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Removed the Master Volume on my 81 Vibrolux

Discussion in 'Amp Tech Center' started by Middleman, May 24, 2017.

  1. May 24, 2017 #1
    Middleman

    Middleman Friend of Leo's

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    I've been curious for awhile whether the Master Volume mod I did on my Vibrolux back in 1985 was sucking the life out of my amp. I put the MV in using the old Craig Anderton article from that era which back in the day seemed like a really cool idea if you wanted to get your Fender amp to work like a Marshall amp. Have to say I was never really crazy about the sound of an overdriven Fender preamp section but I wrote the experience off as a learning experience, left the MV on 10, and went my merry way.

    Recently I read a poster thread in which they indicated that their MV mod made their Fender amp kind of flat sounding and lifeless and I have to admit, my 81 has been sounding like that in comparison to several new amps I have picked up along the way. So with that in mind I pulled the assembly and caps and rewired the amp back to the original state. You know what...it sounds a lot better. More touch sensitivity, more lively I would say. I am not sure that just because you can, you should when it comes to amp mods. Truthfully, when I hear before and after comparisons on YouTube, rarely do I think there was a dramatic improvement. Just slapping a mod into an amp which is not overall designed around the mod may not make sense. In this case, glad I reversed the process.
     
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  2. May 24, 2017 #2
    Ringo

    Ringo Poster Extraordinaire Silver Supporter

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    I am not familiar with the Craig Anderton MV, there are different types of MV and some sound much better than others. As you found out just putting a MV in a vintage Fender doesn't make it into a Marshall or a Boogie, and I don't really know why you'd need one on a Vibrolux Reverb, they sound great stock IMO.

    Sounds like you got your mojo back!
     
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  3. May 25, 2017 #3
    Middleman

    Middleman Friend of Leo's

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    Yeah, back in 1984 or 85, the Marshall craze was in full bloom, power soaks and the like. There was an article in Guitar Player magazine by Craig which provided a rough schematic and step by step for adding a master volume to a Marshall or Fender amp. It was an enlightening article for the times. There was no internet or source of data i.e. schematics unlike today and information for modifying amps was known to very few people i.e. the local radio and TV repairman, which is where you went when your amp was on the fritz. There were maybe one or two books on push pull circuits so this article was at the front end of an era regarding modifying amps. Alex Dumble was unknown to most people at this time.

    You are absolutely right by the way, I was expecting some killer overdrive tone like a Marshall or Boogie and it just wasn't there. I was a college student and the Vibrolux was my only amp so I tried to make it more versatile. It didn't work out. Back then I didn't know about touch response, sustain or even how to set my guitar and amp properly. This came later. I would say this amp is probably one of my better sounding amps after taking out that MV control. The mojo is definitely back.

    I've got to quit reading all these mod articles, maybe a nice amp project would be a better use of my tweaking habit.
     
  4. May 25, 2017 #4
    Aspiringluthier

    Aspiringluthier TDPRI Member

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    Have you tinkered with mini amps at all? that's where I'm at, way too afraid to try repairs or mods on larger amps. (That and I am without the knowledge.)

    There are guys on youtube doing some neat stuff already. As for me I just got my first Fender mini amp powered by a 9v. My plan is to attach a cheap, but good sounding pc speaker to it and wire it all in a cool box. I have an old chair in the garage with this bamboo mesh backing that would look killer on an all-wood amp. I plan to make knobs of wine corks soaked in some kind of resin.
     
  5. May 25, 2017 #5
    robrob

    robrob Poster Extraordinaire Ad Free Member

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    I'm a fan of the Trainwreck Type-3 master volume because it's super simple and adds no capacitors to the signal chain. It's easy to temporarily alligator clip the MV into an amp and try it before doing any soldering or hole drilling. With a push-pull pot you can get a combo MV/Vox tone cut. Pull up for a master volume, push down for the high cut tone control.

    [​IMG]

    For new build amps my favorite MV of all time is the Frondelli master volume. It's similar to the Lar-Mar but doesn't require the 2.2M bias safety resistors.

