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Danelectro Nifty Fifty Mods - Pots

Discussion in 'Amp Tech Center' started by ruger9, Apr 8, 2015.

  1. ruger9

    ruger9 Poster Extraordinaire Ad Free Member

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    I got zero hits in the regular amp forum, so I figured I'd give a shot here... it's probably the more appropriate forum for the question anyway....

    I stumbled across a couple of vids of this amp, and they surprised me how good the amp sounded... started looking up reviews, and these little solid state amps get raves. Just got one off eBay... and I am impressed....

    Really nice clean tones, and some very good semi-dirty tones... I'm amazed at how good this thing sounds, being solid state, non-modeling, and made by Danelectro lol.

    Sounds as good or better than my C600 (definitely better than the C600 for any kid of dirt), with more tonal shaping options. Really digging it (I may sell my modded C600)... with one exception:

    The "Sweet/Dirty" control, which is just a gain/preamp control, gets REALLY dirty REALLY fast... like, I can't even use it above about 10:00-10:30 because it sounds like a fuzz box. AND it dumps a TON of high end into the signal. Up until that point tho, it sounds great.

    Without getting too crazy with mods- because I've been down this road many times before- I'm looking to tame that a little.... here are my ideas, I'd love to get some input:

    1) the gain pot is a B100K. Replace with an audio taper for a more gradual increase in the gain, at least in the first 2/3 of the rotation.

    2) reduce the value of the pot to 50K or even 25K...or even 10K?, in an effort to reduce the high end getting through

    What do you think?
     
  2. bender66

    bender66 Poster Extraordinaire

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    I'd like to hear any input on this question too. I've been curious about these little amps.
     
  3. Cleeve

    Cleeve Tele-Holic

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    I don't have the schematic, but I assume the amp is like every small solid state amp with that size speaker- a TDA2040 or similar five-pin TO-220 cased power op amp with two TLO72 or similar voltage op amps for preamp, one stage driving a pair of either diodes or LED as clippers.

    You can experiment with the gain control or whatever the name of the control was by soldering a resistor between the wiper and ground. That's an old way of faking an audio taper with a linear pot, for example if you had a 100k pot where the input is one end of the conductive element and the other is at chassis ground, the output signal the wiper, putting resistor between the wiper and ground, say a 10k for example, would make the middle of the pot be whatever 10k in parallel with 50k is instead of 50k as it would be without.
    If it does have clipping diodes, sometimes putting a small capacitor across the pair of diodes will tame the brash clipping high end garbage, you'd have to experiment.
     
  4. ruger9

    ruger9 Poster Extraordinaire Ad Free Member

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    That is correct- 2 TLO72s and 2 LEDs.

    Thanks for the info on the resistor and cap....

    .... would a "bright cap" across that pot work? A bright cap bleeds highs to ground as the pot is turned up, right?
     
  5. Cleeve

    Cleeve Tele-Holic

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    A bright cap connects between the wiper and the other end that's not ground to add highs, but connecting it like you said will indeed work, connected from wiper to ground-it would be a "dark cap" i guess.
    Google up some sites about effects like the one "technology of the tube screamer" for example to search for info about the capacitor and how to snub out the diode racket.

    Sometimes the clipping diodes are done a more clever way resembling the setup a tube screamer has, the diodes in the feedback of an op amp, which makes the cap thing different to implement, being in a feed back path.
    But if it's like vox does it in the pathfinders, it's just a pair shunting the output of an op amp to ground.
     
  6. ruger9

    ruger9 Poster Extraordinaire Ad Free Member

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    I found this:

    Mellowing out distortion using a capacitor around diodes

    You can put a capacitor in parallel around the 2 diode pair and mellow out the high end of the distortion. Increasing the capacitor value will cut out more and more of the highs.
    Changing the capacitor value will alter how much highs get cut from the distortion. Start with 100pf and start working up. Try 250pf, then 470pf etc..
    Buzzwords: "Smooth out", "focus"

    there was a little diagram, but it's not a pic file, so I can't figure out how to imbed it...

    here's the link:

    http://www.diystompboxes.com/pedals/mods.html


    I can't read schems, so the diagram in the link is kind of greek to me..... here's a pic of the board (note: the LEDs in this pic have already been swapped out for silicon diodes, and the TLO72s have been swapped out too.... but it shows you the layout - this isn't my personal amp, it's one that has already been modded-)

    [​IMG]
     
  7. Cleeve

    Cleeve Tele-Holic

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    If you can verify either by using a meter or by looking at the underside of the board that the two diode leads near the edge of the board are connected together and the pair of diode leads toward the center of the board are also connected together, then (assuming the above is yes) the capacitor should connect from the edge pair of diode leads to the other pair of diode leads, or simply across either one of the diodes.
    If you have done the 1n4007 deal already and they are sticking up from the board like the one pictured, you can tack- solder a cap across the diode on top of the board.
    I don't know how experienced you are with soldering, so I'll just give you the hint- tin both leads with a little solder on the diode and trim the cap leads and shape them to rest on the spots that you applied solder to on the diode leads, then away from the board apply solder to the cap leads so the cap can be pressed against the diode with the freshly solder-coated leads touching, allowing you to melt the already-applied solder coated leads together with the iron without having three hands.
    That was the thousand words that should have been a picture!!
     
