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Disappointed by Ruby chip amp from RunOffGroove

Started by UsableThought, February 01, 2016, 11:49:01 PM

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UsableThought

Having built only pedals before, my first venture into something that could be called a solid state "amp" was the Ruby from RunOffGroove. It is one of a family of related little 9V or 12V chip amps - Little Gem, Smokey, Noisy Cricket, etc. - all built around an LMN386 or similar. The Ruby differs from the Little Gem by having a buffer & some other minor tweaks.

I found the instructions helpful; they included some minor mods, a few of which I tried out. Also since at one point I was contemplating an 18V version of the LMN386, I started wondering whether the bias for the buffer transistor's gate would need improving rather than just having the bias resistor go to ground. I know nothing at all about this but a lucky Google brought me to AMZ's page on simple buffers, and I added the "reference voltage" tweak at the top of that page to the Ruby's buffer. Along with that I raised the value of the bias resistor to 10M, again as suggested by AMZ. I ended up staying w/12VDC, but even then the changes to the buffer circuit seemed to make the amp sound moderately better to my ear.

And that's about all I can find to really like about the Ruby - the slight improvement in sound from fiddling with the buffer. While tweaking, I have been running it on a breadboard with a 12" speaker from a Yamaha combo. The circuit is not noisy at low gain despite all the jumpers. But the amp suffers from what I would consider a rather crude breakup (if that's the right term) - it sounds similar to but not quite as appealing as the AMZ dirty boost pedal I built some time ago. The buffer moderates this breakup making it a bit more constant and fizzy, with which low gain at 12VDC is OK; but it is still very inconsistent, e.g. more breakup the higher up the neck you go, which is frankly weird.

The next step in my various little projects has always been to build a finished version - and I was all set to do that, when I stopped & asked myself, why? This amp is anything but versatile. If the tone could be moderated with pedals that might help a bit, but the Ruby doesn't seem to like pedals much: RunOffGrove warn you in their FAQ that anything but unity out of a pedal will overdrive a 386-based amp, and I can tell you from experiment that the result is unpleasant. Putting a passive tone pedal on, followed by just enough boost to get back to unity, didn't work work at all. A reverb pedal worked OK so long as I kept the volume low to minimize breakup.

So probably I will not build it, but disassemble it. I am starting to accumulate so many parts that at this point I really need to organize them better - right now I have "big box of caps" and "big box of resistors" plus "other box of resistors" plus "bigger boxes here & there that I just throw hardware into," etc. You get the picture. But with as many parts as I've got, it is becoming slowly easier for me to build small circuits here or there without having to order absolutely everything fresh. Just a question of what circuits.

I didn't have super high hopes but after reading the glowing descriptions at RunOffGroove for the Ruby and elsewhere for the Noisy Cricket, it seems apparent that some guitarists are able to take pleasure from a simple amp more easily than I can. My only consolation is that from what I read, should I keep muddling my way along w/ SS, apparently this is the lowest level of circuit, and other amps and preamps can sound a lot better.

Crude schematic below with my minor changes from stock Ruby - also I included polarity protection w/parallel diode plus fuse in main branch.


Enzo

Well, welcome to the first day of the rest of your electronics life.   Sorta.

As with anything, some will like a thing and some won't.  Some will like it because they made it themselves and it worked, no matter how poorly.  Some will not like it because they had expectations it could never meet, work or not.

if you made one and it worked, great, move up from there.  This is about as simple an amp as you can make.  It necessarily will have many limitations.

Store your parts?  I have been soldering for 60 years, and have been accumulating parts that long.  Having owned and operated a commercial pro audio shop  for the last 22 years, after having run someone else's pro shop for years, I have all my storage needs met.  But much as I like those 60-drawer units, they take up a lot of space.  My small and excess parts have been stored in envelopes, and as I strike my shop, I am inventorying many more parts into envelopes.

Google: coin envelopes.  Easier for you to look at them than me describe them.  You can buy them by the box at Office depot or Staples or any other office supply.  I used a smallish size, I am not at the shop, but I think 3x5-1/2".  A little larger than playing cards, and long enough to fit resistors without bending.  They are made of that tan colored manila paper like larger document envelopes.   They hold up very well, and if one wears, then just make a new one.

I write the contents on the flap, and stack them like files in a drawer, in a box, flap facing me.  All manner of small parts are easily stored this way.  I sort them, one type per envelope, but you could put several types into one if you like.  Numerical or alphabetic order.  Easy and cheap storage, yet effective and space efficient.

