Sl-x 2100 Choke Mod?

Discussion in 'The Workbench' started by SpHj, Oct 30, 2017.

  1. SpHj

    SpHj Well-Known Member

    Joined:
    Nov 8, 2013
    Messages:
    489
    Likes Received:
    501
    Location:
    Ontario, Canada
    I’m thinking I may try this...what would you guys recommend? ( Brand, Henries)

    Thanks all!
     
  2. mickeydg5

    mickeydg5 Well-Known Member

    Joined:
    Sep 30, 2011
    Messages:
    25,059
    Likes Received:
    12,022
    Location:
    US of A
    Go for a 5 to 7Hy, Hammand or ClassicTone.
     
  3. SpHj

    SpHj Well-Known Member

    Joined:
    Nov 8, 2013
    Messages:
    489
    Likes Received:
    501
    Location:
    Ontario, Canada
    Hrmmm, I was looking at the Hammond 194G 3H 250mA. What kind of a difference would 2/4 Henries make?

    Thanks guys!
     
  4. mickeydg5

    mickeydg5 Well-Known Member

    Joined:
    Sep 30, 2011
    Messages:
    25,059
    Likes Received:
    12,022
    Location:
    US of A
    I understand the JCM900 and maybe SLX to be top frequency heavy. The larger coils will lend a hand to he bass side.
     
    Last edited: Oct 31, 2017
  5. SpHj

    SpHj Well-Known Member

    Joined:
    Nov 8, 2013
    Messages:
    489
    Likes Received:
    501
    Location:
    Ontario, Canada
    Gotcha, good to know!
     
  6. ampmadscientist

    ampmadscientist Well-Known Member

    Joined:
    Jun 26, 2014
    Messages:
    17,865
    Likes Received:
    12,055
    Location:
    Bio-Isolation Lock Down
    I think it (a choke) would make absolutely no difference what-so-ever to the low frequencies.

    But here's what will:
    A bypass cap across R7, 2.2 uF 35v or larger...and the + of the cap faces pin 3 on V2a.
    Well, maybe I would use .68...
    http://drtube.com/schematics/marshall/cd0109-iss4.pdf

    This is what a choke is for:
    to get more hum out of the B+ supply.
    This is a choke calculator:
    https://www.ampbooks.com/mobile/amplifier-calculators/LC-ripple-filter/

    Yes well, I have gone over it and the answer was to bypass R7 with a capacitor.
    Because, V2 has no low frequency response without it...therefore....no bass in = no bass out.
    This is the basic problem w/ JCM 900, in general...

    Here is another great calculator which will help fix bass response problems:
    https://www.ampbooks.com/mobile/amplifier-calculators/cathode-capacitor/

    https://www.ampbooks.com/mobile/amplifier-calculators/pi-pa-bass-response/
     
    Last edited: Oct 31, 2017
  7. mickeydg5

    mickeydg5 Well-Known Member

    Joined:
    Sep 30, 2011
    Messages:
    25,059
    Likes Received:
    12,022
    Location:
    US of A
    No it will not boost or route more low frequency in the signal chain but it will help hold voltage more stable during high current demand of low frequency passages. He may or may not notice it depending on the playing, speakers or cabinet but it does not hurt to opt for a larger choke if adding one.

    Anyone else adding and modifying the resistor or choke between power tube plate and screen care to comment expressing there findings?
     
  8. 92lx50

    92lx50 Member

    Joined:
    Dec 27, 2012
    Messages:
    60
    Likes Received:
    9
    Location:
    Tampa, Florida
    I just finished overhauling a 2500 SLX. New electrolytics and filter caps, bridge rectifier and all new iron. I figured since I was getting new transformers, I may as well get a choke too. I can't tell you what the difference is since the amp wasn't working when I got it, but I can tell you the last thing it lacks is bottom end. I doubt the choke had anything to do with it, but I'm sure the new transformers and caps did. 20171007_143404rr.jpg
     
  9. SpHj

    SpHj Well-Known Member

    Joined:
    Nov 8, 2013
    Messages:
    489
    Likes Received:
    501
    Location:
    Ontario, Canada
    Thanks for your input guys, I ended up ordering the Hammond 194G (3H, 250mA) as my local supplier has them in stock. This amp isn’t lacking in the Bass department, but I may try tweaking the NFB for a little more output while I’m in there. Hopefully the choke will give me a little more clarity at higher volumes/live as that’s my main concern with the amp.
     
