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Rivera Boost Mods - R55

Discussion in 'Amp Tech Center' started by soundchaser59, Jan 12, 2014.

  1. Ike286

    Ike286 Tele-Holic

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    There are two other forums that I somewhat regularly visit, and this one is usually the best for everything.

    Definitely great people here. :)
     
  2. redeyedjim

    redeyedjim TDPRI Member

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    Mod a Clubster 25 channel 1 boost?

    I debated between bumping this thread and starting a new one, so if a mod feels this should be split off into its own topic, let me know and I'll do that.

    So..as I posted last month, I did the mods as described here to the two boost circuits on my Chubster 40. Both mods work great! No issues, all is well, and the world's a beautiful place.

    Over the weekend, I picked up a second (used) Rivera, the smaller Clubster 25-110, because I'm attracted to its size and feature set. It packs a lot into the footprint of a small 1x10 combo.

    For anyone unfamiliar with these, they are a two channel, 2x6V6, 25w, 1x10 or 1x12 combo with reverb. The lead channel (Ch. 1) has a pull boost feature, while the clean channel does not. Like all Rivera boosts, this one is pretty aggressive out of the gate, and there is no stock means of adjusting it. I'd like to change that, and make it adjustable - it's max value can be about the current value, but in typical use I'd like to try some lower boost settings.

    Here's the schematic for the amp:

    [​IMG]

    And here I've isolated what I think is the boost circuit, if you can call it that:

    [​IMG]

    I'm hoping someone can take a look at this and either confirm my thinking or set me straight: is modding this as simple as replacing R113 (2.2M ohm) with a 2M or 5M pot, similar to the Chubster boost mods? And would an audio taper be preferred over linear?

    Thanks for any light you can shed on this!
     
    Last edited: Dec 23, 2014
  3. Ike286

    Ike286 Tele-Holic

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    It looks like you are right, make 2.2M adjustable so you could have bigger or smaller amounts of boost.
     
  4. redeyedjim

    redeyedjim TDPRI Member

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    Awesome -- thanks for taking a look! I'll probably give it a try tonight or over the holiday and will post the results.

    One follow up question, and sorry if this exposes me for the dummy I really am: if I'm replacing a 2.2M fixed resistor with a 2M (or 2M variable + 200k fixed ) variable one, how will that give me bigger amounts of boost than the stock 2.2M fixed value? Or did you just mean that when it was engaged I'd be able to adjust it within a range of almost no boost to the current boost level? I may be unclear of just how this circuit works, but I thought that more resistance = more boost?

    Thanks, Ike -- your help with this is very much appreciated, both now and earlier in this thread!
     
  5. Bendyha

    Bendyha Friend of Leo's Silver Supporter

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    The bigger the resistance, the cleaner the unboosted state. If you put a poti in there, the lower the resistance, the more signal will be getting through to the tube, and so the higher the gain. This is why when you pull the switch now, the full signal gets through - set fixed boost. If that is enough maximum boost for you then, if you can find one, put in a revers log 3M poti, which will let you tone down the gain to an even cleaner state than it now has. If you don't desire to get that cleaner, and would like to be able to dial in a bit more boost, keeping the lowest boost much as it is now, then; use the 3M Revers log, and change the relationship of the values of the following voltage divider resistors - R116 & R117 from the 221K & 100K, which is sort of like a set lin. poti turned up 2/3 of the way. I would try replacing the 221K maybe with a 820K.
     
    Last edited: Dec 23, 2014
  6. redeyedjim

    redeyedjim TDPRI Member

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    Thanks, Bendyha. To be clear, I DO want to lower the gain of the boost when it is engaged, not increase it. So if the current boost, when engaged, is "100", I want to be able to experiment with boost levels between, say, 10 to 100 (to be arbitrary).

    Could I accomplish this just by putting a 1M or 2M poti in series with the current 2.2M fixed resistor?

