Ruby Amp Help

[jdiala]

Hello everyone!

I've come here before just to read and get ideas but now I need a little help. I just completed building it using this layout but with the bassman mods. I also didn't have a 10k pot for volume so I took a 250k pot and wired in some resistors in parallel to turn down to a 9.6k pot (they sent me the wrong pots...). As for the mods, I didn't have a 2.2k resistor lying around so I wired two other resistors to make a 2.35k resistor. I also didn't have a 220pF cap so I wired two 470p caps in series.

I was able to get it built and working just fine but the board was hanging out of my enclosure because I wanted to test everything before stuffing it back into the enclosure. I enjoyed for all of 5 minutes. Then I bumped the enclosure by accident and now all I get is popping and crackling coming from the amp. I checked all my solder joints and redid any that I thought looked cold and cleaned off all the flux paste residue. I also ran a razor blade between the strips to ensure there were no solder bridges. I'm not sure what else to do... Can anyone help me figure this out? Thanks!

Layout: http://electro-music.com/forum/phpbb-files/ruby_158.gif
Bassman Mods: http://www.runoffgroove.com/ruby.html

[petey twofinger]

what power supply are you using ?

[jdiala]

Generic 9V wall wart. I also tried a 9V battery although the only ones I had were near death so they weren't much help.

[jogina111]

loose 386.

[jdiala]

So I've popped the LM386 out of the socket and pushed it back in nice and tight and it still doesn't make music. It just crackles and pops regardless of if I'm strumming a chord or not.

I've gone and measured everything I can on the circuit. Here are the values I've got. Some of the fluctuated like crazy so I put the range that I saw. I don't have an fresh batteries so I used the wall wart to measure everything. The wall wart works with guitar pedals and such so it seems to be okay.

Power Supply - 9.5V

LM386
Pin 1 - 1.7V - 2V
Pin 2 - 0.6V - 1V
Pin 3 - 0V
Pin 4 - 0V
Pin 5 - 8.8V
Pin 6 - 9.5V
Pin 7 - 8.8V
Pin 8 - 2.3V - 3.0V

MPF102
Gate - 0V - 0.2V
Source - 9.1V
Drain - 9.5V

[jogina111]

I built the same amp but I have the pots and jacks on board. Got no problems except the loose 386 so I have it socketless and twala! No problems now. Also consider a bad 386 ic.

[jdiala]

I swapped LM386s and it still pops and crackles. I've taken it apart completely and I'm going to try rebuilding it from scratch.

[deadastronaut]

hold on, the mpf102 is the wrong way around in that vero layout....but i'm guessing you saw that!..

[Jussi]

Shouldn't you have the caps in parallel?

capacitors work the opposite way of resistors. In parallel, they add up (like resistors in series). In series, they act like resistors in parallel.

http://www.tpub.com/neets/book2/3e.htm

[jdiala]

How much heat can the MPF102 take? Would applying too much heat from a solder iron cook it? I originally built it as I saw and then flipped it around after.

[deadastronaut]

hmmm not sure, but i would socket it anyway...just to be sure.

or clamp some pliers on it while soldering to dissipate the heat...

[jdiala]

I'm a little stuck on getting the buffer section to work. Seeing as it's a simple practice amp for kicks, I thought I might forgo the onboard buffer and install a simple volume pot instead. Would it be as simple as having the guitar input connected to lug 1 of a 250k pot, connecting lug 2 to the amp's input at pin 2 and then grounding lug 3 of the pot?

[deadastronaut]

yep pretty much like this...

http://www.aronnelson.com/gallery/main.php/v/chickpea/clean+amp2.gif.html

this ^  is a very clean amp...note cut between pins 1-8...or it will not be clean...