Newbie Ruby amp problems

[superxorn]

Hi,

I started enthusiastically building a Ruby amp as a learning project. I have virtually no previous experience building electronics. I build an amp, taking the schematics from runoffgroove.com/ruby.html, but all I get is hissing sounds, snaps and pops from the speaker.

I did my best debugging, checking that everything goes where everything should go (checking contact). I also built a second unit, with the exact same results, which leads me to believe that I have missed something.

Here is some pics of my attempt:

[MikeH]

Hello, and welcome to the forum!  If you haven't already checked out this thread: http://www.diystompboxes.com/smfforum/index.php?topic=29816.0 take a look at it and report back with your findings.  This thread will explain to you how to gather the info needed for folks here to help you get your build up and running.

[superxorn]

Hi,

I'll do the things in that thread  I have gone through the circuit, checking the routing tens of times, and it's a simple circuit, so it should work 

[MikeH]

Hi,

I'll do the things in that thread  I have gone through the circuit, checking the routing tens of times, and it's a simple circuit, so it should work 

Mother nature never bends the rules for anyone   

[punkin]

i see something that looks like an unintentional short in ut third photo. 9 from right...7 from top...other than that its hard to tell whats going on there.

[superxorn]

Hi,

It's not an unintentional short, it's soldered in place. It's the D from the transistor, the +9v, a leg from the IC and the + side of the 100uF capacitor.

It's easier to follow -- and what I followed when building it (schematic is hard for me to read) if you look at this diagram:

[mantella]

I just built this one last night actually, and got it working. The only thing I can tell that I did differently is that I socketed the transistor. Maybe you burned it out putting it right on the board --?

[superxorn]

Yes, it seems like everyone building it seems to get it to work ... but me  But then again, the might know something about electronics too.
I swapped the FET with a new one, connecting it with wires so it wouldn't be burned out by heat, but to no avail. Still doesn't work. But I'll get these plug-in things for transistors to ensure they are not burned out by heat, seems sensible.
Next thing I'll go through the circuit with the troubleshooting scheme that was suggested to me before. I'm getting slightly disgruntled 

[doc_drop]

It sucks when a circuit doesn't work. I hate that! I usually manage to get it working over time, so keep at it. Do the trouble shooting thing, and check your pin voltages. That can really tell a lot about where the issue is.

The good news is that some of my favorite builds were ones I had to trouble shoot the most. There is something about the first time you finally get one fired up that is even better than having it work the first time.

But of course there is also my bag o' falure (aka spare parts) that I resort to when debugging stops being fun. I am stubborn, so I have to force myself to give up sometimes, but it is better than probing for weeks with no results. (I'm at about a 10% failure rate at this point.)

But I think you'll get this one going. Just sort out the pin voltages and post them as suggested.

Sorry I can't help more.

[superxorn]

Hi,

I have followed the debugging text with the following results:

• The parts are new and of the right values (I ordered them for the project)
• I checked the pins for the IC and transistor and they should be connected correctly. IC(LM386): www.national.com/mpf/LM/LM386.html and transistor(MPF102): www.fairchildsemi.com/pf/MP/MPF102.html
• When plugged in, it sounds gives a low pitched crackling sound. It starts out a little lower in volume, and goes up after a few second to a constant volume. Turning the pots or playing the guitar changes nothing
• Circuit is hooked up to a 9v wall wart

I get the following voltages when multimeter is hooked to ground:

• + lead: 8.97v
• IC pin 1: 1.7v
• IC pin 2: 2.1v
• IC pin 3: 0v
• IC pin 4: 0v
• IC pin 5: 0.6v
• IC pin 6: 8.97v
• IC pin 7: fluctuates between 5v and 7.5v
• IC pin 8: 1.9v
• Transistor G: 1.77v
• Transistor S: 2.38v
• Transistor D: 8.97v
• Ground on the board: 0v
• Out 0v
• In 1.85v

Sorry I didn't post these readings at once

LM386 pins:

[doc_drop]

Hmmm. I don't have my circuit here at work to check your voltages, but I don't see anything too suspicious. Hopefully someone else can chime in if they see something.

But, one more question. How are you connecting this to a speaker, and what kind of speaker are you using?

Ruby's are very particular regarding what speaker they work with. They do seem to prefer 8 Ohms, but it depends on the speaker. When I did my simplified version, I had a Dayton muliti-media speaker I had spent $26 for. I built the circuit on a breadboard first and I changed a few caps and resistors, and strapped a cap across the speaker terminals, before I liked the sound.

[superxorn]

I have been using a 8" 8ohm speaker cabinet, and now last time I used headphones (don't know the ohm). Didn't work with either :S

[doc_drop]

Well, I'm stumped. Anyone else?...

[Brymus]

Do you have one lug of your volume pot grounded?
All three lugs have thier own connections for a voltage divider ,unlike a variable resistor where two lugs are connected.
Also did you double check your pinout on the transistor?
Its a neat little amp dont give up.
Try a fresh circuit on your breadboard using new components sometimes you get a bad chip or transistor.
You may add a trimmer to your transistor to bias it but it should work at 9 V
also do you have 3 resistors I could only see 2 in your pic?

[superxorn]

Hi,

Do you have one lug of your volume pot grounded?

Yes, lug 1 on volume (B10k) is connected to ground.

Also did you double check your pinout on the transistor?

I checked it about ten times. I checked how it looks in the manufacturer diagram, where the GSD are and turned it accordingly.

Its a neat little amp dont give up.

I'm feeling less then cheerful right now

also do you have 3 resistors I could only see 2 in your pic?

I have a 10 ohm one too. It shows in the first pic.

Well, I still didn't get the thing up and running. I thought that maybe I connected something wrong, but I just can't seem where that should be.

I changed the speaker this time around, really small one, 8ohm, 0.8w. Still no result. Which leads me to believe that, if I didn't connect stuff to the wrong place, I have faulty components. But they were new and I built two circuits, so that would be quite unlucky for me if that would have happened.

I connected the pots according to this diagram:



Then, the "out" of the 220uF is connected to the red(+) cable of the speaker, and the other one is connected to circuit ground. The "in" from the transistor ground is connected to the guitar(+) and also to ground(tip and shield of the connector).

I think I got the caps right, the gray stripe indicated - I guess.

I turned the pots to max position and read the voltages again.

• + lead: 8.97v
• IC pin 1: 1.7v
• IC pin 2: 1.6v
• IC pin 3: 0v
• IC pin 4: 0v
• IC pin 5: 0.58v
• IC pin 6: 8.97v
• IC pin 7: 4.7v
• IC pin 8: 1.7v
• Transistor G: 1.77v
• Transistor S: 2.45v
• Transistor D: 8.97v
• Ground on the board: 0v
• Out 0v
• In 1.8v

If you guys can't see anything wring, I guess a component is broke. I can't measure the caps with my multimeter, so I can't see if anything is wrong with them, nor the IC or the transistor. The transistor and IC should be ok since they were nowhere near heat.

[B Tremblay]

The gate of the FET should read zero volts.  Pins 2,3,4 of the 386 should also be at zero volts.  Pin 5 should be close to half the supply voltage.

[superxorn]

Thanks,

There I have something to work with. I'll see what I can do with it