  10. ampmadscientist

    ampmadscientist Well-Known Member

    Joined:
    Jun 26, 2014
    Messages:
    17,865
    Likes Received:
    12,055
    Location:
    Bio-Isolation Lock Down
    I think a lot of this choke transformer stuff is imaginary.

    I think the solution to sound quality in these designs is in the preamp, not the power supply....not the OT either.

    The Marshall Transformer: there is nothing wrong w/ it. It's a perfectly good transformer.
    Unless it's bad, there is no reason to change it.

    Sure...the new transformers have better frequency response...BUT the preamp is intentionally made to remove low frequency.
    and so, unless there is bass "in" the audio, it won't come out of the transformer...no matter what transformer.

    And you can make the power supply stiffer....but you still don't have any bass to start with.
    No bass in = no bass out.
    That's the real issue. Throwing money at it does not fix that.
     
    anitoli likes this.
  11. SpHj

    SpHj Well-Known Member

    Joined:
    Nov 8, 2013
    Messages:
    489
    Likes Received:
    501
    Location:
    Ontario, Canada
    These don’t have a Choke from the factory, hence adding one. I’ve not once stated anywhere looking to add “Bass” to my signal, don’t know where that came from.
     
  12. anitoli

    anitoli Well-Known Member Gold Supporting Member

    Joined:
    Jul 9, 2011
    Messages:
    8,456
    Likes Received:
    10,719
    Location:
    Lewiston, Maine U.S.A.
    I gotta agree with the amp mad man on this one. I don't think a choke or a resistor makes any difference. If the bass ain't there it ain't there. I thought my 6100's 3rd channel had tons of bottom end until i bought a Fender Dual Showman Red Knob and that thing knocked the light out of my ceiling.
     
  13. SpHj

    SpHj Well-Known Member

    Joined:
    Nov 8, 2013
    Messages:
    489
    Likes Received:
    501
    Location:
    Ontario, Canada
    Did you not read my posts? We’re getting a little off topic...I do not have a lack of Bass issue whatsoever.
     
    Last edited: Oct 31, 2017
  14. anitoli

    anitoli Well-Known Member Gold Supporting Member

    Joined:
    Jul 9, 2011
    Messages:
    8,456
    Likes Received:
    10,719
    Location:
    Lewiston, Maine U.S.A.
    I wasn't replying to you..................
     
    SpHj likes this.
  15. SpHj

    SpHj Well-Known Member

    Joined:
    Nov 8, 2013
    Messages:
    489
    Likes Received:
    501
    Location:
    Ontario, Canada
    Noted, and I fixed my post as well. No harm meant!
     
  16. anitoli

    anitoli Well-Known Member Gold Supporting Member

    Joined:
    Jul 9, 2011
    Messages:
    8,456
    Likes Received:
    10,719
    Location:
    Lewiston, Maine U.S.A.
    Cool.
     
  17. mickeydg5

    mickeydg5 Well-Known Member

    Joined:
    Sep 30, 2011
    Messages:
    25,059
    Likes Received:
    12,022
    Location:
    US of A
    Maybe it is the other JCM900 that are top heavy frequency wise. As HpHj said he was going to add a choke so I mentioned what a larger choke might do for the situation but it all depends as I had mentioned earlier.
     
  18. SpHj

    SpHj Well-Known Member

    Joined:
    Nov 8, 2013
    Messages:
    489
    Likes Received:
    501
    Location:
    Ontario, Canada
    Got my Choke in today, will update my findings after I install her this afternoon

    [​IMG]
     
  19. SpHj

    SpHj Well-Known Member

    Joined:
    Nov 8, 2013
    Messages:
    489
    Likes Received:
    501
    Location:
    Ontario, Canada
    Got the Choke installed, after playing her for a solid 1/2 hour I didn’t feel any sag/swells like I did before. Seems a little tighter for palm muting as well, although that may just be a placebo effect. All in all, worth the 1/2 hour of my time.

    [​IMG]
     
    92lx50 likes this.
  20. mickeydg5

    mickeydg5 Well-Known Member

    Joined:
    Sep 30, 2011
    Messages:
    25,059
    Likes Received:
    12,022
    Location:
    US of A
    Wait a minute. Are you palm muting everything or just chugging low chords?
     

Share This Page