Foxx Tone Machine debug/HELP!!

[jhferguson]

Ok I went through the debug thread and have a nice template all typed up and ready to get my readings on the transistor when I noticed that everything on the board is reading at the same voltage as the 9v.

9v = 8.5

Q1
C = 8.5
B = 8.5
E = 8.5

D1
A = 8.5
K = 8.5

All resistors and caps read that way as well. I am kind of new to a multimeter when it comes to measuring the voltages of small things like transistors and diodes so I could very well be doing something wrong. According to the GGG website the measurements should be something like this.

9v = 9.26

Q1
C = 2.2
B = 0.73
E = 0.16
Q2
C = 7.5
B = 2.2
E =1.6

Is this an obvious sign of something specific? The pedal itself actually works but the sound is very washed out and it only really sounds good with the sustain turned up all of the way and even then it does not sound that good and fades out quickly but I can heart it wanting to work...lol What do I need to do in order to get some real readings that I can troubleshoot with? Btw, I have the multimeter set on 20v DC. Thank you for your help.

[jhferguson]

Ok update....almost embarrassed to say this but in my haste I did not insert a 1/4 plug in order to activate the effect. Once I did that I was able to get the measurements that I needed in order to get the correct support. So here it is....thanks for looking.

As the title states I have been working on the Foxx Tone Machine clone from the GGG website.

Here are the links to the schematic and the layout and wiring diagram that I used.

Schematic - http://www.generalguitargadgets.com/pdf/ggg_ftm_sc.pdf?phpMyAdmin=78482479fd7e7fc3768044a841b3e85a
Diagram - http://www.generalguitargadgets.com/pdf/ggg_ftm_lo_2fsw.pdf?phpMyAdmin=78482479fd7e7fc3768044a841b3e85a

The PCB came from the GGG website and I followed the layout exactly and even though I used my own parts for the board I did not make any substitutions. The Transistors are all 2N3904's. Also, It is a negative ground circuit.

The pedal works, but not like it should. The LED's come on when they should and the Fuzz and Octave work as well but not to their full potential. The pedal works the best when the sustain is turned all of the way up. That is when you can hear the effect wanting to work but it fades out and even with the sustain turned all of the way up the notes only hang for a second or two until they fade out again. Also when the pedal begins to fade out you can hear some popping and cracking as well. If you play a power chord as soon as you hit the strings the effect fades out and then slowly fades back in becoming louder over time until it does the same fade out as mentioned above with the pops and cracks. It is just a real washed out sound. I have listed the voltages below and compared them to what they should be according to the GGG website.

My Measurements    GGG Measurements
9V = 8.55                    9V = 9.26

Q1                              Q1
C = 2.2                      C = 2.2
B = 0.74                     B = 0.73
E = 0.13                     E = 0.16

Q2                            Q2
C = 6.8                    C = 7.5
B = 2.2                    B = 2.2
E = 1.6                    E = 1.6

Q3                           Q3
C = 0.8                   C = 7.28
B = 1.4                   B = 0.78
E = 0.8                   E = 0.21

Q4                           Q4
C = 7.5                   C = 7.63
B = 0.7                   B = 0.84
E = 0.13                   E = 0.26

D1
A = 0 but when I engage the switch it measures 2.8
K = 0 but when I engage the switch it measures 2.7

D2
A = 4.3 but when I engage the switch it measures 2.8
K = 4.2 but when I engage the switch it measures 2.7

D3
A = 0 and when I engage the switch it measures 0
K = 0 and when I engage the switch it measures 0

D4
A = 0 and when I engage the switch it measures 0
K = 0 and when I engage the switch it measures 0

Also the positive side of all of the electro caps measures higher than the negative side (with the negative side measuring 0 on most of them) even with the switches engaged except for one. C5 (according to the schematic) measures 1.6 on the + side and 0 on the – side but when I engage the switches it changes to 1.6 on the + side and 2.4 on the – side. Thank you in advance for your help.

[jhferguson]

May be a little early but.....bump!!

