    jhundt Poster Extraordinaire

    Age:
    63
    Mar 23, 2003
    Netherlands
    I would like to hear a sound clip of your amp kM.

    I didn't realize that the CVR had a bias trem. I think I better take a look at that circuit...

    next time I open mine I'll try the parallel cap as suggested by SoK66 and see what I get.
     

  15. kosmonautmayhem

    kosmonautmayhem Tele-Meister

    432
    Jan 11, 2010
    Chicago
    I counted the pulses at slowest speed. Looks like I'm getting about 135 bpm.

    I'll try to get a clip recorded this week of some clean and pretty vibrato stuff.

    Cheers,
    kM
     

  16. jhundt

    jhundt Poster Extraordinaire

    Age:
    63
    Mar 23, 2003
    Netherlands
    so it looks like we're about the same speed. I'd like to hear your stuff. This is the only amp I have with a Vibrato, and I have never found a way to use it that works for me.
     

  17. kosmonautmayhem

    kosmonautmayhem Tele-Meister

    432
    Jan 11, 2010
    Chicago
    I see that! I'm pretty happy with the results. I think it could be a touch faster, but I often don't go fo rthe super fast stuttery trem. If I need something like that, I'll use a pedal. I have a boss tremolo that sounds good if I want a more blackface trem sound.

    I'd be happy to share. I don't own a single amp without bias-vary trem come to think of it! :eek:
    I like it mostly for clean stuff. I don't think it sounds too great with a lot of fuzz or saturation though, unless you're going for a dramatic effect. I like to keep it somewhat subtle to add dimension.
    Its one of my favorite effects. I'd love to get an amp with harmonic trem too, like some of the mid-sized brownface amps had....Almost like a uni-vibe.

    kM
     

  18. Scotty 2

    Scotty 2 Tele-Holic

    887
    Jun 22, 2007
    Ft.Pierce,Florida
    jhundt,,I use my tremo mostly for slow country ballads and
    church hymns..also speed on 1 and intens on about 3?,,to just help
    color signal for most any song.Anyway,,I like it :D
     

  19. jhundt

    jhundt Poster Extraordinaire

    Age:
    63
    Mar 23, 2003
    Netherlands
    @ Scotty - that is the way to use it, I guess. I think I have to try it out with a full band situation. When I use it at home I find that the constant pulse is more annoying than pleasing. But maybe in the group it will fit better.
     

  20. sonicreducer

    sonicreducer TDPRI Member

    7
    Aug 22, 2010
    Los Angeles
    Hey fellas, I'm considering doing the 1 meg resistor swap to increase the depth of my trem. It's a '76 Princeton Reverb. I was wondering would I have to make any other adjustments to compensate for the smaller resistor or is it that simple? Will it affect the bias of my amp? I've got a 220k and a 430k resistor at 1/2w and 5% tolerance. Thanks!
     

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