The dsl joey mod thread

Discussion in 'The Workbench' started by TwinACStacks, Apr 5, 2010.

  1. TwinACStacks

    TwinACStacks New Member

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    Well Gang, because I'm getting weary of emptying my inbox with questions concerning the DSL INFO thread, LOL, I've decided to post the "meat and potatoes" of the Mods for the DSL series without the additional Banter between contributors. Joey Voltage was kind enough to provide some open-source mods which form the basis for the alterations, Along with input from the rest of the resident BRAIN TRUST: JON, JCMJMP and the MAJOR. My Humblest appreciation and Thanx to all of You. These Guys are GREAT to have on your side folks....

    Me? I'm an electrician but in NO WAY am I an AMP TECH!! I'm just dangerous enough to try it all. I've owned 5 DSLs in a Love-Hate relationship with the Red and Green Channels. (Actually I'm beginning to believe that this is really a SINGLE CHANNEL AMP with 4 Distinct MODES!!!) THIS time around I decided to call upon the experts to help make it True Love, and we all know True love is hard to find...


    FIRST: (AFTER DISCHARGING THE LETHAL VOLTAGES IN YOUR CHASSIS!!!) Determine which version of Boards that Your DSL contains Using this link:
    Marshall DSL

    There are about 5 different Version (issue) boards used. The mods are centered around the Front Board (Pre) and Tubeboard (Main) and are based on THESE TWO VERSIONS, if yours don't match up you have a different version:

    JCM2 60-02 iss5 (Tube) AND JCM2 61-00 iss1 (Front)


    Front Board:

    NOTE: THESE MODS AFFECT THE RED LEAD 2 MODE ONLY (removing C12 will also darken Lead 1)

    1M Resistor from Wiper to Ground on Vr3 ****
    C12 Lower to 150pf or REMOVE (I removed it)
    C10 replace with .0022 uf
    R20 Remove and JUMPER

    **** These can be bridged on the other side of the Board. Find the 4 Pins that are the Actual Pot terminals, (Not the Two Board mounting pins), follow the Traces. The inner one that has R19 on it is the WIPER, the outside one that connects to Con 5 pin 2 is the Ground. ( Using your meter set to continuity works well here) Solder your 1M across these 2 pins leaving the legs long, then bend flat to board using a piece of electrical tape attached to the board to insulate the leads from accidentally shorting out to any other exposed solder connections. Electrical splicing tape works quite well here as it adheres to the board better than vinyl electric tape.


    Mainboard:

    NOTE: THESE MODS AFFECT ALL CHANNELS/MODES

    C9 replace with 1000pf (.001uf) 500V
    C12 replace with 1uf 63V

    Here is a Link for the Caps:

    MKS2-1/63/5T WIMA Polyester Film Capacitors


    Now if You find that the overall texture of the amp is, or has become too dark:

    Mainboard:

    Replace R30 (470k)with 68k to 220k resistor this will Decrease the Fizziness and the OVERALL GAIN as well and also brighten the Amp. I personally Piggybacked, (using a pair of test leads), a range of resistors across the Legs of R30 from 82k to 1M and decided I liked 1M the Best. This brought the Value of R30 to 320k. I then soldered it in place across the legs of R30. This way it is easily changed if I decide on a different value without pulling the PIA Mainboard!!! This particular Mod is pretty much season to taste. One of the Techs or Myself can figure out what value you need for "Piggybacking", or you can try and figure it out yourself:

    R1XR2 Divided By R1+R2= the Total resistance of Both Resistors combined. Use the Value of R30 (470)k for R1 and the resistor You want to try as the value for R2. (Try: 82k, 120k, 220k, 330k, 470k and 1m)

    Also if You find that the Green CRUNCH Mode is too boomy especially with the deep switch engaged:

    Frontboard:

    C8 replace with .001uf to .0022uf (I used .0015uf)

    Here's a link: http://www.mouser.com/ProductDetail...EpiMZZMsh%2b1woXyUXjyBw8LYChpgf%2bpPFAhHPmAM=


    THESE ARE THE EXTENT OF THE ORIGINAL MODS.


