Increasing filter cap value on JCM 800

Discussion in 'The Workbench' started by JM5010, Mar 5, 2021.

  1. JM5010

    JM5010 Active Member

    Joined:
    Nov 11, 2017
    Messages:
    356
    Likes Received:
    61
    Recently i read a thread about Blockhead amps. In summary, they make modded marshalls with the Jose mod. Found one in the sold listings on Reverb, and saw some gut shots.

    One thing that caught my eye were these 330uf filter caps.
    AB25F792-4D3B-4123-B966-78DD929BEA10.jpeg

    What is this cap mod doing to the amp besides reducing hum?

     
  2. thetragichero

    thetragichero Well-Known Member

    Joined:
    Jun 6, 2010
    Messages:
    3,201
    Likes Received:
    1,148
    Location:
    flo rida
    more filter capacitance would give the amp a "tighter" feel all things being equal
    is it worth it? maybe
    it could also be that they got a good deal on 330uf in bulk so used them where otherwise they'd use smaller values
     
    JM5010 and South Park like this.
  3. JM5010

    JM5010 Active Member

    Joined:
    Nov 11, 2017
    Messages:
    356
    Likes Received:
    61
    I may try this out in my amp. Perhaps that tightness is what i am missing
     
  4. XTRXTR

    XTRXTR Active Member

    Joined:
    Feb 14, 2021
    Messages:
    133
    Likes Received:
    79
    @JM5010
    I tried adding more capacitance to my 2204, didn't know that was a mod. I was just testing whether the ripple was reduced. It is reduced but the amp did get a stiffness some might call that tight. I don't know if my ears were playing tricks on me but it seemed more hiss too. I played it on the bench for a while and my ears got fatigued quickly so I stopped. Next day I removed the jumpered in caps and played again. It seemed much better to me and the spikeyness was not there.

    I would test it on the bench a couple days with it in and out and then make a decision of your own. Tone is so subjective. Remember to test at stage volumes to be sure.
     
    JM5010 likes this.
  5. JM5010

    JM5010 Active Member

    Joined:
    Nov 11, 2017
    Messages:
    356
    Likes Received:
    61
    Perhaps this is best combined with plate bypass capacitors?
    The Blockhead amp that i looked at specifically was based on the SE Lead Mod (Doug Aldrich mod). Maybe in order to tame the extra capacitance and hiss that is added, it is also a good idea to add some caps across the plate resistors. They did this on V1
     
  6. southbound suarez

    southbound suarez Active Member

    Joined:
    Sep 11, 2012
    Messages:
    120
    Likes Received:
    80
    Location:
    so. cal.
    Wow, seems like this is counterintuitive and taking some of the life and feel away from these amps .
    Plate bypass capacitors?
    If the amp needs to be tamed then by all means neuter it!
     
    JM5010 likes this.
  7. XTRXTR

    XTRXTR Active Member

    Joined:
    Feb 14, 2021
    Messages:
    133
    Likes Received:
    79
    Can you provide a schematic to this mod so we can look at it? My amp is still on the bench and will be until I fully test out the mods I want. Then I am rebuilding/rewiring it. The point is I want to use it as my test model until I find the tone and capabilities I want.
     
  8. JM5010

    JM5010 Active Member

    Joined:
    Nov 11, 2017
    Messages:
    356
    Likes Received:
    61
    Here’s the closest thing to the SE Lead Mod schematic. It’s basically the Lead channel of the CAE 3+ SE preamp inside of a JCM 800 with the increased filtering.

    http://millerguitar.com/schematics/CAA-3_SE.png
     
  9. JM5010

    JM5010 Active Member

    Joined:
    Nov 11, 2017
    Messages:
    356
    Likes Received:
    61
    Well, that is the goal and that’s how they are designed. If Martin Golub was still alive maybe he’d be able to chime in. The SE Lead Mod does not sound like a typical marshall at all
     

Share This Page