Dsl1 (2018 Vietnam Version) Mod's

Discussion in 'The Workbench' started by Mavrim, Oct 16, 2018.

  1. Mavrim

    Mavrim Member

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    I bought a used DSL1 a few months ago for $230 total. Removed the chassis to investigate what was inside. I noticed that the output transformer had an unused wire inside that was tie wrapped in the wire bundle. After ohming it out I decided that it has to be an 8 ohm tap. The only output is 16 ohms. With these small one watt amps, it is ok to mismatch output impedance without damaging the amp. I read that one of the marshall designers did that with one of the 50th anniversary models to get better tone. I added another output jack next to the 16 ohm jack. When wiring it up, I found that marshall had swapped the ground and hot on the pcb spade connection. So I swapped them and wired in the new lead. I recall that it was white. With a meter I read 1.6 ohms on the 16 ohm output and .9 ohms on the unused lead that I assume is 8 ohms.

    I set up my DSL1 using the new 8 ohm output that I installed. Cabinet is a lead 12 slant fitted with an 8 ohm 12" celestion vintage 30. I also swapped out the stock ECC82 power tube with an RFI ECC82. Amp sounded incredible! Then I switched the 8 ohm speaker to the factory 16 ohm output and it did not sound as good. So I can see this mod as being a good thing for those with 8 ohm cabinets.
     
    Last edited: Oct 16, 2018
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  2. Mavrim

    Mavrim Member

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    DSL1 Wire Bundle.jpg Extra output lead tie wrapped in output transformer lead harness. 8 ohms???
     
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  3. Mavrim

    Mavrim Member

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    DSL1 8ohm Jack 01.jpg DSL1 8ohm Jack 04.jpg
     

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  4. Mavrim

    Mavrim Member

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    Ground wire on 8 ohm output jack attaches to ground on PCB as shown.
    DSL1 8ohm Jack 03.jpg
     
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  5. Mavrim

    Mavrim Member

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    8 ohm output jack added next to the original 16 ohm output jack. Need to label this as 8 ohms.

    DSL1 8ohm Jack 02.jpg
     
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  6. Mavrim

    Mavrim Member

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    Next, thinking about adding a presence control, NFB in/out switch, cathode capacitor bypass switches...
     
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  7. Mavrim

    Mavrim Member

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    PS - The built in attenuator switch for .1 watts only works on the original 16 ohm output and not on the additional 8 ohm jack. I will investigate that at a later time.
     
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  8. Mavrim

    Mavrim Member

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    ECC82 output tube V3 goes directly to the output transformer. Plates connections 6 & 1 go to transformer. So there is no question of a mosfet output stage. I believe that the phase inverter is a mosfet design...
     
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  9. Mavrim

    Mavrim Member

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    Thinking I might remove the additional 8 ohm output jack that I installed and replace it with a SPST toggle switch to select 8 ohm and 16 ohm. 16 ohm orange wire going to PCB would go to switch and 8 ohm white wire would go to opposite side of switch. Switch center would then connect where the orange wire went on PCB. This way the attenuator circuit would work for both outputs. The original 16 ohm output jack would now become selectable for 8 or 16 ohms. Too bad I drilled that large hole, now I need to use a large toggle. If doing this mod fresh, I would have used a mini toggle switch.
     
    Last edited: Oct 17, 2018
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  10. bobq

    bobq New Member

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    Hello everyone

    I've made your modification to 8 ohm and it's works perfectly.

    Thanks a lot

    Is it possible to change valves to improve our sound?

    Thanks a lot
     
  11. pedecamp

    pedecamp Well-Known Member

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    Im hoping somebody can figure out a mod for these amps to rid some of the compression in its tone. Great little amps just too much compression for my liking.
     
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  12. slagg

    slagg Well-Known Member

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    Still looking for someone to find the bright cap on the clean classic channel.I think it effects both channels and will reduce a lot of the compression that is killing the tone.
     
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  13. slagg

    slagg Well-Known Member

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    can anyone tell me if c30 is the bright cap
     

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  14. ampmadscientist

    ampmadscientist Well-Known Member

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    If you have the schematic it would be helpful.
    Either that or the amp itself to draw a schematic from.

    The basic Marshall formula is to compress the highs (the higher the frequency the more compression)
    and to leave the lows clean.
    The lower the frequency, the more clean it becomes in other words.

    And when you hear "too much compression," it often means that the lower frequencies are being compressed too much....resulting in a kind of muddy overload when the amp is pushed.
     
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  15. pedecamp

    pedecamp Well-Known Member

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    Thats what Im hearing.
     
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  16. Micky

    Micky Well-Known Member VIP Member

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    Has anyone found the schematic for this amp yet?
     
  17. slagg

    slagg Well-Known Member

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    no luck yet
     
  18. luciferschild

    luciferschild New Member

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    i snapped some shots of the pcb, would anyone out here in marshall land be willing to trace out the schematic? im trying to find the negative feedback for presence and resonance controls. would be nice to know if c30 is the bright cap also.
    [​IMG]
    [​IMG]
     
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  19. luciferschild

    luciferschild New Member

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    got a pencil sketch done up, will try figure out a way to computerize it when i get a chance. many frustrations tracing this board - looks as if they have gone out of their way make this difficult. like covering traces with components. curious about the 18k slope resistor, 10k mid pot and 0.047uF tonestack caps as well as the different approach to the tone shift. anyone know if those yellow caps are polyester or polypropylene?
     
  20. slagg

    slagg Well-Known Member

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    Awesome ! Someone needed to do this. Is c30 the Bright cap?If so it will be the first thing to mod.
     

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