GGG Sample and Hold Pedal

[newperson]

Hi again,

Back for some more help.  Could someone tell me what area to look for a problem with my pedal?  No sound is coming through when the effect is on.  Comes through when bypassed.  First off, I am trying the NTE996 replacement for the CA3080E right now because I am waiting on my SmallBear order.  Has anyone got this pedal to work with these NTE996 IC's?  Also, should the 2Meg pot's legs 1 and 2 be tied together?  The layout shows 1 left open.  I am using the 2 battery layout as on the GGG layout. 

My audio probe findings:
The 100K pot has sound coming out of it for legs 3 and 2 but not 1.  It is acting as a Vol pot.  The 2Meg pot has leg 1 open.  It will control the speed of ticking (real slow to fast) if I hold onto the pot, but goes away when I am not touching it. 

Here are my readings so far:

Battery: +9.38 on one side and -9.41 on the other side of the set.

Q1 -3904
E  -.82
B -.19
C 8.55


Q2 -BF245A
D 8.55
S 7.78
G 7.78

Q3 -3906
E .51
B 0
C -7.87

Q4 -2N2222A
E -1.94
B -8.86
C -9.43

Q5-BF245A
G1.69
S9.39
D.02

Q6 -BF245A
G 9.39
S 9.11
D 9.39

Ic1 -NTE996
1 -0
2 .02
3 -3.6
4 -8.83
5 -8.2
6 7.96
7 8.73
8 0

IC2 -NTE996
1 0
2 .25
3 0
4 -8.82
5 -8.24
6 -3.75
7 8.71
8 0

IC3 -LM741CN
1 -9.63
2 0
3 0
4 -9.65
5 -9.63
6 -.31
7 9.58
8 0

IC4 -LM741CN
1 -9.49
2 0
3 0
4 -9.5
5 -9.47
6 .07
7 2.46
8 -0

IC5 -LM741CN
1 -9.48
2 -4.87
3 -4.95
4 -9.49
5 -9.47
6 -7.26/-7.41
7 9.44
8 0

[newperson]

Any stabs,

Paul.

[toneless]

Well, really I can't be of any help but I'll make a guess that the last BF245 has wrong voltages.
I tryed to build this fx a few years ago with no luck, I hope you'll find the problem soon.

[newperson]

Hi,

I changed the last FET with no change.  I recorded the numbers again and used the audio probe in hopes someone could walk me through what should and should not be happening.  The "Y" and "N" tells if sound is coming through the unit.  I hooked up a Sine wave for the sound source.  Here are the numbers again and if sounds is coming through each transistor and IC.  Also remember that I am trying the NTE996 right now how I am waiting for the CA3080e IC to come in.  I see that the first IC does not have soud coming out of it.

The two batteries died some from my last readings. 
Battery +8.91
-8.84


Q1-3904
E y  -.79
B y -.16
C n 7.82


Q2-BF245A
D n 7.82
S n 7.04
G n 7.05

Q3-3906
E n .66
B n 0
C n .63

Q4-2N2222A
E y -1.34
B y -8.25
C n -8.83

Q5-BF245A
G y 1.68
S n 8.14
D y .02

Q6-BF245A
G n 8.14
S n 8.13
D n 8.89

Ic1-NTE996
1 n 0
2 n .02
3 n -7.03
4 n -7.44
5 n -5.42
6 n 6.9
7 n 7.67
8 n 0

1c2-NTE996
1 n 0
2 n .21
3 n -0
4 n -7.44
5 n -6.79
6 n -6.88
7 n 7.66
8 n 0

IC3-LM741CN
1 n -8.79
2 n -0
3 n -0
4 n -8.8
5 n -8.78
6 y in and out .02
7 n 8.87
8 n 0

IC4-LM741CN
1 n -8.78
2 y 0
3 n -0
4 n -8.8
5 n -8.78
6 y .07
7 n 8.86
8 y 0

IC5-LM741CN
1 n -8.78
2 thumping -4.21
3 higher pitch thump -4.41 to -4.51
4 n -8.79
5-n -8.78
6 thump -6.58 to -6.73
7 n 8.85
8 n 0

Thanks for ANY help,
Paul.

