Adding reverb to 2204

Discussion in 'The Workbench' started by cruisemates, Jan 23, 2021.

  1. cruisemates

    cruisemates Active Member

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    If you read my earlier posts you know I once had a Metropolis Loop in this amp with a solid state driven spring reverb (Accutronics) installed. I worked GREAT and I only took it out for the purists who do not want any mods (I installed it as a 95% fully reversible mod - no drilled holes).

    But I really miss amp reverb in this amp - so I have read a ton on different ways to drive reverb with added tubes.

    But I have also read about people using the Accutronics digital reverb bricks - the only challenge is figuring out a way to install them without adding the loop back in.

    These are usually made to run on 5v DC, and require typical guitar impedance. I figure I could easily just adapt a pre-made 5v power supply and connect it to the AC in. Some folks talk about adapting a 7805 voltage regulator to the heater current, but that actually seems like too much trouble.

    My biggest challenge is figuring out where I can tap audio signal into go to the brick, and how to bring bring it back. The idea is to make it mostly "plug & play". The loop gets tapped at the Treble pot wiper (iirc) and gets returned to the master volume INPUT. But I am not sure about impedance or other things I need to match.

    Does anyone actually know a way to do this? I would like to build the reverb circuit and the power supply into one big project enclosure I could just glue into the case and run as few wires into the chassis as needed.
     
  2. Chris-in-LA

    Chris-in-LA Well-Known Member

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    If you’re going with a digital reverb, you might as well use a pedal.
     
  3. Max Gahne

    Max Gahne Active Member

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    To use your heater supply you'll have to rectify it then use the voltage reguator. The BTDR2 and 3 both sound great, I've built lots of pedals using them. I haven't put one in an amp's signal path yet but probably will some day. Where to split/merge the signals and how to do it I haven't experimented with. There's a thing called a BitMo reverb using the BTDR2 that can be added to the VHT Special 6s. They sell the layout/schematics so I haven't found one online. I'd like to see how they do theirs for clues. They do appear to use mixing resistors. It should go between the treble pot and MV pot like you said and I suspect that because of impedance issues you'll have to put back in the loop or add a JFET or IC buffer. So after all this I'd put back in the origional system you liked so much. My amps are for me, not for purists or anyone else for that matter.
     
  4. cruisemates

    cruisemates Active Member

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    I have looked into using the heater supply and seen schematics for it - but most people agree it is overkill when you can easily just add a 5V adaptor to your circuit and tap the 120 VAC lines. I have also built a few reverb pedals with both PT2399 ICs (more like delay) and with Accutronics blocks (better for reverb) - and also with an actual spring reverb in a JCM800 2204 where I built a 9V DC solid-state send & recovery preamps circuit tapped with a Metropolis loop.

    I also have the VHTs and have modded them. The difference is thae VHT 6 Special has DC heater circuits so it is easy to tap for power to the brick. The 12/20 has a more typical AC heater circuit, but I have not yet seen anyone build a reverb for one of these (those amps even supply 9v DC for pedals in the back of the amp - an ingenious inclusion).

    The most important factor for my 2204 is that I do not want a pedal up front - it just does not operate the same as reverb in the amp just before the master volume. Overdrives will distort a reverb pedal up front so they sound awful. I really want to figure out a way to tap the audio path inside the amp after the tone stack and return it to the master volume (like the Metropolis loop does). Powering the Belton (or Accutronics) brick is not the hard part - inserting it into the signal path at the right impedances is the challenge here.
     
  5. Gene Ballzz

    Gene Ballzz Well-Known Member

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    @cruisemates
    Yeah, even using the digital "brick" it appears you should probably re-install your Metro loop. The most appropriate spot for the reverb is at a part of the circuit path that will be far in excess of the rated input voltage/Vin of 1.5 Vpeak. And I totally get and agree with your assessment of reverb sounding like doo-doo in front of the amp. And unless you are really worried about resale value, I'd say "Screw them purists" and have the amp you want the way YOU want it! For that matter, a properly and well installed Metro Zero Loss Loop, even with holes drilled won't likely detract a lot from the value. Its a small price to pay to be able to enjoy your preference! Then comes another question: Is your 2204 one of the ones with four speaker jacks?
    Just My :2c:,
    Gene
     
  6. cruisemates

    cruisemates Active Member

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    I was looking at some voltages and there is a spot right after V2a that is in that 1.5 Vdc range. But it is really odd that no one has found an easier fix (plug & play) for this. I was just messing with my brick installed in a pedal and it sounds OK but SO MUCH LOUDER on rhythm than on lead. I don't know exactly why reverb acts so much better when it is installed after the MV, instead of in a pedal, but it just does.

    But now I am thinking I could reinstall the loop with 3 cables coming out of the chassis into a breakout box that sits in the head cabinet (Hot glued that will peel off) - so no drilled holes at all. I don't think it would be that hard and you get exactly what you want.

    Also - I have checked prices on Reverb and in general, a "stock" 2204 - with everything like the schematic is not likely to fetch much if any more than a modded one. In fact, mods often seem to add value there. It is only the purist collectors who want to see a "stock" - like all original. But that is also kind of a joke because 40-year-old mustard & electrolytic caps don't sound like new.

    I saw a YouTube where some guy found NOS mustard caps and they sound GREAT - much better than the old original mustard caps the amp was A/B with. It makes me think it is the age of the cap more than the type that matters - but some may disagree.

    Also - 4 speaker jacks? No, only two. I have two vertical inputs and two more to spare covered by the tolex.
     
  7. thetragichero

    thetragichero Well-Known Member

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    there are so many fantastic fv-1 based reverb pedals these days that if you're not using a spring reverb (which really i could give or take anyway) you'll get a lot more/better sounds just having a loop with a pedal in it. as far as i understand those belton reverb bricks are just a few pt2399 delay chips anyway. great for simple analog-sounding digital delays but we they worth using in place of an actual tank? meh
     
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  8. cruisemates

    cruisemates Active Member

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    Yeah, the brick was cheap - but as I said, I had mounted a spring reverb in there with the loop. Word is the older Accutronics springs sounded a lot better than the new ones and it was an old one. I think you are right about the bricks being pt2399s. They don't sound that good, but I only have a mix control (no tone or send pots) on it. I see your point though.

    This is my demo that just happens to have the reverb installed - notice the chords & lead have the same amount of reverb - that doesn't happen with a pedal upfront. However, if need be I can get by with setting the right amount for just chords, and use less on leads since I loop a delay pedal into my gain pedal anyway.

    (go to 0:34)

     
  9. Gene Ballzz

    Gene Ballzz Well-Known Member

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    My limited experience tells me that the MOD brand tanks sound considerably better than the newer Accutronics units. My JTM30 originally had an Accutronics that never sounded great, but just "so-so." After a few years it stopped working altogether and I didn't bother replacing it for a few more years. I then bought the MOD of the same appropriate number/spec and was so much better than the original that I almost couldn't believe it!
    Just Sayin'
    Gene
     
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