Crackly Ruby Amp - Help!

[suprleed]

I've built a 12v Ruby amp and have been playing around with it over the last several weeks.  I've noticed at medium to high volume and gain settings that I'm getting some unwanted background noise and was hoping the wise folks here could help me identify the source.

When I strike a chord, it will first ring out clear and then as the chord decays I get this nasty crackling sound in the background along with the dying chord.  I'm not sure if I'm just overloading the 386 chip and getting some crackly distortion (seems a little odd at only medium gain and volume settings) or if its possibly coming from a bad speaker connection?  I'm running the Ruby into a custom 2x8 speaker cab I built.  Maybe I need a better speaker cable to connect them with?

Any thoughts would be greatly appreciated.  Thanks.

[petemoore]

I've built a 12v Ruby amp and have been playing around with it over the last several weeks.  I've noticed at medium to high volume and gain settings that I'm getting some unwanted background noise and was hoping the wise folks here could help me identify the source.
  Hard to say exactly.
  When I strike a chord, it will first ring out clear and then as the chord decays I get this nasty crackling sound in the background along with the dying chord.
  It's possible to get these chips hot, watch you don't burn yourself when feeling the OA temperature.
I'm not sure if I'm just overloading the 386 chip and getting some crackly distortion (seems a little odd at only medium gain and volume settings) or if its possibly coming from a bad speaker connection?
  I've had bad speaker connection do what you describe, but it should be pretty easy to test for or just install solid continuity between output and speaker coil.
  I'm running the Ruby into a custom 2x8 speaker cab I built. 
  This could be any ohmage, establish the ohmage, the amount of resistance in these coils, when applied to the amplifier, limit current to some degree, if the ohmage is low, current would be high, certainly possible for that current to bake the chip.
  Maybe I need a better speaker cable to connect them with? 
  I know it sounds schnyde, but since I'm not there, what does it look like, then test it...wiggle it around and see if the sound changes, it takes only a light speaker wire to carry this load.
  Any thoughts would be greatly appreciated.
  The chip has to have room for voltage swing to work, something around 1/2v, seems like if the chip was baked, the bias would drift.
  Since no mention of ohmage, the ohmage question is mentioned, what is the combined ohmage of the speakers ?
  Thanks.

[suprleed]

I'm using an 8 ohm cab (two 4 ohm speakers in series), so I don't think I'm passing excessive current to fry the chip...but tonight when I get home from work I'll touch the chip and see if its hot (carefully of course).  I'll also double check all my connections to make sure they are tight.  I may have another 386 chip laying around, I guess I could swap out the chips and see if that makes any difference.

[jimbeaux]

This is my "Ruby" experience.

When I first tried it out - I used a cheap speaker (no enclosure) & a 9 volt battery that I had laying around & it sounded lousy.

I then built an enclosure for it, used a JRC386D, added a quality Weber 6" Speaker & with a fresh alkaline 9-volt battery I can turn it up loud enough in my apartment to aggravate the neighbors. Difference in sound is amazing! Amazing how loud a 1/2 watt is.

Hope this helps.

- Jimbeaux

[suprleed]

This is my "Ruby" experience.

When I first tried it out - I used a cheap speaker (no enclosure) & a 9 volt battery that I had laying around & it sounded lousy.

I then built an enclosure for it, used a JRC386D, added a quality Weber 6" Speaker & with a fresh alkaline 9-volt battery I can turn it up loud enough in my apartment to aggravate the neighbors. Difference in sound is amazing! Amazing how loud a 1/2 watt is.

I know what you mean!  Mine runs on a 12v regulated wall wart with the NJM386D chip (close to 1 watt) thru my 2x8 cab with 2 Jensen speakers.  At low volumes when I don't get the crackle it sounds sweet.  But I want to crank the sucker and really let her rip!  That's why I'm frustrated with this crackle problem, its holding the ole Ruby back.  I'll see if I can do more troubleshooting tonight...

Rock on

[arawn]

you might also double check your pots, I have had "bad" Pots that crackled in certain areas or a bad connection to a pot do similarly!

[suprleed]

I double checked all my connections and tried to clean up a little the lead dress a bit inside the chassis.  I also fiddled around with my pedal chain going into the amp.  Surprisingly these measures seemed to help.  I only noticed the crackle once at max volume and gain settings.  Makes me think I may be amplifying some unwanted crackle/noise from somewhere in the pedal chain.  Maybe I have a bad connection somewhere in the pedal chain.  I'll do more investigating tonight.

Thanks all for your comments.   

[WaxDragon]

I've not committed it to a board yet, but I have a LM386 based amp here.  I'm using the UTC LM386 which claims 1W @ 16v rail into a 16Ohm speaker.  I'm running it off a wall wart into the cab of my Valve Jr, it sounds great, loud and the chip runs cool!  From what I've read, the RC network on the output prevents oscillations and distortion.  I got some strange distortion of out it when that capacitor was too small.