Need help troubleshooting Ruby amp

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I assembled on a breadboard a small Little Gem amp from Runofgroove, and everything sounded just fine.
Then I decided to build a ruby and things didn't go so well...
Thing is I get lots of crackling noise when playing at lower volumes, I think the noise is still there when playing louder, but it's less noticeable.

Removing the gain bits (pins 1 and 8) does not help.
If I keep the ruby circuit and connect the guitar input directly to the 386 chip (ie not using the jFet, like the little gem), every thing sounds fine! :p
Because of this I thing the problem is on the Jfet chip.
Is it possible that I got a bad jfet?! its a MPF102

Thanks :)
I tried that, seems the oposite is happening, if I ser the guitar knob louder I think it sounds ok (it's midnight here, cant try louder as the folks are asleep ;)).
When I play the guitar at lower volumes I get no sound if I play soft, if I play a little harder I get sound but it's terrible, gets a little better the harder I play :p
Will try again tomorrow at higher volumes, might as well try a better breadboard :)

I looked at the circuit and at the datasheet of the advanced analog devices AZ386 audio amplifier. The sample circuit on the datasheet seemed very similar to your board. doesn't have the jrc386 listed. The device has absolutely no noise specification. It is optimized for low current use for battery operation. If a new JFET doesn't help, and there aren't any construction problems listed above, I wouldn't expect much fidelity of it. One tip, check your DC battery voltage when playing, if under 7 get a new one.
I'm getting decent fidelity out of ST33078 and JRC4560 IC's, but they don't have enough power to drive a speaker. See this link for noise & hum wars using a wall supply. People doing speakers usually start with a chip amp like an LM3686. Those have their own thread under amplifiers.
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I had similar problems with this amp. I thought that JFET circuit was wrong. So I designed and simulated this little thing below. On diagram there is BF244, but should be BF245C. R4 is for simulation purposes only. Also you should add 220pF capacitor between opamp's input and ground...


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R4 simulates both 386 input and components before it (like potentiometer). I haven't done it yet (lack of time), but I made some simulations...
My complete design is below. I added some extra parts for normal/bassman mode of operation. And I removed the capacitor connecting JFET's source to drain. It's not necessary, since the capacitor between 386 input and ground works better. R2 is very important - determines the input impedance. It can range from 1.5 Mohm to even 10 Mohms. But be careful - this preamp has pretty big gain, so higher R2 might cause it to be overdriven...
The simulation was done in bassman mode with maximum distortion settings applied - that's why distortion is so high...


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Just wondering, I ordered caps (the 47nF and 100nF ones) that look a bit diferent from what I'm used to.
Are they ok for this application?


The caps:
Capacitors - Polyester film capacitors and capacitor kits

Photo of my stupid bread-board ruby attached :p
(the staples are working as a heat sink for the 386 as sometimes it got a bit hot :D)


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Ruby v1.2 noise elimination, performance Information

Hello diyAudio, I just joined yesterday, and having had a problem with the Ruby amp had to sign up so that I might share some information that might help others experiencing the same problem. By the way, I love the Ruby amp, it really is a wonderful 1/2 watt practice amp when it works like it should. I can build a ruby (parts at hand) in under 5 minutes on a bread board, and, they always work great, full volume & gain with good clear sound. They are best when used with an actual guitar speaker, check out a Jensen MOD 8"-20 watt, 4 or 8 ohm (MOD-8-20) guitar speaker from Antique Electronic Supply, also known as Tubes and More. Well, I digressed, on the bread board worked great, when I would carefully transfer to perfboard, using a magnifying glass, checking each connection and checking for solder bridges and all pot and jack hookups being correct, the amp would squeal, and make all kinds of noise, if at all. I used the same parts that were on the brdbrd, how could this be. I took voltage readings of all the jfet pins, lm386, etc. on a brdbrd version that work good and those are: V+=8.94, D,1,=8.93/4, S,2,=1.64, G,3,0.0v, pins 1 & 8 (gain) on LM386 should be the same 1.33v, with pots turned down all the way, volume down also. pins 2, 3, & 4=0.0v, Pin 5=4.44v, Pin 6=8.93v(+v), Pin 7=4.46v and the speaker wire Positive(+)= 3.93+,-,variable, usually going down in volts. Readings on the Perfboard showed high volts 7-8+ on Gate pin, mostly the same as bread board on LM386 Pins 1-8. I started checking with Plus Probe, with ground clipped to circuit negative rail. I decided to check the actual circuit board it's self, on the Phenolic board material, and, near the edges there was no voltage reading, around the J-FET (MPF-102), there was voltage present, 8+v, where it should not have been. I cleaned the area with a tooth brush and HEET, ethyl alcohol, and scored fairly deep, not too, around all the pins, x & Y, and then tested the amp which now worked perfectly, pots worked when they did not, and was virtually silent as far as scratch, pops, etc.. full gain, full volume. Its most likely not your parts, my pots cost .50 cents. You can also use a 2N5457/8 or J201 J-FET in place of MPF-102. Check out Electrosmash's Ruby amp review, most informative. I'd like to thank All American Five Radio, most excellent electronics tutorials, and, John Audio Tech, both on YouTube, for the help they have been, still fairly new to electronics. Chip amp enthusiasts will learn a lot form John Audio Tech on proper grounding paths and other chip amp related information. Sorry if long winded, lots to tell. I'm happy to be a new member of diy Audio, and, I hope this information is of some help. Triple check your work, take your time, and dont be afraid to try and fail, I guarantee you will learn something from it. Be good. Cass, Oregon, USA.
Dont be afraid to fail