[newperson]

bump

[Peter Snowberg]

I'm sorry I don't have any answers for you, but I wanted to point out to everybody your excellent debugging information!

Great job and best wishes for a fast debug!

[newperson]

Thank you,

I tried two CA3080e ICs today with the same results.  No sound.  I also noticed while messing around with my meter that I do not understand how pulling out the plug turns off the unit from using the batteries.  Does anyone know how that works?  I am using the GGG layout for this project and have not changed any of the parts.  Also, should I be reading 18 volts anywhere?  I really do not understand how the +- 9volt thing works for this unit.

Paul.

[Ry]

Hold on and I'll take some readings on mine.  I've been out of town for a while, so it's going to take me a while to catch up on things enough to help you out.

Ry

[newperson]

That would be great.  I changed and swapped out different transistors tonight without any luck.  I can get some crazy sounds by placing my hand on back of the board.  Lots of low sounds and some ticking.

Paul.

[newperson]

I probed around more to find that the 100k trimmer on the top puts out -+ 9volts and the 10k trimer adds noise to the ticking.  The top of R22 (when looking at the GGG layout) has sound and the bottom of it does not.  Strange that the knobs control things but there is no output without using the audio probe to cause noise to come out from somewhere in the middle of the board.  I hear the ticking in many places and some static white noise in a couple, but I do not hear any random noises.

Where should the -+ 9volt trimmer be set?  0 volts.  I read in the past posts someone suggested the middle of the trimmer which comes out to 0volts.  And to set the 10K clockwise which is the noisest point. 

I have seen others ask in the past posts, but I will ask again.  For the people that got the GGG layout to work did you change anything from the layout to get to work?  Or did it work stright from the layout? 

And how does this unit turn itself off?  I do not see how pulling out the input jack could cause this. 

Thanks for any help,
Paul.

[newperson]

Nothing new today.  Going to try new 741 tomorrow.

[Ry]

I don't have time to post my readings right now, but something is strange with Q2 and Q3.  Check the board around them for jumpers and make sure you have the pinouts right on your transistors.

The Emitter of my Q3 is at around -8.3v (running off of a +/-9.5v power supply).  Q2 is as follows on mine:
D 9.11
S 0
G -0.07

Does any signal come through in either mode when you slowly turn R26?  I know that it took me a while to get the trimmers set to actually get a signal to come through.

Ry

[Roobin]

I also noticed while messing around with my meter that I do not understand how pulling out the plug turns off the unit from using the batteries.  Does anyone know how that works?

At least I can answer this bit...

When you insert a mono jack into a stereo jack, the battery -ve connects to the ground via the jack. Pulling the jack out breaks the circuit.

[newperson]

Hi, 

Checked out Q2 and Q3 and did not find any jumpers.  Should the pin outs be the same as the layout for the BF245a?  Are these the Jfets that you used?  Would you suggest another Jeft for the 3 on the board?  Also how to you check Jfets?  Can you use a meter or the transistor checker on the meter?  And finally, should the 2meg pot legs 1 and two tied? 

I did notice that Q1,2, and 3 change readings with the sample filter switch switched.  Most are +/- .2 volts but the Q3 collector changed a lot.  It moved from -7.89 to -3.74 volts. 

