Problems with Ruby LM386 amp on breadboard

[Hydrilla]

Hi all,

I am trying to put together an LM386 amp using the Ruby layout, and despite more than half a dozen tries, it isn't working.  I am not very good at reading schematics yet (trying to learn) so I have been using layout images that people have posted, this being the most recent one- https://noisylittlebugger.net/diy/guitar_pedals/BeavisBoard_Projects/bbp_Ruby_Rev_1_1.pdf

It seems that I have it set up correctly according to the image at least, but I am getting no sound from the input jack, and when I turn the 10k pot up, it makes a loud beep of varying pitch, going up in frequency as I turn it up. 

I am using an LM386N-1 and have tried 2 different ones, and I am using an MPF102.  For power I have tried both a 9v battery and 4 AA batteries.  I have tried it both with a pot and a resistor between pins 1 and 8, with the same result.  Suggestions would be appreciated, I am obviously doing something wrong. 

[pinkjimiphoton]

i bet its the jfet. if it's socketed, pull it out and see if ya get signal to pass if ya jumper it.. or go to pin 2 or 3 with a small metal probe.
if the 386 is working, you'll hear it come thru the speaker.
i've had this issue in the past, and it's usually the jfet. i got so sick of dealing with 'em i made my own circuit with regular npn transistors.

can ya post the voltages of the fet and the 386? put your black meter lead to ground, and set your scale to dc 20 volt range. check the voltage at all three pins of the fet and all 8 of the chip. also post battery voltage, and voltage once it gets to the board.

if the voltages look right that you post, we'll be able to help ya figure it out. but i bet it;s the damn jfet.they don't like heat, they don't like static and are easy to kill.

[Hydrilla]

I appreciate the reply- I swapped out the JFET before checking voltage on it, and the old one was definitely bad.  No more loud beep, and I am getting sound from the input jack, although it is so quiet that it is barely louder than a solid body electric guitar unplugged.

[pinkjimiphoton]

sounds to me like your ground may be bad somewhere on the breadboard to a component. breadboards do wear, and sometimes quickly.
if you're getting sound, that's good.

but what are your voltages? that can tell a lot more.

somewhere something needs to have the nodal connection revisited. wiggle stuff around and see if it suddenly gets loud.

make sure ya got your volume pots wired correctly too. can't do much more without voltage readings tho

[Hydrilla]

That makes sense.  It is a new breadboard but the pot, speaker, and input jack aren't soldered, I have wires held to them with gator clips.  I'm betting this could be part of the problem.  Funny about the JFET- when you're new at something and it isn't working, it is easy to just assume you are doing something wrong, and to disregard the possibility of a bad component.  This applies to more stuff than electronics.

I am about to leave for the weekend to go see a Dick Dale concert in Chattanooga (an excuse to check out a new-to-me city), and will have to troubleshoot more in-depth when I get back. 

[deadastronaut]

check for continuity on your power rails..

some breadboards split the rails halfway..

[Hydrilla]

Interesting, I didn't know that. I will check it. I have jumper wires connecting one side to the other, but I assumed each side would be connected the whole length of the side.

[bluebunny]

Interesting, I didn't know that. I will check it. I have jumper wires connecting one side to the other, but I assumed each side would be connected the whole length of the side.

You might get a clue from the red and blue stripes painted down the side.  If they have a break, then it's likely that the rails do as well.

Edit:

This:



vs. this:

[Fndr8875]

People who use 386 chip amps.....do you use a regular guitar cable as your speaker cable? I built the noisy cricket a while back, using the radioshack ic board beavis created. A instrument cable worked fine. Being as its such a low wattage/power device is there any benefit to using a speaker cable? I have some actual speaker cable from radioshack but don have any 1/4" connectors. I could rig up some kind of connectors if thee would be a noticable sound improvement. About the lm386 being low wattage, that really doesnt mean anything, as i built an EQD acapulco gold, JESUS CHRIST! I have a 20 watt solid state amp w 10" speaker and if i turn it up to like 3 its blasting my ears off. I know there is a mod to put a pregain knob on it, but i etched mine so id have to look up exactly how it connects. Its a great sounding distortion but insanely loud.

[PRR]

> guitar cable as your speaker cable?

Short cable, amp not able to blow-up skinny wire-- that's fine.

Long (10 feet 3m or more) guitar cable may have enough stray capacitance to upset some amplifiers. Probably not, but best to use un-shielded wire for speaker more than a few feet away.

Skinny or low-C guitar wire with 100+ Watt heads-- you might melt it.

Maximum sound at long distances (50' 15m), use good-gauge wire to reduce losses.

[Hydrilla]

I am back from my trip, so I should be able to check voltages tonight.  I can say that my breadboard is exactly the same as the top one, so there is no issue there, assuming no manufacture defect. 

[Hydrilla]

Here are the voltages.  I am back to loud beeping, with the pitch controlled by the volume pot.   

https://youtu.be/ihXbXc9D1FY

1- 1.36
2- 0.2
3- 0.3
4- 0.3
5- 3.64
6- 8.2
7- 4.08
8- 1.36

1- 7.32
2- 7.38
3- 8.17

[Ben Lyman]

Have you tried "star grounding" everything?

[Hydrilla]

No I haven't, but I will.

[pinkjimiphoton]

Here are the voltages.  I am back to loud beeping, with the pitch controlled by the volume pot.   

https://youtu.be/ihXbXc9D1FY

1- 1.36
2- 0.2
3- 0.3
4- 0.3
5- 3.64
6- 8.2
7- 4.08
8- 1.36

1- 7.32
2- 7.38
3- 8.17

i'll have to check, but them voltages don't look a little funky to me. pin 3 and 4 should show zero voltage cuz they connect directly to ground.

i would run a knife between traces and make sure there's no bridges. make sure there's no bridge somehow between output and input.

[Hydrilla]

OK thanks.  Since it is such a simple and proven circuit, I am tempted to just go ahead and build it, copying one of the layouts that are out there.

[slashandburn]

Pin 2  and pin 3 of the 386 seem too close for me, one goes to ground , the other should see some kinda input signal. Check pot wiring and the guitar input signal.

Pin 6 8.2v.  A fresh battery might help.

A lot of Ruby amp schematics call for a 100n cap on pin 7. Might be sufficient but after advice on here I tend to follow other designs which throw in a 10uf polar cap. It probably overkill and maybe not needed but might help with oscillations.

Hope you get it up and running. It's a fun little circuit and makes a surprisingly pleasant racket.

[anotherjim]

1- 7.32
2- 7.38
3- 8.17

Assuming those are FET readings, they are terrible. Gate should be 0v.

Have you got the FET pinout right?

[Hydrilla]

Thanks guys.  I will check the breadboard for what you said, pinkjimiphoton. 

Yes, FET readings.  I don't know if I have the FET pinout right or not.  It wasn't until very recently that I knew there could be a difference even with the same name.  I thought they were all basically the same, and if you follow a diagram based on which way the flat side was facing, it would be the same.  I am using an MPF102 by the way. 

[slashandburn]

Sorry dude, I'm less experienced with the fets, didnt pick up on those looking off.

9v to the Drain,
Guitar input to the Gate
Cap from the volume pot to the Source.

According to the ROG article, you could try a j201 or a 2n5457 if you have either of those.  Just take care with the pinout, check the datasheet, you might need to bend some legs around to get the pins in the right order. 

If transistors are proving too much of a pain in the ass, you could chose the cop out route like I did and use an op-amp buffer/gain stage infront of the 386 instead of the tranny.  A few more parts, but the pinouts of op-amps is a bit more standard than with Trannies.