Ruby Problems

[christobean]

ok, so about 3 weeks ago i built the ruby, and that didnt work.  no sound or anything.

then last night i tried the dual ruby with 2 LM386-4s and all the proper parts, except that i am running it on an 18v power supply and that i am using 2 seperate pots instead of a dual ganged one. all i get when i turn it on is a really loud buzzing soung. the sound didnt change when i turned the pots or turned the gain switch(breaking the connection between pins 1 adn

anyone have a clue what could be wrong in either, but particularly the dual ruby?

thanks

[MetalUpYerEye]

Did you build them on perf or pc board? I'm gearing up to build myself a Dual Ruby and posted the layout by purpletheory to have it double-checked (and was lucky I did!) it turned out there was a problem with a few connections...

Pin 2 of the first 386 should connect to ground, NOT to lug 2 of the volume.
Pin 3 of the first 386 should connect to lug 2 of the volume.

As for your normal Ruby, mine did the same thing. It wanted to be temperamental with me for the first day or so until I had checked all my solder points and given everything a good "wiggle" and then she fired right up and I haven't had any problems since. I did connect 2 speakers to my Ruby and at first I connected them in parallel, which produced the effect you're describing (no sound whatsoever). Once I soldered them back in in series, everything was cool again.

Also check to see that your 386's are rated for 18v or higher, my LM386 are only rated for 12v.

[christobean]

ahh that is the same pcb layout i used. i am just starting to be able to follow the path of the circuit and have an idea what happens, im no where near being able to look at a layout and being able to find errors.
i will have to switch those two pins, is there any certain way you suggest to fix this?

since i am using an LM386N-4, it handles up to 22v.  it looks like all other versions of the 386 supplied by National Semi. only handle up to 15 volts.
thanks

also, i would suggest building from the center out because i started with the 2 sockets for the 386s and had a tough time getting the resistor and cap in between

[MetalUpYerEye]

Thanks to Pyrop for his suggestion to use the Little Gem MK2 schematic to compare with the Dual Ruby layout. The Little Gem MK2 uses 2 bridged 386 chips as well, only some of the other components are different and it favors a switch for gain boost (pins 1 and rather than a 5k gain pot. If i'm not mistaken, the volume pot is also located in a different spot. The schematic for LGMK2 can be found at the bottom of this page: http://www.runoffgroove.com/littlegem.html

When it comes to PCB's, i'm very primitive and use very cave-like tactics so I suggest more than just considering asking for a second opinion on this, but if I was in your predicament this is what i'd do;

Unsolder lug 2 of the volume pot and resolder it directly to pin 3 of the first 386. Since there is no trace other than where the 2 386's connect and underneath them, i'd try to cram the wire in with pin 3 of the 386 and solder them together. (I told ya I was barbaric)
The second step is pretty much the same...
Since volume pot lug 1 connects to ground and its so convieniently close, put a jumper (piece of wire) across from pin 2 of the first 386 to where pot lug 1 connects on the board.

I in no way promote my primitive tactics, so use them at your own risk.

PS. Your 386's take up to 22v? My shitty Radio Shack ones only take 12...

[christobean]

ha, i have been known to use much sketchier methods in my projects.
if you set up an account at national semiconductors (national.com i beleive) you can get 5 samples of the LM386N-4's shipped to you.  i dont know where you can buy them, but i am on the lookout because i only have one more of the samples.

[christobean]

i just realized that my 100 uF cap is only rated at 16v, will it be ok running 18v??

[TheBigMan]

Not advisable, for 18V I'd want a 25V cap or higher.

[MetalUpYerEye]

I'm with TheBigMan on this one, I try to keep my cap ratings a good bit higher than what I'm using (for 9/12v use 15v caps, for 18v use 25/35v caps, etc) I'm not sure what it'll do if you run a 16v cap at 18v, but i doubt it will explode or do anything that could harm you beyond a burnt finger or two. Probably wont last too long though. If you're going to experiment with it, have a spare 25v cap on the side for replacement and wear gloves.

[christobean]

would not having that cap. up to the right voltage tolerance be causig that load buzzing that i gte? i fixed the pot problem, and still all i get is a buzz when i plug it in...

[mdh]

Why don't you try running your dual Ruby on 9-12V or so? That will be more familiar territory for those of us who have built LM386 amps, and it will eliminate one of the possible sources of trouble (the 18V supply). If you're still having problems, then try following the instructions in "What to do when it doesn't work." I'm not exactly one of the gurus around here, but if you post voltages using a 9V or 12V supply (preferably a battery, to eliminate power supply filtering issues), I'll try to help you troubleshoot it.

I would also suggest that it would be worthwhile to focus on getting the single Ruby working first of all. It's simpler, and more people have built it.

[christobean]

i am using my iron at 40 watts, could the problem be that i killed the lm386s?

[mdh]

i am using my iron at 40 watts, could the problem be that i killed the lm386s?

That certainly could be it. Most people use sockets for ICs, as suggested in your other thread. It's also possible to solder ICs with a pretty hot iron without damaging them, it just depends on how fast you are. Try desoldering the existing chips, replacing them with sockets, and putting in new chips. That might solve your problem.