Ruby amp - loud buzzing when connecting pin 1 and 8

[Fingersoup1]

Electronics newbie here.  Decided to make a Ruby amp for my first build. Attempted to breadboard it and just got some heavy buzzing.  Decided to jump whole hog into soldering it onto perfboard as I've read this circuit can get finicky about distances.  I've followed the layout exactly, and the only substitution was a 2n5457 in lieu of the MPF102. 

As I'm short on pots, I've run leads to a breadboard to avoid soldering them down while I test the circuit.  I had pretty clean audio, until I noticed the gain pot was loose.  When I pushed it down, the noise skyrocketed. Dialing back the grain didn't help much.  I've tried a direct connection between pins 1and 8 to see the noise return.  I've also tried swapping out the pot to no avail, and swapping out the LM386 several times to no avail.  Connected on 1 and 8 gives me buzz.  Keeping the pins disconnected gives me a useable albeit fairly quiet amp.

Any suspect areas I should look at?  Any mods to the circuit that would let me add the gain pot so I can get a bit more crunch from the LM386?

Circuit schematic and layout: http://www.runoffgroove.com/ruby.html

[antonis]

I've tried a direct connection between pins 1and 8 to see the noise return.

Did you try "indirect" connection..??
(via a 560R resistor, say..)

[Fingersoup1]

The initial connection was through a pot as per the schematic.  I tried adjusting, and while the noise did get slightly lower, it was leaps and bounds quieter disconnected.  I tried the pot followed by a 220uf cap, as a video is watched cleaned up the sound of a different lm386 circuit by doing so.  No luck for me, it just lowered the pitch of the buzz.  I did grab a sub-100k resistor (can't remember which) and there was still heavy buzz.  I thought if I wanted something in between full gain and the default 20 gain disconnected I should stay between 0 and 100k for the resistor.

[antonis]

R.O.G.'s schem calls for a 1k Gain pot.. 

[Fingersoup1]

Noted.  I'm away from my build ATM and should have read the schematic before posting. I assure you the pot is 1k.  Triple checked all my parts before building.  Now the resistor I used in lieu of,  that's a crapshoot.  Regardless, any connection I've made between 1 and 8 causes the buzz.

I guess I'm wondering, is this a common issue with LM386 IC?  Given the circuit works without them bridged, is it possible I have 6 bad LM386 chips from 2 different suppliers?  Should I focus on a certain part of the circuit?  Are there workarounds if I happened to just get noisier ICs?
 

[Marcos - Munky]

Be sure to keep that 100uF cap as close as possible to pin 6 of the 386.

[Sooner Boomer]

I think the 220uF cap you used is too big.  The TI datasheet for the LM386 shows a 10uF elect. between the gain pins (1, for a maximum gain of 200.  I'd try the 10uF and see if you get the buzz, and control gain with a put across  output.  Some of the newer LM386s are prone to buzz/squeal, and need power supply and other caps as close to the IC as possible.

[pinkjimiphoton]

you need a resistance between pins 1 and 8, not a short. try as suggested a 1k pot.

220u fine. its job at the output is to block any potential dc getting thru, think of it as an output transformer. you can go smaller, but don't go bigger.
the 10r resistor should probably be fairly beefy.. i'd go at least 1/4 watt on it.
check your grounds.
also look for solder bridges around the chip.
i don't like perf for first builds. really easy to contaminate the joints with the crud that seems to melt sometimes. squeals are almost always ground or bad solder joint related usually.
breadboards are notorious for the springs squeezing parts back out of the sockets just enough to lose a connection. they also tend to hum more cuz they aren't shielded.

before modding a circuit, try it stock first and get THAT working. resist BUM at all costs!!


*BUM: Blind Urge to Mod

the ruby is fairly easy to get going  usually.
check your grounds
make sure pot cases are grounded as well, sometimes it doesn't matter, sometimes its crucial
keep the electros physically as close as possible to the chip

[Fingersoup1]

My thought with shorting 1 and 8 was essentially to provide max gain...  My understanding is that a pot goes from 0 resistance to the pot's max resistance.  Bridging with 0 resistance is like a pot having the wiper dialed all to one side..

As noted above, I did actually use a 1k trim pot.  Going off memory instead of looking at the build or schematic was the error there.

I'm thinking part of my problem is distance. Although I didn't think 6 inches away for a trim pot would be an issue for the gain.  I've wedged a 100 ohm resistor into the socket to bridge pins 1 and 8, and I have less hum (albeit still more significant than expected).  I think I'm going to try a rebuild moving the 100uf cap closer to the chip, and actually solder the trim pot to the perfboard instead of running it off the perfboard to a breadboard (it's the only 1k pot I have and the closest electronics shop is 1hr away).  I have one perfboard hole space between the chip and the cap per the RoG perfboard layout...

Now, is the critical factor wire length from the cap to pin 6 of the chip, or is it more of an EMI thing and the cap needs to be close physically despite wire length?  Should I go so far as to jank out and place the cap on the opposite side of the board in an attempt to make the distance the width of the perfboard, or is the layout in the RoG article good enough for more modern noisier parts?  Will one perfboard hole make much of a difference?

As for using perfboard, I've got a bit of experience soldering by fixing traces of old components that broke off of a PCB, I've just never built anything from scratch before.  I'm ok with it, although I'm going to try using wire for bridging most of my holes next build instead of solder bridging, as it can be messy adding so much solder to the board.  Surprisingly I had no shorts first time... At least the amp worked first time (not including the hum caused with pins 1 and 8 being connected) unlike the breadboard which just hummed and buzzed without any input signal being audible at the speaker.

As for the 220uf noted being too big, it was a second 220uf put between pins 1 and 8 he advised to try swapping out to a 10uf.  That mod came from a YouTube video I caught on another lm386 amp that had a lot of noise.  Supposedly the cap cleaned it up.  There was no cap on pin 7 in that build so I figured I'd include it here to see if there's any value to having one there, especially if I have a 100nf ceramic on pin 7 per the schematic.

BUM aside, the mods were attempts at troubleshooting.  I mean, it could be a bad joint somewhere, but the perfboard build went waaay better than breadboard attempts, so I figure I'm at least close.