    Now THIS is the "while You are in there" section of the Mods that SHOULD be performed.

    C46 if You have one. This is an underspeced Cap that apparently is to prevent parasitic oscillations. It can short out and Take out the board it's on, as well as your OT. Either CUT it OUT or replace it with a +1000V version of the same value (22pf). I say "apparently" because I have heard nothing about anyone experiencing oscillations after removing this cap completely.

    Change out the Grid Blockers on the Mainboard. Most versions have 220K in place, replace with a more normal "Marshall" value 5k6 resistor. I'm of the understanding Alan Bradley Carbon Comps are suited quite well for this, I used regular +/- 5% carbon films from Radio Shack that I had on hand.

    The locations for these are: R7, R10, R66, R70

    Also because of frequent run-away biasing problems That appear to be temperature related, Upgrade the Bias resistors. I suggest a more temperature-stable precision metal film 1/4 to 1W, PRP or Vishay Dale.
    Here is a link for the PRPs: Sonic Craft High-End DIY Audio Parts

    The locations and Values of the Bias resistors are: on the Mainboard
    R68 33K
    R77 10K
    R67 220K
    R69 220K

    One last preventive measure, On the rear of the chassis the speaker output jacks should have separate grounds installed. the 4&8 ohm jacks are grounded through the 16 ohm jack, (which Bypasses via an open/close contact), the 4&8 Ohm jacks when the 16 Ohm is used. Sometimes this contact doesn't close because of Dirt etc. so when You are plugged into the 4, 8, or Both, the Amp is actually seeing No load at all and: Bye-Bye OT and Maybe more. If You use only the 16 Ohm jack this is not a concern. This can be accomplished by soldering a short piece of wire to the shoulder of W6 Ground connection and to one of the metal bands on either the 4 or 8 ohm jack that is closest to the inside rear surface of the Chassis.
    When this is done however there will be no auto disconnect. ALL 3 jacks will be active ALL the time. Please DO NOT try and run 3 Cabs at the same time!!!

    Now for the FUN Stuff:

    Replace the OT and Add a Choke.

    Add a 3H Choke at the R71 Resistor (270R 7Watt) on the Mainboard. Remove R71 and connect the two wires for the choke in its place. You can mount it behind the power Trans at the Rear of the Chassis. You will need to swing the Powerboard out of the way for drilling. TIP: Because this resistor is mounted with a LOT of solder, (and I was a little afraid of overheating and lifting the traces), I simply snipped the body off the Legs and soldered my wires directly to the leg remnants. Very un-professional and very effective.

    A MAJOR sound Modification is the replacement of the puny Stock Dagnall OT. JCMJMP has drop in replacements on: Marshall DSL
    Also they are available from Mercury Magnetics, I believe Jon deals in these. Because I had a deal fall into my lap, I used a replacement for a 100 Watt Plexi: a Dagnall C1998 or the Later version C2668. These you can find on Ebay or VERY good Clones from Marstrans or Metro Amp.

    For those of You electing to go this route, Here are the Wiring Directions For the 100 Watt Dagnall C1998/2668 Plexi Stand-up mount OT.(also the Marstran and Metro Clones)

    NOTE: THIS TRANSFORMER IS FOR THE 100 WATT DSL. FOR 50 WATT use a 784-139 Plexi CLONE.

    Dagnall Plexi Primaries/ Stock DSL Dagnall
    RED.............................................White (goes to V5,V6)
    White.......................................... Blue CT
    Brown.......................................... Purple (goes to V7, V8)


    Dagnall Plexi Secondaries/ Stock DSL Dagnall
    16 Ohm Green................................Red
    8 Ohm Yellow.................................Orange
    4 Ohm Black.................................. Green
    Comm. Brown................................ Black

    For the 50watt 784-139 Clone:

    784-139 Primaries/ Stock DSL Dagnall
    RED.............................................White (V4)
    Brown..........................................BLUE CT
    White..........................................Purple (V5)

    784/139 Secondaries/ Stock DSL Dagnall
    16 Ohm Gray.........................................RED
    8 Ohm Green.........................................Orange
    4 Ohm Yellow........................................Green
    COMM. Orange......................................Black

    If desired you can also change out the Power Xformer, although there is much less impact on the sound. They are also available as drop-ins from JCMJMP or Mercuries from Jon. I don't believe there are vintage-type repros available with the low voltage power taps needed for the DSL channel switching at this time.