  8. ruger9

    ruger9 Poster Extraordinaire Ad Free Member

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    Firstly, thank you so much for the help!!! I'm not a huge modder, but I like to tinker with cheap stuff, "diamonds in the rough" as it were, to see if I can get them closer to diamonds lol.

    I can solder, I'm no expert, but I've done quite a bit of this kind of work, but thanks for the tips.

    SO- just so I understand- if I wanted to start experimenting with cap values, I could just add one in parallel with one of the diodes? (after verifying where the leads go, as you indicate above)? I will disassemble my personal amp and take a couple of pics.... underside of board.... [I have not touched the amp- so the LEDs should still be in there]
     
  9. Cleeve

    Cleeve Tele-Holic

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    Yes, you can use clip leads to try various cap values in parallel with one diode, since you still have the leds in place you may need to solder some wire or follow the trace to find good places to temporarily connect the experimental cap.
    You might prefer the led clipping with the right cap across them to the 1n4007 pair, led let a bit more voltage swing through.
     
  10. ruger9

    ruger9 Poster Extraordinaire Ad Free Member

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    Well, from everything I'm reading, LEDs have more headroom than other diodes.... and while silicon or germanium might be "warmer", they'll have less headroom/distort sooner. This amp does NOT need to distort sooner!! lol So I probably will leave the LEDs and experiment with cap values first.

    Pics:

    [​IMG]

    [​IMG]

    [​IMG]
     
  11. Zipslack

    Zipslack Tele-Meister

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    You could try using 2-3 germaniums in series to replace the one LED so that you get the higher headroom with the softer clipping, or even try adding a Ge in series with each existing LED. Probably won't be any better than the snub-cap, but it may be the sound you're after...who knows?
     
  12. waparker4

    waparker4 Doctor of Teleocity Ad Free Member

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    Forgive me if I'm wrong but I think
    LED=1.5 V
    Silicon = 0.7 V
    Ge = 0.3 V

    Do you have a schematic for the amp?
     
  13. ruger9

    ruger9 Poster Extraordinaire Ad Free Member

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    No schematic anywhere. I've scoured the net. And very few info on specific mods. I only found one person who modded it, that's his picture 1st one in this thread.
     
  14. Cleeve

    Cleeve Tele-Holic

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    That looks just like a pathfinder 10 with better pots.
    I see from your pics that the leds are as we hoped so you can solder your cap under the board using all four existing solder spots .
     
  15. ruger9

    ruger9 Poster Extraordinaire Ad Free Member

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    All 4??? The cap only has 2 leads...lol I figured I'd solder a couple of leads underneath, then test out the different caps that way, less soldering to the board that way. But do I use all 4 solder spots? I thought I just use 2... 2 on the same LED?

    And I'm still seriously considering the resistors to change the pot taper and bleed off some highs... BELIEVE me, there's plenty of highs to spare! lol
     
  16. Cleeve

    Cleeve Tele-Holic

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    I was saying all 4 since it's two pair of parallel connections anyway, just for more support if you wind up putting the cap underneath.
    But using just two is the same thing electrically.
    Good idea to test various caps with leads first though.
     
  17. ruger9

    ruger9 Poster Extraordinaire Ad Free Member

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    Hey Clint,

    Well, I can't get the caps to have ANY affect at all. I tried many different values, in the end I even connected 3 820pf caps in parallel to get a "2460pf" cap, and it made zero difference.

    I tried running the cap in parallel with one of the leds, then I tried "crossing" them, running the cap lead from one LED to the other, as well as "criss-crossing" those leads as well..... is there a "trick" to this? I though I could use any of the 4 LED solder spots , no?
     
  18. waparker4

    waparker4 Doctor of Teleocity Ad Free Member

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    Just across 1 LED
     
  19. ruger9

    ruger9 Poster Extraordinaire Ad Free Member

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    That was the first thing I tried, didn't have any affect??? (and that was with the "2460pf cap".... and I just tried it again- across 1LED, nothing.

    Is it possible I need MUCH larger values in this circuit? The recommendation to start at 100pf and go up was for dirt pedal designs....



    Regarding the "dark cap" idea above.... any idea what value resistor would be a good place to start experimenting?
     
  20. Cleeve

    Cleeve Tele-Holic

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    Just to check that we're barking up the right tree, try a big cap- like a
    .1uF across those LEDs.
    The output of op amps can drive pretty hard, and the current-limiting resistor looks like it's a 1kOhm so a healthy current could be behind the signal driving those diodes, thus a larger cap value may be needed.


    I know where one of those amps is at a music store all the way across town from me, I may go nab it if it's still there when I get back to town.
     
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