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Smokey amp vII

Last update: Mon Oct 15 22:56:20 2018
kalshagar - Smokey amp vII

Version 2 Info

Based around a LM386 amplifier (in my case a JRC 386), the idea was to make it for a guitarist colleague, and also for myself maybe.
... continued from Smokey amp vI
20101103: worked on the amp tonight on a breadboard. Well, I understood a few more points, by testing and looking at other schemas of smokey-amp like (in the link section):
  • The final cap between output and speaker controls the tone. By changing the value your amp will sound different.
  • Some people use a pull-down resistor (1 M ohm) between input%20 and ground ... don't really hear a difference
  • Using a tiny ferrite on the input doesn't improve the sound much, but if not present there is no sound at all or extremely hashed sound on the breadboard version... wtf?
  • A pot on the gain is not necessary, really, it's like the volumn on the guitar itself
  • A 10 ohm and cap to ground the output pin makes no sound any more on the speaker (but some people have that)
  • On the breadboard version, no much background noise : why ?
  • Sound is really distorted, specially the low tone strings. Playing hard rock/metal is cool with it, playing a ballad or folk is so-so (bass end up so loud and sustained that if completely hides the high tone strings). "Nothing else matters" doesn't sound so good.
  • The "small cap" (22pF) between the input%20 and input- pin is not a killer ... but on the version 1 (not breadboard) it doesn't have that much of bad impact if not really positive. I think I hear less the radio since I put the little cap which can understand since it must eat-away small variations, aka. that faint radio in the back.
20101104: again spent some time playing with the breadboard version, got a few more interresting conclusion
  • VERY IMPORTANT : a big fat cap between the power rails make the sound much better. Indeed, the amp must generate a lot of variations on the power supply and it distorts the sound and make it sensitive to the ambient magnetic noise.
  • IMPORTANT : add a pot for the gain, or at least a little resistor since at maximum level the noise is too low. But just lower it a little, and the sound becomes much much better.
  • Adding a cap between guitar input and input%20 (like a 47uF) make the sound a bit cleaner but I would say with a little less "detail" (sorry, I'm not good at music neither). However sound is more clean. Maybe there is a tradeoff here?
  • A cap between output and ground is not necessary (no big difference). And if you put a resistor, mind that a single 10ohm baby will get burning in a few seconds... make it serial with a cap if you want. Maybe it worth being tried?
Anyway, thanks to all this, I'll make a version 2 this weekend. Hope result will be nice ^^
20101108: made version 2 on Friday evening. No cap on the input, but a ferrite. Is it a crime or something great (or just useless) ? Dunno. Put also a BIG FAT cap (470 uF) on the power rail and that's a killer : barely no more noise and sound is much more clean. Also important. this one has a gain control pot (10k, too big but I have nothing smaller currently) which is very good : full power you still have noise, but if you just lower it a bit, then bye bye noise and enjoy a clear sound that is plenty sufficient for playing at home on the sofa. Schema coming soon...
20101110: found some guy's comment on I copy the guy's comment on a separate page to keep it. Thanks for sharing, that will be most useful I guess.
20101118: well I tried many tricks, tried to implement many alternate Smokey amp like the Smokey Tone Amp of BeavisAudio, variations found on internet ... same : I've got lots of noise. A pot on the gain and a big cap between power rails make things better but no miracle here, I've still got lots of distortion and a background noise. Impossible to get a clear and clean noise.
20101128: it's not because sound is not perfect (hum hum ... far from it in fact) that I should not use it and case it into something. As you can see on the right hand picture, I cased it in a metal "hot lemon tea" can. The plug is in the top cap, and the speaker at the bottom. I tried to fix the speaker with nut and bolts, but to fix the nut to the speaker I soldered it but it didn't stay in place once a little force is applied. Maybe with an arc soldering tool I could, but nothing like that at home, so I will replace it with steel wires, should do the trick.
Only interresting stuff is that now - from power goes to the middle section of the 6.3 mm plug and goes back from the top (not the tip, the other side). Benefit ? Well, no need for a switch, if nothing is plugged in, the circuit is open and battery unused. Got the idea by seing a real SmokeyAmp once.
... continues on Smokey amp vIII


Version 2, with gain pot and tone control (useless)
Version 2, case into a metal can of hot lemon drink.


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