Questions about Ruby from Runoffgroove.com

[wesman26]

So more recently I've discovered runoffgroove.com and realized that it has some really cool projects on it.  The first thing I looked at was the new Ginger pedal since I'm primarily a bassist, but the more I looked around the more cool stuff I found, until eventually I came across the Little Gem and then the Ruby.  I got the idea that one could make a pretty cool 9V powered mini amp voiced via the Ginger and powered via the Ruby.  Obviously though I have some questions.

First off, what kind of modifications could be done to the Ruby to make it more bass friendly?  Obviously there are the Bassman mods posted on the page, but that's not quite the same thing.

I was also wondering what kind of impedance I should look for in a speaker.  The Little Gem page says 4 Ohms and up is fine, but the Ruby page doesn't specify (though I suppose it's probably very close).  The same goes for wattage, where the Little Gem says 1/2 to 1W, the Ruby doesn't specify (though again it's probably very close).

Thanks in advance,
--Wes

[Uma Floresta]

Same 386 chip, so I'd assume same speakers would work.

[Zipslack]

As far as mods for bass, you could try using slightly larger coupling caps at the input.  Too much will probably make things "farty", so you may want to try with the normal caps first.  Both designs are based around the 386 audio amp chip, so they both use the same speaker impedance - go with 8 or 16 ohms (I think 16 works best, but YMMV).  386 chips come in 4 varieties - 386-1, -2, -3, -4.  The 386-4 allows 1W output, while the others are 0.25 to 0.75W output.  The -4 can also handle a higher voltage which translates to more clean headroom.  There are slight difference between the LM and JRC versions of the chips, so check the data sheets for proper operating voltage.  These things are fairly simple, but can be temperamental to get working right (JRC chips seem to be easier to work with) without a lot of noise/distortion/hiss.

I recommend the Ruby, as it gives me a cleaner sound that I prefer.  If you prefer more distortion, go with the Gem - the output rheostat is a little pricey, though.

[DavenPaget]

If you have a JRC386BD , that's the 1W chip .
JRC386D is only 500mW , but these are the originals .

[JRM]

I've just tested mine with my headphones (added that for night playing with the kids sleeping) and it has a terrible hiss. The hiss decreases a little bit with the battery instead of the psu. I've housed it in a wood box with no shielding. Circuit is ok, I don't know what I can do. Chip is used is LM386.

[DavenPaget]

I've just tested mine with my headphones (added that for night playing with the kids sleeping) and it has a terrible hiss. The hiss decreases a little bit with the battery instead of the psu. I've housed it in a wood box with no shielding. Circuit is ok, I don't know what I can do. Chip is used is LM386.

The smokey ... wasn't meant to drive a headphone with low hiss , since it's PSRR is only 40-50db , so it's quite poor , building a cmoy would be better for headphones

[JRM]

I actually have a cmoy for my hi-fi system. But it's stereo and has RCA stereo inputs. Of course I could make a special cable and use it also for the guitar. But I would prefer to stay with the dedicated Ruby with the advantage to enable the drive of a small speaker that would be easy to carry to holidays or small rehearsals. I think I have to leave with the hiss if I can't kill it.

[Zipslack]

There's a diagram somewhere on the runoffgroove site about adding a headphone-out to a ruby.  Basically, put a small limiting resistor in series (10 Ohms or so) and a small cap across the jack to tame hiss/highs (dunno...2 pf maybe).

[JRM]

Yes, I've already found it also. But it wasn't on runoffgroove it was on generalguitargadgets. A 47uF cap between tip/sleeve and GND on the headphones jack will do it, forming a Zobel network with the 10 Ohm resistance already added on the runoffgroove FAQ schematic.
http://www.generalguitargadgets.com/pdf/ggg_ruby.pdf?phpMyAdmin=4a28f86a515b7883e7bc35a68d4e7b6d&phpMyAdmin=78482479fd7e7fc3768044a841b3e85a

http://www.runoffgroove.com/faq.html

[DavenPaget]

He wants to kill hiss .

[JRM]

I've tried the solution of ggg but it has the poor side effect of cutting too much highs (my strat sounds poorly that way). Another sugestion that I've found is to place a 10k resistance in series with a 10pF or 22nF (seen both values in different schems) between pins 1 and 5 of the LM386. I'll check it out by the end of the week.

[wesman26]

I'm fine with it cutting highs since it's primarily going to be used for my bass.

[JRM]

For bass it's easier. On the other hand, adding a 10k resitance in series with a 22nF cap between pins 1 and 5 will make a bass boost and is said to also kill the hissing. I haven't tried it yet but I don't have an accurate source for that design as hiss killer. One that seems to be tested is this one: http://www.wentztech.com/radio/Technical/Misc/lm386.html
but I don't know it's effect on the overall frequency response.