May I get a little help please

[whomeno]

I have built a vero of handmade hells gain. I have been over this board for 2 days now and still nothing. I have sound going into tl074 at pin5 and out pin 7. that is where it stops.
I have 9 volt going in to board.
my voltages are as follows

7660S
1 7.67        5 -6.71
2 4.25        6 3.43
3 0             7 3.93                 
4 -2.97       8  7.67 




TL072
1 0             5 0
2 0             6 0
3 0            7 0
4 -6.76       8 7.67

TL074
all zero but pin4 7.66 and pin 11 6.75

[Rob Strand]

Check for shorts along the two tracks going to pins 1 and 2 of the TL074 (ie LEDS, 220pF cap and gain pot).
(FWIW, make ground sure the wire under the TL074 goes to pin 3.)

Actually your PCB pic looks clean nonetheless it's worth checking.  Maybe check for shorts at the pot itself.

[idy]

Did you mean to say 074 pin 11 is -6.75? Since it is connected to pin 4 of 072 and these is the -v pins we would hope it to be negative.

[whomeno]

Can you see my image. I can not

[whomeno]

I'm going to do a new board. I got some coming today. I could not find any shorts at all.
Thanks

[Rob Strand]

Can you see my image. I can not

I can see all your images.

I check over a few things (not the entire build) and it looked OK.

The idea is to slowly work through the circuit.

There is a 220nF at the bottom right.  It connects to pin 7 of the TL074.
Are you getting audio on both sides of that cap?

If you have a short across the gain pot, or the 2 LEDs you not get signal out of pin 1 of the TL074.
It is possible to damage the LEDs.   Just check for a short with your multimeter  across the pin 1 and 2 of the TL074.
Now, if the gain pot is fully closed the pot itself will short out those pin normally and no signal will pass.
You need to set the gain pot to the middle for testing.

[Rob Strand]

I'm going to do a new board. I got some coming today. I could not find any shorts at all.
Thanks

It's up to you.   Seems like a lot of work if it is just a silly mistake somewhere.

Your build looks pretty neat and the parts of the layout I've checked make sense and match the schematic and layout.

If the signal stops at one point it's normally fairly easy to work out why.

[antonis]

Your PCB holder clamps looks like metalic to me..

If indeed they are, they short last 4 board rows..

P.S.
C28 (220μF on schematic - 100μF on layout) must be reversed..!!
(positive leg to GND & negative leg to -V)

[duck_arse]

[whomeno]

ok now I got sound, but if I move the volume up and down I get weird noise from it.
new voltages changed volume pot out still the same
tl072
1 0
2 0
3 0
4 6.78
5 0
6 0
7 0
8 7.67

7660s
1 7.68
2 4.27
3 0
4 -2.96
5 -6.79
6 3.42
74.55
8 7.68

tlo74   
all zeros but pin 4 7.57  and pin 11   -6.68

[whomeno]

ok update 2;10 pm
on tl072 pin 1 good signal pin 5 good signal pin 7 this is where it is bad. no shorts

[idy]

Confirm that there is a jumper under the 072 between pins 6 and 7. May need to remove IC to see under socket. power off confirm continuity between pins 6 and 7. This gives negative feedback and configures Opamp as buffer.

[whomeno]

jumper is present between 6 and 7. reflowed solder to it. Still the same no change
there is continuity between pins 6 and 7

[whomeno]

it seems as soon as i touch the volume pot it goes to crap

[antonis]

If so, don't touch it..!!

P.S.
Sorry guys, but I can't keep answering as an "invisible" subject..

[Rob Strand]

it seems as soon as i touch the volume pot it goes to crap

Try connecting the metal casing of the pot to circuit ground.

You might be getting oscillation.

Keep the input wires away from the output wires.

[whomeno]

Rob,
Did not work. any other ideas?

[Rob Strand]

Rob,
Did not work. any other ideas?

There's many possibilities.

Overall the design is pretty good as far as fending off oscillations but there's couple of cracks which might cause what you are seeing.   Also at this point I'm assuming oscillation but there's a chance it could be noise from the ILC7660.

Things to try,
- add a 100pF from the wiper of the volume pot (100k) to ground.
- add a 1k resistor in series the OUT wire on the PCB (top right).  Place the resistor at the PCB end of the wire.


Oh, for good measure keep the volume pot grounded.

Really all the pots should have the chassis grounded - especially when debugging a problem like this.

[whomeno]

ok did all that. now can hear tone but has a high pitched squeal with it

[Rob Strand]

ok did all that. now can hear tone but has a high pitched squeal with it

OK so we might be on the right track.     It's looking like an oscillation problem.
The 7660S has pin 1 connected to +V so it shouldn't whine.

I guess the next thing to add would be say 100pF from the IN terminal on the PCB to ground.
To be honest you shouldn't *need* that but it's a good thing to add while debugging.

If you have an audio probe perhaps listen to the output of each opamp stage and see if the whine
appears on all opamp outputs.  You might need to crank the distortion control up a bit.

Some things to help narrow down the problem:
- Do you hear the whine when the volume control is on minimum?
- If no, does the whine suddenly appear at some setting of the volume control.
- Does the distortion control setting or treble control setting make it worse?

Did you  fix the 3.3k resistor duckarse mentioned before?