I changed the chips and the transistors and still have no luck with this project.  I made new readings:

Battery  B2: +9.75
B1: -9.86


Q1-2N5088
E y  -.7
B y -.09
C n 8.82


Q2-BF245A
D n 8.81
S n 8.03
G n 8.04

Q3-3906
E n .56
B n 0
C n -7.89  change-3.74 w/switch

Q4-2N3904
E n -2.46
B n -9.16
C n -9.73

Q5-BF245A
G y 1.71 loud static and click
S n 8.88
D y .06 loud static

Q6-BF245A
G n 8.88 very quiet click
S n 8.87 very quiet click
D n 9.63 very quiet click

Ic1-Ca3080e
1 n 0
2 y .02
3 n -8.15
4 n -8.84
5 n -8.85
6 n 8.69
7 n 8.73
8 n 0

1c2-CA3080e
1 n 0
2 n .25
3 n -0
4 n -8.84
5 n -6.79
6 n -.10
7 n 8.71
8 n 0

IC3-KA741
1 y -9.64 very quiet click/sound bleed
2 y -0
3 n -0
4 y -9.66 very quiet click
5 y -9.63 quiet click w/ sound source
6 y .43 loud
7 y 9.56 quiet click
8 y 0 quiet sound bleeding

IC4-KA741
1 n -9.61
2 y 0
3 n -0
4 n -9.63
5 n -9.61
6 y .06
7 n 9.54
8 y 0

IC5-KA741
1 y -9.6 click
2 y -3.48 click
3 y higher thump -4.96 to -5.07
4 n -9.6
5-y -9.58 quiet click
6 y -7.37 to -7.53 click
7 n 9.5
8 y 0 click bleed



Thank you for reading this far,
Paul.

[Ry]

I used J201s for the FETs, but the pinouts appear to be the same (at least for the Siemens part that I looked at the data sheet for)...that said, the readings for all of the FETs are way off.  There is no room for the signal to swing on Q2 and 6 because all of the pins for them are realtively close together in voltages.  The readings for Q5 is strange as well, but just because the pins are not anywhere near the voltages I have.

Check to make sure that you have the pins soldered into the correct pads, they may be turned around.  Or get some J201s and replace them.

Read up on N-channel FETs from this article originally written by R.G., the entire document is at www.geofex.com, under the 'Guitar Effects Debug' link.  I recommend you look through it all at some point, but for now, you're interested in this bit:

N-channel JFETs

JFETs are weird. They're a bar of conductive silicon (I don't know of any available JFETs in germanium) that has a gate junction. The source and drain are at opposite ends of the bar of silicon. Where bipolar (NPN and PNP) transistors normally don't conduct until you turn them on, JFETs normally conduct until you turn them off. An N-channel JFET with its gate at the same voltage as its source will happily conduct all the current it can. To turn it off, you have to reverse bias the gate to a voltage lower than the source. If you keep making the gate more negative than the gate, the JFET will eventually cut off entirely.

For an N-channel JFET to be operating as a linear amplifier, the drain (kind of like a collector) must be at a higher voltage than the source pin. The gate must be at a lower voltage than the source to have any control of the current. A JFET with a gate voltage equal to or higher than the source pin is saturated. A JFET with its gate less than the source voltage may be amplifying or may be cut off. Best to debug this with the Audio Probe.

JFETs are sometimes used as variable resistors. In this case, the gate will be held in the range of operation voltages as though it were a linear amplifier; that is, 0 to minus a few volts.

There is no good way to say how much the gate of a JFET must be negative from the source to be linear or cut off. It varies a lot from JFET type to JFET type, and even as much as four to one in the same type number.

IC1 1 looks a little off on pins 3 and 6 but it may be related to the problems with Q2.

The legs of the 2M pot should not be tied.  Look at the parts placement diagram, leg 1 is not connected to anything.  The other two legs are soldered to the board.

I hope this helps!

Ry

[newperson]

Hi again and thanks for continuing to work with me on this. 

I put some J201s in tonight and took all new readings.  I had to use two different brands.  Q5 and Q6 are the same and Q2 is different J201.  Lots of numbers changed and there is a good bit of movement in some of the readings now, but still no sound coming through. 

What is your voltage reading where the battery comes into the board?  Are you getting +9 and -9 on the two different sides?
Do these readings look any better? 