    You can use some quick connects, I wanted to be neater and installed Molex.

    Lastly, SEEK OUT SOME GOOD NOS TUBES: MartyStrat54 is THE hookup for this.

    For those who need/want to KNOW what these mods DO, (courtesy of Joey):

    on the pot board:

    put a 1M resistor from the wiper to ground of Vr3: This has a dual function. It limits the amount of drive signal possible for low frequencies below 169hz (not taking in account for any other low frequency roll off's below this point of course). full up, frequencies below this point will be down -6db, and flat. it also slightly alters the peak response of the shelving filter created by R19,C11, and Vr3.

    keep C12 or remove: Keeping C12 alters the R19,C11,Vr3 shelving filter further by moving the beginning of the upward shelf high at lower gain settings (because the top half of Vr3, anc C12 are now in series with R19/C11 ignoring other circuit impedences of course) giving an edgier sound. when about 3/4 of the way up the shelving effect becomes negligable, and eventually the cap is shorted out by Vr3. Removing it obviously will darken the tone of OD1, and OD2 by removing this effect, but also does so because this now puts larger resistance in series with the grid of the next valve, whose input capacitances will creat a lowpass filter with this resistance, and bleed highs further.

    replace C10 with a .0022uf: Reduces the amount of low frequencies passed on to the next stage in conjunction with R19, Vr3, and the source impedence of the driving stage. this has the bennifit of tightening the sound by somewhat tailoring the bass content within the guitars useable range, and can encourage a higher mix of second order harmonic content (but thats for another discussion). this will also help with potential blocking.

    jumper R20: adjusts the strenght of the afformentiond shelving filter.

    on the tube board:

    C9 1000pf (.001uf)creats a single pole high pass roll off of around 3.2Khz which is around the fundamental of highest note of the guitar. there are also very few useful harmonics for guitar above this, or that can really be reporduced by most guitar speakers. it also can reduce hiss, as well as rolls off the glassy harmonics of the 220K plate load.

    C12 1Uf provides a more useable mid shelving for overdriven guitar while retaining some current induced feedback for low frequencies. also sounds good for the clean mode as well

    Joey Voltage


    BE CAREFUL!!!!!! The voltages inside these amps can KILL YOU....DEAD. If You are unsure about what You are doing ASK!!! Or take/send your Unit to a qualified Tech, any of the Techs behind this thread are outstanding!!!

    Hope You Guys and Ladies, enjoyed the JOEY MODS THREAD, and good luck with your quests for good tone with the MOST AWESOME MARSHALL HEAD EVER...

    Here are some additional links for Parts:

    http://metroamp.com/
    http://marstran.com/
    http://www.mouser.com/Home.aspx
    http://tubesandmore.com/

    TWIN
     
    Last edited: Apr 7, 2010
    Razvan S., nkd, Dave Marshall and 2 others like this.
  2. jcmjmp

    jcmjmp Well-Known Member

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  3. 6StringMoFo

    6StringMoFo Well-Known Member

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    I'd be interested in Transformers and the upgrades for the 2 channels to clean and balance them out.

    Voodoo has some nice mods for them, anyone know what mods their doing to them?
     
  4. Joey Voltage

    Joey Voltage New Member

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    2, and 3 are easy to deal with. we have already discussed the deep switch. Stock, in conjunction with C29, the opamp creates a bandcut filter with a resonant frequency in the 50hz region which appears as a boost when the feedback is returned. you can shift the resonant frequency up by adjusting the value of C29. a good place to start is 1uf - 2.2uf, and the cap makes a difference on how wide the Q of the filter is. If you want a wider Q, stick with tantalum or electrolytic. If you want a slightly more precise Q, go with film.

    with three, there are many ways to go about this, and I think the easiest is just to play around with the tonestack a little, and exploit the circuitry that is already there for the "shift" function.
     
