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Thursday, 24 May 2012

Rangemaster with switchable input caps

Request.  This is your standard Rangemaster, but with a 5K trimmer instead of the 3K9 to help bias the transistor, and 6 switchable input caps to go from treble boost to more of a full range boost.  It would be easy to add a 3PDT toggle to switch between a germanium or silicon transistor, but I would expect them to bias differently and so don't know how good it will sound switching to silicon when the transistor is biasd for a germanium.

As always though, have a play with the circuit and see what you like, and remember if you want to use this daisy chained with negative ground effects, you could always use the Negative Voltage Converter.



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30 comments:

  1. Jason29 May 2012 at 14:15

    Nice!!! Thank you good sir!

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  2. Jason29 May 2012 at 14:28

    I see a lot of Rangemaster schematics with two 47uf electrolytics. One of them is not needed for this layout I assume? I don't mean to 2nd guess you, just like to know how these things work. Thanks again for taking the time to create this layout

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    1. Jason29 May 2012 at 16:07

      May have found my answer. Seems like it isn't really needed for a battery only circuit?
      http://www.diystompboxes.com/smfforum/index.php?topic=82070.0

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    2. Anonymous29 May 2012 at 16:31

      Hi Jason, Mark is away till the weekend so I guess he'll answer any questions when he's back.

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    3. Jason30 May 2012 at 12:06

      From IvIark...

      "But in answer to your question yes the other 47u is a power supply filter cap and wouldn't be required with a battery. You could still add one if you wanted, just put it from the first to third row on the right hand side of the board above the trimmer, and daisy chain the ground wire to go from the bottom to the third row. Also remember the positive side of the cap would need to go to ground. "

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  3. mirosol26 August 2012 at 10:22

    Whoah. Tag it.

    I flipped the 47µ and used MP38A (measuring 85 hFE), thus making it NPN negative ground.

    Very versatile and amazing sounding booster. This was my first brush with rotary switch, but gladly those are quite simple to comprehend - and your image did help a lot :).. With the bassiest 150n cap on board it pretty much sounds like all the ODs that are trying to mimic Marshall 18. Which is not a bad thing at all.

    For the reference, the trimmer set at 1,82K gives out the sweet spot for me and that particular transistor.

    This will get a high spot on the list for to-be-boxed.

    Thank you!
    +m

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    1. IvIark26 August 2012 at 10:37

      Awesome, nice one mate

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    2. mirosol26 August 2012 at 11:25

      Just one more hint for anyone building this :)

      Mind the pinout. I used thin heat shrink for the legs..
      +m

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  4. mirosol28 August 2012 at 08:08

    Monday, Late night boxing: http://mirosol.kapsi.fi/varasto/boxes/6Master.JPG

    I noticed that the bigger caps on board and high output pickups on guitar give out lots of saturated, broken sounding overdrive. When guitar volume is decreased 2-6%, the amplification clears up. Stock rangemaster cap doesn't break it - that sounds pretty much 1:1 with my AC127 rangemaster. I thought about swapping the MP38A for one with higher gain, but blaah. I'm not going to bother. It's like it is. And it rocks. And has lotsa Mojo, with capital M.
    +m

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  5. Olav14 September 2012 at 12:15

    Besides the MP38A for NPN, what transistors would you recommend for PNP? There's too many to choose from if you're a n00b like me. Gets confusing...
    Also, the 'symbol' on the bottom right of the populated vero is a trimpot maybe? Judging by the positions of the 'legs' I'd say it is, just I haven't seen that before. What size load would you recommend? Any help appreciated.

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    1. IvIark14 September 2012 at 12:38

      2N404A's are really good, if you're looking at Russian then GT308B (or sometimes marked GT308V ir IT308#), GT309B, GT402B, MP16B, MP20B, P416B

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    2. IvIark14 September 2012 at 12:38

      Oh and yes it's a 5K trimmer

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  6. Olav14 September 2012 at 15:12

    That was quick! Thanks Mark!

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  7. Unknown17 December 2012 at 23:29

    Hello Mark,
    just a little explanation about the wiring.

    We assume that the input must be wired to the "A" pole of the rotary switch, and then the 6 associated lugs respectively to the board, as shown in the picture.

    So, where should I wire the Input wire shown on the veroboard picture which is directed to the 1M (pulldown, I suppose) resistor?

