Orange Squeezer Driving me NUTS!!!

[Blues_Boy_4096]

Hi all!

This supposedly simple build is litterally driving me insane!

Here's the problem: I can't get sound out of it!!

Already changed:
   - IC
   - Transistors
   - Capacitors
   - Trim pot
   - Diode

When I probe it, I get no sound at all right after R2, and therefore nothing after that.
When I turn up the pot (volume), the static noise increases, leading me to assume the pot is working (also checked with a multimeter).

Any thoughts?

Thanks in advance.
Jorge

[oldrocker]

What schematic were you working from? (Website etc...) 

[bwanasonic]

By R2, do you mean the series resistor right after the input cap? Are you getting signal after the input cap? If so, then R2 must be the problem. If not, then either C1 (input cap) or the input jack has a problem. If you are not getting signal two components into the circuit, there is probably no point replacing parts *downstream* from there. Are you sure your audio probe is functioning properly?

Kerry M

[Blues_Boy_4096]

What schematic were you working from? (Website etc...) 

I'm using the schematic from GGG.

Here's what I get when probing:



BTW, I've already changed the resistor...and checked with the multimeter and it's reading 81k..

[Paul Marossy]

Are you positive that one end of that resistor isn't accidentally connected to ground via a solder bridge or something?

[Blues_Boy_4096]

Are you positive that one end of that resistor isn't accidentally connected to ground via a solder bridge or something?

I've checked over and over and didn't see any shorts...

I'm driving insane..... aaaargh....

[oldrocker]

I don't know if this will help but check this over.  It should be the same as what you built but is styled a little different.  Sometimes it helps to see it drawn up different and to see what might be wrong.
http://www.logmonster.com/images/full/?pic=orgsqz_1150914534-422-12515.jpg

[bluesdevil]

Don't give up yet..... we have all gone completely insane at one point debugging.
A couple of questions:
Are you using a printed circuit board from GGG? Or did you make your own or perf it?
Also did you check the pinouts of the trannies with the manufacturers data sheet before soldering them in?
With your multimeter in continuity mode, are you getting a short when placing a probe on the .047uf cap side of the 82k resistor lead (not on solder or pad) and the other on the copper trace it's supposed to be connected to?

[R.G.]

Have you read "What to do when it doesn't work" and done that?

[Blues_Boy_4096]

OK, some updates on the issue...

I've etched a new layout (Tonepad's), and populated it: same result - no sound at all.

Then, I tested all the resistors and found out that the 390k resistor was dead, hence nothing happend after that point.

Changed the resistor and, for the first time after a few weeks, at last, some sound at the other end of the board...

BUT, not good at all !!! Too much noise.

So, I got my multimeter and got some readings of the voltages, which were:

IC

1- 8.47v
2- 8.47 v
3- 0
4- 0
5- 4.83v
6- 4.93v
7- 4.93v
8- 8.99v

Q1 (according to Tonepad's layout)

G- 0
S- 0
D- 0

(I suppose the problem is here at Q1)

Q2 (according to Tonepad's layout)

G- 0
S- 1.18v
D- 8.99v

The transistors are socket-ed and so is the IC, and they've all exchanged for others, with the same result...

One other thing, when I turn the trimpot, nothing happens to the voltages.

I'm also bypassing the 3PDT switch and the LED, so it's working straight in and out...

HELP, PLEASE !!!!

[birt]

get it off of your nuts for a start




(sorry for the lame joke)

[DuncanM]

You might try removing Q2 - the circuit should pass signal (it might be loud and clipped though).

If Q2 is bad, it could pull the input down after R2.
Removing C2 might help as well - then you'd have nothing from the output side interfering with the input side...
Oh, and check Q2 is the right way round......... And also C3.

Try to get the forward signal path working and then look at the gain reduction path back to the input.

Good luck.

[R.G.]

The opamp voltages look OK.

Q1 (according to Tonepad's layout)
G- 0
S- 0
D- 0

This one is clearly a problem, either of measuring the voltage, or of soldering/pinout/etching. This JFET is what reduces gain. Right now, Vgs=0V, so it's fully on, and probably has a resistance of about 200 ohms or less between drain and source. That means that it is shunting all of the signal to ground through the 4.7uF cap on its source.

(I suppose the problem is here at Q1)

That is correct.

Q2 (according to Tonepad's layout)
G- 0
S- 1.18v
D- 8.99v

Well, the source does come up some, but that's intended to pull up the gate as well. This transistor is set up as a constant current source of a few milliamps, and it's being held at ground as well as Q1's gate. Just offhand, I'd look for shorts to ground in the network that includes Q2 gate, the 4.7uF cap, the 10K trimmer, and Q1's source. Maybe check that with a DMM first and see if the meter thinks it's grounded. If not that, I would check for pinout on Q1 and Q2.

Tell us what you find.

[DuncanM]

Sorry, I was looking at the GGG schematic where Q1 and Q2 are the other way around...     

Pull Q1 and see what happens.