    Thanks for your help, and sorry to be a little thick headed about this.
     
  7. Bendyha

    Bendyha Friend of Leo's Silver Supporter

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    [​IMG][/url][/IMG]
    This is from the Fender Concert II, a Rivera design. Here he just takes the 100K out of the schematic- This would also be an option, but I would still prefer to increace the R116, and keep R117 as a grid load.
     
  8. Bendyha

    Bendyha Friend of Leo's Silver Supporter

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    No, not in series. You need a poti to replace the 2M2. Lin. if you can't find a revers log.
     
  9. redeyedjim

    redeyedjim TDPRI Member

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    My goal is to have an external boost adjustment, identical in function to the boost adjustments I added to my Chubster. Max boost (when engaged) would be approximately equal to the current default boost value, and I would add a range of adjustment below that point when the boost is engaged.

    Since you have a much better grasp of this than I do, could I ask you to spell out the components I would need to change or add to make that possible? I had thought it was going to be as straightforward as replacing once existing fixed resistor with a variable resistor, but it seems like there is a little more to this mod than that. And if you don't feel like explaining these things to a noob, I will absolutely understand.

    Thanks either way!
     
  10. Bendyha

    Bendyha Friend of Leo's Silver Supporter

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    Simple. Get a revers log (or Rev. Audio as it might be called, same thing) 3M poti. Most Fender spare parts suppliers should have one. Solder this in series with the switch.
    Job done.
     
  11. redeyedjim

    redeyedjim TDPRI Member

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    Got it. Thanks!! I will give that a try and report back. Thanks for your help and for patiently explaining this to me!
     
  12. Ike286

    Ike286 Tele-Holic

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    From what I can see, the 2.2M reduces the amount of signal getting through (unboosted) so the boost is bypassing the resistor. If you use a 1M resistor, your regular tone with increase a little in volume/gain, and the boosted volume will remain the same, but relative to the regular volume, it will seem like a more reasonable jump. So you could also put a resistor on the switch, so the regular clean stays the same, and then you adjust how much it bypasses the 2.2M, instead of adjusting the clean signal to make the relative jump (boosted) smaller.
     
  13. Bendyha

    Bendyha Friend of Leo's Silver Supporter

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    This 3m poti, when the switch is engaged, will be parallel with the 2M2 that is there. This gives a value of about 1M3. So going back to your
    "boost levels between, say, 10 to 100 (to be arbitrary)."
    I'm judging you will actually have a range of, say, 50 to 100 ...........ish.
    Try it first,it may be enough, but to get a bit more out of the mod we will have to make it rather more complicated.
     
  14. redeyedjim

    redeyedjim TDPRI Member

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    Thanks, Ike. Actually, I think I was able to do a better job of communicating what I want from this mod in my back-and-forth replies to Bendyha: it isn't the jump in volume that I am trying to remedy, as I like the way the lead channel sounds when the boost is NOT engaged. However, when the stock boost IS engaged, I find the resulting tone to have too much gain and "thickness" to it. I want to dial back the amount of the boost when it is engaged, without affecting the tone of the lead channel when the boost is not engaged.

    Thanks! I don't think I will be able to find a local source for the poti I need before Christmas, so I just ordered a 3M reverse audio poti, and hopefully it will be here next week.
     
  15. rickcruz

    rickcruz NEW MEMBER!

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    Hi guys,

    This was an interesting and thrilling thread to read. I've searched the internet to no avail, until I found this thread by (for lack of a better term) knowledgeable Rivera amp techs.
    My problem is different from the mods that you have been discussing in this thread. I cannot get any sound from Channel 1. If I "totally crank" everything on Channel 1, I can get a faint, "cold bias" sounding tone. When I switch back to Channel 2, everything functions as normal. This amp is a Suprema 55.
    Let me know if you have any more questions. Can you help? I only get a voicemail message at Rivera.
     
  16. Wally

    Wally Telefied Ad Free Member

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