[dwmorrin]

Q3                       
C = 0.8                 
B = 1.4                   
E = 0.8

There's a problem.
What's going on there?
Check the resistor values, and connections.  Use eyeballs and multimeter on ohms setting, without power.
Recheck the voltage too.  C and E being exactly the same could just be a clerical error.  Otherwise, it would indicate a short (low resistance check, from C to E), or a very saturated (hard ON) Q3 due to too high a base voltage.

[jhferguson]

Ok noob question here I apologize. When I check resistor values on Ohms do I still leave one end of my multimeter on the source ground or am I measuring each end of the resistor? Am I just looking for continuity here or should the meter show me the value of the resisror? Or should it zero out? I double and tripple checked C and E btw and ended up with the same results.

[Mark Hammer]

If one ed actually goes to ground, then you can measure that resistor between any ground point and the non-ground end of the resistor.  If neither end goes to ground, or if you simply want to be sure, stick your probes on each end of that resistor.

keep in mind that there is no assurance that the only path you are measuring is ONLY that resistor.  There can often be parallel resistances included between the two points where your probes touch.

[jhferguson]

Ok could be a couple of things wrong here. First of all there are five 100k resistors on my board and each one measures between 53k and 57k. Also there is a 470k resistor measuring around 150k. So I have 2 diodes that I don't think do anything, 1 transistor that is not measuring correctly, five 100k resistors and one 470k resistor that also seems fudged. Replace all of these?

[Mark Hammer]

If they were "fudged" you would expect there to be an open circuit.  But more relevantly, when you touch your probes to any two points on a board, you are reading not just the resistance of the component your are interested in, but the combined parallel resistance of every possible path between those two points.  When they are all placed in parallel, the outcome could very well be much less than what the stripes on the outside of the resistor of interest say.

For the moment, make sure that:

a) all transistors are oriented properly
b) all electrolytic caps are oriented properly
c) there are no unintended solder bridges or other shorts on your board
d) nothing is shorting out against the chassis
e) all switches function properly

[jhferguson]

The 2 diodes that I mentioned are showing "open". The 1k's and even the 220pf measure exactly what they are. So I do not think that I am reading the resistance between any other points except for the two points of the resistor that I am touching. And after touching every one of the 100k's they all measure between 53k and 57k. Also (again) the 470 measures differently that it should. There are higher and lower resistors on the board that measure what they say that they are within the 1 to 5% as labeled.

The Transistors are oriented correctly because I am using the PCB from GGG and the orientation is on the board. Also for the electrolytic capacitors, the transistors, and the diodes. No bridges exist. The board stands off of the enclosure and doesn't touch any of the sides, the pots have to touch the enclosure as well as the switches but they are the only things touching. And the switches function properly. I know that because the effect works, but as mentioned earlier in the post it just isn't working to its full potential. Which is why I started checking individual components.

[Mark Hammer]

Diodes need to be measured differently than resistors, and the right probes need to be on the appropriate ends of the diodes.

[dwmorrin]

First of all there are five 100k resistors on my board...

...and none of them are connected to Q3, where your problem lies.  So I wouldn't sweat the 100k resistors just yet.

If you really want to check them, just desolder one side, lift one leg out, and then measure.  That will ensure a good reading.
However, if you're not a great "desolder-er" then hold up that task until we've reason to suspect a bad 100k, because we don't want to add to your troubles with an accidentally botched desolder job.

The dc voltages for Q3 are contained by C7 and C8... Q3, R14, 15, 16, 17, and C7, 8, 9 all make up a little subcircuit that stands on it's own... no matter if a 100k somewhere else is bad.

The collector voltage for Q3 is way too low.  Triple check all the components I just mentioned, look once more for shorts around there, double check those orientations, etc. etc... and pics of the board never hurt.

[PRR]

> Q3     
> C = 0.8
> B = 1.4
> E = 0.8

Transistors often try to do what their Base tells them to do.

GGG sez like 0.8, you have 1.4V here.

Look at the circuit around Q3 Base. There's 150K up to 9V, and 15K down to zero. At first blush, we expect the Base to be near one-tenth of 9V. Actually 1/11th of 9V. Or 0.82V. Which is near-enuff what GGG says (Base will pull it down a bit) and way-off from what you have.