  5. jcmjmp

    jcmjmp Well-Known Member

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    Yup!
    2) You can also play around with C28 for the upper frequency cutoff, although the effect will not be as drastic as changing C29.
    3) If there's any demand of the mid cut button, I can post some simple mods for those. The basic devices that are involved are C19, R36 & C22. Depending on what you're after, you can change these devices to get to where you want with the mid cut.
     
  6. jcmjmp

    jcmjmp Well-Known Member

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    The Voodoo Mods are probably very similar (in essence) to the mods listed above.
     
  7. 6StringMoFo

    6StringMoFo Well-Known Member

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    If someone wants to make a few bucks, put together a few kits with (recommendations) on Choke and Transformers
     
  8. Joey Voltage

    Joey Voltage New Member

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    Well, I guess the Idea is to give more control to the user because that is who is playing through the amp inevitably, not any of us!, and not all of these mods are going to work for everybody. It's more of a resource than a money maker
     
  9. thrawn86

    thrawn86 Well-Known Member

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    Twin, you've been Stickied!! Congrats! :applause:
     
  10. Buggs.Crosby

    Buggs.Crosby New Member

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    3 stickies in the sites history of this section...2 this year?....strange days indeed
     
  11. LPMarshall hack

    LPMarshall hack Well-Known Member

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    What is a sticky?
     
  12. Landshark

    Landshark Well-Known Member

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    Now here's a good one... It says tone shift on the front plate... Is there a value to produce a "mid boost" rather then a cut?
     
  13. Buggs.Crosby

    Buggs.Crosby New Member

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    Permanent thread...it will always be at the top of the page also
     
  14. Joey Voltage

    Joey Voltage New Member

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    yep
     
  15. jcmjmp

    jcmjmp Well-Known Member

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    I'll post a "mid boost" mod when I get a chance to look and analyze that part of the circuit.
     
  16. LPMarshall hack

    LPMarshall hack Well-Known Member

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    Aahh...ok, tks.
     
  17. Joey Voltage

    Joey Voltage New Member

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    It's easy, and there are many differen't ways you can do it. The most popular method is to increase the value of the treble cap, but you want to becareful because you can make other controls ineffective. Like wise if you want to give your self a "cloth baggy" Iron maiden type mid range, you put a .001uf cap from wiper to ground of the mid pot, this will shunt some upper mid frequencies when the pot is increased. If you want to make the midband less lossy, you can increase the value of the mid pot.

    There's tons of other crap you can do, and if you don't use the deep switch you can even increase C29 to the point where you are moving the resonance frequency up in the 750hz-1K range. you can also add many different interstage networks and loops.
     
  18. jcmjmp

    jcmjmp Well-Known Member

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    Mid Shift Boost MOD

    Joey suggested some good ideas, especially about using the deep button as the mid boost.

    My take on this, is different. To get a bit of a boost with the mid cut button, I would change R36 to 33K and run a wire to make it run in parrallel with R35. In conjunction with this, you can try lowering C21 a little, to like 18n to re-adjust the bass from the R36 change. I would also experiment with C19 to also run it in parrallel with C20 to get more mid band in BUT increasing the value of this cap will move the mids lower, which may not be what you want to do. Adjust to taste.

    If you want more mids but still be able to get good range with the Mid Shift button out, replacing the 22k mid pot with a 100k pot is a good idea. You'll have more range and more mids with the control cranked.
     
  19. TwinACStacks

    TwinACStacks New Member

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    :) JC that 100K mid pot sounds interesting. Will it give appreciably more Range? Will the Korg Pots (11mm) from AES fit. Exactly what type/manufacturer are on the DSL anyways? Vr3 has 4 Pins, that much I know...

    :):) TWIN
     
  20. Joey Voltage

    Joey Voltage New Member

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    I would go for 50KL, If you go too high, it will make the other controls not as effective, as there would be minimal loading. Although you have to keep in mind alot of the analysis of tonestacks really only applies to small signal theory.
     

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