Here are the new readings:
Battery  B2: +9.19
B1: -9.32


Q1-2N5088
E y  -.7
B y -.09
C n 8.92


Q2-J201_DZ4Z
D n 8.9
S n -5.72
G n 0

Q3-3906
E y .51 click / switched -.8 to +.48
B n 0
C y click -8.43

Q4-2N3904
E n -1.96
B n -8.7
C n -9.27

Q5-J210
G y -3.59 loud static and click
S y -.06 to .36 click
D y .06 loud static

Q6-J201
G y -.119 to +.43  click
S y -.06 to +.9  click
D n 9.13

Ic1-Ca3080e
1 n 0
2 y 0 very very quiet
3 n 0
4 n -9.0
5 n -8.85
6 n -0
7 n 8.6
8 n 0

1c2-CA3080e
1 n 0
2 n 0
3 n -0
4 n -8.74
5 n -8.46
6 n 0
7 n 8.83
8 n 0

IC3-KA741
1 y -9.21 very quiet click/sound bleed
2 y -0
3 n -0
4 y -9.22 very quiet click
5 y -9.2 quiet click w/ sound source
6 y -.3 loud
7 y 9.11 quiet click
8 y 0 quiet sound bleeding

IC4-KA741
1 n -9.18
2 y -0 static
3 n -0
4 n -9.21
5 n -9.18
6 y .06
7 y 9.1 quiet click
8 y 0 low bleed noise

IC5-KA741
1 y -9.19 click
2 y -1.35 to -2.3  click
3 y higher thump -4.62 to -4.68
4 n -9.17
5-y -9.16 quiet click
6 y -6.91 to -6.97 click
7 n 9.08
8 y 0 click bleed

Thank you once again,
Paul.

[Ry]

Okay, we're starting to get somewhere.   Q6 looks correct.  Q2 has a problem at the Gate (see my notes about the comparison with my readings below) and Q5 might be a little off.  Here are my readings and notes for Q2 and Q5:

Q2:
D: 9.11
S: 0
G: -0.07 - This is a very important reading.  The gate of Q2 comes from the output of IC1.  There is something wrong here, check this connection and the components around it.

Q5:
D: 0.01 - This pin looks okay on yours.
S: varies between +/- 1.7 or so
G: varies between +/- 1.25 or so

You need a good noise transistor tuned in via the trimmer R27 to get the same voltage readings I have on Q5.  You say that you're hearing some static on your S and G pins.  This is a good sign, it means that your noise source is working and that your Q5 is probably okay, it just needs some tuning.

Try to get this pedal to work in the Filter mode.  Forget about the sample/hold function for now.  We'll tackle that once the filter is working. 

Here's what I recommend to try getting this pedal running:

2) make an audio probe and print out a copy of your schematic.  Inject a guitar or other audio signal at the input and probe each step of the audio path.  If it vanishes, take a look at the the components around where it vanished.  Double check all of the board connections against the schematic.

[newperson]

I will audio probe again today.  But in case you read this before I write back, what legs should have a signal output for IC1 and IC2?  The 3080e ICs. 

I will try to replace them again to see if that is a problem.  I do not see why I am not getting hardly of any sound out of them.

Paul.

[newperson]

The Ca3080 datahsheet states:
                                                     sound output
1 NC                               0             n
2 INV. Input                     0             y (very quiet)
3 Non-INV. Input              0             n
4 V-                                -9.0         n
5 Amplifier Bias Input       -8.85       n
6 Output                          -0           n
7 V+                               +8.6        n
8 NC                               0             n


So I am guessing that NC means something like (not connected).  And I should hear my signal out of leg 6?  Is that a correct guess.  My last night's readings are to the far right.

Paul.

[newperson]

Here is a layout image.  The black dots means no sound.  No dot means sound.

Paul.
http://i48.photobucket.com/albums/f212/new_person/SHaudioprobe1.jpg