    [​IMG]
     
  6. May 25, 2017 #6
    Middleman

    Middleman Friend of Leo's

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    Yeah the one I used was similar to the trainwreck but used a pair of .1 600v caps tied in conjunction with the .1s already on the phase inverter section. Something about that setup was a tone soak.
     
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  7. May 29, 2017 #7
    FenderLover

    FenderLover Poster Extraordinaire

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    The article was December, 1982...
    The Anderton mod was essentially the same bad idea (IMO) the Frondelli, but there's no accounting for taste, and people like what they like. The PI goes to the pot wipers, providing a constantly changing load on the circuit, not to mention the changing time constant. I believe it truly represents what most people don't like about MV mods. It was one of the first mods that I did to my '74 Princeton. Pre-internet, like you said. I thought, "Hey, this is cool." Not for long. That was back when Princetons and Champs were practice amps that no one wanted. Drill a hole in the faceplate? why not....D'oh!

    A Fender is best left alone. It does what it does all by itself.
     
  8. May 29, 2017 #8
    Middleman

    Middleman Friend of Leo's

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    Couldn't agree more. I was just jamming in the garage with this amp and it sounds amazing. It was in the middle of the pack along side my other amps. It just moved to the head of the class.

    I drilled my hole in the back of the amp for the MV by the way. But if there is one legacy thing I can pass along to others it's don't add an MV to a vintage Fender. There is no gain (small joke).
     
  9. May 29, 2017 #9
    robrob

    robrob Poster Extraordinaire Ad Free Member

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    A master volume is always going to change the load, power tube bias, grid leak resistance, grid stopper resistance or something else.

    I like the Frondelli master volume because it adds no capacitors, keeps bias voltage and grid leak resistance constant and allows the load and grid stop resistance to vary. Turning down the MV add grid leak resistance which helps reduce blocking distortion. The Frondelli MV will not leave the power tubes with no bias voltage with a pot failure, even without tack-on safety resistors. No MV is perfect but I think the Frondelli is best.
     
    Last edited: May 29, 2017
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  10. Sep 27, 2018 #10
    Moen

    Moen NEW MEMBER!

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    This is somewhat an old post, but you seem to have good experience with the Frondelli master volume, so I'm asking you anyways.
    I was wondering if you had some tips for implementing a Frondelli MV in a project I'm working on.
    Would this be an acceptable approach for a cathode biased solution?

    first post btw
    Thanks
    upload_2018-9-27_17-42-49.png
     
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  11. Sep 27, 2018 #11
    schmee

    schmee Doctor of Teleocity Silver Supporter

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    I have tried I think 3 of the popular 4 MV's in Fender style amps. Tone sucking devices for sure.
     
  12. Oct 9, 2018 #12
    robrob

    robrob Poster Extraordinaire Ad Free Member

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    Moen, that MV will work just fine.
     
  13. Oct 10, 2018 #13
    wanderin kind

    wanderin kind Tele-Meister

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    overdrive.gif
     
  14. Jan 28, 2019 #14
    dogmeat

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    thinkin about doing a Hoffman Plexi & it has a Master Volume pre inverter. would a post inverter be the better way to go? as in, no pre inverter MV, and only the Lar-Mar post inverter MV
     
  15. Nov 7, 2019 #15
    jamesdlow

    jamesdlow TDPRI Member

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    I've been thinking about doing one to my '68 custom vibrolux. Which Master volume type did you have on there?
     
  16. Nov 13, 2019 #16
    Middleman

    Middleman Friend of Leo's

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    Well this was back in 1981 so there was only that magazine article and radio shack parts. Although I remember using orange caps. It was possibly a simplified version of the Trainwreck schematic. It worked as advertised but didn't bring anything to the sound of the amp.
     
  17. Nov 14, 2019 #17
    BobbyZ

    BobbyZ Doctor of Teleocity

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    Went down that moding road myself. What I figured out was if you want an old Fender to do Boogie or Marshall stuff. Just buy a Boogie or a Marshall. Or a modern Fender like a Pro Sonic for that matter, too bad they stopped making those. Point is there's a whole lot out there that does that sort of thing so why mess up an old Fender?
     
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