Ruby troubles - Need some help please

[tjcombs]

I'm having some trouble with a Ruby I built. I've done some searching and it seems other people have this same problem. None of the threads have helped me so far. I get a loud squealing as I turn up the volume and gain pots. The squealing changes pitch and tone as I rotate the pots. Both pots affect the pitch.
Here's some info.

Ruby From G.G.G.
http://www.runoffgroove.com/ruby.html
http://www.generalguitargadgets.com/pdf/ggg_ruby.pdf
Here are the mods I've made. I used a 5K Gain pot instead of a 1K, and I have a speaker wired in to the box instead of an output jack.
I subbed a J201 NPN for the MPF102. I've used a socket and checked the pinout. I'm confident I have the transistor in the right way, but I've switched it around with no luck. I also used a lm386n-1 instead of an lm386 but was informed by the guy at the electronics store that the pinout was the same for the 2. He told me that the lm386n-1 was just a newer version of lm386. I've also checked datasheets and they show the same pinouts as well. The rest of the info on the datasheets was beyond me unfortunately.
I used a 550K and a 1Meg resistor wired in series for the 1M5 Resistor.

It's negative ground.
Once, I got guitar tone through it by manually touching the transistor VERY LIGHTLY to the spots where it solders in, but only once for a split second. I've removed the socket and soldered the tranny directly to the board with no results. I've since replaced the socket. I'll be getting a new tranny tomorrow to try that.


Battery Voltage unplugged  9.06
Battery + where it meets the board 9.06

IC 1 (only 1)
1 - 1.42
2 - 0 (these 3 zeros worry me)
3 - 0
4 - 0
5 - 4.48
6 - 9.07
7 - 4.52
8 - 1.42

Q1 (only 1)
G - 9.05
S - 8.28
D - 9.07

All the voltages are correct on the Electrolytic caps, higher on the + side.
I'm quite certain that all my offboard wiring is correct as well. (Obviously I could be wrong  )
Anyways, I hope this is enough info to help.
Thanks in advance.
TJ

[darron]

my first thought was "hmm. squealing when you turn the volume up? maybe guitar feedback" haha... then I realised how stupid that is.

i had another stupid idea today.. why don't they give the traffic report in any of the papers... ohh yeah..

[brett]

Hi
it seems to me that the jfet bias might be way out or you might be putting DC into the 386.  Check that cap between the JFET and the pot is connected as per the schematic.  If that's ok, check the resistor on the drain of the JFET.  There's also a chance that the JFET is dead.
good luck

[tjcombs]

Hi
it seems to me that the jfet bias might be way out or you might be putting DC into the 386.  Check that cap between the JFET and the pot is connected as per the schematic.  If that's ok, check the resistor on the drain of the JFET.  There's also a chance that the JFET is dead.
good luck

Dead Jfet was my first thought as well. Thanks! I'll try those

[tjcombs]

Hi
it seems to me that the jfet bias might be way out or you might be putting DC into the 386.  Check that cap between the JFET and the pot is connected as per the schematic.  If that's ok, check the resistor on the drain of the JFET.  There's also a chance that the JFET is dead.
good luck

I'm looking at the schematic and other than the LED 1K resistor, there's no resistor on the drain that I can see. There's a 3K9 on the source, and a 1M5 on the gate. Also, by the cap are you referring to the 0.047uf cap? If so it's non polarized and I've checked the solder connections. Am I mistaken here somewhere? Maybe I should check my offboard wiring yet again. I'll also try another speaker just for kicks. Thanks!

[tjcombs]

I just removed every component from the board, and every offboard connection, removed as much of the solder as I could, cleaned the board, re-installed every component, wired it up and still the same problems. Could this mean that the tranny or IC the issue?
Thanks!
TJ

[slacker]

From your first post the problem is round the jfet. You should have 0 volts on the gate, 9 volts on the drain and some low voltage on the source. To get voltage on the gate you've either got some solder bridges, a dead jfet or you're using a jfet with a different pinout to the layout.
The voltages on the 386 look fine, and using an LM386N-1 is fine, that's what mine uses.
If you want to test the rest of the circuit just connect your guitar or whatever to pin 2 of the 386, that should work well enough to prove everything else is right.

[Minion]

You also should make sure that you have the Pin out right for the Fet because when you look at schematics and see a Jfet symbol you automaticly assume that the Gate of the Fet is the Middle pin but if you look at the Pin out of the Fet you are useing you will see that the "Source" is actually the middle pin so if your PCB layout has the Gate as the Middle pin you will have to bend the Gate Pin on the fet so it goes into the middle Hole on the PCB and the Source goes were the Gate pin was (Source and Drain are usually interchangeable)

Also it would be good to Put say a 5k trim pot on the Drain Pin so you can easilly bias the fet as Fets have such a wide range of perameters per device that what Biases one fet will not necessarilly bias another of the same type.....


Cheers

[tjcombs]

Actually, I just tried something this morning. I bent the pins on the JFET to try different pinouts and it turns out that the source and drain were interchanged and it works fine now. I am going to go ahead and get the proper transistor because the JFET is giving me a lower volume output than there should be.
Thanks so much for all your help guys I really appreciate it.