I would re-re-re-examine R14 R15.

In traditional codes, one has a yellow stripe and one has an orange stripe. In some lights, in some stripe-paint, with some eyes, these can look a LOT alike.

And with too much screw-up experience, and clue-teasing, I'm wondering if your R14 "150K" is really a _15K_. That gives nearly the right wrong value on R17 emitter resistor. But not quite, so it may be something else.

[jhferguson]

Ok to address C7, C8, and C9 they measure as follows

C7 = 0.8 on the + side and 0 on the - side
C8 = 1.47 on the + side and 0 on the - side
C9 = 0.8 on the + side and 0 on the - side

Almost exactly the same as with the transistor. R14, R15, R16, and R17 are all measuring correctly and I have quadruple checked the striped codes on them to ensure they are what they are supposed to be. The diodes were measured properly and I double checked with an Electrical Engineer to make sure that I am doing it correctly and that my multimeter is set to the correct setting. I tripple checked the orientation and everything is oriented correctly as well. I would upload pics but I have been working on this pedal at work during my lunch break at work and cannot access websites like photobucket from my work laptop. I would work on it at home but because I have 2 small children and home, once I am home my day is all about them. No way I would get this kind of peaceful free time to work on small components with those two around..lol Anyway, I will have to remember to take pics and upload them if I can once I get home. Thank you all for the help and advice.

[jhferguson]

Ok I think I fixed it! Well...helped it anyway. When initially soldering the board I created a solder bridge. Wanting to keep it clean I cut the solder bridge and I guess I cut too deep or something because when I created a solder bridge between R15 and the base of Q3 it is now reading closer to what it should.
                                   
                                    What it should read
Q3                                Q3
C = 6.98                        C = 7.28
B = 0.76                        B = 0.78
E = 0.15                        E = 0.21

However, D3 and D4 still read funny. When I set my meter to test diodes and I test D1, and D2 with black on the side with the stripe and red on the other side I get a reading of 365. Reverse the red and black and I get nothing. I am told that is how they should measure. Nothing on one side and something when the leads are reversed. On D3, and D4 they measure the same no matter which way I orient the leads. Should I go ahead and replace them? Thanks

[Mark Hammer]

However, D3 and D4 still read funny. When I set my meter to test diodes and I test D1, and D2 with black on the side with the stripe and red on the other side I get a reading of 365. Reverse the red and black and I get nothing. I am told that is how they should measure. Nothing on one side and something when the leads are reversed. On D3, and D4 they measure the same no matter which way I orient the leads. Should I go ahead and replace them? Thanks

They are reading exactly what they should.  D3/D4 are in parallel with each other, which means that the current has two choices of paths to follow.  In the case of D1 and D2, each of them is the only path available in that part of the circuit.  So it matters which meter lead goes where for those diodes, but doesn't matter for D3/D4.

Actually, let me retract that last bit.  You will get a reading for D3/D4, regardless of which lead goes where, but the specific reading may be different, depending on which lead goes where.  For instance, if the diode with its stripe going to ground has a forward voltage of 520mv, and the other diode in that pair has a forward voltage of 545mv, then you'd get the one reading if your black lead was on ground and your red lead at the non-stripe end of that diode, and the other reading if you flipped the leads around.

Keep in mind that diodes, being directional, do not function the way that resistors or caps in parallel would,.

[jhferguson]

Awesome! Thanks for the info. I can't wait to get home and try it out. Inidentally out of the five 100k resistors that were measuring between 53k and 57k now one of them reads 100k, two of them read between 79k - 82k and the other two still read in the 53k - 57k range. But hey it is an improvment. I will post later if all is well.

[jhferguson]

So that was what was causing the issue. I cut the solder bridge and accidentally cut too deep severing the original connection via the board. Once I soldered the 15k resister to the B of Q3 she sounds great! Thanks for the help this was an awesome learning experience!!

[Mark Hammer]

Excellent!  Live with it for a bit, and maybe then we'll talk mods.