Modding my head for more reverb

Discussion in 'Amps and Cabs [BG]' started by Taylor Livingston, Jul 25, 2009.

  1. Taylor Livingston

    Taylor Livingston Supporting Member Commercial User

    Dec 25, 2002
    Oregon, US
    Owner, Iron Ether Electronics
    I know most bass players will respond first, "Reverb?" and then "more reverb?"

    Yes. I like reverb. I want more. Here's the schem:

    http://www.schematicx.com/view-schematic/univox-u-1011-amplifier-schematic/

    I'd like to either be able to get more reverb mix, or just cut off the clean signal entirely, so I get only wet reverb signal. What's the best way to do this? Seems like I could cut the clean signal right before the second 12AX7, but I'm not sure if that would cause problems. I want to make this selectable, obviously.
     
  2. Bootzilla

    Bootzilla Guest

    May 4, 2009
    I'm not going to dl the schems now but might I just say that a circuit is always a little more complicated than it looks. You could also just play through a clean amp and get yourself a reverb pedal... maybe a SPRING CHICKEN DELUXE LIMITED EDITION!!!!

    http://www.malekkoheavyindustry.com/index.php?page=spring-chicken

    warning: I only posted the spring chicken because it gets so much love in the effects forum :D. You should check out other verbs as well (there are much cheaper ones out there).

    btw. Maybe I'll look into it later and see if I can make some sense out of it.
     
  3. Taylor Livingston

    Taylor Livingston Supporting Member Commercial User

    Dec 25, 2002
    Oregon, US
    Owner, Iron Ether Electronics
    I'm pretty familiar with reverbs, having owned a ton, including 3 all tube spring reverbs besides my head. A digital pedal and real spring reverb have nothing in common, especially the Spring Chicken, which is just a Belton reverb module with the datasheet schem wrapped around it. I'm pretty handy with DIY effects, so if I wanted to go that way I'd build my own. Although digital reverb is good for some things, it's not what I'm looking for right now.

    But I do appreciate the suggestion. :)
     
  4. Bootzilla

    Bootzilla Guest

    May 4, 2009
    Ok just checking :D

    Edit: Just took a quik look at the schem and maybe you could get a different value resistor just before the verb pot or change the verp pot to a different value (don't know if it would be higher or lower). You could also (just a wild guess) put a trim pot before the tube. I don't have any experience with amps so take these ideas with a grain of salt.
     
  5. T-Bird

    T-Bird Guest

    Hi.

    Well You could mod the Ch2 to be the tremolo channel and cut the signal path from V1a to V2a so all the signal for the V2a would go through the reverb section. Without knowing the internal resistance of the reverb circuit it's hard to tell whether it changes anything though.

    Easy to try, so if You're positive that you know about all the safety procedures, go ahead.

    Surprizes the heck out of me that You haven't tried that already though, are You sure you know what you're doing?
    Usually "If You have to ask, you probably don't" applies.

    Be safe.

    Regards
    Sam
     
  6. Taylor Livingston

    Taylor Livingston Supporting Member Commercial User

    Dec 25, 2002
    Oregon, US
    Owner, Iron Ether Electronics
    Yeah, that's fair. I am pretty good and experienced with low voltage SS stuff, but I'm too chicken to mess around with HV so far. I keep thinking I'll start with simple stuff like this, but then folks like you put the scare in me. ;) It's probably good, though.

    I guess if I decide to do this I'll just have a tech do it.
     
  7. BassmanPaul

    BassmanPaul Inactive

    If you want more reverb you can try increasing the signal going to the 6AN8 reverb driver. That level is controlled by the ratio 0f the 470K to the 68K at the pentode control grid. Increase the value of the 68K to 100K or more and try that. You will have to listen for distortion appearing in the wet reverb signal if you overdrive the driver or tank too much. you could also make these resistors into "dwell" control by substituting a 500K pot.

    The 220R cathode resistor for the reverb recovery amplifier could be increased to 2K2 to allow more gain. Ensure that the 50K pot on its grid is at max.

    Paul
     
  8. Jerrold Tiers

    Jerrold Tiers

    Nov 14, 2003
    St Louis
    More drive may or may NOT help, since at a certain point the drive is saturated and there is no more power input.

    Adding gain or adjusting the return level, either with the 330K resistor or elsewhere (not many choices) may lead to reverb feedback, since the total gain from speaker back to the springs may be too high.

    Also, the circuit itself is very interactive, adjusting one thing will affect another as well.

    There are two control pot sections, are they tied together? Or is one a separate adjustment inside? The one directly off the pan return is an obvious place to look if they are separate.
     
  9. beans-on-toast

    beans-on-toast

    Aug 7, 2008
    It might be a good idea to check the reverb related pots with an ohm meter to make sure they are up to spec. Sometimes pots don't go all the way to zero or the maximum resistance.

    Another possibility is to put in a different reverb pan to see if you can get a richer sound. See the Accutronics web site http://www.accutronicsreverb.com/). The pans are not all compatible. Perhaps they can tell you which ones would work in your amp.
     
  10. BassmanPaul

    BassmanPaul Inactive

    Everything Jerrold says is true enough, however without significant circuit changes there's only so much you can do. More drive to the tank resulting in more out of the recovery amp or more gain on the recovery amp itself. Too much of either will lead to problems. Overdriven tank and possible feedback from the tank. Just how far you can go will have to be tested experimentally.

    Paul
     
  11. You're not really saying "reverb" you're saying "spring reverb"

    Modifying maybe isn't what you want. Overdriving a spring you get sprong.

    If you visit other tube boards you'll read that tubes do wear. And they have a variance from tube to tube - so try changing them.

    You could also try changing the reverb spring tank. If it's not sealed it could be corrosion on the springs.

    You're already moving away from authentic spring reverb sound by talking about modifying it - why not just pick up a reverb pedal or rack effect. They go from subtle to extreme.
     
  12. Passinwind

    Passinwind I know nothing.

    IME, messing with the verb itself is usually counterproductive. Attenuating some of the dry signal at the sum point where the verb returns is simple and effective in many cases. If you need more specifics, find a tech who knows how to do it. ;)
     
  13. BassmanPaul

    BassmanPaul Inactive

    Y'know Charlie you are right! Didn't think of subtracting what you don't want to emphasize what you do. Good thinking brother!

    Paul
     
  14. Jerrold Tiers

    Jerrold Tiers

    Nov 14, 2003
    St Louis
    The subtracting might work..... but there is only so much gain.... that's a simple circuit, and you need to get to full output without a lot of hiss and noise. Reducing the "dry" signal might require adding gain later, with more noise......

    And you still could end up with acoustic feedback issues.

    Worth a try, though, probably.

    And, actually, the drive is often weak.....but I dunno about that particular one. I made a really high power drive for the old Ampeg SS-70, and it was a LOT hotter than most others, without bad effects.... you may be able to boost yours a bit.