A typical flap might read:
resistor   1//2w  220k  mf 
mf for metal film, as opposed to CC or cf , carbon composition or carbon film. ww for wire wound.

zener 1N4744 1w 15v

diode 1N4007  1A 1000v

xstr  MPSA06  80v 500ma NPN TO92
xstr is my abbreviation for transistor,  if a darlington type I add darl.

Big TO3 transistors are not suited to this, but envelopes free up drawers in my 60-bins, so I keep the TO3s there.

Some parts might have additional information.  I reserve the flap for basic part identification, but I can write over the whole side of the envelope if I want.  On ther I might add a manufacturers part number, like Peavey or Fender, in case I want to order from them in the future or if my generic is one of those.  I might note that this transistor is a good sub for some other.  Or this is the cathode transistor in Music Man amps, or whatever.  And sometimes I want to know where I got it, so I note they came from Mouser or Digikey or Allied, or peavey, or AES, or...or...or...

On a fee of them, I peeled the sticky label off the bag they came in from Mouser and just stuck that to the face of the envelope.

I used to have huge piles of screws.  One day I sorted them into machine screws, sheet metal screws, and wood screws.  Stored them in peanut cans or jars.  One day I sorted the metrics from the imperial thread machine screws. Then another day I sorted the metrics into 3mm, 4mm, 5mm, etc, and another time the imperials into 4-40, 6-32, 8-32, 10-32, 10-24, etc.   You can sort as much or as little as seems useful.  I have a smaller drawer bin for 6-32 etc.  At the sporting goods department of my local megastore, I find plastic fishing lure boxes, with the innards separated into square sections.  I sort screws into that.  a similar product is in the sewing and craft section for storing embroidery yarns or thread bobbins.  Either way, a snap lid box with 24 small inner cells, is great for sorting small hardware like that, and inexpensive.  I've seen similar boxes in music stores holding selections of guitar picks.

I have one such box with all my jack and pot nuts sorted.  ANother with various jacks, like Cliff types.  PC mount XLRs in another.  Those flat section boxes stack on a shelf, and it is easy to slide the one I want out of the pile.

I do recommend putting the effort into storage, otherwise every time you want a part for a project, you are interrupting your electronics work to rifle through a bag of mixed parts.

UsableThought

Thanks for the organization tips. I know there was a thread on M-E-F.com where similar stuff got discussed, but now I am going to have to get real - so instead of boxes, envelopes (or maybe envelopes in boxes) sounds good to me. As you say if I don't know what I have or where it is, it makes things harder.

UsableThought

#3
Enzo, I like the coin envelopes idea for parts, but what I'm stuck on is drawers or boxes to put them in. What do you use? I've Googled a lot but most boxes come in odd sizes, too shallow or too big. In the threads on MEF you mention drawers but nothing specific. And there is one person who uses smaller size envelopes & is able to stick them in boxes meant for baseball cards; but I'd prefer the larger size envelope that you suggest.

The big plastic 60-drawer units all seem to have drawers that are too small or shallow (top to bottom) - esp. since I'd rather have the envelopes upright so small parts don't fall out since they will be unsealed.

For now I will just use whatever boxes I have at hand & not get too picky.

These are those threads over on MEF -

http://music-electronics-forum.com/t32576/

http://music-electronics-forum.com/t40883/

Enzo

If baseball card size envelopes will fit a resistor length, sure, why not.  I picked my size because it looked most optimal when I was at the store. 

Cardboard boxes are everywhere, if I find one of good dimension, if it is way too tall, a box cutter or Xacto knife will cut it town to size.  In fact I can find one I like and the top half can be another box for me, just tape the flaps back shut.  The envelope boxes need to be large enough to hold a reasonable number of envelopes, but not so large as to not fit on a shelf.   So a 15" speaker box would be a poor choice.

The 60-drawers are too small for something like 22uf 450v caps, but it takes hundreds of resistors to fill one, like even 1000 1/4 waters.  They hold probably 10 TO3s.   I do have some drawer units with fewer, larger drawers, and they work good for larger caps.

I am too cheap to buy anything, if I don't have to, but those clear plastic shallow storage tubs like Rubbermaid and Sterlite make to slide under a bed, could hold a ton of envelopes, and yet easily store under a bench.