Hi diyAudiophiles, Fail and fail often. Jeri Elsworth, a self taught electrical engineer, said those words in a YouTube video, how true. Its only by hanging tough, you will learn. I recently found stray voltage on my perf board, most likely from flux, I inspect all solder connections with a magnifying glass and check for solder bridges, dragging Iron between pins, connections, etc.. I build the Ruby v1.2 1/2 watt Guitar practice amp, and, having found stray voltage on Phenolic Board Material, where it should ordinarily not be, I scored around the JFET mpf102, and the amp performed perfectly, full volume and full gain. But, I finally figured out what was the problem, at least for me. Double and triple check your work, its really cool when your project works like you want it to, Output baby, thats what were talking about. Take care, be good. C.
An Introduction and help with Ruby v1.2 Guitar Amp, LM386 Monobox

Hello diyAudiophiles, My name is Cass and I live in Oregon in the Coast Range, about 35 minutes from Lincoln City, Oregon, which is on the coast. Willamina, OR would be my town, I live about 4 miles outside Willa. It was named after a pioneer gal of the same name, go figure. I am into chip amps, building my own power supplies, and, FM Transmitters (TX), as well as other kinds of test equipment, and, LM386 Monoboxes and higher watt chip amps, LM3886, TDA 2003, 2040/50,etc.. All very interesting, and a good way to learn electronics. I am self taught, and, have a problem now and then to learn from. Like I mentioned in a previous post, on the v1.2 Ruby amp, check for stray voltage on the Phenolic material of your perf board, clean with alcohol and score in an X,Y axis around the pins of the JFET, MPF102, 2N5457/8, J201, etc., then clean again with alcohol. Can score around LM386 socket or chip, I use an 8 pin DIP socket, and, other connections just to be sure, take voltage readings with DVM to verify. The secret I learned about the LM386 Op-amp from John Audio Tech on You tube, very good channel, is separate ground paths for power, input and output, you will be very pleased by the results of doing this. One more thing I do on the Ruby is build the amp in two (2) stages. One part is the LM386, and, I build around the socket (chip), then, the JFET is another section, with power and ground rails on the appropriate side, Pin 4 on LM386 is ground, and, Pin 6 is plus volts, so, the rails are on those sides respectively. Thats all on that for now. We here in Oregon, have been having a really nice summer this winter, with temperatures at 60 plus degrees, T-shirt weather here. I really love hobby electronics, and, especially making something you can use, tangible results. Keep on it, and, dont be afraid to fail. Check every possibility, you never know. Remember its not what you know, its what you dont know that matters. Have fun, be good. Peace and love from Oregon, C.
Poor performance from Ruby amp or LM386 mono box amp

Hi diyAudio Community, Poor performance from the ( I think) most awesome Ruby Amp, at only a 1/2 watt +-, can most likely be attributed to stray voltage on your phenolic perf board. Not considering solder bridges, which hopefully you inspected for, I use a magnafying glass, can be caused from solder flux and may work or play fine for a few minutes, then, sound quality becomes increasingly worse. The pot, J-FET , and, the venerable LM386 are most likely good. I have built about 20 Ruby amps and a good number of LM386 little mono box amps and have encountered this problem on a number of occasions. Provided that you built circuit on a bread board, if it works, parts are good, and, that when you solder your circuit to perfboard the performance is no good, you probably have stray voltage. Clean the solder side of circuit board with 91% Isopropyl alcohol, I use HEET, ethyl alcohol, score around the J-FET pins in an x,y, axis, then clean again with alcohol and an old tooth brush, odds are will work great. In building Ruby amps, I do it in 2 sections, 1st the LM386 section, which I place on right hand section of board, carefully making one connection at a time, triple check your work, then, install J-FET and make your connections one at a time, check pin out and watch which resistor goes to what pin, the .047uF (473) capacitor, etc.. I build them in a some what linear fashion, following the schematic and even one built on a bread board. I just made a little LM386 mono box amp and had poor performance until I cleaned, scored, and, cleaned it again, now it works perfectly. I also used the star grounding pattern, where the grounds are separated out for input, power and output. They all junction right at pin 4, ground on LM386. John Audio Tech on YouTube is a great channel for chip amp enthusiasts, check it out. Try this, and I believe you will have good success in making a great sounding amp, etc.. Be good, Cass.
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