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Friday, 22 February 2013

Sparky 5 Watt Amplifier Stripboard Veroboard Layout


I thought it was about time to tackle something that's been on my todo list for a while and that is to make a follow up to the infamous Ruby amp (made by Runoffgroove.com) which is a popular circuit among the DIY community.

So I thought the best idea was to use an amplifier IC in the same family as the Ruby's amp IC which after an extensive 5 minute search on Texas Instruments website lead me to the LM384 (DATASHEET) which is a 5 watt mono audio amplifier.
it needs a minimum of 12 volts to run though I would run it at 15 volts

All the way up it goes into crazy distortion but before that it is a really nice sounding amp, you get a nice clean and then the louder it goes the more it clips - but nicely - I must do some sound clips!

it powers a 1 x 12" cab very nicely - I've not tried it with a 2 x 12" cab yet but I think it will be fine.

so I introduce to you the SPARKY Amplifier - why did I call it the "SPARKY"? fuck knows, I think it was cause I was watching that cartoon where the piano comes to life.







13 comments:

  1. paul, any reason you chose a 741 for the front end?
    just curious, nice to see a normal chip being used instead of some expensive piece of twat.

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  2. I actually designed it around the TL071 but I then realized I had none so I used a 741 cause I have lots of them
    and the LM384 is only $2 ish so all in all this is a very cheap amp considering the sound it gives you

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  3. Would you please record a clip in which you show us how dirty it gradually becomes ?

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    Replies
    1. I will do when I get time to, I'm currently working on the MKII version so all of everything is plugged into that and various breadboards - the new one has a bass / treble EQ

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  4. Hi Paul
    I built this one, it sounds good at low levels but it quickly goes into crappy gated sounding distortion and even oscillation. I omitted the pot and put a 220 ohm resistor between VR1/VR2 and a 18K resistor between VR2/VR3. That makes the level fixed at a nice sounding "sweetspot". It's just alittle bit distorted but sounds nice. Insted I added a "pre-gain" pot going into the circuit to control the volume.

    I didn't have a 2,7R resistor though, so I tried a 10R (sounded bad) and a link insted (sounds better). What is the purpose of the 2.7R?

    I'm running it at 9v now, will 12 or 18 volts make alot of differance? It would be nice if it could be alittle louder at this semi-clean setting I've got... I've tried with a charge pump but that didn't work. Made the Sparky sound gated/starved...

    However, the circuit doesn't play well with other stomp-boxes. I've tried a few and most are turning the amp into oscillation and crazy noise. Even my Hermida Zendrive that loves to be stacked had the same problem running into the Sparky. Exceptions were my Catalinbread DLS (with a charge pump) and Runoffgroove English Channel which works fine going into the Sparky.

    Any way to solve this issue? I would love to built a stompbox circuit into the front-end.
    BTW, I've got a good 600ma power supply.

    Cheers
    / Fredrik

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    Replies
    1. the 2.7 ohm resistor is for stability and stop it oscillating - or at least help it not to.
      if you have 4 10ohm resistors - put them in parallel (make them into a resistor canoe) this will give you 2.5 ohms which will be better

      a charge pump won't work with it because it can't source enough current to run the LM384 - I can't remember what it draws off hand but it's a lot more than 100mA that you typically get from a MAX1044 or a 7660/1054

      the higher the voltage - the louder you will be able to get it before it distorts.
      it doesn't do well with overdrive pedals cause it doesn't have a proper preamp - that's why the english channel does sound good because that is a preamp of sorts.

      I have been working on a MKII of this with a decent front end but progress is slow cause I feel like crap haha.

      also there is a very similar amp project that doesn't have the problems you're having called the "Tonesucker" elsewhere on my page

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  5. Hi, what happens if I use a 560 uF cap instead of the smaller 470 uF cap at the output?
    sincerely,
    Olle

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    Replies
    1. nothing really - I just chose an arbitrary high value capacitor for that bit

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    2. Great, because that is what I had in stock, except some 3300 /35 and 6800 /35 caps which might be overkill...

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  6. is there any reason why back to back diodes on the feedback loop of the 741 wouldn't work to give some OD?

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    Replies
    1. I would say - try it out and see what happens

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  7. What do you think of using two germanium 1N34A? Would it be better?
    Greetings, thanks.

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  8. Built this amp a while ago, but I ditched the diodes since I do not like hard diode clipping, and wanted it to sound a bit cleaner at higher volumes.
    I also replaced R5 with a 250K pot in order to get a Gain pot, and I found my sweet spot about 1/4th the way up on the pot.
    Now it breaks up with a nice crunch/overdrive when pushing the volume, and it stays quite clean until you get the volume past 2'o clock.
    It now also handles pedals much better and has become a perfect living-room amp for my purpose.
    Sounds great with my 10" Celestion Vintage 30 speaker mounted in an old reel-to-reel cabinet from the 60's.

    As for power, I use a 12v Moped Battery (I live off-grid) that last me about a week with active playing before I have to recharge it.
    Brilliant!!!

    Thanks for all your efforts and contributions.
    Looking forward to your MK.II version...

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