    Thank you kindly :)

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    1. IvIark18 December 2012 at 09:20

      Just daisy chain from A on the rotary switch, or alternatively you could put the pulldown resistor directly on the stomp switch between the board input pole and the ground lug for the LED and then leave it off the board entirely.

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  8. Madferret2 February 2013 at 15:11

    To use an NPN transistor with this, is it just a simple case of swapping the 47uf cap direction as Miro said or is there more to it? I've managed to end up with a lone NPN Germanium with usable leakage and I thought this would be an excellent project for it.

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    1. IvIark2 February 2013 at 15:30

      Yes turn the 47u and +9V to top row, ground to bottom

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    2. Madferret2 February 2013 at 15:42

      Thanks Mark, much appreciated.

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    3. Madferret2 February 2013 at 18:52

      After having had a mess about with the booster I'm now trying to get it biased properly. I've done a bit of reading on Geofex and one of the articles suggests biasing the collector to around -7 (I'm guessing that will be +7 for me) should there be a noticeably better sounding spot or is it just a case of getting the voltage to 7v. Sorry about all the questions it's the first time I've done a circuit that's required manual biasing.

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    4. mirosol2 February 2013 at 19:00

      Tune it by ear. When it sounds good, you'll hear it.
      +m

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    5. mirosol2 February 2013 at 19:02

      Bias voltage is crucial on most JFETs to get them working correctly. Here that's not as important as different germaniums need different voltages to sound good.
      +m

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    6. Madferret2 February 2013 at 19:21

      Thanks, there are some sections that sound really bad and the spot I had it set to sounded about right so I figured it wouldn't really matter if it wasn't bang on 7v but I just thought I'd check. Thanks again.

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  9. Kinski19 August 2014 at 20:41

    I'm on a PNP Ge roll! Just built this.

    MP20A, 100 hfe, biased to about 7v.
    Sounds damn good. Used a voltage inverter.
    I'll post pics when it gets boxed. Thanks again!

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  10. Kinski20 August 2014 at 23:10

    Sounds freaking awesome. Thanks again. Ended up with a 77 hfe, MP20A. Biased closer to 8v.

    First time I ever put a rotary in a 1590A. Fits nicely, actually.

    https://lh4.googleusercontent.com/-8FnaAgUqv18/U_UcOOLucWI/AAAAAAAAAvM/Q8XED529scs/s512/range1.jpeg

    https://lh6.googleusercontent.com/-HhqOP2rwq3Q/U_UcOOGQxhI/AAAAAAAAAvI/pO0Ow2gaojk/s512/image%2520%25282%2529.jpeg

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    1. IvIark20 August 2014 at 23:41

      Thanks for the pics. I can't believe the aggravation you all put yourselves through with 1590A's! :o)

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    2. Kinski20 August 2014 at 23:49

      Ha! No aggravation really. More of a fun challenge. Gets kind of easy after a while.

      All my 1590A builds work great, and have noise issues. They are great for touring. I can bring my pedalboard on the plane in a backpack thanks to these small pedals (and super flat pancake patch cables).

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    3. IvIark20 August 2014 at 23:59

      I'd love to have more patience with them, they'd be an absolute God-send for me with a rack tray. But I just don't have the patience unless it's a buffer or a SHO :o)

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  11. Travis21 August 2014 at 01:30

    Wow I can't believe you fit an SP6T in a 1590A let alone the charge pump daughter board. That is impressive

    I got a 9mm alpha SP4T for a modded Rangemaster in a 1590B. It would definitely fit in a 1590A, but I don't really like those little guys

    Anyway, I got the same MP20A (presumably from the same seller by the looks of the insulating tubing) and decided on that for my latest Rangemaster build as well. It's a bit smoother in the top end, which lends itself nicely to this circuit

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    1. Kinski21 August 2014 at 14:00

      Thanks. The rotary actually fits really well, and left just enough room for 9mm pots above it. I could have even put two pots up there, but the circuit only needed one.

      And since the rotary only required half its pins, I clipped off the other ones, which left the perfect platform for the voltage inverter to sit on (with a bit of velcro). It might look a bit sloppy in there, but everything is solid and stable.

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  12. Percy Hornickel7 September 2020 at 19:01

    I´ve build a NPN versión with an AC127 transistor and switchable input caps, works great. I`ve tried to install 1M ohm pull down resistor mod but it change the tone a little. Don´t know why, pull down resistors are supposed to increase impedance and discharge the input/output caps and not affect the tone. Does somebody knows whay this is happening? Thank you

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